Respiratory Distress

It is important to recognize the radiographic patterns of conditions that may lead to severe respiratory distress in the neonate. Common respiratory illnesses encountered in the Neonatal Intensive Care Unit (NICU) include surfactant deficiency disease (SDD) and/or its complications, transient tachypnea of the newborn (TTN), neonatal pneumonia, and meconium aspiration syndrome (MAS). Neonates with these conditions are commonly evaluated with chest radiographs. The patient’s clinical information is critical for the correct interpretation of the radiographs, such as gestational age, method of delivery, and other factors surrounding the birth.

Surfactant Deficiency Disease

SDD, also termed hyaline membrane disease, almost exclusively affects premature infants (i.e., less than 36 to 38 weeks gestation). The lack of surfactant in the lungs of premature infants causes collapse of pulmonary alveoli, which leads to poor oxygenation. Infants with SDD demonstrate signs and symptoms of respiratory distress at birth, manifested by grunting, nasal flaring, retracting, and tachypnea. The radiographic findings of SDD may be present at birth, although in some cases the findings evolve after 12 to 24 hours. Classic radiographic findings of SDD are low lung volumes with diffuse, bilateral, granular opacities (Fig. 6-1). These opacities improve after treatment with exogenous surfactant. Infants with SDD are often in severe respiratory distress and require mechanical ventilation.

Figure 6-1 Chest radiograph in a premature infant with surfactant deficiency demonstrates an endotracheal tube in place. There are bilateral, diffuse granular opacities within the lungs with air bronchograms.

Air Block Complications

Infants on mechanical ventilators are at risk of developing complications secondary to barotrauma or volutrauma. This is especially true for infants with underlying lung disease such as SDD. Air may rupture outside of the alveoli, entering the perivascular or peribronchiolar spaces and giving rise to interstitial lucencies termed pulmonary interstitial emphysema (Fig. 6-2). The air may also dissect into the mediastinum, pleural space, or pericardium. On a supine chest radiograph, a pneumothorax tends to collect anteriorly along the heart border or inferiorly above the diaphragm (Fig. 6-3), and is manifested as a paracardiac lucency (for a medial pneumothorax) or a deep costophrenic sulcus (for an inferior pneumothorax). A cross-table lateral view is often necessary to demonstrate the anterior location of the air (Fig. 6-4). Pneumomediastinum causes anterior displacement of the thymus in a “spinnaker sail” configuration (Fig. 6-5). Pneumopericardium outlines the heart border without extending superior to the great vessels (Fig. 6-6).

Figure 6-2 Chest radiograph in a premature male infant demonstrates an endotracheal tube in place. Branching cystic lucencies within the left upper lobe (arrow) are consistent with “pulmonary interstitial emphysema.”

Figure 6-3 In this premature infant lucency adjacent to the left heart border and projecting over the left hemidiaphragm (arrows) indicates the presence of a pneumothorax.

Figure 6-4 A cross-table lateral chest radiograph in the same infant as in Figure 6-3 demonstrates the anterior location of the pneumothorax (arrow).

Figure 6-5 Chest radiograph in this premature baby demonstrates the thymus displaced anteriorly by pneumomediastinum (arrows).

Figure 6-6 Chest radiograph in this premature infant status post ligation of a patent ductus arteriosus demonstrates a lucency projecting adjacent to the cardiac apex (arrow), consistent with pneumopericardium.

Transient Tachypnea of the Newborn

Infants with TTN are often full-term infants delivered via cesarean section. The course of delivery does not effectively clear the fetal lung fluid, which is why this entity is also referred to as “retained fetal lung fluid.” Coarse interstitial opacities on chest radiographs are often present, indicative of underlying pulmonary edema. A pleural effusion, and/or fluid tracking along the fissures, is commonly present. The hallmark of TTN is return of the radiograph to normal in 24 to 48 hours, which coincides with resolution of tachypnea.

Neonatal Pneumonia

Neonatal pneumonia is most commonly secondary to an ascending vaginal infection, the most common infectious agent being Group B streptococcus. A major risk factor for neonatal pneumonia is prolonged rupture of the amniotic membranes. The most common finding on chest radiographs in neonates with pneumonia is bilateral alveolar densities with air bronchograms. The radiographic findings are often difficult to distinguish from other conditions, such as SDD or MAS. Serial films are most helpful in distinguishing between these entities.

Meconium Aspiration Syndrome

MAS is diagnosed by the presence of meconium below the level of the vocal cords at birth. Infants with MAS are usually post-mature, or have experienced intrauterine stress. The thick, tenacious meconium causes obstruction of small- and medium-sized airways, which leads to areas of both atelectasis and overinflation. The meconium can cause a chemical pneumonitis and also inactivates surfactant within lung alveoli. Chest radiographs in infants with MAS reveal coarsened interstitial densities and bilateral parenchymal opacities interspersed with areas of hyperaeration (Fig. 6-7). MAS is the most common respiratory disease to cause a pleural effusion in the first few days of life.

Figure 6-7 Chest radiograph in a full-term baby girl with meconium aspiration demonstrates coarse interstitial lung markings, a focal opacity projecting over the right mid-lung (arrow), and a small left pleural effusion (arrowhead).

Posterior Urethral Valves

Posterior urethral valves (PUVs) are the most common congenital cause of bilateral renal obstruction. Their embryologic development is complex and has been previously described in the literature. Briefly, PUVs consist of an obstructing membrane, or persistent urogenital membrane, at the level of the verumontanum in the posterior urethra of male infants. This membrane causes varying degrees of bladder outlet obstruction and bilateral hydroureteronephrosis. The diagnosis is often made in utero and should be suspected in any male patient who fails to void within 24 hours of birth.

Ultrasound (US) examination of patients with PUVs reveals dilated renal collecting systems and ureters bilaterally (Fig. 6-8). The bladder is often greatly distended, and the bladder wall may appear sacculated, thickened, or trabeculated. The dilated posterior urethra has a “keyhole” configuration at ultrasound. Voiding cystourethrogram (VCUG) is the standard of care for the diagnosis of PUVs. The bladder is usually of large caliber and may require a larger than expected volume of contrast to reach capacity. Bladder wall trabeculations and diverticula are often present. When reflux is present, the refluxed contrast will be diluted by the preexisting urine within the dilated ureter and renal collecting system. The degree of hydronephrosis is often massive. Images of the urethra acquired during voiding demonstrate an abrupt change in caliber between the dilated posterior urethra and the normal-caliber anterior urethra (Fig. 6-9). In some cases the obstructing membrane is identified at the point of transition. The verumontanum is often enlarged and is identified as an intraluminal filling defect along the posterior wall of the urethra just proximal to the valves.

Figure 6-8 A, Sagittal US image of the right kidney in a male infant with posterior urethral valves demonstrates dilated renal calyces (arrow) and a dilated proximal ureter (arrowhead). B, Transverse US image of the bladder in the same patient demonstrates a distended urinary bladder. Dilated distal ureters can be appreciated posterior to the bladder (arrowheads).

Figure 6-9 Lateral-oblique voiding fluoroscopic image acquired during voiding cystourethrogram (VCUG) on same patient as in Figure 6-8 demonstrates a distended urinary bladder with several small diverticulae (black arrowhead). There is an abrupt change in caliber from the dilated posterior urethra to the anterior urethra (white arrowhead). The enlarged verumontanum can be identified as a filling defect in the posterior urethra (arrow).

The treatment for PUVs is ablation. Even after the valves are ablated the long-term sequelae of the bladder outlet obstruction in utero can be catastrophic with renal failure developing by early childhood. Ultimately, the degree of renal function is of primary importance in determining patient outcome, as massive vesicoureteral reflux (VUR) in utero may cause severe renal dysplasia that leads to renal failure. PUVs must be differentiated from other causes of bilateral hydroureteronephrosis in infancy, including prune-belly syndrome, bilateral ureterovesicular junction obstruction, transient bilateral VUR, and the rare “megacystis-microcolon-intestinal hypoperistalsis syndrome.” The findings at VCUG should readily differentiate PUVs from these other entities.

Intestinal Obstruction

Intestinal obstruction is one of the most common neonatal abdominal emergencies. The obstruction is classified as either a high or low obstruction depending on whether it occurs above or below the level of mid-ileum. Babies typically present with abdominal distention, vomiting, and failure to pass meconium within 24 to 48 hours. The distinction between a high and a low obstruction is often made on the basis of plain abdominal radiographs. If the radiograph demonstrates one or few dilated loops of bowel, the obstruction is likely a high obstruction. If the radiograph reveals multiple dilated loops of bowel, the obstruction is a low obstruction (Fig. 6-10). In a baby with intestinal obstruction the correct interpretation of the plain film is critical in directing the most appropriate next course of action.

Figure 6-10 Plain radiograph of the abdomen in a full-term newborn infant with bilious vomiting demonstrates multiple dilated loops of bowel.

A high intestinal obstruction may be secondary to duodenal atresia or stenosis, jejunal atresia or stenosis, or malrotation. An upper gastrointestinal (UGI) examination is often requested in order to identify the level of obstruction. The UGI also assists the surgeon in determining the urgency of surgery. In duodenal atresia or stenosis, the obstruction almost always occurs at the level of the ampulla of Vater. Abdominal radiographs in duodenal atresia often reveal the classic “double bubble” sign in an otherwise gasless abdomen. The dilated gas-filled “bubbles” represent the stomach and duodenal bulb. This is virtually diagnostic of duodenal atresia in the correct clinical setting. In cases of incomplete duodenal obstruction, radiographs will reveal gas in distal bowel loops. At UGI examination, there is often a focal area of narrowing within the duodenum through which a tiny amount of contrast may pass. In some cases, the stenosis may be secondary to a duodenal web, which appears as a curvilinear filling defect extending across the duodenal lumen (Fig. 6-11). Coexistent congenital anomalies are not uncommon, most often in the form of congenital heart disease. Approximately 30% of babies with duodenal atresia or stenosis have Down syndrome.

Figure 6-11 Fluoroscopic spot image acquired during upper gastrointestinal examination in a newborn infant with bilious vomiting demonstrates a dilated duodenum proximal to a partially obstructing duodenal web (arrow).

Low intestinal obstruction may be secondary to meconium ileus, ileal atresia, small left colon syndrome (functional immaturity of the colon), colonic atresia, and Hirschsprung’s disease. A contrast enema is the study of choice to elucidate the diagnosis. Meconium ileus almost always occurs in infants with cystic fibrosis. On contrast enema, a microcolon is present. A microcolon is a colon of universally small caliber (1 cm or less in diameter). Its presence implies that the colon has never been used. Bowel atresia proximal to the distal ileum does not lead to a microcolon because the succus entericus produced by the distal small bowel allows the colon to achieve a normal caliber. In patients with meconium ileus refluxed contrast in the distal ileum reveals multiple filling defects within the distal small bowel. These filling defects represent inspissated meconium. In ileal atresia, on the other hand, it is not possible to reflux contrast past the atresia into the terminal ileum. In functional immaturity of the colon, the descending colon and sigmoid colon are small in caliber compared with the normal ascending and transverse colon. These patients are often infants of diabetic mothers. In colonic atresia the visualized colon at contrast enema will be a microcolon, and contrast will be unable to pass proximal to the atresia. In Hirschsprung’s disease there is a transition from normal bowel that is of normal caliber to aganglionic bowel that is small in caliber (Fig. 6-12). Classically, this transition occurs at the level of the rectosigmoid. In normal infants the rectal diameter should be greater than the sigmoid diameter, although in Hirschsprung’s disease this relationship is reversed. Ultimately, a biopsy is required to confirm the diagnosis.

Figure 6-12 Anteroposterior fluoroscopic spot image during contrast enema in a newborn baby with bowel obstruction reveals a “sawtooth” mucosal pattern in the rectum (arrow). The recto–sigmoid relationship is reversed. This child had Hirschsprung’s disease.

Esophageal Atresia

Congenital atresia of the esophagus is a rare abnormality that may occur as an isolated abnormality or as part of a larger spectrum of abnormalities. In most cases there is an associated fistula to the trachea. The diagnosis is almost always suspected clinically when an infant has trouble feeding, or there is difficulty passing a nasogastric tube into the stomach. Radiographs help to confirm the diagnosis when there is no gas identified within any bowel loops in the abdomen. If placement of a nasogastric tube has been attempted, the tube will be identified above the diaphragm on the radiograph, often in a dilated, gas-filled, esophageal pouch (Fig. 6-13).

Figure 6-13 Babygram performed on this newborn demonstrates a nasogastric tube within a dilated esophageal pouch in this baby with esophageal atresia (arrow). There is no gas within the abdomen to suggest a tracheoesophageal fistula.

Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a gastrointestinal condition that occurs in 2% to 3% of neonates, most commonly premature infants. Mortality rates in infants with NEC range from 15% to 40%. The pathogenesis of the disease is thought to be related to relative immaturity of intestinal motility and barrier function, as well as abnormal bacterial colonization. Neonates with NEC often present within the first 2 weeks of life with feeding intolerance, vomiting, abdominal distention, blood in the stool, and/or generalized lethargy. Abdominal radiographs are the modality of choice for the initial evaluation of neonates with suspected NEC and for monitoring its progression. An early sign of NEC is a mildly dilated and fixed loop (or loops) of bowel on serial abdominal radiographs. Pneumatosis intestinalis, or air within the wall of the bowel, is considered a hallmark of NEC (Fig. 6-14). Pneumatosis represents by-products of the metabolism of bacteria within the intestinal wall. While the bubbly lucencies of pneumatosis can often be mistaken for stool on an abdominal radiograph, it is uncommon for an infant younger than 2 weeks of age to have stool within the colon. The presence of portal venous gas and pneumoperitoneum on an abdominal radiograph usually indicates more severe disease and/or perforation of the bowel. Portal venous gas appears on abdominal radiographs as lucent, branching, linear structures within the liver (Fig. 6-15). When pneumoperitoneum is present the falciform ligament is visualized on a radiograph secondary to the presence of outlining air on both sides (Fig. 6-16). Both sides of the bowel wall are also visible (Fig. 6-17). The abdomen may appear abnormally lucent when large amounts of gas collect anteriorly within the abdomen on a supine film (Fig. 6-18). A cross-table lateral view of the abdomen is helpful in confirming the presence of free air under the diaphragm (Fig. 6-19).

Figure 6-14 Abdominal radiograph in this premature infant with necrotizing enterocolitis demonstrates circumferential lucencies surrounding a bowel loop in the left upper quadrant consistent with pneumatosis intestinalis (arrows).

Figure 6-15 Abdominal radiograph in this male infant with severe bowel ischemia secondary to congenital heart disease reveals branching lucencies in the liver consistent with portal venous gas (arrowheads).

Figure 6-16 Abdominal radiograph in a premature infant with clinical necrotizing enterocolitis demonstrates air outlining the falciform ligament (arrow) as well as air outlining the undersurface of the diaphragm (arrowhead). This child had a perforation in his ileum at surgery.

Figure 6-17 Abdominal radiograph in this premature infant with perforated necrotizing enterocolitis demonstrates air beneath the diaphragm (arrows) and outlining the bowel wall (arrowhead).

Figure 6-18 Abdominal radiograph in the same patient as in Figure 6-16 taken several hours later demonstrates hyperlucency of the liver (white arrow) and free air under the diaphragm (arrowhead), as well as air outlining loops of bowel (black arrow).

Figure 6-19 A cross-table lateral abdominal radiograph in this infant with perforated bowel demonstrates a large amount of free intra-abdominal air (arrowheads).

Most cases of NEC are treated medically, usually with bowel rest, gastric suction, antibiotics, and hydration. Surgery is usually not performed unless there is evidence of bowel perforation (i.e., free air). Plain radiographs are critical in evaluating the progression of the disease. A changing bowel gas pattern, as opposed to dilated bowel loops that remain fixed on serial abdominal radiographs, is an important radiographic sign, as this often coincides with clinical improvement.

Hypertrophic Pyloric Stenosis

Hypertrophic pyloric stenosis (HPS) is a condition that affects young infants usually between 3 and 6 weeks of age. While normal at birth, these infants develop gradual onset of nonbilious emesis over the first several weeks of life, commonly described as “projectile” in quality. In severe cases dehydration and malnourishment will ensue that may be accompanied by marked electrolyte imbalances. The disease is caused by overgrowth of the muscularis layer of the pylorus. The mucosal layer also becomes hypertrophied and redundant, which causes obstruction of the lumen. The precise etiology for HPS is unclear.

Abdominal radiographs in infants with HPS often demonstrate a dilated, gas-filled stomach (unless the stomach has been decompressed with a nasogastric tube). Peristaltic contractions within the stomach give the appearance of a “caterpillar stomach” (Fig. 6-20). Ultrasound is the imaging study of choice for the diagnosis of HPS. When HPS is present, the pyloric channel is nearly always visualized and appears both thickened and elongated (Fig. 6-21). The hypertrophied pyloric channel fails to relax despite vigorous peristaltic contractions in the stomach. The hyperechoic mucosa is redundant and crowded and often protrudes into the antrum, a finding termed the “nipple” sign. The length of the pyloric channel is variable and can range between 14 and 20+ mm. Measurements of muscle thickness are more reliable for the diagnosis of HPS. A muscle thickness greater than 3 mm is consistent with pyloric stenosis. It is important to document the passage of fluid from the gastric antrum into the duodenal bulb. In normal patients the normal pyloric ring bridges these two structures (Fig. 6-22). Careful observation of this region over the course of the examination reliably allows differentiation between a normal and an abnormal study.

Figure 6-20 Abdominal radiograph in this 1-month-old infant with pyloric stenosis demonstrates a dilated stomach. A wave of peristalsis gives the stomach the appearance of a caterpillar.

Figure 6-21 A, Transverse US image in a 5-week-old infant demonstrates the thickening of the pylorus and the redundancy of the mucosa in the pyloric channel (arrow). This patient had hypertrophic pyloric stenosis at surgery. B, Longitudinal image of the pylorus in the same infant demonstrates the mucosa projecting into the antrum, a finding called the “nipple” sign (arrowhead).

Figure 6-22 Longitudinal US image through a normal pylorus (arrow), which appears as a cleft separating the stomach antrum and the duodenal bulb.

Prior to the advent of ultrasound, UGI examination was performed to confirm the diagnosis of HPS. While the thickness of the pylorus muscle is not discernible at UGI examination, there are other imaging signs that suggest the diagnosis. The pyloric channel appears elongated at UGI examination as wispy, linear tracts of contrast pass through the canal, a finding called the “string” sign (Fig. 6-23). The “shoulder” sign is the name given to the appearance of the thickened pylorus impression on the dilated stomach antrum. Vigorous peristaltic contractions in the stomach occur without associated relaxation of the pyloric channel. Imaging over time allows reliable diagnosis of pyloric stenosis, as contrast is never able to pass through the channel in more than tiny wisps at a time.

Figure 6-23 Fluoroscopic spot image from an upper gastrointestinal examination in a 1-month-old boy with reported bilious emesis. The pyloric channel is elongated, and only a small trickle of contrast is able to pass through (arrowheads). Hypertrophic pyloric stenosis was confirmed at subsequent US.

The current treatment for HPS is pyloromyotomy, which can be performed laparoscopically. In this procedure the hypertrophied muscularis is divided and the mucosa is allowed to bulge through the incision (i.e., the muscle is not sutured over). This procedure has been extremely effective at reducing the mortality rate in infants with HPS, which is now well below 1%.

Malrotation

“Malrotation” is a term used to describe an arrest in the development of the midgut that may occur at various stages of embryologic growth. This developmental arrest leads to a spectrum of abnormal rotation patterns of the intestinal tract. In patients with malrotation peritoneal or “Ladd’s” bands form as a result of disorganized embryologic attempts to fixate the malrotated bowel. These bands may lead to bowel obstruction by crossing over a loop of bowel and compromising the integrity of its lumen. The “malfixated” intestines have a propensity to twist around the mesentery leading to a midgut volvulus. The compromised blood supply to the bowel can lead to bowel infarction, sepsis, and eventually death. In a previously well infant presenting with bilious emesis midgut volvulus is a primary clinical concern. While symptoms related to malrotation may theoretically occur at any age, they are more likely to occur in the first month of life. In most cases malrotation is an isolated defect with no predisposing genetic susceptibility or associated syndromes. Some conditions, however, are nearly universally associated with malrotation, including gastroschisis, congenital diaphragmatic hernia, and omphalocele. The heterotaxy syndromes also are associated with malrotation.

Abdominal radiographs and gastrointestinal contrast studies (UGI) are of paramount importance in making the diagnosis of malrotation. The bowel gas pattern is often normal in the presence of malrotation. A normal abdominal radiograph should not preclude further investigation in a child with clinical concern for malrotation. A UGI examination evaluates the course of the duodenum and the position of the duodeno-jejunal junction (DJJ). In normal patients the duodenum has a characteristic C-sweep that consists of four portions: the duodenal bulb and the descending, transverse, and ascending portions (Fig. 6-24). The descending through ascending portions of the duodenum are fixed in the retroperitoneum. The DJJ is normally located to the left of midline at the level of the duodenal bulb. When the DJJ is inferior or medial to this position, it is considered abnormal (Fig. 6-25). There are a few rare exceptions to this rule, which include previous surgery in the abdomen, abdominal masses that displace bowel, and marked gastric or colonic distention. A “corkscrew” configuration of the duodenum implies that a midgut volvulus is present. Midgut volvulus causes a closed loop bowel obstruction. The bowel may appear tapered or “beaked” at the level of obstruction, with proximally dilated bowel loops. Despite all of these findings, the diagnosis of malrotation remains difficult to make with certainty in up to 30% of cases in light of the subtlety of the findings and the overlap with normal anatomy. If the course of the duodenum is not straightforward, serial abdominal radiographs can be performed to follow the contrast distally to the colon. When malrotation is present, the small bowel is commonly located on the right side of the abdomen, and the cecum may also be abnormally positioned.

Figure 6-24 Fluoroscopic spot image from a normal upper gastrointestinal examination. The duodenal C-sweep has a characteristic course, and the duodenojejunal junction is located to the left of midline at the level of the pylorus.

Figure 6-25 Upper gastrointestinal examination in a newborn baby with gastroschisis repair demonstrates malrotation.

The preferred treatment for infants or children with malrotation is a Ladd’s procedure. This surgery, often performed laparoscopically, entails reduction of a midgut volvulus, division of obstructing peritoneal bands, placement of the bowel in a state of nonrotation, and appendectomy. The urgency of surgery depends on whether a midgut volvulus is present at the time of diagnosis. Since all patients with malrotation are at risk of volvulus, even those patients without a volvulus proceed to surgery semi-urgently. Recurrence of volvulus after Ladd’s procedure is rare, but can occur.

Intussusception

Intussusception is one of the most common causes of bowel obstruction in young children. Intussusception occurs when one segment of the bowel (the intussusceptum) telescopes into the bowel immediately distal to it (intussuscipiens). This occurs most often in children between 6 months and 3 years of age. Common presenting symptoms are vomiting, lethargy, and bouts of irritability where the child draws his or her legs to the chest. The more classic symptoms of a palpable abdominal mass and “red currant jelly stool” are present in only the minority of cases and should not be relied on to suggest the diagnosis. Bloody stool is a manifestation of sloughed intestinal mucosa, which is a late finding in the disease and is present in less than half of all cases. The implications of delayed diagnosis may be devastating, as a persistent intussusception leads to bowel ischemia and perforation. Most intussusceptions in children are idiopathic, while the remaining cases are secondary to the presence of a pathologic lead point (PLP). PLPs include Meckel’s diverticulum, colonic polyps, lymphoma, duplication cyst, or underlying diseases of the bowel such as Henoch-Schönlein purpura. The most common site for intussusception to occur is at the hepatic flexure, of which ileocolic intussusceptions are the most common type. Small bowel intussusceptions also may occur. Small bowel intussusceptions are usually transient phenomena that may not cause symptoms. They are likely to reduce spontaneously, and air reduction enema is not therapeutic. Imaging evaluation of the child with suspected intussusception begins with abdominal radiographs. Supine and left lateral decubitus views are recommended. The decubitus film, by allowing the cecum and ascending colon to assume a nondependent position in the abdomen, allows air to fill the cecum when an ileocolic intussusception is not present or if the cecum is not filled with stool. The sigmoid colon is often located within the right lower quadrant in young children, and one should be careful when excluding intussusception based on gas-filled bowel loops in this location. The “meniscus” sign and “target” sign are terms used to describe the radiographic appearance of a soft tissue mass in the colon (Fig. 6-26). Small bowel dilatation and air–fluid levels may be present signifying the presence of a small bowel obstruction (Fig. 6-27). Despite these signs, half of all abdominal radiographs are diagnostically unhelpful in the diagnosis of intussusception, and further evaluation is required.

Figure 6-26 Abdominal radiograph in a 2-year-old boy with abdominal pain reveals a soft tissue mass within the right upper quadrant in the region of the hepatic flexure (arrow). This was confirmed with US to represent an ileocolic intussusception.

Figure 6-27 Abdominal radiograph in a 1-year-old boy demonstrates multiple air–fluid levels and dilated loops of bowel. This child had an ileocolic intussusception confirmed at US.

For confirmation of intussusception, ultrasound is the preferred modality. When the sonographer is familiar with its imaging appearance, intussusception is identified in all cases. Intussusception has a characteristic appearance in both transverse and sagittal planes. In the transverse plane, an intussusception appears as a mass usually between 3 and 5 cm in diameter that has a “target” or “doughnut” configuration of alternating hypo- and hyperechoic layers (Fig. 6-28A). In the sagittal plane the mass assumes a “pseudo-kidney” configuration. Color Doppler is used to evaluate the vascularity of the bowel and is a promising predictor of bowel viability (Fig. 6-28B). Enlarged mesenteric lymph nodes may be present at the site of intussusception, which may function as a lead point. Imaging pitfalls in the diagnosis of intussusception include stool in the cecum, thickened loops of small bowel in the right lower quadrant, and the normal psoas muscle. Each of these structures may be mistaken for an intussusception. It is also important to appreciate the difference between small bowel intussusceptions and ileocolic intussusception. Small bowel intussusceptions are usually treated conservatively, whereas ileocolic intussusceptions proceed to enema reduction or surgery. The diagnosis of small bowel intussusception is suggested by the location of the intussusception (outside of the right lower quadrant), small diameter (less than 2 cm), and short-segment involvement (less than 5 cm).

Figure 6-28 A, Transverse US image in a 1-year-old child with crampy abdominal pain demonstrating the “target” appearance of an ileocolic intussusception. The “intussuscipiens” is delineated by arrowheads. B, Sagittal US image in the right lower quadrant in the same patient demonstrates the presence of color Doppler flow to the intussuscipiens (arrowheads).

Fluoroscopically guided contrast reduction enema is a widely accepted and utilized method of treatment for ileocolic intussusception. Contraindications to performing an enema include shock, peritonitis, or radiographic evidence of perforation. Although different contrast agents are used, air is preferred at our institution. After inserting a rectal catheter into the buttocks air is insufflated into the colon. The intussusception is visualized fluoroscopically as it is reduced back through the colon (Fig. 6-29). A successful reduction involves the reduction of the intussusception beyond the ileocecal valve (often with a visible “pop”) with reflux of air into the small bowel. Air reduction enema is successful in over 80% of cases. When the enema is not successful, surgery is curative. A rare, but serious, complication of the air reduction enema is bowel perforation leading to tension pneumoperitoneum, which necessitates emergent needle decompression. Perforation occurs in approximately 1.5% of cases.

Figure 6-29 Fluoroscopic image obtained during air reduction enema in this child (who is prone) demonstrates the soft tissue mass at the hepatic flexure (arrow). Later images demonstrated complete reduction of this ileocolic intussusception.

Acute Appendicitis

Acute appendicitis is the most frequent condition in children requiring emergent abdominal surgery. Acute appendicitis is caused by obstruction of the appendiceal lumen that leads to accumulation of fluid and secondary inflammation and infection. Luminal obstruction is most often secondary to the presence of a fecalith, but may also be secondary to lymphoid hyperplasia, foreign bodies, or mass lesions (i.e., lymphoma). Perforation is common in pediatric patients. The frequency of perforation increases as the age of the patient decreases. Children who are suspected of having acute appendicitis warrant imaging evaluation that is both expeditious and accurate in order to avoid complications of perforation, such as abscess formation, bowel obstruction, and sepsis.

Graded-compression sonography is an appealing imaging modality for the initial evaluation of children suspected to have acute appendicitis. The advantages of ultrasound include the lack of ionizing radiation, the lack of patient preparation, and the lack of sedation. The patient is often able to precisely localize the site of pain in order to direct the sonographer to the appropriate area. Disadvantages of ultrasound are that US is highly operator dependent, the accuracy of the study is largely impacted by the body habitus of the patient, US is poorly accurate at diagnosing a normal appendix, and US is often not able to determine if the appendix is perforated.

CT examination is highly sensitive for the diagnosis of acute appendicitis. In many cases, CT may also provide an indication that the appendix has perforated. In many institutions, a negative or equivocal ultrasound for appendicitis prompts a CT scan. Depending on the institution, various combinations of oral and intravenous contrast are used. Although CT is more highly accurate at diagnosing appendicitis than US, US is often performed initially in children in an effort to avoid or reduce the inherent risks of radiation exposure. Therefore, it is important to be familiar with the imaging features of acute appendicitis with US as well as CT.

On US, the inflamed appendix appears as a blind-ending, tubular structure with bowel signature. When pressure is applied, the inflamed appendix is noncompressible. On transverse images the appendix will have a “target”-sign configuration that is made up of the alternating layers of the appendiceal wall. While no exact measurement defines an acutely inflamed appendix, in general practice an appendix with a diameter greater than 6 mm is considered abnormal. Secondary signs of appendicitis include free fluid in the abdomen or pelvis, enlarged mesenteric lymph nodes, and fluid collections adjacent to the appendix that represent abscesses.

Many of these same imaging features for US also apply to CT. CT findings of acute appendicitis include a maximal outer luminal diameter greater than 6 mm, lack of oral contrast within the lumen (if oral contrast was administered), an appendicolith, and periappendiceal inflammatory changes. Associated findings include enlarged mesenteric lymph nodes, free fluid, and inflammatory changes in the adjacent bowel. The presence of free air and abscess formation are important signs that the appendix is likely perforated.

Although appendicitis is common, its imaging features are not always straightforward. Given the variability in the location and position of the appendix, the clinical symptoms can be misleading. If the appendix is located within the pelvis in a young woman, appendicitis may simulate an ovarian process such as torsion of the ovary or hemorrhagic ovarian cyst. Likewise, a subhepatic appendix may present with right upper quadrant pain simulating gallstones, or flank pain concerning for pyelonephritis.

Meckel’s Diverticulum

Meckel’s diverticulum is the most common congenital anomaly of the gastrointestinal tract, found in 2% to 3% of the general population. A Meckel’s diverticulum is a true diverticulum along the antimesenteric border of the distal ileum that results from incomplete atrophy of the omphalomesenteric duct in fetal development. Its lining consists of normal small bowel mucosa, though in some cases ectopic gastric or pancreatic mucosa may be present. It is most often located in the right lower quadrant. There is no known association with other congenital malformations. Asymptomatic Meckel’s diverticulum occurs with nearly equal frequency in boys as in girls, although symptomatic Meckel’s is more common in males. While most Meckel’s diverticula are asymptomatic, when symptoms do occur, it is most often a result of a complication of the diverticulum and is more common in children than adults.

Forty percent of children with vitelline duct anomalies such as Meckel’s diverticulum are symptomatic. The most common symptoms are abdominal pain, nausea, vomiting, and rectal bleeding. Hemorrhage and obstruction are the most common complications. In patients presenting with hemorrhage related to a Meckel’s diverticulum, ectopic gastric mucosa is almost always present. The bleeding is caused by peptic ulceration within the gastric mucosa and/or the adjacent ileal mucosa, and is typically painless. The presence of ectopic gastric mucosa serves as the basis for the “Meckel’s scan,” or 99m-Tc-pertechnetate scintigraphy. Given the relatively low sensitivity of this examination, however, a negative result often has little impact on clinical management when a Meckel’s diverticulum is strongly suspected. Arteriography and contrast studies may be helpful in these instances, although these evaluations may be superseded by colonoscopy or laparoscopy.

Bowel obstruction secondary to Meckel’s diverticulum can occur secondary to volvulus, intussusception, inversion of the diverticulum into the bowel lumen, inclusion of the diverticulum into a hernia, or diverticulitis. Persistent attachments of the diverticulum to the umbilicus may be the cause of bowel obstruction. A transition point may be identified on CT where proximal, dilated bowel loops abruptly change caliber to collapsed, distal loops, although the obstructing band itself is not visible. The diverticulum can also serve as a lead point for intussusception and should be suspected in any child presenting with intussusception who is outside the typical age range for idiopathic intussusception. Acute Meckel’s diverticulitis may mimic acute appendicitis in a child presenting with abdominal pain, fever, and vomiting. Visualization of a normal appendix is helpful in distinguishing these two entities, as well as identifying the ileum at the base of the diverticulum. This assessment is much more easily made with CT than with US. Identification of an enterolith on abdominal radiographs or CT is useful for suggesting the diagnosis of Meckel’s diverticulum in the setting of obstruction, especially when located in the right lower quadrant. There may be mixed-attenuation fecal material entrapped within the blind-ending diverticulum.

Mesenteric Adenitis

Not all children presenting to the emergency department with abdominal pain have an abnormality requiring emergent diagnosis and treatment. In the absence of other abnormalities, a child’s symptoms are often attributed to an entity called “primary mesenteric lymphadenitis.” Enlarged mesenteric lymph nodes on CT or US may be the only imaging abnormality present. The etiology for the lymphadenopathy is unclear, although a nonspecific gastrointestinal inflammation may be the underlying cause. While there is no precise size criterion that defines an abnormally enlarged mesenteric lymph node in children, a node with a short axis diameter greater than 8 mm is considered enlarged. Whereas these measurements are based on data acquired with CT, the diagnosis may also be made on the basis of US findings.

Omental Infarction

Omental infarction most often occurs in obese children. This entity is best recognized at CT, although it can also be detected with US. Patients often present with right lower quadrant or diffuse abdominal pain, and fever and elevated white blood cell count are often not present. Imaging studies (CT and US) demonstrate normal-appearing bowel, including the appendix. The presence of hazy, increased attenuation within the anterior abdomen in the region of the omentum is a hallmark of this diagnosis. The diagnosis may also be suggested at US by detection of an echogenic, masslike structure just deep to the anterior abdominal wall in the area of pain. If no other abnormalities are appreciated, this entity can be treated conservatively with prophylactic antibiotics and analgesics.

Urinary Tract Infection

The diagnosis of a urinary tract infection (UTI) in children is based on symptoms, bacterial growth in the urine, and other laboratory markers. Distinguishing between upper tract (i.e., pyelonephritis) and lower tract (i.e., cystitis) infection is based on clinical criteria such as the presence of a fever. Young children with a first-time UTI or any child with a febrile UTI warrants imaging evaluation of the urinary tract. The goal of imaging in children with UTI is to exclude an underlying structural abnormality that predisposes the child to develop infection, to evaluate for an obstructed urinary system or other pathology that would require urgent intervention (e.g., abscess), and to evaluate for evidence of renal damage such as scarring. Pyelonephritis in children is often secondary to vesicoureteral reflux. Although cortical renal scintigraphy is the most sensitive imaging technique for detection of acute pyelonephritis, it is rarely performed emergently. Most young children with a febrile UTI are evaluated for vesicoureteral reflux with a VCUG or radionuclide cystogram (RNC). These evaluations can be performed several days or weeks after the initial infection. Children presenting to the emergency department with a complicated UTI (persistent fevers despite antibiotics, or clinical signs and symptoms concerning for severe illness or sepsis caused by a UTI) warrant evaluation with ultrasound.

In patients with acute pyelonephritis, ultrasound may reveal focal areas of decreased attenuation. These same areas demonstrate decreased vascularity with color Doppler US. Urothelial thickening is often present. A severe infection may evolve into renal abscess or perinephric abscess. At US these collections appear as hypoechoic or anechoic masses with increased through-transmission (Fig. 6-30A). A renal abscess may simulate a solid mass at US. In these instances, contrast-enhanced CT is performed. At CT an abscess will appear as a focal, hypoattenuating mass (Fig. 6-30B). While the wall of the abscess enhances after contrast administration, the central portion of the abscess will not enhance. A perinephric abscess is suggested by fluid or soft tissue attenuation within the perinephric space. These collections may penetrate through Gerota’s fascia and involve surrounding structures, such as the psoas muscle. Urine cultures in patients with renal abscess are negative in up to 20% of cases.

Figure 6-30 A, Transverse US image through the kidney in an 8-year-old boy 1 day after a negative appendectomy was performed. A hypoechoic collection is present at the lower pole of the right kidney (arrows). B, Coronal reformatted image from a CT scan performed with oral and intravenous contrast demonstrates a hypoattenuating collection at the right lower pole (arrows) that does not enhance. This collection was later found to represent a renal abscess, and a drainage catheter was placed. Incidentally, this child had negative urine cultures.

Hydronephrosis

Hydronephrosis refers to dilatation of the urinary collecting system caused by an obstruction to the normal flow of urine. The obstruction may occur anywhere along the urinary tract from the renal calyces to the urethra. Stasis of urine and increased pressures within the collecting system may have deleterious effects on the kidney over time and lead to progressively worsening renal function. A dilated urinary collecting system is not always obstructed. VUR, for example, causes transient dilatation of the urinary collecting system. An obstructing ureteral calculus or stricture may lead to proximal hydroureteronephrosis (dilatation of both the renal collecting system and the ureter) that is indistinguishable from VUR. Determining the cause for a dilated collecting system is not always straightforward. Often other clinical parameters are necessary to make this determination, as well as additional imaging evaluation.

Ultrasound is the modality of choice for evaluating for hydronephrosis. Communication between multiple cystic-appearing, dilated renal calyces and the renal pelvis is an important finding at US. If these cystic spaces do not communicate with each other or with the renal pelvis it is more likely that the patient has cystic renal disease rather than a dilated collecting system. Color Doppler ultrasound is helpful in demonstrating prominent vessels in the renal hilum so that they are not mistaken for a dilated renal pelvis. The ureters are not typically visualized at US unless they are dilated. A dilated distal ureter can often be visualized posterior to the bladder at the level of the ureterovesicular junction (UVJ). If a single ureter is dilated at this level, the obstruction is likely at the UVJ; if both ureters appear dilated at this level the obstruction is likely within or below the bladder (although bilateral UVJ obstruction can occur). Imaging of the bladder may reveal wall thickening and/or trabeculations in patients with an underlying abnormality, such as a neurogenic bladder. Intraluminal debris or calculi may be present within the bladder of patients with concurrent UTI.

Ureteropelvic Junction Obstruction

A common cause of hydronephrosis in children is ureteropelvic junction obstruction (UPJO). UPJO may be secondary to either intrinsic or extrinsic factors. Prenatal US detects many children with intrinsic UPJO; therefore approximately half of all children presenting later in childhood with intermittent UPJO have an extrinsic abnormality such as a crossing vessel. UPJO is often an intermittent phenomenon. Children with intermittent UPJO present with episodic abdominal pain, nausea, and vomiting. The severity of pain correlates with the rapidity of the onset of symptoms rather than the degree of distention of the collecting system. Hematuria is present in approximately half of patients and aids in elucidating the urinary system, rather than other abdominal organs, as the source of symptoms. UPJO is more common in males, and occurs most often on the left side.

The ultrasound appearance of UPJO is a dilated renal collecting system on the patient’s symptomatic side during the acute pain crisis (Fig. 6-31). The proximal ureter will appear dilated with an abrupt tapering at the level of the crossing vessel. US should be performed during the pain crisis since the hydronephrosis is present only when the patient is experiencing symptoms. Unilateral hydronephrosis is not specific for UPJO, nor does US evaluate the functional status of the kidney. While additional investigation is often required before treatment can be initiated, US is critical in the preliminary imaging of patients with suspected urinary tract obstruction.

Figure 6-31 Sagittal US image through the kidney in this 6-month-old baby with ureteropelvic junction obstruction. The kidney (arrows) is barely visualized secondary to the massive hydronephrosis.

Urolithiasis

While less common in children than in adults, urinary tract calculi are an important cause of flank pain and urinary tract infection. The majority of urinary tract calculi in children are located in the kidneys or ureters. Boys and girls are affected with nearly equal frequencies. Abdominal or flank pain is the most common presenting complaint, but is present in less than half of children with renal stones. Other signs and symptoms include pyuria, hematuria, nausea, vomiting, fever, and urinary retention. Smaller children who are not able to verbalize their symptoms more commonly present with symptoms of infection rather than specific complaints of pain. The majority of pediatric patients with urolithiasis have an underlying predisposition to forming stones. These predisposing conditions include congenital structural disorders of the urinary system (e.g., UPJO or “horseshoe” kidney), metabolic disorders (e.g., hypercalciuria or cystinuria), prolonged states of immobilization leading to urinary stasis, enteric disease causing intestinal malabsorption, and recurrent urinary tract infections.

The imaging evaluation of a child with suspected urolithiasis is performed with US, CT, or both. US is an appealing first-line imaging modality because it detects complications of urolithiasis such as hydronephrosis or perinephric fluid without the use of ionizing radiation. At US, renal calculi appear as echogenic foci with posterior acoustic shadowing (Fig. 6-32). US also has the advantage of evaluating the renal parenchyma for changes of medical renal disease or evidence of scarring. US is less sensitive than CT for detection of urinary tract calculi and is poorly accurate at diagnosing calculi that are confined to the ureter. CT is often performed in children who have persistent urolithiasis symptoms despite a normal US examination.

Figure 6-32 Sagittal US image through the right kidney in a teenage girl with known renal calculi. An echogenic calculus is present in the lower pole with posterior acoustic shadowing (arrows).

Unenhanced CT (without oral or intravenous contrast) is highly sensitive for the detection of urolithiasis in pediatric patients. Lower-dose CT protocols have been developed that minimize radiation risk to patients. Diagnosis of urolithiasis on CT is facilitated because phleboliths, which often mimic ureteral calculi in older patients, are rarely encountered in children. Secondary CT signs of urolithiasis are helpful in confirming the diagnosis, and include proximal ureteral dilatation, renal enlargement, hydronephrosis, decreased renal attenuation, the tissue rim sign, and perinephric stranding. The tissue rim sign refers to the circumferential rim of soft tissue attenuation surrounding a ureteral calculus (Fig. 6-33). These secondary signs of urinary tract calculi are less commonly encountered in pediatric patients versus their adult counterparts. Proximal ureteral dilatation and renal enlargement are the most commonly detected secondary signs, and occur in approximately half of patients. Perinephric or periureteral stranding, rarely encountered in the pediatric patient, may be secondary to the decreased amount of perinephric fat in this population.

Figure 6-33 Axial image from a noncontrast CT performed in a 17-year-old boy with left groin pain and a negative scrotal US. There is a tiny calculus at the left ureterovesicular junction (white arrowhead) with periureteral stranding.

Scrotal Hernia

If the testes have not descended into the scrotum by 1 year of age cryptorchidism (failure of the testes to descend into the scrotal sac), inguinal-scrotal hernias, and hydroceles may result. While these conditions are most often detected on physical examination, it is not uncommon to make the diagnosis at ultrasound. Plain films are diagnostic of scrotal hernias in infants when the finding of bowel gas in the scrotum is noted (Fig. 6-34). Since this is not a common finding, US is the imaging modality of choice for evaluation of a scrotal hernia when the physical exam is inconclusive. Herniated omentum appears as an echogenic structure outside of the testis and epididymis. Bowel loops containing both air and fluid may also be visualized within the scrotum. Visualization of bowel peristalsis during imaging is an important finding to note when herniated bowel is identified within the scrotum. If bowel is identified within the scrotum but no peristalsis is visualized during the entire examination, the bowel may be strangulated. An akinetic, dilated loop of bowel observed at US in a hernia sac is reported as a highly sensitive and specific sign of bowel strangulation. A strangulated scrotal hernia is an indication for urgent surgery.

Figure 6-34 Abdominal radiograph in a newborn infant with several loops of mildly dilated bowel reveals gas projecting over the scrotum at the inferior aspect of the image (arrow). This infant has a scrotal hernia.

Epididymitis

Epididymitis, or epididymo-orchitis, is an infection of the epididymis and/or testis and is a common cause of acute-onset scrotal pain in children. Typically, scrotal pain associated with epididymitis or epididymo-orchitis is relieved when the testes are elevated over the symphysis pubis, a maneuver that is called the Prehn sign. In contradistinction, the pain associated with testicular torsion is not relieved by this maneuver. While the causative agent in epididymitis is usually not identified in young children, the infection usually originates in the prostate gland or bladder and spreads to the epididymis and testis via the vas deferens and spermatic cord lymphatics. A congenital anomaly of the urinary tract may be present. In adolescents the cause is most often a sexually transmitted infection.

Ultrasound examination of a child with epididymitis demonstrates enlargement of the epididymis (primarily the head) with heterogeneous echotexture. On color Doppler evaluation there is increased blood flow to the epididymis and/or testis (Fig. 6-35). A reactive hydrocele may be an associated finding. When the entire testis is involved, it is often enlarged and has altered echogenicity. On gray-scale imaging findings alone, the appearance of the testis may mimic a diffusely infiltrative disease such as leukemia or lymphoma, although the clinical presentation should suggest the correct diagnosis.

Figure 6-35 A, Sagittal US image through the left testis in this 17-year-old male with left scrotal pain. The left epididymis is enlarged and hyperemic. B, Sagittal US image in the same patient demonstrating the normal right testicle for comparison.

Torsion of the Testicular Appendages

While there are four testicular appendages, only two are commonly visible at ultrasound: the appendix testis and appendix epididymis. These appendages are remnants of embryonic ducts and serve no real function. Because they are attached by a small pedicle, they are prone to torsion. Torsion of these appendages is one of the most common causes of acute scrotal pain in children. The appendix testis is more commonly affected than the appendix epididymis, although it is often difficult to identify the offending appendage. Patients are usually young, prepubertal males who complain of acute-onset scrotal pain. On clinical examination there may be a bluish discoloration of the skin at the site of pain, which is called the “blue dot” sign and is pathognomonic. At ultrasound the torsed appendix is often identified as a round, extratesticular, extraepididymal mass lacking color Doppler flow (Fig. 6-36). A reactive hydrocele may be present, as well as scrotal wall skin thickening.

Figure 6-36 Transverse US image through the testis on a teenage boy with scrotal pain. A mixed echogenicity structure (arrowhead) is connected to the testis by a thin stalk (arrow). Color Doppler US failed to demonstrate flow within this structure. The child was given a presumed diagnosis of torsed testicular appendage and was treated conservatively.

Testicular Torsion

The testis and epididymis attach to the inner scrotal wall by a broad attachment. When this attachment is too narrow, it may function as a pedicle around which the testis may twist. This twisting, or torsion, compromises the blood supply to the testis, which may lead to infarction of the testis. Scrotal pain is often the presenting complaint in boys with testicular torsion, a condition that requires emergent treatment to maintain viability of the affected testis. Testicular salvage rates are greatest when surgery is performed within 6 hours of the onset of symptoms. After 24 hours the testis is usually no longer salvageable. Patients with the “bell clapper” deformity, where the tunica vaginalis joins high on the spermatic cord, are more prone to testicular torsion than the general population.

Ultrasound is the preferred imaging examination for the diagnosis of testicular torsion because of its high sensitivity and specificity. Gray-scale US findings are often completely normal when torsion is present, and the testes may appear symmetric with respect to both size and echogenicity. A small hydrocele may be present on the affected side. Within a few hours of the onset of symptoms, the scrotal wall will appear thickened, and the testis and epididymis appear enlarged and hypoechoic (secondary to inflammation and/or hemorrhage). Color Doppler is crucial for the diagnosis of torsion. The lack of demonstrable blood flow to the affected testis (assuming appropriate US settings are used) is virtually pathognomonic for torsion (Fig. 6-37). In prepubertal patients it is often difficult to demonstrate the presence of blood flow even in normal testes. Testicular scintigraphy is often used as an adjunct to US when a diagnosis of torsion cannot be made with certainty. Given the added delay of scintigraphic examinations, however, some surgeons operate on the basis of an equivocal US. The treatment for testicular torsion is detorsion of the affected testicle, and orchiopexy, where the testis is affixed to the scrotal wall to prevent torsion from recurring in the future.

Figure 6-37 Transverse US image of bilateral testes in a teenage boy with left testicular pain. There is no color Doppler flow to the left testis. This patient had testicular torsion confirmed at surgery.

Ovarian Torsion

Acute onset of adnexal pain in a young or adolescent female is concerning for ovarian torsion. The Fallopian tubes are long in children and the ovaries are hypermobile, which increases their susceptibility to torsion. Although normal ovaries may torse, most often there is an ovarian or paraovarian cyst or mass that predisposes the ovary to torsion by functioning as a fulcrum around which the ovary can twist. The ovary becomes twisted around its pedicle leading to various degrees of hemorrhagic infarction. If surgery is not performed expeditiously, future fertility and hormonal regulation may be compromised. There is a slight predilection for torsion to involve the right ovary. When the right ovary is affected, the diagnosis is more difficult to establish given the number of other conditions that present with right lower quadrant or pelvic pain such as appendicitis, Meckel’s diverticulitis, and inflammatory bowel disease. The median age of patients with ovarian torsion is 11 years.

Pelvic US is the study of choice for evaluation of ovarian torsion. Normal ovaries often appear hypoechoic relative to the adjacent pelvic tissue, and have an ovoid or ellipsoid shape. While the size of normal ovaries varies, mean ovarian volumes are approximately 1.2 cm³ in prepubertal girls and 5.8 cm³ in pubertal girls. Microcystic follicles are routinely identified in normal ovaries. When the ovaries demonstrate normal gray-scale imaging characteristics and have a normal size and shape, color Doppler evaluation is usually not necessary. If, however, one ovary appears abnormally large relative to the other side, torsion may be present. In nearly all cases of ovarian torsion, the affected ovary is massively enlarged and has a round or globular configuration. In neonates and young girls ovarian torsion is commonly seen as a large cystic mass with fluid–debris levels. In young or adolescent girls the more classic imaging appearance is an enlarged, echogenic ovary with multiple enlarged peripheral follicles. In other cases, the ovary may appear as a complex cystic mass secondary to the presence of an underlying cyst or tumor (Fig. 6-38). Color Doppler evaluation of the ovary will often reveal an absence of blood flow, a finding classically associated with ovarian torsion. However, torsion may be present even if arterial waveforms are demonstrated because the ovary has a dual blood supply (from both the uterine and ovarian arteries). The presence of arterial waveforms within the ovary should not sway the diagnosis away from ovarian torsion if the gray-scale imaging findings and physical examination are consistent with torsion.

Figure 6-38 Sagittal US image of the pelvis in a 15-year-old girl with right lower quadrant pain. The bladder is nearly empty (arrowhead), and there is a large, complex cystic mass within the pelvis that contains a mural nodule (arrow). The uterus is posterior to this mass (arrow). Color Doppler revealed no convincing flow to this mass. At surgery the patient was found to have a right ovarian teratoma that had torsed.

Hemorrhagic Ovarian Cyst

Although hemorrhagic ovarian cysts are common, their imaging appearance is widely variable. Hemorrhagic cysts are almost exclusively encountered in menstruating, adolescent females. Hemorrhagic cysts develop at the time of ovulation when vessels surrounding a corpus luteal cyst rupture, giving rise to hemorrhage within the corpus luteum. As the cyst evolves over time, the sonographic features change with the stage of clot retraction. Patients may present with acute-onset adnexal pain, which may be severe.

Physiologic ovarian follicles measure less than 3.0 cm in diameter. Most hemorrhagic cysts measure 3.0 to 3.5 cm in diameter, have a thin outer wall, and demonstrate posterior acoustic through-transmission. Fine, reticular septations resembling a fishnet pattern are a common finding at US. These septations represent fibrin strands, which contain no blood flow. In some patients the hemorrhagic cyst contains retracting clot. While a large portion of the cyst appears anechoic the retracting clot appears as an adherent, echogenic structure within the cyst that contains no blood flow. In rare cases, when the clot becomes very small it can simulate a mural nodule and raise concern for ovarian neoplasm. Fluid–fluid or fluid–debris levels can also be demonstrated within a hemorrhagic cyst. Hemorrhagic cysts can be complicated by rupture, with free spill of hemorrhagic contents into the pelvis. When this occurs, echogenic fluid is demonstrated within the pelvis surrounding the uterus and adnexa. In some cases, the hemoperitoneum may be massive.

Other causes of adnexal pain include tubo-ovarian abscess, ectopic pregnancy, and pelvic inflammatory disease. In patients who are sexually active, these diagnoses should also be considered within the differential. Human chorionic gonadotropin results are critical for the accurate interpretation of a pelvic US examination in a sexually active female with complaints of pelvic pain.

Hematocolpos/Hematometrocolpos

Patients with imperforate hymen present at the time of adrenarche with cyclic bouts of pelvic pain that correspond to menstruation episodes. The patient may not be aware that she has begun menstruating due to the lack of passage of blood products from the obstructed vagina. The diagnosis of hematocolpos is often made on the basis of physical examination, as the hymen may appear to be bulging outward secondary to accumulated secretions. In some cases US may suggest the diagnosis when a thorough physical examination has not been performed. In rare cases, the patient may have a congenital uterine anomaly with an obstructed hemivagina. In these cases the diagnosis is clinically more confusing since the patient will appear to menstruate normally given the presence of an unobstructed hemivagina.

US examination in these patients reveals a round or oblong-shaped midline or paramidline pelvic mass that compresses the bladder anteriorly and rectum posteriorly. The mass appears hypoechoic with posterior acoustic transmission. Internal echoes are present within the mass, reflecting the complex nature of its contents (hemorrhage). If only the vagina is involved, the uterus will be visualized separately from this mass (Fig. 6-39). When the uterus is affected, only a thin rind of normal uterine tissue may be visualized. Patients will most often experience relief of symptoms once hymenotomy is performed.

Figure 6-39 Sagittal US image through the pelvis in a 13-year-old female with severe, crampy abdominal pain. Inferior to the uterus (arrow) there is an oblong-shaped mass (arrowhead) with low-level internal echotexture. The mass is within the vagina. This patient had hematocolpos at surgery.

Stridor

Stridor is a term used to describe a high-pitched sound caused by partial obstruction of the airway. Stridor can have an inspiratory, expiratory, or biphasic pattern (both inspiratory and expiratory). An inspiratory pattern suggests an upper airway cause (e.g., epiglottitis). An expiratory pattern suggests a lower airway etiology (e.g., tracheomalacia). A biphasic pattern suggests a glottic or subglottic obstruction (e.g., subglottic hemangioma). Imaging evaluation of the child with stridor is commonly performed with neck and/or chest radiographs depending on the pattern of stridor and associated clinical findings.

Retropharyngeal Abscess

In addition to stridor, patients with retropharyngeal abscess typically also present with symptoms of neck pain and fever. Radiographs of the neck are often requested to evaluate the retropharyngeal soft tissues. Due to the wide range of ages and sizes within the pediatric population, precise measurements of the retropharyngeal soft tissues are not as reliable as relative measurements for determining the presence of soft tissue swelling. The thickness of the retropharyngeal/prevertebral soft tissues should not be greater than the anteroposterior diameter of the adjacent vertebral body (Figs. 6-40). False thickening of the retropharyngeal/prevertebral soft tissues can occur if the child’s neck is in flexion, or if the film was acquired with the child in end-expiration. Although CT can be used to further evaluate positive findings on neck radiographs, it is often prudent to repeat the lateral radiograph of the neck with the patient in a more exaggerated extension or in full inspiration when the initial radiographs are felt to be falsely positive.

Figure 6-40 A, Lateral neck radiograph in a 3-year-old child with fever and neck pain reveals thickening of the retropharyngeal soft tissues (arrows). B, Sagittal reformatted image obtained from subsequent CT of the neck demonstrates evidence of retropharyngeal cellulitis (arrow).

Another common cause of acute stridor within the nasopharynx and oropharynx is enlargement of the tonsils and adenoids. This diagnosis can be readily differentiated from retropharyngeal abscess on the basis of findings made on lateral radiograph of the neck (Fig. 6-41). Enlarged adenoids and tonsils cause encroachment on the nasopharyngeal and oropharyngeal airway, without associated thickening of the retropharyngeal soft tissues.

Figure 6-41 Lateral radiograph of the neck in an 11-year-old female with difficulty breathing demonstrates enlarged adenoids (arrowhead) and palatine tonsils (arrow).

Epiglottitis

Epiglottitis is inflammation and enlargement of the epiglottis, aryepiglottic folds, and supraglottic tissue. Epiglottitis is a life-threatening condition caused by both viral and bacterial etiologies. Haemophilus influenza B has historically been the most common cause of epiglottitis, although its incidence has decreased since the development of the Haemophilus influenza B vaccine. The epiglottis can be identified at the level of the hyoid bone on lateral radiographs of the neck. On lateral neck radiographs “thumblike” enlargement of the epiglottis and thickening of the aryepiglottic folds are findings consistent with epiglottitis (Fig. 6-42). Children for whom there is high clinical and radiographic concern for epiglottitis are often examined in the operating room with the presence of an anesthesiologist, as airway compromise may be precipitated by manipulation of the hypopharynx, and urgent intubation or tracheostomy may be necessary.

Figure 6-42 Lateral neck radiograph in a 6-year-old boy with fever, sore throat, and drooling. Image demonstrates thumb-like enlargement of the epiglottis (arrow). This child had epiglottitis.

Croup

Viral croup (laryngotracheobronchitis) is the most common cause of acute stridor in children. Findings on chest or neck radiographs include narrowing of the subglottic airway. This is best visualized on the anteroposterior projection as the “steepling” or loss of the normal shouldering in the subglottic region (Fig. 6-43). Bacterial tracheitis, also known as membranous croup, is another serious upper airway infection that is seemingly becoming more common as viral croup and epiglottitis have decreased in incidence. The diagnosis of bacterial tracheitis can be suggested on radiographs if subglottic narrowing is seen in conjunction with tracheal irregularity or a soft tissue membrane.

Figure 6-43 Anteroposterior radiograph of the neck in this 2-year-old child with stridor demonstrates “steepling” of the subglottic airway (arrow) secondary to viral croup.

Glottic/Subglottic Masses

Subglottic masses may present in an emergent setting when a superimposed viral or bacterial illness causes exacerbation and acuity of symptoms. The most common glottic mass is a papilloma, and the most common subglottic mass is a hemangioma. Extrinsic mass effect from mediastinal or neck masses can cause airway compromise. Bronchogenic cysts, foregut duplication cysts, and vascular rings can cause airway narrowing and acute symptoms when coexistent with an acute respiratory infection. Any abnormal deviation of the trachea (besides the mild contour deformity from the normally positioned left-sided aortic arch) should be investigated (Fig. 6-44). Fluoroscopy and contrast esophagram can be performed to confirm the presence of mass effect on the airway and adjacent esophagus. If these initial studies demonstrate an abnormality, CT or magnetic resonance imaging (MRI) can better visualize the abnormality.

Figure 6-44 Anteroposterior radiograph of the neck in a teenage boy with Down syndrome demonstrates a right lateral impression on the subglottic trachea (arrow) secondary to a mass that was later found to represent a spindle cell tumor.

Foreign Body

The majority of patients with an aspirated foreign body (FB) are between the ages of 1 and 3 years. The FB may become embedded anywhere along the airway in children. Symptoms of aspirated FB include choking, wheezing, coughing, and dyspnea. Patients with an aspirated FB require bronchoscopy for removal of the object. Clinical history, radiography, and fluoroscopy can all be used to determine if a FB has been aspirated. If the FB is caught at the level of the vocal cords, the pharynx may appear hyperinflated on neck radiographs. Aspirated FBs are likely to settle into the right mainstem bronchus, given that the latter typically has a more vertical orientation than the left mainstem bronchus. In children with a history of suspected aspirated foreign body, inspiratory and expiratory chest radiographs evaluating for areas of air trapping are performed. Bilateral decubitus views can be performed in place of expiratory films in younger patients who are not able to cooperate for inspiratory and expiratory imaging. In a normal patient, both lungs should collapse equally on an expiratory film, and the dependent lung should collapse on a lateral decubitus film while the nondependent lung expands. When the dependent lung does not collapse on decubitus films, air trapping is implied, and an aspirated FB must be suspected (Figs. 6-45). Radiographs cannot exclude the presence of an aspirated foreign body, and false-negative radiographs are common. Negative radiographs should not preclude bronchoscopy in a child with a convincing history or physical examination consistent with aspirated FB. Occasionally, when the diagnosis of FB aspiration is delayed, postobstructive pneumonia may develop. In some cases, plain films may reveal that the FB has not been aspirated, but rather is lodged within the esophagus (Fig. 6-46).

Figure 6-45 A, Left lateral decubitus chest x-ray in a 22-month-old with cough and suspected foreign body aspiration fails to demonstrate normal collapse of the dependent left lung. B, Right lateral decubitus film in the same patient demonstrates normal collapse of the right lung. This patient was found to have a peanut in the left mainstem bronchus at bronchoscopy.

Figure 6-46 Lateral radiograph of the neck in this child demonstrates an ingested radio-opaque foreign body lodged within the esophagus posterior to the trachea.

Pneumonia

Lower respiratory tract infections are one of the most common indications for imaging the chest in pediatric patients. Bacterial pneumonia is manifested on a chest radiograph as an area of focal air space opacity without associated volume loss (Fig. 6-47). Pneumonia may be complicated by pleural effusion or parenchymal necrosis. Lobar pneumonias are the most common presentation of a bacterial pneumonia in children. Radiographs are often repeated after completion of antibiotic therapy to assess the resolution of the consolidation. If there has been no significant improvement after appropriate treatment, additional imaging with CT is warranted. If a patient has had multiple, appropriately treated, recurrent pneumonias in the same location, a CT scan of the chest may be warranted to assess for an underlying anomaly predisposing the patient to recurrent illnesses, such as pulmonary sequestration. In young children, bacterial pneumonia may also present on chest radiographs as a round mass, aptly called “round pneumonia.”

Figure 6-47 Anteroposterior chest radiograph in this teenager with symptoms of pneumonia demonstrates a focal opacity in the lingula (arrow), consistent with pneumonia.

Patients with sickle cell disease are prone to acute infiltrates on radiographs, termed “acute chest syndrome.” While these patients are often treated with antibiotics, not all of them truly have an infection. Pulmonary infarctions can have an appearance similar to that of infection, and studies suggest that evaluation of the location and age of the patient may be helpful in predicting whether there is an underlying infection in these “acute chest” patients.

Bronchiolitis

Viral bronchiolitis is one of the most frequent causes of infant hospitalization during the winter. Infants with bronchiolitis present with wheezing, cough, and respiratory distress. Nontoxic-appearing infants with classic symptoms usually require no imaging. Chest radiographs are often obtained when the diagnosis is unclear, or when an underlying bacterial pneumonia is suspected. Chest radiographs often reveal evidence of airway disease, which include areas of atelectasis, air trapping, and bronchiolar wall thickening (Fig. 6-48). Atelectasis and air trapping are findings related to underlying bronchial obstruction caused by edema and secretions. Bronchiolar wall thickening is most prominent in the perihilar regions on chest radiographs.

Figure 6-48 Anteroposterior chest radiograph in this infant with wheezing reveals hyperinflated lungs with areas of atelectasis and air trapping, as well as peribronchiolar wall thickening. This child was treated for bronchiolitis.

Pneumothorax

Acute shortness of breath in an older child may be secondary to a spontaneous pneumothorax. Pneumothoraces in this age group are often caused by rupture of a small subpleural bleb, typically located at the lung apex. Chest radiographs reveal variable degrees of collapse of the affected lung, and the visceral pleura will be identified as a discrete line paralleling the chest wall. A shift of the heart and mediastinum to the opposite hemithorax is consistent with tension pneumothorax, which requires immediate decompression (Fig. 6-49). Patients with an underlying parenchymal bleb will often have recurrent pneumothoraces if the bleb is not resected or if pleurodesis is not performed. CT is more sensitive than plain radiographs for visualizing tiny blebs. CT is often performed after reexpansion of the affected lung has occurred to best visualize the peripheral lung parenchyma. Patients with underlying pulmonary disorders such as cystic fibrosis and Langerhans cell histiocytosis are at higher risks for spontaneous pneumothoraces due to the presence of blebs and cysts.

Figure 6-49 An anteroposterior chest radiograph performed on a teenage girl with acute-onset shortness of breath demonstrates complete collapse of the right lung with inferior displacement of the right hemidiaphragm and mild shift of the heart into the left hemithorax, consistent with tension pneumothorax.

Skull Fractures

The leading cause of death in the pediatric population is traumatic brain injury. Patterns of acute intracranial injury are similar to the adult population and are further discussed in other chapters. There are, however, certain special considerations to keep in mind when evaluating the pediatric brain. Skull fractures in children are often difficult to detect given the presence of open sutures in these young patients. Plain skull radiographs are useful for evaluating fractures in certain situations, although CT has largely supplanted plain radiographs for this diagnosis. This is largely in part due to the superior capability of CT to evaluate for complications of fracture, such as intracranial hemorrhage. The detection of skull fractures can be subtle even on CT. Skull fractures must be distinguished from the normal sutures (Fig. 6-50). Cranial sutures are usually symmetric and lack overlying soft tissue swelling, in contrast to skull fractures (Fig. 6-51). Accessory and anomalous sutures can also be mistaken for skull fractures. If oriented along the axial plane of the CT scan, skull fractures may not be visible on the axial images. It is critical to evaluate the scout image so that these fractures are detected. The degree of comminution of the fracture, depression or displacement of fragments, and additional intracranial findings such as hemorrhage, mass effect, and edema are all important associated findings. Bilateral fractures, complex fractures, or fractures that cross a suture line, especially in patients without an appropriately significant traumatic history, may be signs of nonaccidental injury (NAI). NAI should be suspected when the history does not support the radiographic findings. Although subdural hematomas may be present in victims of NAI, hemorrhage of different ages does not necessarily equate with abuse, especially in children with underlying enlargement of the extra-axial spaces.

Figure 6-50 3D reconstructed images of the calvarium from a head CT of an infant demonstrate normal sutural anatomy. A, The metopic suture has fused (arrowhead). Normal coronal suture (arrow). B, Normal sagittal (arrow) and lambdoid sutures (arrowheads).

Figure 6-51 Lateral skull radiograph in a 6-month-old boy who was a victim of nonaccidental injury demonstrates a right parietal skull fracture (arrow).

Hypoxic Ischemic Injury

Patients who have a history of near-drowning may suffer hypoxic ischemic injury of the brain secondary to profound asphyxiation. The resultant cerebral edema and infarction can be subtle on CT, especially in the early stages after the event. Lack of visualization of normal sulci, an abnormally dense cerebellum, and loss of normal grey/white matter differentiation should suggest underlying cerebral edema. These patients are often followed clinically with imaging repeated over the next several days to further evaluate the extent of hypoxic ischemic injury.

Hydrocephalus

Hydrocephalus refers to the overaccumulation of cerebrospinal fluid within the ventricular system. Children with hydrocephalus often present with headache, vomiting, and lethargy. Hydrocephalus may be secondary to congenital or acquired factors. Congenital hydrocephalus may be secondary to in utero infection, aqueductal stenosis, or malformations of the brain (Chiari or Dandy-Walker). Acquired causes of hydrocephalus include infection, hemorrhage, and obstructing mass lesions. The ventricles will appear dilated on CT, and hypoattenuating areas adjacent to the ventricles represent sites of transependymal cerebrospinal fluid absorption. Abnormal dilatation of the ventricles may be defined by several criteria, including visualization of the temporal horns of the lateral ventricles (usually not visible), upward bowing of the corpus callosum, and enlargement of the frontal horns of the lateral ventricles as compared with the calvarial diameter measured from the inner tables (greater than 50%). Depending on the cause of the hydrocephalus, all of the ventricles may not be equally dilated. In aquaductal stenosis, for example, the third and lateral ventricles will appear dilated while the fourth ventricle is normal.

Assessing the size of the ventricular system and extra-axial spaces can be challenging in infants. Prominence of the extra-axial spaces in infants is often benign and self-resolving. Infants are often detected at a routine visit to the pediatrician to have an enlarging head circumference. This occurs typically between 3 and 9 months of age with expected resolution by the age of 2 years.

Venous Sinus Thrombosis

Venous sinus thrombosis (VST) can be caused by a variety of different factors, both local and systemic. Local processes include mastoiditis and intracranial neoplasm; systemic processes include genetic predisposition to hypercoagulopathy, underlying malignancies, and medications. In young children, severe dehydration can lead to venous stasis and thrombosis. These patients usually present with lethargy, irritability, and/or seizures.

VST can be detected on the basis of findings made on head ultrasound, CT, and MRI. On US, images obtained through the anterior fontanelle of young infants will demonstrate the lack of Doppler flow within the superior sagittal sinus. On noncontrast CT, thrombus within a venous sinus will appear abnormally dense (Fig. 6-52A). This finding may also be seen in dehydrated patients with an elevated hematocrit level. If this is the case the attenuation of the arteries and veins should appear similar, whereas in VST the sinus will appear denser than the arteries. At contrast-enhanced CT the “empty delta” sign describes the appearance of an intraluminal filling defect (i.e., thrombus) within the dural envelope. MRI is more sensitive for detection of venous thrombosis. Findings on MRI consistent with VST include absence of normal flow voids and abnormal signal intensity within the sinus (Fig. 6-52B). Indirect signs of VST include collateral venous channels, cerebral hemorrhage, and signs of increased intracranial pressure. VST may lead to venous infarction and hemorrhage in the cortex and/or basal ganglia, depending on the sinuses involved.

Figure 6-52 A, Axial CT image through the brain demonstrates hyperattenuation (arrowhead) within the straight sinus. B, MR venography confirms the absence of flow within the straight sinus (arrowhead), consistent with sinus thrombosis.

Meningitis/Encephalitis

Meningitis is a clinical diagnosis, often made on the basis of history and laboratory markers, including cerebrospinal fluid analysis. Imaging of patients with meningitis is usually not performed unless complications are suspected, such as encephalitis, epidural abscess, or venous sinus thrombosis. In these instances, contrast-enhanced MRI is the most appropriate imaging evaluation, although the diagnosis can also be suggested based on findings made at CT. In a child with clinical and laboratory findings consistent with intracranial infection, the effacement of sulci and subtle differences in attenuation of the cortical gyri on CT scan suggest parenchymal infection such as encephalitis. On MRI, the involved brain parenchyma will appear abnormally increased in signal on fluid-sensitive sequences (Figs. 6-53). Cerebellitis, or inflammation of the cerebellum, may be suggested on noncontrast head CT by areas of abnormal hypointense foci within the cerebellum, often in a pattern mimicking the longitudinal pattern of the cerebellar folia (Fig. 6-54). Often a recent history of a viral infection or immunization can be recalled. Cerebellitis may be suggested by CT, but abnormalities may be subtle and MRI is usually the diagnostic study.

Figure 6-53 A, Axial CT image through the brain in a 4-year-old boy with a history of otitis media followed by changes in mental status reveals loss of normal gray–white differentiation and effacement of sulci. B, T2-weighted MR image reveals diffusely abnormal signal intensity throughout the cerebellar hemispheres. This child had encephalitis.

Figure 6-54 Axial CT image obtained in a young girl presenting with ataxia reveals abnormal hypoattenuating lesions within the cerebellum (arrows), consistent with cerebellitis. This was later confirmed at MRI.

Cervical Spine Injury

Pediatric cervical spine injury is relatively uncommon, with an incidence between 1% and 2%. Younger children (less than 8 years) are more apt to injure the upper cervical spine (C1–C2) than older adolescents (greater than 8 years), who are more apt to injure the lower cervical spine (C3–C7). This pattern of injury is thought to be due to the mechanics and structure of the maturing cervical spine. The multiple synchondroses in the upper cervical spine are points of relative instability. The relatively large size of the head in a child in comparison with adults places increased stress on the upper cervical spine. The causes of cervical spine trauma are also different in the two age groups, with motor vehicle accidents being the primary cause of injury in the younger group and sports/recreation injuries the leading cause in the older group.

Despite the widespread availability of CT scanners in many emergency departments, plain radiographs of the cervical spine are still the mainstay for evaluating pediatric cervical spine trauma. There are many imaging pitfalls in the evaluation of the cervical spine in children. Knowledge of the multiple synchondroses of C2 is important for the accurate diagnosis of injury. The possibility of fracture at the synchondrosis of the dens should be raised if there is anterior angulation or displacement of the dens in relation to the body of C2. The ring apophyses of the vertebral bodies are normal structures that may be mistaken for avulsion or chip fractures. The normal pseudosubluxation at C2–C3 (due to ligament laxity in young children) may raise concerns in clinicians unfamiliar with this common appearance. Patient cooperation is often limited in the younger age group, and it may be difficult to impossible to obtain odontoid views.

Algorithms to direct the most judicious use of radiology in clearing the cervical spine have been suggested. In an effort to limit the radiation exposure to pediatric patients, limited use of CT for cervical spine evaluation is recommended. Initial evaluation of the pediatric cervical spine should be performed with plain radiographs. If concern for occult fracture persists after initial radiographs, focused CT can be performed through the levels of concern. If a cervical spine fracture is present CT may then be performed through the entire cervical spine to exclude additional fractures. There is a small subset of patients with injury to the cervical spine without radiographic abnormalities. This more commonly occurs in younger patients (less than 8 years).

Mastoiditis

Fever and ear pain are common symptoms of otitis media (OM) in young children. OM is diagnosed on the basis of physical exam findings, and is commonly treated with antibiotics. Imaging is not indicated for uncomplicated OM. Lack of response or progression of symptoms while on antibiotics may prompt further evaluation for complications of OM or other causes for the patient’s symptoms. When mastoiditis or other complications of OM are clinically suspected, a CT through the temporal bones should be performed with intravenous contrast. Fluid within the middle ear on CT scan is consistent with OM. Mastoiditis is often associated with OM and represents extension of infection from the middle ear into the mastoid air cells, as these structures are contiguous. Bony erosion or intracranial extension of infection (such as a subperiosteal abscess) is evidence of coalescent mastoiditis, and surgical intervention may be required (Fig. 6-55). Given the proximity of the dural venous sinuses to the temporal bone, particular attention should be paid in order to exclude secondary venous thrombosis.

Figure 6-55 Axial CT through the temporal bones in a young child with complicated otitis media demonstrates abnormal fluid attenuation within the mastoid air cells on the right (arrow) with osseous destruction consistent with coalescent mastoiditis.

Cervical Adenitis

Children presenting to the emergency department with enlarged cervical lymph nodes, fever, and an elevated white count often have a diagnosis of cervical adenitis. Cervical adenitis is a nonspecific inflammation of the lymph nodes that can be secondary to bacterial or viral infection. Imaging is performed in cases where there is concern for abscess formation. Ultrasound is often performed initially to evaluate the superficial, or palpable, lymph nodes. US is excellent at differentiating between solid and cystic masses, and can identify abscesses or fluid collections that are amenable to drainage. While US evaluation may be sufficient for evaluating superficial lymph nodes, signs and symptoms of a tonsillar infection such as trismus, drooling, and sore throat may prompt an evaluation with contrast-enhanced CT. CT can identify a potential peritonsillar abscess and assess the mass effect on the airway, as well as assess for displacement, compression, or thrombosis of adjacent vessels. Thrombosis of the internal jugular vein or a tributary vein in association with peritonsillar abscess is termed Lemierre syndrome. Lemierre syndrome is usually caused by the bacterium fusobacterium. Nontuberculous mycobacterial infection can be suggested in a child with low-density lymphadenopathy particularly when a draining sinus tract is present. In the absence of a draining sinus tract or signs/symptoms of infection, the differential diagnosis for multiple enlarged lymph nodes in a child includes lymphoproliferative disorders, such as lymphoma.

Anterior midline neck infections should suggest an underlying congenital abnormality such as thyroglossal duct cyst or dermoid cyst. Abscesses along the anterior border of the sternocleidomastoid may represent a sequela from lymphadenitis or superinfection of a second brachial cleft cyst. If CT of an “acute onset” neck mass demonstrates a multicystic collection with internal fluid/fluid levels, the diagnosis may be a lymphatic malformation. This diagnosis becomes even more likely if the multicystic collection crosses compartments within the neck.

Salter Harris Fractures

One of the most well known fracture classification systems is the Salter Harris (SH) classification, which describes the different appearance of fractures that occur at the physis of young children. SH1 fractures solely involve the growth plate (physis) (Fig. 6-56). SH2 fractures extend through the metaphysis into the growth plate (Fig. 6-57). SH3 fractures extend through the epiphysis into the growth plate. SH4 fractures extend from the metaphysis, through the growth plate, into the epiphysis. SH5 fractures are crush injuries to the growth plate. The significance of fractures that occur at the physis is that they may cause early fusion of the physis and lead to growth disturbance. Two distinct SH fractures are the triplane and juvenile Tillaux fractures, which typically occur in the older adolescent skeleton and are most common in the distal tibia. The triplane fracture is a complex SH4 injury that has a vertical component through the epiphysis, a horizontal component through the growth plate, and an oblique component through the metaphysis (Fig. 6-58). The Tillaux fracture is an SH3 injury involving fracture of the anterolateral aspect of the growth plate and epiphysis (Fig. 6-59). Fusion of the tibial growth plate begins centrally, proceeds medially, and completes laterally. The Tillaux pattern is secondary to injury after the medial distal tibial growth plate has fused. When Tillaux or triplane injuries are suspected or diagnosed by radiographs, CT is typically performed, because decisions for orthopedic repair hinge on the appearance of the fractures and measurements of distraction.

Figure 6-56 Anteroposterior radiograph through the wrist demonstrates widening of the distal radial physis (arrow). The patient was focally tender at this site. This finding is consistent with an SH1 fracture.

Figure 6-57 Lateral radiograph through the distal phalanx of the great toe demonstrates an SH2 fracture (arrow).

Figure 6-58 A, Anteroposterior radiograph through the ankle in this teenage boy after a sporting injury reveals a fracture through the tibial epiphysis (white arrow) that extends through the lateral portion of the physis (arrow). B, Lateral radiograph of the ankle reveals the obliquely oriented metaphyseal component of this triplane SH4 fracture (arrow).

Figure 6-59 Coronal reformatted image obtained from a CT examination through the ankle in this teenage boy after his having sustained injury to his ankle reveals a fracture through the distal tibial epiphysis (arrow) that extends through the lateral portion of the physis (arrowhead). This is called a Tillaux fracture, a specific type of SH3 injury.

Plastic Bending Fractures

Plastic bending fractures are seen in the long bones of children who have suffered axial load injuries. These fractures appear as bowing contour deformities. Buckle or torus fractures are seen as minimal disruptions or irregularities in the cortical contours, particularly common in the long bones of the forearm (Fig. 6-60). Greenstick fractures demonstrate cortical continuity along one aspect of the bone and obvious fracturing or splintering of the opposite cortical margin. Toddler’s fractures are hairline cortical tibial fractures seen in walking older infants and young children (Fig. 6-61). These pediatric fractures are often initially overlooked, due to the subtle differences in angulation or cortical continuity. Certain buckle fractures, plastic fractures (bowing deformities), hairline fractures, SH1 fractures, and impaction fractures can be subtle and are more evident if a contralateral view is obtained. When clinical suspicion is high but initial radiographs appear normal, follow-up radiographs may demonstrate periosteal reaction, sclerosis, or increased conspicuity of the fracture line as evidence of healing injury.

Figure 6-60 A, Initial lateral radiograph of the wrist obtained at the time of injury in this young girl with wrist pain demonstrates a subtle buckle fracture of the distal radius (arrow). B, A follow-up radiograph performed 10 days later reveals linear sclerosis at the fracture site (arrow) indicative of healing.

Figure 6-61 Anteroposterior radiograph of the tibia in a toddler demonstrates a subtle lucency within the shaft of the distal tibia (arrow) as well as periosteal reaction along the lateral cortical surface of the bone (arrowhead). This child sustained a toddler’s fracture of her tibia.

Elbow Fractures

The elbow is a particularly complex joint to evaluate for injury in the pediatric skeleton. Due to the multiple ossification centers, predominance of radiolucent cartilage, and common site of injury, elbow fractures are particularly prone to false negative plain film interpretations. Knowledge of the normal anatomic alignment of the elbow, as well as of the appearance and timing of the ossification centers, is essential when evaluating the elbow. “CRITOE” is a common mnemonic that describes the typical order in which the ossification centers appear (capitellum, radial head, internal epicondyle, trochlea, olecrenon, external epicondyle). Bowing of the anterior fat pad (“sail” sign) and visualization of the posterior fat pad indicate a joint effusion (Fig. 6-62). The presence of an effusion does not necessarily connote a fracture, although it reflects significant traumatic injury to the joint. The radiocapitellar line drawn through the midshaft of the radius should always intersect the capitellum. Absence of this relationship represents dislocation of the radial head from its normal anatomic articulation with the capitellum. The anterior humeral line drawn along the anterior cortex of the humerus should intersect the middle third of the capitellum. If the line intersects the anterior third of the capitellum or passes anterior to the capitellum, a supracondylar fracture should be suspected. This line can lead to false positive assessments in nonlateral projections. Care should also be used in the extremely young patients with minimal ossification of the capitellum. A mnemonic such as FOOL (fat pads, cortical outlines, ossification centers, anterior humeral and radiocapitellar lines) can remind the busy radiologist to look for the presence of effusions, subtle buckle fractures, avulsed or “missing” ossification centers, and radial head dislocations or subtle supracondylar fractures.

Figure 6-62 Lateral radiograph of the elbow demonstrates the “sail” sign of an elbow effusion (arrow). The posterior fat pad is also visible (arrowhead). This child was treated for an occult supracondylar fracture.

Septic Hip

Patients presenting with hip pain may have septic arthritis of the hip joint, which requires emergent diagnosis in order to avoid permanent joint damage. The presence of a hip effusion can be suggested on anteroposterior radiographs of the pelvis by asymmetric widening of the femoral head–acetabular teardrop distance on the affected side, although radiographs are not sensitive for this diagnosis. Ultrasound is an excellent tool for determining the presence of a hip effusion. Using a high frequency linear transducer along the long axis of the femoral metaphysis, an effusion will appear as a hypoechoic collection ballooning outward from the cortex of the femoral head and neck (Fig. 6-63). Imaging the normal asymptomatic side demonstrates the asymmetry in the amount of fluid in the symptomatic joint. Transient synovitis cannot be differentiated from a septic hip sonographically. The diagnosis is determined by the histopathologic evaluation of the aspirated fluid. In a child with hip pain, the presence of fever, elevated white blood count, increased erythrocyte sedimentation rate, and elevated C-reactive protein should help direct the decision to perform hip aspiration.

Figure 6-63 US images obtained along the long axis of the hips bilaterally demonstrate evidence of a hip effusion on the left (arrows), the patient’s symptomatic side. Note cortical surface of the femur (arrowheads).

Other causes of hip pain in children include Legg-Calve-Perthes (LCP) disease and slipped capital femoral epiphysis (SCFE). LCP is idiopathic avascular necrosis of the hip. Most commonly occurring in 4- to 8-year-olds, the early radiographic signs may be subtle. Subcortical lucency along the proximal femoral epiphysis may be the first imaging sign of the disease. Cortical collapse, sclerosis, and deformity of the head and neck are seen in more advanced disease. SCFE is often diagnosed in the slightly older age group (ages 8 to 12), and is more common in overweight children. On anteroposterior radiographs, early SCFE can be seen as subtle asymmetry of the growth plates, while more advanced SCFE will have lateral displacement of the proximal femoral metaphysis with respect to the epiphysis. Often the slip is better seen on the frog leg lateral view, where the offset of the epiphysis and metaphysis is better demonstrated (Fig. 6-64).

Figure 6-64 Frog leg lateral view of bilateral hips reveals widening of the physis on the left (arrow) and posteromedial displacement of the left femoral epiphysis, consistent with slipped capital femoral epiphysis.

Nonaccidental Injury

When interpreting pediatric imaging studies, one must be constantly on the lookout for signs of nonaccidental injury. Certain types of osseous injuries have a high specificity for NAI. Posterior rib fractures, for example, are highly specific for NAI and may be detected on chest or abdominal radiographs obtained for unrelated history, such as cough or vomiting (Fig. 6-65). Other fractures highly suggestive of child abuse are classic metaphyseal lesions, sometimes referred to as corner or bucket-handle fractures (Fig. 6-66). Spiral fractures of the long bones in infants who are not ambulatory are also worrisome for NAI. When clinical concern is raised or when a radiographic finding is suggestive of NAI, a full skeletal survey should be performed with high-quality, small-field-of-view technique. Multiple fractures, particularly if they are of varying ages, should alert radiologists to the possibility of abuse. A follow-up skeletal survey in 2 weeks can be suggested to assess for additional injuries that may not be visible on initial radiographs. There are few metabolic disorders that can mimic the osseous injuries seen in NAI, the most common being osteogenesis imperfecta (OI). These disorders are very rare, and often there are other clinical findings or a family history to suggest the diagnosis.

Figure 6-65 Anteroposterior radiograph of the chest in this 6-month-old boy who was a victim of a nonaccidental injury reveals healing left posterior rib fractures (arrows).

Figure 6-66 Anteroposterior radiograph of the femur in the same child as in Figure 6-65 reveals a metaphyseal fracture of the distal tibia (arrow).