Ulcerative Colitis

Chronic ulcerative colitis is an idiopathic inflammatory disease of the colon that typically affects older children and young adults; an infantile form has been described that is devastating and often fatal (e-Fig.107-1). The disease is characterized by mucosal inflammation, edema, and ulceration, and it is accompanied by submucosal edema in the early stages and fibrosis in the later stages. Transmural disease is uncommon. The disease may be localized in the distal colon, or it may spread to involve the entire colon and the terminal ileum. Skip areas are not characteristic, and their presence should raise the diagnosis of Crohn disease.

Fatal outcomes are less common than previously, but they still occur. Bloody diarrhea may appear explosively in as many as one third of affected patients, but the majority come to medical attention with progressive chronic diarrhea. Occasional patients are seen with toxic megacolon, in which marked dilation of the large bowel, primarily the transverse colon, is seen. Many children are first seen with nongastrointestinal symptoms, of which severe growth retardation is the most common and clinically striking. Arthritis may precede the colon symptoms; typically, it is monoarticular or pauciarticular and affects large joints, although seronegative spondyloarthropathy is seen in some affected males. Skin rashes, uveitis, digital clubbing, stomal ulcers, and hepatic dysfunction (primary sclerosing cholangitis and autoimmune hepatitis) occur in a variable number of children, but less frequently than in adults. Patients with ulcerative colitis for 10 years or longer are at risk for colonic carcinomas, which arise in areas of dysplastic mucosa rather than in adenomatous polyps, and may be multiple.

Crohn Disease

Crohn disease that affects the small bowel is discussed in Chapter 105. The disease can affect the colon and the small intestine. Two features that favor the diagnosis of Crohn disease over ulcerative colitis are the frequent sparing of the rectum, and the presence of skip areas in Crohn disease. Colonoscopy is often the initial examination in patients with suspected Crohn colitis, because it allows visualization of early changes and permits biopsy for diagnosis. Capsule endoscopy is commonly used in both adult and pediatric practice to visualize small-bowel abnormalities.⁴

Ulcerative Colitis

Abdominal radiographs are most often nonspecific; typically, they show an absence of recognizable stool from affected colonic segments, and they may show evidence of mucosal edema or “thumbprinting” (Fig. 107-2).⁵ Patients with toxic megacolon should not undergo contrast enemas because of the high risk of perforation.

Double-contrast barium enema, formerly the diagnostic imaging procedure of choice, has been replaced by colonoscopy with biopsy.4,6 Ulcerative colitis always affects the rectum, with contiguous proximal involvement. Skip areas do not occur, although different parts of the colon may not be equally affected. The terminal ileum may become secondarily affected when there is proximal colonic involvement; terminal ileal involvement is known as backwash ileitis (e-Fig. 107-3). Ultimately, the colonic wall becomes stiff, shortened, and tubular—the “lead pipe” colon—secondary to fibrosis of the submucosa (e-Fig.107-4). Late-stage disease produces presacral thickening, and retroperitoneal fibrosis is a rare complication.

Computed tomography (CT) or magnetic resonance imaging (MRI) can be performed to investigate disease activity (abdominal pain, fever, or other symptoms), to diagnose complications, or to identify associated liver or biliary disease.7,8 When ulcerative colitis is active, cross-sectional imaging shows colonic wall enhancement with preservation of the smooth outer contour of the bowel (e-Fig.107-5). Surrounding fat stranding, mesenteric adenopathy, ascites, and, when perforation occurs, abscesses may also be evident, but extramural changes are much less common than in Crohn disease. In chronic ulcerative colitis, fatty changes may occur in the submucosa.

Crohn Disease

As with ulcerative colitis, double-contrast barium enemas are seldom used today for diagnosis or monitoring of disease activity. Characteristic aphthous ulcers are small and superficial, seen as an elevated edematous halo with a central umbilication caused by barium in the shallow ulcer crater. Eventually, the inflammation becomes transmural, and the characteristic “rose thorn” configuration develops from deep ulcers that extend into the thickened bowel wall. A “cobblestone” pseudopolyposis pattern, similar to that seen in the small intestine, may be apparent: areas of edematous mucosa separated by areas of denuded mucosa and deep ulcerations.⁹ Small-bowel follow-through (SBFT) examinations can identify complications of diseases that affect the colon, and sequelae such as enteric fistulae (Fig. 107-6). Enteroclysis is helpful in unmasking focal areas of disease activity, such as strictures (e-Fig. 107-7). Crohn disease is more likely to lead to colonic strictures than is ulcerative colitis.

CT and MRI are very useful in evaluation of the disease activity and its complications (see Chapter 105). Extent of extramural inflammatory changes and affected loops of bowel can be identified, as can development of abscess or colonic strictures (Figs. 107-8 and 107-9).

Newer imaging techniques include CT or MR enterography and CT or MR enteroclysis, which hold promise in improving the identification of disease activity and its complications. In CT enterography, the patient drinks a negative bowel contrast agent that distends the lumen more than water or traditional positive contrast and that does not mask vascular mucosal enhancement.10,11 CT enteroclysis, like small-bowel enteroclysis, is performed by using high-flow contrast introduced via nasoduodenal intubation. It is more invasive than enterography, but it provides a more controlled volume challenge to the bowel in order to define the presence of sinus tracts and fistulae and to differentiate stricture from inflammation of the bowel wall.¹² CT enteroclysis has shown value in both detecting and excluding partial small-bowel obstruction and to guide specific therapies in these challenging patients.

Increasingly, pediatric centers are using MR imaging, rather than CT to avoid radiation exposure.² Magnetic resonance enterography (MRE) yields equivalent images of the small and large intestine and the intraabdominal organs.^13,14 MRE is able to differentiate active inflammation from chronic inflammation in the layers of the bowel wall. Furthermore, CT and MRE are able to identify intraperitoneal complications such as fistulae and abscesses. MRE is also superior to CT for the diagnosis and management of perianal fistulae (Fig. 107-10).^15–17 Some centers will image the entire abdomen and pelvis during these MR studies, because these patients may have inflammatory processes that involve the liver, pancreas, or biliary tree.