Chronic inflammatory conditions of the gastrointestinal tract are typically associated with fluctuating symptoms of diarrhea, crampy abdominal pain, and variable amounts of bleeding. Systemic manifestations generic to any chronic inflammatory process, (e.g., fever, fatigue, and weight loss) as well as a variety of extraintestinal manifestations (e.g., arthritis, uveitis, aphthous stomatitis, and pyoderma gangrenosum) are also often seen. True abdominal catastrophes fortunately occur with uncommon frequency. In this article, clinical scenarios associated with inflammatory bowel disease (IBD) that present with acute abdomen are reviewed with an emphasis on recent trends in diagnosis and management.

This discussion will be limited to the two most common types of IBD: chronic ulcerative colitis and Crohn's disease. Both of these conditions are chronic inflammatory conditions of undetermined cause that primarily affect the digestive tract, resulting in the aforementioned clinical signs and symptoms. A variety of immunologic abnormalities have been described<sup>27 MacDermott R.P. Alterations of the mucosal immune system in inflammatory bowel disease J Gastroenterol 1996 ;  31 : 907-916

Cliquez ici pour aller à la section Références, 34 Sartor R.B. Cytokines in intestinal inflammation: Pathophysiological and clinical considerations Gastroenterology 1994 ;  106 : 533-539

Cliquez ici pour aller à la section Références</sup> which are of likely pathogenetic significance.

The nature of the abdominal emergencies seen in IBD can be better understood by reviewing some of the clinical and pathologic hallmarks of these conditions. Ulcerative colitis is characterized by chronic mucosal inflammation, almost universally involving the rectum with proximal extension to involve a variable length of contiguous colon. The small bowel and upper gastrointestinal tract are not involved in this process. When the distribution includes the rectum and sigmoid colon only, the term ulcerative proctosigmoiditis may be applied. Disease, up to and inclusive of the splenic flexure, is described as left-sided colitis while involvement of the entire colon is termed universal or pancolitis.

Regardless of the extent of disease, bloody diarrhea is almost a hallmark of the disease. Presenting complaints can also include tenesmus, mucoid rectal discharge, fecal urgency, crampy abdominal pain, and fever. Paradoxically, a small number of patients may have constipation, perhaps reflecting altered motility. This is usually seen in patients with primarily distal disease (proctitis or proctosigmoiditis). Physical examinations may be unrevealing in patients with milder disease, whereas patients with very active disease may demonstrate resting tachycardia, fever, cachexia, pallor, distention, and abdominal tenderness with or without signs of peritoneal irritation. Such alarming physical findings are considerably more apt to occur with widespread disease or in the setting of associated fulminant colitis or toxic megacolon.

Histologically, the inflammatory process is marked by an abundance of neutrophils and lymphocytes with varying amounts of plasma cells and macrophages within the lamina propria. Crypt abscesses, with collections of neutrophils within colonic crypts, are frequently seen. Mucin depletion from goblet cells is a characteristic, although not a pathognomonic, feature. Segments of superficial mucosa may be completely ulcerated and replaced with mucopurulent exudate; the formation of pseudopolyps is often noted. In uncomplicated ulcerative colitis, the inflammatory process is entirely confined to the mucosa and lamina propria.

Crohn's disease is characterized by a transmural, segmental inflammatory process that can affect any part of the gastrointestinal tract. About 40% of patients demonstrate involvement of the terminal ileum along with varying degrees of colonic disease. Approximately 30% of patients have limited small bowel involvement only whereas approximately 30% demonstrate isolated colitis. Ninety percent of patients, with some element of small bowel disease, have involvement of the terminal ileum. Of those patients with isolated colonic disease, about two-thirds will have diffuse involvement with segmental disease in the remainder; rectal sparing is a frequent finding. Manifestations of perianal disease including fistulae, sinus tracts, and abscesses are common. Disease of the esophagus, stomach, or duodenum is much less common, occurring in only a small percentage of patients.

The clinical characteristics of Crohn's disease are more varied than those of ulcerative colitis, reflecting differing pathophysiologies and the heterogeneity of bowel involvement. Given the transmural nature of the inflammatory process and its predominant distribution in the ileum and right colon, it is not surprising that right lower quadrant pain is a frequent presenting complaint. The pain may be related to the inflammation itself, as well as to fibrosis with associated obstruction; diarrhea is also a prominent feature. Patients frequently present with weight loss and fever. The initial presentation is at times mistaken for that acute appendicitis leading to unnecessary surgical intervention.

In comparison to ulcerative colitis, the most salient histologic feature of Crohn's disease is its propensity to extend beyond the mucosa and submucosa. Transmural extension is quite common. The cellular component of this inflammatory response consists mostly of lymphocytes and macrophages. The presence of noncaseating granulomata, although considered diagnostic, is seen in about 50% of cases. Superficial aphthoid ulcers can be seen early on. Deep, fissuring, or serpiginous ulcers often are seen in association with transmural inflammation. These ulcers may penetrate into other viscera including other loops of the bowel, bladder, vagina, or abdominal wall, resulting in fistula formation. Massive bleeding from deep fissuring ulcers can occur, but is surprisingly unusual. Intramural deposition of collagen can be quite striking, which along with edema and inflammation can lead to varying degrees of bowel obstruction. The degree of increase in wall thickness or the length of bowel stenosis may play a role in the pathogenesis of fistula formation and perforation.<sup>38 Tonelli F., Ficari F. Pathological features of Crohn's disease determining perforation J Clin Gastroenterol 1991 ;  13 : 226-230  [cross-ref]

Cliquez ici pour aller à la section Références</sup> Finger-like projections of mesentery, so-called fat wrapping, can be seen along the serosal surface.