Nontrauma Abdomen

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CHAPTER 9 Nontrauma Abdomen

Nontraumatic causes of acute abdominal pain may be secondary to a wide variety of etiologies. When diagnostic imaging is clinically indicated in evaluating these patients, it is critical to localize signs and symptoms to properly triage the patient to the correct imaging modality. For example, in women with pelvic pain, ultrasonography is the imaging modality of choice for initial evaluation. For the abdomen, ultrasonography or computed tomography (CT) is typically used, possibly preceded by plain radiography, depending on the patient’s presentation.

In patients with acute abdominal pain, one may consider broad categories of disease including inflammatory, infectious, obstructive, and vascular conditions. In the following sections, these broad categories should be remembered as the various causes of acute abdominal pain are discussed, including bowel, pancreaticobiliary, liver, genitourinary, and splenic. Finally, nonspecific emergent imaging findings with a host of underlying etiologies, often requiring urgent clinical intervention, are discussed.

BOWEL DISEASE

Pathology related to the bowel, including small bowel and colon, represents a significant percentage of acute abdominal pain. Again, one may consider the underlying etiologies of bowel disease in the categories of obstructive, infectious, inflammatory, and vascular. Often, plain radiographs of the abdomen are acquired in patients with suspected underlying bowel disease, commonly followed by CT for more definitive characterization.

Diseases Causing Bowel Obstruction

Diseases causing bowel obstruction include gastric outlet obstruction and volvulus, peptic ulcer disease, mechanical small bowel obstruction, small bowel volvulus, colonic obstruction and volvulus, and adynamic ileus. These are covered in the following sections.

Gastric Outlet Obstruction

Gastric outlet obstruction refers to any entity causing a mechanical obstruction to gastric emptying. Differential considerations are broad and include malignant etiologies such as pancreatic cancer, gastric cancer, and ampullary and duodenal cancer, as well as cholangiocarcinoma. Benign causes of gastric outlet obstruction in adults include peptic ulcer disease, gastric polyps, bezoars, caustic ingestion, gallstones (Bouveret syndrome), and pancreatic pseudocysts. Secondary inflammation or spasm resulting from pancreatitis or acute cholecystitis can cause gastric outlet obstruction. Infectious etiologies of gastric outlet obstruction include abdominal tuberculosis. Gastroduodenal intussusception is a rare cause of mechanical obstruction, typically related to an underlying lead point, which includes benign and malignant neoplasms.

Patients with gastric outlet obstruction present with nausea and vomiting, the hallmark symptoms. Normally these symptoms are temporally related to recent ingestion of a meal, and the vomiting often consists of undigested food. In more chronic cases, weight loss may be described, and in severe cases, patients may present with dehydration and electrolyte imbalances.

Imaging Findings

Plain radiographs may demonstrate a markedly dilated stomach, which may be either air or fluid filled. Infrequently, plain radiography may suggest an underlying diagnosis, for example, an irregular mass lesion identified as a filling defect in cases of malignancy such as gastric cancer. Filling defects may also be identified on plain radiographs in cases of bezoar obstruction. In Bouveret syndrome, a calcified gallstone may be identified in the duodenal bulb.

In patients presenting with acute symptoms of nausea and vomiting, a CT scan may be acquired for further evaluation. Similar to radiography, CT clearly demonstrates the often marked distention of the stomach. CT is also helpful in characterizing the underlying etiologies of obstruction. Malignant causes are seen as enhancing soft tissue mass lesions arising in the stomach in cases of gastric cancer, or slightly more distally around the pancreatic head or ampulla in cases of pancreatic cancer, cholangiocarcinoma, and ampullary and duodenal cancers. Distinction among the latter can be difficult because the area of origin contains quite a bit of overlap.

In cases of peptic ulcer disease (PUD) obstructing the stomach, the ulcer may, rarely, be identified, but the secondary CT findings of gastritis are typically seen as focal thickening of the gastric wall with hyperenhancement of the mucosa related to the inflammation. In these cases, the focal area of inflammation should be scrutinized for a central ulcer seen in PUD. Often, the distinction between PUD and underlying carcinoma is difficult in these cases based on CT. Similar to PUD, in cases of obstruction secondary to inflammatory etiologies such as pancreatitis or cholecystitis, the epicenter of inflammation will be seen around the respective organs, but the secondary inflammation of the stomach may be identified on CT as mural thickening, possibly with hyperenhancement of the mucosa.

Gastric outlet obstruction secondary to various benign etiologies is often apparent, as in cases of pancreatic pseudocyst obstruction. Hyperplastic polyps, the most common form of gastric polyp, may, rarely, cause gastric obstruction and may be seen in the region of the prepyloric antrum as they cause obstruction by prolapse into the pyloric channel. On CT, the appearance is that of a pedunculated, soft-tissue attenuation filling defect. In cases of Bouveret syndrome, the obstructing gallstone may be identified as a calcified filling defect in the duodenal bulb. Bezoars are seen at CT as mottled-appearing filling defects within the stomach, although these may be seen more distally within the gastrointestinal tract and have been reported to cause small bowel obstructions.

Gastric Volvulus

Gastric volvulus, an abnormal rotation of the stomach around its axis, in its acute form represents a surgical emergency. Gastric volvulus may be classified as one of two forms or a combination of the two: mesenteroaxial or organoaxial. In the mesenteroaxial form, the less common form, the stomach rotates around the axis bisecting both the lesser and greater curvatures of the stomach. In the organoaxial form, the stomach rotates around the axis connecting the gastroesophageal junction (GEJ) and the pylorus.

In cases of gastric volvulus, the Borchardt triad of upper abdominal pain, retching without vomiting, and inability to pass a nasogastric tube may be present. This triad is reported in up to 70% of acute cases of gastric volvulus.

Imaging Findings

The most common causative factor of gastric volvulus in the adult population is diaphragmatic defects, so plain radiographs may demonstrate an intrathoracic, gas-filled viscus. In cases of mesenteroaxial volvulus, supine radiographs may demonstrate typical findings of a spherical lucency with a characteristic “beak” in the region of the distal stomach. Upright radiographs show differential air–fluid levels at different heights in cases of mesenteroaxial volvulus. Organoaxial volvulus, on the other hand, characteristically reveals a single air–fluid level in an abnormally transversely oriented stomach.

In patients presenting with a clinical suspicion of a gastric volvulus, an urgent upper gastrointestinal series can secure a prompt diagnosis. In cases of gastric volvulus, an obstruction may be identified at the site of volvulus. Mesenteroaxial volvulus demonstrates a barium-filled stomach with the GEJ below the antrum and with the typical “beak” seen in the region of the distal stomach, as on radiography. If barium gets past the GEJ, an “upside-down” stomach is seen. Transverse position of the stomach as well as an abnormal inferior location of the GEJ suggest organoaxial volvulus.

With the multiplanar capabilities of multidetector CT (MDCT) scanners, patients with suspected gastric volvulus may undergo a CT scan in the initial diagnostic evaluation. As on radiography, CT typically demonstrates the presence of a hiatal hernia, commonly the paraesophageal type, or diaphragmatic eventration, which increases the likelihood of organoaxial gastric volvulus. Multiplanar reformations are particularly useful in defining precisely the anatomy of the volvulus. Like fluoroscopy, CT demonstrates the abnormally positioned gastric antrum located superior to the GEJ; an “upside-down” stomach when the rotation is complete. Organoaxial volvulus demonstrates an abnormally transverse lie of the stomach and an inferiorly positioned GEJ given its axis of rotation. As organoaxial volvulus is more often associated with diaphragmatic defects, the stomach is often identified in the thorax at the time of volvulus.

In cases of gastric volvulus on CT, especially the organoaxial type, complications of ischemia may be identified, including pneumatosis and portomesenteric vein gas. Mesenteroaxial, unlike organoaxial, volvulus is more frequently incomplete and less likely to cause acute complications such as necrosis.

Peptic Ulcer Disease

Peptic ulcer disease, most commonly secondary to Helicobacterpylori, rarely presents acutely. However, complications relating to PUD, such as acute hemorrhage or gastroduodenal perforation, may present acutely. Additionally, the somewhat more subacute presentation of gastric outlet obstruction may require imaging evaluation, as detailed above. Causes of peptic ulcers other than H. pylori include nonsteroidal antiinflammatory drug use, Zollinger-Ellison syndrome, various infections such as cytomegalovirus, chemotherapy, and radiation. Bleeding complications related to PUD usually do not require imaging evaluation.

Epigastric to left upper quadrant burning pain and bloating, temporally related to meals and possibly radiating to the back, are the common description of PUD-related pain. Nausea and vomiting as well as anorexia may be described. A sudden onset of pain suggests perforation. Patients with acute hemorrhage often present with hematemesis.

Mechanical Small Bowel Obstruction

Mechanical small bowel obstruction represents a relatively common cause of abdominal pain and is a frequent indication for abdominal imaging. The most common cause of mechanical small bowel obstruction is adhesions from prior surgical intervention. Other common causes include malignancy, acute inflammatory processes, and hernias. Less common causes include gallstone ileus and small bowel intussusception.

Patients with mechanical small bowel obstruction typically present with abdominal pain, nausea, vomiting, abdominal distention, and constipation. Commonly, the abdominal pain is colicky or intermittently cramping. Initially it may be mild, with progression of symptoms as the duration increases. Vomiting initially consists of gastric contents, followed by more distal bowel contents including bile and finally feculent material. The temporal relationship between the onset of bowel obstruction and symptoms of vomiting is related to position of the obstruction, with more proximal causes presenting with vomiting earlier in the episode of obstruction. The vomiting may result in dehydration and electrolyte imbalances. In comparison with colonic obstruction, vomiting occurs earlier and commonly precedes constipation.

Imaging Findings

The initial imaging evaluation of patients with suspected mechanical small bowel obstruction often includes plain radiographs. The diagnosis of small bowel obstruction on plain radiography involves the visualization of distended loops of small bowel filled with air or fluid. The differentiation of small bowel loops from the colon is achieved by identifying the valvulae conniventes, also known as plicae circulares, of the small bowel, which are thin, mucosal folds extending across the entire small bowel loops. The haustral folds of the colon, on the other hand, are thicker bands alternating with the thick folds termed plicae semilunares, which do not cross the entire lumen of the colon. The small bowel loops are more central in the abdomen, with the colon seen along the periphery. Typically, 3 cm is accepted as the upper limit of normal for the diameter of the small bowel. The presence of a hernia as the cause of a small bowel obstruction may be suggested by plain radiographs based on the presence of small bowel loops in unusual locations, such as the inguinal canal, distal to dilated loops of small bowel. Alternatively, radiographs demonstrating protrusion of a segment of small bowel, as evidenced by a short segment of bowel clearly outlined by air outside the abdominal wall, again distal to dilated loops of small bowel, may indicate a hernia as the underlying etiology.

CT is often used for further characterization in patients with suspected mechanical small bowel obstruction. Similar to radiography, the diagnosis on CT involves identifying distended air- and fluid-filled loops of small bowel, typically greater than 3 cm in diameter. The small bowel “feces” sign, which is the presence of air and particulate matter within loops of small bowel resembling feces, is a finding commonly seen in small bowel obstruction and is helpful in its diagnosis by suggesting increased bowel transit time. Often, CT allows for the diagnosis of the exact point of transition between distended loops of small bowel and the more normal collapsed loops of small bowel and possibly for identifying the underlying cause of the small bowel obstruction (Fig. 9-1).

Closed loop obstructions are a subset of mechanical small bowel obstructions demanding acute clinical intervention. The term closed loop obstruction signifies the presence of two transition points, one of which is found at the proximal extent of the closed loop and one at its distal extent. The vascular supply of these segments of small bowel is often compromised in this setting, and ischemia and necrosis may quickly ensue. Although the diagnosis of a closed loop obstruction might be suggested on plain radiographs by the presence of a short segment of distended small bowel, as well as transition points that may or may not be visualized, this diagnosis is typically confirmed by CT. The CT imaging findings include a sharp transition point, or “beak,” at the proximal and distal extent of the closed loop. CT findings suggesting ischemia, including vascular engorgement, and ascites, as well as abnormally decreased enhancement following intravenous contrast administration, often require emergent intervention. More ominous CT imaging findings, including pneumatosis intestinalis, may also be seen and are discussed below.

As noted, adhesions from prior surgical intervention are the most common cause of small bowel obstruction and are notoriously difficult to directly visualize with imaging, and often diagnosis remains one of exclusion. However, secondary signs such as abrupt angulation of small bowel loops, and adherence of small bowel loops to nondependent surfaces such as the anterior parietal peritoneum, lend credence to a diagnosis of adhesions as the underlying cause, especially when found at the transition between distended and normal small bowel loops.

Hernias are a second common cause of small bowel obstruction. CT is used to further characterize these hernias, which may be complex in some cases. Common types of hernias include inguinal hernias, umbilical hernias, incisional hernias, and Spigelian hernias in the location of the linea semilunaris (Fig. 9-2). Among less common causes of mechanical small bowel obstruction are internal hernias, including congenital or surgically acquired rents within the mesentery as well as a myriad of other named internal hernias that have been described. CT images including multiplanar reformations are often employed to further characterize these complex hernias.

Gallstone ileus is a rare but interesting form of mechanical small bowel obstruction. In this case, a gallstone erodes into the adjacent duodenum and goes on to obstruct the small bowel, most commonly at the ileocecal valve. Typical imaging findings include the presence of air within the gallbladder or bile ducts as well as dilated loops of small bowel, often with a calcified gallstone at the distal extent. These findings may be seen on plain radiographs as well as on CT. If the gallstone erodes more proximally and obstructs the duodenal bulb, similar imaging appearances of biliary gas, obstruction, and often visualization of the calcified gallstone are seen and are termed Bouveret syndrome.

Although more common in the pediatric population, small bowel intussusception may also be seen in adults and can cause obstruction of small bowel loops proximally. In adults, one must always consider the possibility of a lead point such as a neoplasm. Other causes of small bowel intussusception in adults include Meckel’s diverticulum and postoperative states especially after gastric bypass. With the increasingly widespread use of CT, transient small bowel intussusceptions are more commonly seen. One may suggest the diagnosis of a transient intussusception based on location and length, as well as the absence of proximal small bowel dilatation (Fig. 9-3).

Small Bowel Volvulus

Although it is often considered a pediatric diagnosis, adults may also present acutely with a small bowel volvulus. Small bowel volvulus can be categorized as either primary or secondary; those with secondary volvulus have an underlying abnormality predisposing to volvulus, such as pregnancy, gastrointestinal tumor, small bowel diverticulum, or intraperitoneal adhesions. A form of small bowel volvulus that often presents within the first month of life is midgut volvulus. It is secondary to malrotation and may also affect adult patients. In these cases, a lack of rotation or incomplete rotation of the gut around the axis of the superior mesenteric artery during embryogenesis, termed midgut malrotation, may lead to acute volvulus of the entire midgut.

Clinical findings are often nonspecific and include abdominal pain, nausea, and vomiting. More specific clinical histories include those in which the patient describes intermittent epigastric pain, possibly related to meals.

Imaging Findings

Plain radiographs are also nonspecific in patients with small bowel volvulus but may demonstrate proximal small bowel obstruction. In cases of midgut volvulus related to underlying malrotation, plain radiographs may demonstrate partial duodenal obstruction with a dilated, air-filled stomach and proximal duodenum.

Currently, CT is the imaging modality of choice in diagnosing small bowel volvulus. As on plain radiographs, secondary small bowel obstruction may be identified proximal to the volvulus. The CT “whirl” sign is often associated with volvulus of the bowel and is seen as a swirling of mesenteric vessels, strands of soft tissue, and loops of bowel. Although sensitive in the diagnosis of small bowel volvulus, the finding lacks specificity, in that most patients demonstrating this finding have been shown not to have a diagnosis of small bowel volvulus. Nevertheless, the “whirl” sign of twisting mesenteric structures, including loops of small bowel, should raise suspicion of a volvulus, and other CT findings such as infiltration of the mesentery and proximal small bowel dilatation may increase specificity. Small bowel volvulus can rapidly lead to vascular compromise, and the CT images should be scrutinized for findings of ischemia, such as abnormal hypoenhancement of the small bowel. As in cases of small bowel volvulus, the “whirl” sign, in which the superior mesenteric vein and loops of bowel are seen to rotate around the superior mesenteric artery, may be demonstrated on CT in cases of midgut volvulus.

Colonic Obstruction

In the adult population, the most common consideration in colonic obstruction is malignancy, specifically adenocarcinoma. Other causes include diverticulitis, volvulus, intussusception, ischemia, adhesions, fecal impaction, and strictures from a number of prior insults, including radiation. Another possible cause of dilated loops of colon is acute or chronic megacolon. When there is underlying severe inflammation of the colon, acute megacolon is referred to as “toxic” megacolon. When no underlying colonic abnormality is present, this condition is referred to as Ogilvie syndrome. Ogilvie syndrome typically presents in hospitalized patients with significant underlying medical illnesses. The acute forms of megacolon are medical emergencies, given the risks of complication, which include sepsis, ischemia, and perforation. The risks of perforation increase significantly when the diameter of the cecum exceeds 12 cm. The cecum is the most likely portion of the colon to perforate, based on Laplace’s law.

Patients with colonic obstruction typically present with abdominal distention and pain as well as nausea and vomiting. Constipation commonly precedes vomiting in colonic obstruction. Depending on the underlying cause, presentation may be acute or more chronic, possibly with changes in the caliber of stool in the case of colonic malignancy. Peritoneal signs are an ominous finding and suggest the possibility of perforation.

Imaging Findings

Typically, plain radiographs demonstrate evidence of air- and fluid-filled loops of dilated colon. A diameter of 8 cm is considered the upper limit of normal for the cecum, whereas 5 cm is considered the upper limit of normal for the remainder of the colon. When acute, colonic obstruction is a medical emergency, given the potential for rapidly developing ischemia, sepsis, or perforation.

CT demonstrates dilated loops of air- or fluid-filled colon proximal to the site of obstruction and is accurate in determining the cause of the obstruction. The CT scans should be scrutinized for signs of perforation, such as free intraperitoneal fluid or air, as well as for signs of ischemia such as abnormal hypoenhancement of the colon. Unlike in the pediatric population, colonic obstruction secondary to intussusception is generally managed surgically, as opposed to radiologically, with reduction via air enema, for example, given the high likelihood of an underlying malignancy. On CT, toxic megacolon demonstrates dilation of air- or fluid-filled colon with wall thickening and a distorted colonic contour or a lack of the expected haustral pattern. Because Ogilvie syndrome lacks the colonic inflammation, CT is unlikely to demonstrate a similar degree of wall thickening and submucosal edema as toxic megacolon. The chronic form of megacolon represents a functional failure of the colon secondary to various underlying etiologies, including chronic constipation. In these patients, it is often helpful, when prior radiographs are available for comparison, to exclude acute colonic obstruction or megacolon.

Colonic Volvulus

Sigmoid volvulus is the most common form of gastrointestinal volvulus. Cecal volvulus is also a relatively common form of colonic volvulus. Sigmoid volvulus represents twisting of the sigmoid colon around its mesenteric axis. Three forms of cecal volvulus are described: axial torsion type, loop type, and cecal bascule. The axial torsion and loop types represent the most common forms. In the axial torsion type, the cecum rotates around its long axis, appearing in the right lower quadrant. In the loop type, the cecum twists and then inverts, ending in the left upper quadrant. In the cecal bascule, the cecum simply folds medially to the descending colon, producing an occlusion at the site of flexion.

Colonic volvulus typically presents with an acute abdomen with sudden onset of colicky pain. Abdominal distention with a tympanitic abdomen may be appreciated. Constipation with inability to pass flatus or stool accompanies cases of colonic volvulus. Borborygmus is frequently seen in cases of colonic volvulus.

Infectious and Inflammatory Diseases

Infectious and inflammatory diseases of the bowel are discussed in the following sections. They include infectious small bowel enteritis, Crohn’s disease and diverticulitis of the small bowel, appendicitis, epiploic appendagitis, omental infarction, diverticulitis, inflammatory bowel disease of the colon, infectious colitis, and foreign bodies.

Infectious Small Bowel Enteritis

A multitude of infectious etiologies may cause small bowel enteritis, including viral etiologies such as rotovirus, norovirus, and adenovirus, bacterial causes such as Campylobacter jejuni, and parasites including Giardia lamblia, all of which may affect the immunocompetent host. Common infectious agents of small bowel enteritis in the immunocompromised host include cytomegalovirus, cryptosporidiosis, and Mycobacterium avium intracellulare.

Nonspecific signs and symptoms of infectious enteritis include abdominal cramping, vomiting, and diarrhea. Although the abdomen may be distended with gas, borborygmi are present, distinguishing this from ileus. Patients may be febrile, and leukocytosis may be present. Especially in immunocompetent hosts, the disease is often self-limited, lasting up to several days. When infectious enteritis is severe, dehydration is a relatively common complication of infectious small bowel enteritis. Currently, fecal testing and, increasingly, immunoassays are used in the clinical diagnosis.

Imaging Findings

Plain radiographs are often nonspecific but may demonstrate mildly dilated loops of small bowel similar to adynamic ileus. In more severe cases, the degree of small bowel dilatation may approach the appearance of a small bowel obstruction.

CT imaging, when acquired, is also often nonspecific and may demonstrate mild to moderate small bowel dilatation and mural thickening (Fig. 9-4). Often, the small bowel is diffusely affected; however, certain infections may present in more specific locations such as the proximal small bowel in cases of giardiasis. In the immunocompromised host, a myriad of other infectious etiologies should be considered, as noted above. Typically, nonspecific small bowel wall thickening and mucosal irregularity are identified in cases of cytomegalovirus and cryptosporidium. In patients affected by Mycobacterium avium intracellulare, hepatic and splenic enlargement, jejunal wall thickening, and enlarged soft tissue attenuation or, less commonly but more characteristically, low-attenuation lymphadenopathy are described.

Crohn’s Disease, Small Bowel

Although Crohn’s disease can affect any portion of the gastrointestinal tract, the terminal ileum portion of the small bowel is the most commonly involved. Crohn’s disease may affect isolated segments of small bowel proximal to the terminal ileum. Usually, however, in cases of small bowel involvement, the colon is also affected.

Common gastrointestinal symptoms include abdominal pain, diarrhea, and weight loss. The crampy abdominal pain associated with Crohn’s disease may be temporarily relieved following defecation. The area of bowel involved may determine the nature of the diarrhea, with those affected by ileitis presenting with watery, large-volume stools.

Small Bowel Diverticulitis

Meckel’s diverticulum, the most common congenital anomaly of the gastrointestinal tract, remains asymptomatic in the majority of patients. However, various complications can ensue, including inflammation, termed Meckel’s diverticulitis. Although less commonly seen than in the colon, diverticula formation may affect any portion of the small bowel from the duodenum to the ileum. Potential complications include bacterial overgrowth and malabsorptive states. Diverticulitis may also affect the small bowel.

Patients with small bowel diverticulitis may present with localized tenderness in the region affected; however, no specific signs and symptoms are pathognomonic for this diagnosis. Often, these patients are febrile and may present with a leukocytosis. Moreover, malabsorptive states may develop and patients may present with diarrhea and weight loss. Although this is a secondary finding unrelated to diverticulitis, it may add credence to a consideration of small bowel diverticulitis. Plain radiographs, not usually used in the diagnosis of small bowel diverticulitis, may show a focal ileus or “sentinel loop” sign in the area of inflammation.

Appendicitis

Appendicitis is a common clinical concern in patients presenting to the emergency department with abdominal pain. In those patients presenting with the classic signs and symptoms, including right lower quadrant pain, leukocytosis, and fever, imaging may not be necessary in making the diagnosis of appendicitis. However, in those patients with atypical presentations or those requiring further characterization of the suspected diagnosis, imaging is often employed. Initially, the appendiceal lumen occludes secondary to a number of causes including fecaliths and lymphoid hyperplasia. Once occluded, intraluminal fluid continues to accumulate, distending the appendix and eventually increasing the intraluminal and intramural pressures to the point of vascular and lymphatic obstruction. Ineffective venous and lymphatic drainage allows bacterial invasion of the appendiceal wall and lumen. If untreated, perforation of the appendix may be a complication.

As noted, the classic description of patients presenting with appendicitis includes right lower quadrant pain, leukocytosis, and fever. Classically, these findings are preceded by anorexia and periumbilical pain. The migration of pain from the periumbilical region to the right lower quadrant is both sensitive and specific in the diagnosis of appendicitis. However, given the normal range of locations of the appendix as well as varying degrees of appendiceal inflammation, patients often present with atypical signs and symptoms.

Imaging Findings

Abdominal radiographs have been shown to have little clinical utility in patients with suspected appendicitis; therefore, cross-sectional imaging may be the initial diagnostic examination of choice. In the minority of cases, a calcified fecalith may be identified in the right lower quadrant. Also, the “sentinel loop” sign may be identified secondary to appendiceal inflammation.

In the younger population, and especially in females, ultrasonography may be used as an initial imaging evaluation given radiation concerns involved with CT. Ultrasound has been shown to have a high diagnostic accuracy in evaluating for suspected appendicitis. Typical findings include the visualization of a blind-ending tubular structure measuring greater than 6 mm in diameter during graded compression. When present, an appendicolith may also be identified as an echogenic, shadowing focus within the lumen of the appendix. Secondary signs of active inflammation, including free intraperitoneal fluid, may be seen. The complications of appendicitis, which include rupture and abscess formation, may also be detected using ultrasound. Technical limitations of ultrasound include patients with an obese body habitus; moreover, given the wide variety of locations of the normal appendix, those located more posteriorly within the peritoneal cavity pose increased difficulty for evaluation.

Pregnant women often pose a diagnostic challenge when presenting with suspected appendicitis. Typically, ultrasound examination is completed to rule out other causes of abdominal pain in this patient population, such as ectopic pregnancy or ovarian torsion. However, as the gravid uterus enlarges, the appendix becomes displaced from its expected location in the right lower quadrant, and it may be difficult to visualize. Unfortunately, the normal appendix is highly unlikely to be visualized by ultrasonography in pregnancy, and further imaging is often requested to definitively exclude appendicitis. However, when the appendix is visualized on ultrasound, the findings of acute appendicitis are similar to those in nonpregnant patients and include the visualization of a blind-ending tubular structure measuring greater than 6 mm in diameter using a graded compression technique.

When the ultrasound results are equivocal or the appendix is not visualized, CT is often employed in patients with suspected appendicitis. In older or significantly obese patients, CT may be the initial imaging examination. CT has been shown to have a very high diagnostic accuracy in the diagnosis of appendicitis. In those patients with appendicitis, the appendix appears enlarged, often with surrounding inflammatory changes, including the free intraperitoneal fluid. When present, appendicoliths are readily identified on CT (Fig. 9-7). There is a large variety in the diameter of the appendix in normal patients, with sizes ranging up to 1 cm. However, mean values range between 5 and 7 mm depending on whether or not the appendix is distended with air. Therefore, in a patient with an appendix measuring slightly greater than the standard cutoff value of 6 mm, secondary signs of inflammation should be sought, such as hyperenhancement, periappendiceal fat stranding or fluid, fascial thickening, or edema at the origin of the appendix as evidenced by thickening of the adjacent cecum, the so-called “arrowhead” sign (Fig. 9-8). Filling of the appendix by orally or rectally introduced positive contrast material is a useful means of excluding obstruction of the appendix and, therefore, acute appendicitis. When the appendix is not visualized, this finding, in the absence of right lower quadrant inflammation, carries a high negative predictive value of appendicitis.

In pregnant patients, ultrasonography is typically employed initially, given risks of ionizing radiation. However, in those patients with an inconclusive ultrasound examination, both CT and, with increasing frequency, magnetic resonance imaging (MRI) are often used. The findings of acute appendicitis on CT in pregnant patients are similar to those in the nonpregnant population.

Given concerns regarding radiation dose to the fetus, MRI is frequently employed to evaluate for suspected appendicitis in pregnant patients. MRI offers high diagnostic accuracy and is an excellent modality for excluding appendicitis. The appendix is considered normal when it is less than or equal to 6 mm in diameter, or is filled with air or contrast material. As on CT, secondary findings such as periappendiceal inflammation are used to increase specificity when the appendix is at the upper limits of normal size. As the gravid uterus enlarges, the cecum and therefore the appendix may be in atypical locations, displaced superiorly by the uterus. Therefore, it is helpful to identify the landmarks of the terminal ileum and cecum in attempting to localize the appendix on MRI in pregnant patients.

Epiploic Appendagitis

Epiploic appendages are small fat-containing, serosal-covered outpouchings of the colon that project into the peritoneal cavity. Appendagitis represents torsion of these outpouchings with subsequent inflammation and thrombosis of the venous supply located centrally. Alternatively, spontaneous venous thrombosis has been described to increase the predilection of subsequent torsion.

Prior to the increasing utilization of CT, epiploic appendagitis was often misdiagnosed as acute appendicitis or diverticulitis given similar clinical presentations. Typically, symptoms include rapid onset of localized pain in the right or left flank, although more chronic torsion of the appendages may result in minimal or no symptoms. The pain is usually constant, and rebound tenderness is often elicited. Patients may present with low-grade fever and leukocytosis.

Omental Infarction

Omental infarction is often idiopathic in its etiology. It has been hypothesized that there may be a congenital anomalous, atypically tenuous blood supply to the omentum in some patients. However, a significant portion of cases are related to recent intra-abdominal surgery. Other associations include strangulation of the omentum such as in inguinal hernias that include portions of the omentum.

Omental infarction may present with acute abdominal pain, but, as in epiploic appendagitis, it typically represents a benign, self-limited disease process. Patients present with acute or subacute focal abdominal pain that may mimic the acute pain of appendicitis and diverticulitis. Again, patients may present with low-grade fever and leukocytosis. Occasionally, the area of infarction may be palpated as an intra-abdominal mass lesion. In some cases, especially those with more severe and prolonged symptoms, operative management is successfully employed.

Diverticulitis

Diverticulitis is a relatively common cause of abdominal pain and is predominantly seen to affect the colon. Diverticulitis represents the inflammation of small outpouchings, known as pulsion diverticula or pseudodiverticula of mucosa and submucosa through the regions of the underlying muscularis propria penetrated by the vasa recta. This is commonly secondary to raised intraluminal pressures common in Western, low-fiber diets and constipation; the sigmoid colon is postulated to be most commonly affected, as it has the smallest diameter leading to the greatest intraluminal pressures. Diverticulitis typically presents as localized, usually left-sided, abdominal pain. More severe disease, especially with the presence of complicating abscesses, may present with systemic symptoms such as fever and may develop a leukocytosis. These patients may also present with anorexia, nausea, and vomiting. The signs of peritonitis may develop with cases of more gross perforation.

Inflammatory Bowel Disease, Colon

Inflammatory causes of colitis include Crohn’s disease and ulcerative colitis, both of which may present with acute signs and symptoms. Crohn’s disease represents granulomatous, transmural inflammation of the bowel with skip lesions in which noncontiguous segments of bowel are affected. Skip lesions are not present in ulcerative colitis. Crohn’s disease most commonly demonstrates an ileocolic distribution, affecting both the colon and ileum, followed by disease isolated to the ileum, typically in its distal portion, or disease limited to the colon. Ulcerative colitis, on the other hand, involves the rectum with continuous involvement of more proximal bowel, and, unlike the transmural involvement of Crohn’s disease, is limited to the mucosa and submucosa with formation of crypt abscesses and mucosal ulceration.

Typical clinical presentations in Crohn’s disease and ulcerative colitis include abdominal pain, tenesmus, and diarrhea. A distinguishing feature may be the presentation of bloody diarrhea in patients with ulcerative colitis, a finding rarely seen in Crohn’s disease. Especially with more severe disease, systemic symptoms such as nausea and vomiting along with malaise and low-grade fever may develop. Typically, Crohn’s disease presents somewhat more insidiously and symptoms may have persisted for several years prior to diagnosis. Also, patients with Crohn’s disease often have perianal disease in the form of fistulae and sinus tracts. Whereas ulcerative colitis rarely involves the small bowel, Crohn’s disease more commonly causes weight loss secondary to malabsorption related to small bowel involvement.