Lymphoma involves the colon either as a primary neoplasm or as a part of a disseminated disease. In contrast to the small bowel, where lymphomas are the most frequent primary, lymphomas in the colon are rare. In secondary colonic lymphoma, the involvement of the gastrointestinal tract follows a previously diagnosed extraabdominal lymphoma (O'Connell and Thompson 1978; Megibow et al. 1983).
The primary colonic lymphoma is usually found in middle-aged or elderly people. Males are twice as often affected as females. Common symptoms include abdominal pain, weight loss, and changing bowel habits with an average duration of about 46 months. Primary colonic lymphomas occur more frequently in the setting of inflammatory bowel disease and immunosuppression and are found most commonly in the cecum or the rectum (Breneton et al. 1983) (Fig. 13.17a-c).
The radiological appearance can be classified as focal or diffuse. The most common focal type is the intraluminal mass (O'Connell and Thompson 1978). These polypoid lesions are lobulated, broad-based, and sessile with or without central ulcerations with only slight CM enhancement. They are often morphologically indistinguishable from adenomatous polyps.
The focal appearance can also consist of an infiltration that results in pronounced eccentric or circumferential bowel wall thickening. As a consequence, the intestinal lumen may be narrowed. However, unlike colon cancer, lymphoma can also show a dilated caliber in the form of an "aneurysmal" dilatation due to infiltration and destruction of the myenteric plexus (Montgomery and Chew
1997). Ulcerations, necrosis, and fistulae between adjacent bowel loops may appear. Regional, mes-enteric, and retroperitoneal lymphadenopathy may be present. Another focal form of lymphoma is the endo-eccentric mass with large ulcerations involving adjacent bowel loops where fistulae can appear (O'Connell and Thompson 1978).
The diffuse form presents with multiple polypoid lesions and is called diffuse mucosal nodularity or malignant lymphomatous polyposis (O'Connell and Thompson 1978; Callaway et al. 1997). The polyps appear smooth and sessile but can also be irregular or pedunculated. Often, the entire colon or a long segment is involved.
The radiologic patterns of primary colonic lymphoma, such as intraluminal masses, polyps, stenosis, and polyposis, are often quite similar to those of carcinomatous stenosis, adenomatous polyps, and familial polyposis, and can also be evaluated by CT colonography (Table 13.4). The possibility of lymphoma should be considered when cecal tumors involve the terminal ileum, when tumors do not invade the pericolonic fat or adjacent structures and when there are secondary findings such as splenomegaly or bulky abdominal lymph node enlarge-
Table 13.4. CTC features of colorectal lymphoma
Common in cecum and rectum (primary / secondary)
Focal, asymmetric or circular wall thickening, lymphomatid polyposis
Lumen dilated or stenotic
Slight CM enhancement
Ulceration, necrosis, fistula
Pericolic invasion (pericolic soft tissue stranding)
ment (Wyatt et al. 1994). However, in most cases, a reliable radiological differentiation is not possible and the specific diagnosis is only possible with histology. In cases of stenosis or incomplete colonoscopy, CTC could be helpful in the evaluation of the pre-stenotic colon. Extracolonic involvement, fistu-lae and lymphadenopathy can easily be evaluated with planar images.
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