Applied Radiology

Diagnosis

Filiform polyposis of the colon

Findings

Double contrast barium enema showed numerous slender filling defects in the colon, typical of filiform polyposis. Colonoscopy with biopsies revealed multiple inflammatory polyps throughout the colon with normal appearing intervening mucosa. Biopsy also showed mild chronic mucosal inflammation and edema without significant glandular distortion or fibrosis.

Discussion

Filiform polyposis is a rare sequela of inflammatory bowel disease, especially Crohn's disease and ulcerative colitis. The term was originally described by Appelman et al¹ and consisted of a characteristic radiographic appearance of numerous slender, finger-like or filiform defects in the colon with a normal haustral pattern. These mucosal lesions are composed of submucosa covered by normal or minimally inflamed mucosa. The surrounding mucosa may be normal, although acute or chronic inflammatory changes may be present. The filling defects have been described as vermiform, worm-like, spaghetti-like, or as resembling the stalk of a polyp without the head.² The transverse colon and descending colon are the most common location, although the polyps can be seen in any portion of the large bowel with the exception of the rectum.^1,3 There have also been reported cases in the stomach and, rarely, in the small bowel.⁴ Filiform polyps of the colon may be misinterpreted as unusual villous adenomas or small carcinomas on colonoscopy. It is of particular importance to differentiate the lesion from carcinoma in long-standing ulcerative colitis or familial adenomatous polyposis. However, there is no known association between filiform polyposis and the development of carcinoma.

The pathogenesis of filiform polyposis is uncertain, although it has been speculated that a previous history of inflammatory disease with long periods of quiescence is involved.^1,2 The polyps seem to proliferate between two adjacent inflamed, ulcerated zones. The development of the polyps is comparable to the reparative process and formation of inflammatory pseudopolyps seen in ulcerative colitis. Pseudopolyps of ulcerative colitis consist of islands of inflamed, edematous mucosa and granulation tissue that layers between denuded and ulcerative areas; while filiform polyps consist of a submucosa core with blood vessels and smooth muscle fibers. The submucosa of filiform polyps is elevated and pulled into the formation of a stalk due to the proliferating and regenerative epithelium. Thus, filiform polyps are different from the typical pseudopolyps of ulcerative colitis, since pseudopolyps consist of regenerating mucosa that stands out only because the surrounding mucosa is ulcerated. However, both filiform polyps and pseudopolyps polyps are seen in the quiescent phase of ulcerative colitis and Crohn's disease.

Filiform polyps usually appear as thin, straight filling defects resembling the stalks of polyps without the heads. The polyps can range in size from 1.5 to 3.0 cm in length and up to 0.5 cm in diameter. The projections can occur as solitary polyps or as diffuse polyposis distributed over large areas of the colonic mucosa. In some cases, a radiating or branching pattern can be identified, particularly at the tip of the polyps.²

These lesions can be confused with unusual villous adenomas, small carcinomas, or mucus threads on barium. The projections can arborize and fuse at their tips and thus form mucosal bridges that can trap fecal material and lead to the formation of a large fecalith, which can cause obstruction. These obstructions have been confused with carcinoma.^5,6 Bleeding can also be encountered in patients with filiform polyposis. If identified, the bleeding is likely to originate from the intervening inflamed mucosa rather than from the polyps themselves, although the polyps do have a rich vascular component. In most cases, when these polyps are identified, there is usually no radiologic evidence of acute colitis and these polyps may be the first due to the presence of inflammatory bowel disease.

Filiform polyposis is a rare form of pseudopolyposis associated with ulcerative colitis, Crohn's disease, and granulomatous disease that is formed by a nonspecific mucosal and submucosal reaction to previous severe inflammation.^1-3 It is important to recognize that filiform polyposis is a benign, radiographically characteristic form of inflammatory polyps that should not be mistaken for a neoplastic familial polyposis syndrome. Filiform polyposis alone is not an indication for surgical resection, but complications, such as acute massive hemorrhage⁵ or intestinal obstruction,^6,7 may necessitate surgical intervention.

1. Appelman HD, Threatt BA, Ernst C, et al:Filiform polyposis of the colon: An unusual sequela of ulcerative colitis. Am J Clin Path 62:145-146, 1974. Abstract.
2. Zegel HG, Laufer I: Filiform polyposis. Radiology 127:615-519, 1978.
3. Spark RP:Filiform polyposis of the colon. First report in a case of transmural colitis. Digestive Dis 21:809-814, 1976.
4. Bray JF:Filiform polyposis of the small bowel in Crohn's disease. Gastrointest Radiol 8:155-156, 1983.
5. Renison DM, Forouhar FA, Levine JB, Breiter JR: Filiform polyposis of the colon presenting as massive hemorrhage: An uncommon complication of Crohn's disease. Am J of Gastro 78:413-416, 1983.
6. Antonow DR, Gebhard RL, Dykosld RK, Sumner HW:Filiform polyposis in Crohn's colitis mimicking toxic megacolon. Dig Dis Sci 26:1051-1055, 1981.
7. Goldenberg B, Mori K, Friedman IH, et al:Fused inflammatory polyps simulating carcinoma and ulcerative colitis. Am J Gastroenterol 73:441-444, 1980.