Etiology, Pathophysiology, and Clinical Presentation

Imaging

Treatment

Initial treatment of both ulcerative colitis and Crohn disease is with medical therapy to suppress the inflammation. However, the majority of Crohn patients (up to 80%) and one third of ulcerative colitis patients will end up needing surgery.18,19 The most common reasons for surgery in Crohn patients are small-bowel obstructions that do not respond to medical therapy because of bowel stricture or adhesion, and bowel perforation that leads to abscess. The most common reason for surgery in pediatric ulcerative colitis patients is active disease that does not respond to medical management or that leads to complications.

Etiology

The toxins produced by the bacterium Clostridium difficile are the most important cause of antibiotic-associated pseudomembranous colitis.20,21 Other, less common toxins include those produced by C. perfringens and Staphylococcus aureus. The diagnosis is a clinical and laboratory one, it is more common in adults than in children, and it is rare in infants. Recently, studies have shown an association of recurrent C. difficile colitis in patients who had undergone remote appendectomy, suggesting a role of immune protection by the normal appendix.^22,23

Clinical Presentation

Pseudomembranous colitis is characterized by fever, bloody diarrhea, cramping, and colonic mucositis. The condition most commonly follows antibiotic therapy and occurs in hospitalized patients who are often debilitated, immunocompromised, or recovering from surgery. However, it may occur without preceding antibiotic therapy in patients in whom the gut flora has been altered, such as after weaning or surgery. The onset of diarrhea may occur within weeks after cessation of antibiotic therapy.

Imaging

The radiographic findings are similar to those of the other colitides.²⁴ Enema is not necessary and should be avoided, particularly in severe cases, to avoid the risk of perforation. Ultrasound (US), MR, or CT findings of pancolitis, with or without ascites, suggest the diagnosis in the appropriate clinical setting.^25,26

Treatment

Preceding antibiotic therapy associated with the colitis should be stopped. The first line of antibiotic treatment is oral metronidazole. Other oral or intravenous (IV) antibiotics may be needed in some patients initially and in the minority who have recurrence.

Etiology

Most cases are caused by a Shiga-like toxin produced by Escherichia coli serotype 0157:H7, found in raw or incompletely cooked beef and unpasteurized dairy products. Additional toxins are produced by other bacterial agents and include Shigella, Salmonella, Yersinia, and Campylobacter. Hemorrhagic colitis is common. Renal and central nervous system complications can markedly affect the course and prognosis of this disease.²⁸

Clinical Presentation

This syndrome is most common during the summer months in children younger than 5 years of age. HUS usually has a gastrointestinal prodrome of diarrhea that precedes clinical evidence of acute renal failure, fever, anemia, and thrombocytopenia.28–30 A positive stool culture for the specific Shiga toxin–producing E. coli pathogen is definitive when positive. Serologic tests for antibodies to the Shiga toxin or to the lipopolysaccharide 0157 can be done, although these are not widely available.²⁷

Imaging

US, CT, or occasionally contrast enema is generally requested before the correct diagnosis is made. The findings consist of thickening of the wall of the involved bowel segment, more typically the colon, seen as “thumbprinting” on abdominal radiographs or contrast enema, and marked bowel wall thickening on CT or US.³¹ The involved segments are typically in continuity without skip lesions, and pancolitis can occur. Fat stranding and free fluid are often seen near the involved segments.³² Toxic megacolon and colonic perforation have been reported, and colonic strictures can occur as a late complication.³³

Treatment

The treatment for HUS is supportive and may include IV fluids, blood or blood products, and supportive renal dialysis if needed.³⁴ Children with Shiga-like toxin E. coli tend to recover renal function in 55% to 70% of cases.²⁷

Etiology

Radiation injury leads to activation of mucosal cytokines and increased levels of inflammatory mediators such as interleukin (IL)-2, -6 and -8.³⁶ Factors that affect the development of radiation colitis include patient comorbidities and, most importantly, the total radiation dose and the volume of bowel irradiated; radiation enteritis tends to develop in patients who have received on the order of 45 Gy, but it can occur with doses as low as 5 to 12 Gy.^35,37

Clinical Presentation

Diarrhea, cramping, and sometimes lower intestinal bleeding are the key clinical features of the acute phase, which is usually self-limiting. Eventually, fibrosis may occur, which leads to stiffness and loss of mobility of the affected portions of the colon. Chronic radiation colitis is a progressive, precancerous disease. Additional complications include partial obstruction and fragility of the bowel, which may culminate in perforation.³⁶ Diarrhea and abdominal pain are additional symptoms in patients with chronic radiation colitis.³⁶

Imaging

Patients with radiation colitis do not usually undergo imaging examinations during the acute phase. Fluoroscopic imaging with either SBFT or contrast enema may delineate the chronic, fibrotic change to the affected colon (e-Fig. 107-11). CT and MR show relatively nonspecific findings of bowel wall thickening; however, the diagnostic finding is the distribution of these changes within the radiation port.³⁵

Treatment

Treatment is related to symptom relief and includes dietary changes with reduction of fat and lactose intake in addition to medications for nausea and diarrhea. Management of patients with chronic disease can be challenging; as many as 30% of patients my require surgery for fistulae, perforation, or bowel obstruction that does not respond to nonsurgical management.³⁷

Etiology

Development of the condition is associated with chemotherapy-related low neutrophil counts; acute lymphocytic and myelogenous leukemia are the most common underlying malignancies in pediatric patients.

The disease most often affects the cecum, hence the term typhlitis. The appendix may be involved and may produce clinical findings that mimic acute appendicitis.³⁹ Edema and inflammation of the colon, including the distal ileum, may occur, and pneumatosis, perforation, or abscess may supervene.

Clinical Presentation

This condition occurs in less than 5% of children with neutropenia. Abdominal pain, diarrhea, fever, and distended abdomen are the common presenting symptoms.

Imaging

Radiographs are typically nonspecific and may show a focal ileus in the right lower quadrant. Often, a sentinel loop of dilated terminal ileum may be seen.⁴⁰ Because the clinical presentation may mimic acute appendicitis, cross-sectional imaging is a critical diagnostic differentiating tool. US shows a markedly thickened cecal wall that may be either hyperechoic or hypoechoic.⁴¹ Intraluminal fluid and ascites may also be identified. CT shows marked thickening of the affected portions of the colon, which is usually more marked in the cecum; surrounding inflammatory change; and free fluid (Fig. 107-12).⁴² Extension of this process may involve the terminal ileum.

Treatment

Management most often is conservative and includes antibiotics, but on occasion, bowel resection is necessary. Recovery is more related to the presence and severity of comorbidities than to the neutropenic colitis.⁴³

Etiology

With the introduction of oral, enteric-coated, high-dose pancreatic enzyme medication, clinicians increased the amount of enzyme supplements to many of these patients. Some that received particularly high doses later came to medical attention with what has been termed fibrosing colonopathy. Children were at higher risk than adults, until strict dosage guidelines were implemented. This entity is now rare because of compliance with appropriate dosage recommendations.⁴⁵

Clinical Presentation

The clinical presentation includes abdominal pain, distension, nausea, vomiting, constipation, and occasionally colonic obstruction. Although nonspecific, these signs and symptoms do not respond to medical therapy.

Imaging

The most common contrast enema findings are colonic strictures, loss of haustra, and colonic shortening.⁴⁶ The bowel wall may be thickened, and ascites may be evident on cross-sectional imaging.

Treatment

Some of these patients require surgery to relieve the obstruction, and they may also require resection of the fibrotic segment of colon.⁴⁵

Etiology

Appendicitis commonly occurs in the setting of luminal obstruction with subsequent distension of the appendix and ischemic mucosal damage, which leads to bacterial overgrowth and invasion of the wall that in turn results in transmural inflammation and ultimately in perforation. Luminal obstruction may be secondary to the presence of fecaliths, hyperplasia of lymphoid follicles, and foreign bodies that include parasites and carcinoid tumors.⁵² The pathophysiology of appendicitis is believed to be a dynamic process that occurs over a 24 to 36 hour period. Although infrequent, subacute appendicitis and spontaneous resolution of acute appendicitis have been described. Spontaneous resolution of luminal obstruction is the proposed pathophysiology in these cases and has been associated with cystic fibrosis and appendiceal lymphoid hyperplasia.^53,54

Clinical Presentation

Appendicitis can be a challenging diagnosis in children; the clinical presentation is reported to be nonspecific in approximately one third.⁵⁵ The classic clinical presentation—early periumbilical pain, followed by migration of localized pain to the right lower quadrant, with associated fever and vomiting—is reported to occur in less than 50% of pediatric patients.⁵⁶ More often, the constellation of findings is nonspecific; this is particularly true in younger children who may be unable to communicate symptoms effectively, resulting in delayed diagnosis and higher perforation rates in this cohort of patients. Initial relief of pain and/or more generalized abdominal pain with fever occur after perforation, which usually results in a local abscess adjacent to the appendix; this is because the perforation is usually contained by the omentum, but generalized peritonitis can also occur. Reported perforation rates in children range from 23% to 88%.⁵⁵

Imaging

Appendicitis demonstrates variable diagnostic findings on various imaging modalities (Box 107-1). Utilization of imaging, particularly CT, is increased in the emergency department for assessment of abdominal pain in children, particularly in those with suspected appendicitis.^57,58 The effectiveness of imaging for suspected appendicitis in children has been debated in the medical literature, which has specifically looked at the impact of imaging on the negative appendectomy and perforation rates. Several studies suggest a stable perforation rate with preoperative imaging,^59–61 whereas others demonstrate a significant decrease in perforation rate, from 35% to 15.5%, with preoperative imaging.⁶² However, a decrease in the negative appendectomy rate has been demonstrated in numerous studies.^62–64 When the appendix is normal, the radiologist must evaluate the images for alternative diagnoses, particulary in young children. The most common alternative diagnoses, in decreasing order of prevalence, are mesenteric adenitis, ovarian cyst, pyelonephritis, infectious or inflammatory colitis, omental infarction (e-Fig. 107-13), and urinary system stones.^65,66

Radiographs

Prior to the advent of current cross-sectional imaging modalities, imaging of appendicitis relied on abdominal radiographic findings, which are often normal or nonspecific in approximately 77% of children with appendicitis.⁵⁶ The presence of a radiographically visible appendicolith, considered to be the most specific radiographic sign of appendicitis, is only present in approximately 5% to 15% of patients with appendicitis.^56,67 Appendicoliths are seen more frequently on CT, range from 43% to 50%, and are multiple 30% of the time (e-Fig. 107-14).^68,69 Additional nonspecific radiographic findings include a paucity of bowel gas or a soft tissue mass in the right lower quadrant; ileus that may be either focal or diffuse; and less often, small-bowel obstruction.⁷⁰ Mild levoconvex curvature of the spine may be present as a result of splinting in response to abdominal pain.

Ultrasound

US using a graded compression technique for evaluation of appendicitis was first described in 1986.⁷⁰ Since that landmark paper, numerous studies have followed to address the efficacy of US and to evaluate additional sonographic findings.^71–75 The limitations of US relate to several factors that include operator experience, larger patient body habitus, and limited field of view. Optimized technique for US evaluation of suspected appendicitis is fundamental to achieve the sensitivity. The examination is performed with a high-frequency linear transducer that ranges from 9 MHz to 15 MHz, depending on the size of the patient. A linear transducer is necessary not just to obtain the appropriate resolution but also to effect adequate graded compression. Graded compression is essential, because it displaces overlying bowel gas and also helps to decrease the distance between the transducer and the appendix. Additionally, compression helps differentiate normal bowel from an inflamed appendix. The compression is “graded,” in that it is exerted slowly, without sudden release, to optimize patient tolerance and prevent rebound tenderness. Transverse and longitudinal scans are performed over the point of maximal tenderness. If the appendix is not identified at this point, additional sonographic interrogation of the right lower quadrant, pelvis, and abdomen is necessary given the variability in location of the appendiceal tip. The most common location of the normal and abnormal appendix is in the midpelvic region over the common right iliac vessels, followed by the retrocecal region, deep pelvic region, and abdomen above the iliac crests.⁷⁶

Sonographic demonstration of the normal appendix is useful in excluding the diagnosis of appendicitis, although in general US is more useful in the diagnosis than in the exclusion of appendicitis. The literature demonstrates wide operator variability with respect to reliable identification of the normal appendix, ranging from 2.4% to 86.2%.76–80 The higher percentages may reflect the advanced technology, improved resolution of US equipment, and improved operator experience. Sonographic findings associated with a normal appendix include a compressible, blind-ending tubular structure without peristalsis; diameter less than 6 mm; absence of wall thickening (less than 3 mm); and presence of a central echogenic line that represents acoustic reflection from the collapsed luminal interface (Fig. 107-15).^74,80,81 The normal appendix can usually be traced to its origin at the base of the cecum (e-Fig. 107-16). Occasionally, the normal terminal ileum, often located just cephalad to the appendix, may be mistaken for a normal appendix, since it is located cephalad of the appendiceal origin. The presence of hypoechoic folds and peristalsis are helpful in differentiating the normal terminal ileum from the appendix.

The single most important US sign of an inflamed appendix is a noncompressible, blind-ending tubular structure with a transverse diameter measuring greater than 6 mm. Additional sonographic signs associated with appendicitis include appendiceal wall thickness greater than 3 mm, wall hyperemia on color Doppler, periappendiceal hypoechoic halo that reflects appendiceal wall edema, periappendiceal hyperechogenicity that reflects periappendiceal edema, and the presence of an appendicolith (Fig. 107-17 and e-Fig. 107-18).^75,77 The secondary sonographic findings vary, depending on the progression of the inflammatory process. Early uncomplicated appendicitis will demonstrate a targetlike appearance with hypoechogenicity centrally as a result of luminal distension with pus or fluid, increased echogencity of the inflamed submucosa, hypoechoic edematous serosa, and increased periappendiceal echogenicity (see Fig. 107-17). As the inflammatory process advances, and suppurative appendicitis ensues, the periappendiceal tissues demonstrate a heterogeneous pattern of increased echogenicity with hyperemia on color Doppler (Fig. 107-19). Increasing appendiceal dilatation, loss of the echogenic submucosal layer, and absence of vascularity with color Doppler are signs of supervening gangrenous change (Fig. 107-20). Although the abnormal appendix may not be visualized with perforated appendicitis, sonographic findings suggestive of perforation include phlegmon with poorly defined bowel loops in the right lower quadrant demonstrating overall increased echogencity, a mass of mixed echogenicity, and focal bowel wall thickening, intraperitoneal fluid, loculated fluid collections, or frank abscess.

Absence of visualization of an abnormal appendix in the setting of acute appendicitis may be due to a retrocecal location, obscuration by superimposed bowel gas, or limited US penetration. Additionally, appendiceal inflammatory changes may be confined to the tip of the appendix.⁸² If the entire appendix has not been visualized on US, and clinical symptoms suggest appendicitis or other intraperitoneal pathology, further imaging may be warranted, particularly if there are secondary signs of right lower quadrant inflammation.

Computed Tomography

CT is highly sensitive and specific for the diagnosis or exclusion of appendicitis in children (Table 107-1), and it is often utilized in the setting of a negative or equivocal US or perforated appendicitis. Scanning parameters should be adjusted appropriately for the size of the child to optimize dose. CT protocols vary with respect to the administration of oral, IV, and rectal contrast in addition to focal imaging versus imaging the entire abdomen and pelvis.^{55,81,83–86} A systematic review concluded that IV contrast alone performs as well as or better than CT with IV and positive enteral contrast for the diagnosis or exclusion of appendicitis.⁸⁷

Although the average diameter of the normal appendix typically approximates 6 mm, actual size may vary on CT, from 2 to 11 mm, because the examination is not done with compression, and the appendiceal lumen may distend with gas or feces. The absence of associated CT signs of appendicitis is helpful to confirm a normal appendix. As is the case with US, the appearance of the abnormal appendix varies with the histopathologic stage and severity of the disease process. The inflamed appendix on CT is a dilated, thick-walled tubular structure with centrally decreased attenuation that demonstrates wall contrast enhancement (e-Fig. 107-21 and Fig. 107-22). An obstructing appendicolith may be present in up to 50% of cases (e-Fig. 107-23).^68,69 Adjacent inflammation produces periappendiceal stranding and fluid. Additional nonspecific findings include intraperitoneal free fluid, cecal wall thickening and thickening of adjacent terminal ileum and sigmoid colon, small-bowel obstruction, and mesenteric lymphadenopathy.⁸⁸

With perforation, the appendix may decompress or may even fail to be visualized. Perforation may result in diffuse intraperitoneal inflammation (Fig. 107-24) or, more commonly, in localized phlegmon and abscess formation (e-Figs. 107-25 and 107-26). Diffuse peritonitis is more common in infants younger than age 2 than in older children. Hepatic abscesses and mesenteric or portal pyelophlebitis can also occur. CT is extremely helpful in identifying and characterizing smaller abscesses and extruded fecaliths that may act as a potential source of recurrent infection.

Computed Tomography and Ultrasound

CT and US are reported to have a nearly equivalent specificity, 95% and 94%, respectively (see Table 107-1).⁸⁹ Although CT has a greater sensitivity than US (94% and 88%, respectively although US is much more variable and operator dependent),⁸⁹ concerns regarding the potential risks of ionizing radiation exposure associated with CT⁹⁰ have prompted increasing use of US in the imaging evaluation of suspected appendicitis. Various imaging algorithms have been described in the literature that include the staged utilization of initial evaluation with US followed by CT for equivocal or nondiagnostic US studiess.^{51,83,91–93}

Magnetic Resonance Imaging

MRI has been reported to yield good results in the evaluation of suspected appendicitis, in both children and adults, using T1- and T2-weighted sequences.94–98 The sensitivity of MR was 97.6%, and the specificity was 97% in one study using a four-sequence protocol.⁹⁹ The abnormal appendix demonstrates thickening of the appendiceal wall with high signal intensity on T2-weighted images, dilated lumen with high signal intensity contents on T2-weighted images, and increased signal intensity of the periappendiceal tissues (Fig. 107-27).⁹⁸ Although MRI has the appealing advantage of no ionizing radiation, the current limitations that preclude routine use of MRI for imaging suspected appendicitis in children include relatively long examination time and limited availability compared with CT. The need for sedation in most young infants remains a current limitation, although faster sequence studies with a mean duration of 10 to 14 minutes have been described and performed without sedation in infants as young as 3 years.⁹⁹

Treatment

Although appendectomy is the mainstay in the treatment of acute appendicitis, the literature is variable on the management of appendicitis and depends on the institution and the individual surgeon with respect to surgical procedure, timing of the surgical procedure, antibiotic therapy, and the clinical presentation of the patient.100–102 Although open appendectomy is still performed by some surgeons, laparoscopic appendectomy has become a preferred surgical approach.¹⁰³ Several studies have suggested that emergent appendectomy may not be necessary, demonstrating that IV antibiotics, along with appendectomies delayed for 12 to 24 hours after presentation, do not significantly increase the rate of perforations, operative time, or length of hospital stay.^104,105 Patients with perforated appendicitis undergo IV antibiotic therapy followed by interval appendectomy several weeks later. If an abscess is present, the child will typically undergo image-guided drainage.¹⁰⁶

Colonic Volvulus

Colonic volvulus refers to a twisting or torsion of a portion of the colon, such as the cecum or the sigmoid. It is less common in children than in adults. When it occurs in children, the cecum is the most common area to twist; in adults, the sigmoid colon is the most common location.

Pneumatosis Coli

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