Crohn's-like clinical and pathological manifestations of giant inflammatory polyposis in IBD: a potential diagnostic pitfall.

Background & Aims: Giant inflammatory polyposis (GIP), characterized by mass-like agglomerations of inflammatory polyps, is a rare complication of inflammatory bowel disease (IBD). We reviewed a series of cases of GIP to determine its diagnostic impact on the clinical and pathologic distinction between ulcerative colitis (UC) and colonic Crohn's disease (CD).

Methods: All colons with GIP resected over a 13-year period were identified prospectively and the corresponding clinical and pathologic records were reviewed.

Results: Twelve cases of GIP were identified, accounting for 0.8% of colectomies for IBD during the same time interval. Preoperatively, 6 (50%) patients were diagnosed with UC, 2 (17%) with CD and 4 (33%) with indeterminate colitis (IC). Postoperatively, 6 of the diagnoses (50%) were revised based on strict histopathologic criteria: all 4 diagnoses of IC to UC, one diagnosis of CD to UC, and one diagnosis of UC to CD, for a total of 10 diagnoses of UC (83%) and two of CD (17%). Significantly, 7 of 10 cases with postoperative diagnoses of UC (70%) had Crohn's-like transmural inflammation exclusively within the polyposis segments attributed to fecal entrapment and stasis and accounting for the Crohn's-like clinical complications in these cases.

Conclusions: This case series of GIP, the largest reported from a single center, highlights the high rate of Crohn's-like clinical and pathological manifestations of GIP and their potential to confound the accurate classification of patients with IBD. A diagnosis of UC should not be amended to CD based on the findings of the polyposis segment alone.