tumor­ -like inflammatory processes that may or may not lie immediately adjacent to the colon (Pereira et al. 2005; Pickhardt and Bhalla 2005). As features may also overlap with those of epiploic appendagitis, the term “focal fat infarction” has been suggested by some authors for both entities (Pereira et al. 2005).

3.5.3\ Value of Imaging

Epiploic appendagitis and omental infarction are causes of acute pelvic pain that are often misdiagnosed clinically as acute appendicitis or diverticulitis. Imaging allows a definite diagnosis in most cases and patients can be managed conservatively.

a

b

3.6\ Crohn’s Disease

Crohn’s disease is a chronic granulomatous inflammatory intestinal disease with a mean age of presentation in the third and fourth decades. It can affect any part of the gastrointestinal tract from the mouth to the anus, often involving multiple discontinuous sites. The small intestine is involved in 80% of cases, most commonly at the terminal ileum. The colon is affected either with or without involvement of the small intestine (Furukawa et al. 2004). Leading clinical manifestations are prolonged diarrhea with abdominal pain, weight loss, and fever. There is transmural inflammation of the bowel which may lead to adherent bowel loops inflammatory masses, fistulae, sinus tracts obstruction, and perforation. Perianal disease such as anal fissures, fistulas, and abscesses occur in 22% of patients with Crohn’s disease, and are often the first clinical manifestation (Williams et al. 1981).

3.6.1\ Imaging Findings

Bowel wall thickening, usually ranging from 1 to 2 cm, is the most consistent feature of Crohn’s disease on CT and MR (Rollandi et al. 1999). Mural stratification (target appearance) is often seen in active lesions, particularly after contrast administration. The intensity of bowel wall enhancement correlates with the degree of inflammation (Gore et al. 1996). Luminal

Fig. 22  Crohn’s disease in CT. Small bowel loops with dilatation and stenoses are demonstrated in two pelvic CT scans (a, b). A loop of ileum shows transmural wall thickening and intense contrast enhancement (arrow) (a). Adjacent mesenteric hypervascularity represents the comb sign (long arrow) and is another sign of inflammatory activity (b). Heterogeneity of surrounding fat with increased attenuation presents fibrofatty proliferation (arrowhead) (b)

narrowing,­ pre-stenotic dilatation, fibro-fatty proliferation of the mesentery, and mesenteric lymph nodes ranging from 3 to 8 mm in size are further common findings (Fig. 22). On CT, fibro-fatty proliferation has a slightly increased attenuation. On MRI, the signal intensity is decreased compared with normal fat separating the bowel loops. Phlegmon and abscesses can occur in the small bowel mesentery, abdominal wall, or psoas muscle or perianally. They are well demonstrated on CT and fat-saturated T1W MR imaging (Furukawa et al. 2004). Fistulas and sinus tracts can also be identified on MR; however, the reported sensitivity (50– 75%) is less than for conventional enteroclysis (Gourtsoyiannis et al. 2002).