Inflammatory fibroid polyps of the gastrointestinal tract: spectrum of clinical, morphologic, and immunohistochemistry features.

Inflammatory fibroid polyps (IFPs) are rare, benign tumors that can arise throughout the gastrointestinal tract. Although the molecular pathogenesis of these lesions has been well characterized, their morphologic features often vary. We report the clinicopathologic findings of the largest series of IFPs to date. A total of 83 IFPs seen at our institution were collected between 1999 and 2012. The specimens included 64 biopsies and 19 resections. A review of the clinical features identified a modest female predominance (47 women and 36 men) with patients ranging in age from 26 to 87 years (mean, 60 y). Involved sites included the esophagus (n=2), stomach (n=31; mainly antrum), small intestines (n=17), appendix (n=1), large intestines (n=31; majority within the rectosigmoid), and anal canal (n=1). Although most patients had a nonspecific presentation, those with small intestinal lesions frequently presented with intussusception. Grossly, the tumors ranged in size from 0.2 to 4.2 cm (mean, 1.7 cm). Histologically, IFPs were centered within the submucosa in all resection specimens, but mucosal extension was found in 74 of 83 (89%) cases. The tumors varied in both cellularity and degree of vascularity. However, the characteristic feature of perivascular onion skinning was present in only 54% (45/83) of the cases. In addition, a short fascicular growth pattern was also noted in 36% (30 of 83) of cases, whereas both features were present in 14 cases (17%). Eosinophils were present in 94% (78 of 83) of cases but varied widely in number from abundant (20/hpf) to sparse (1/hpf). Interestingly, in those cases with sparse eosinophils, prominent hyalinization was also present (11 of 78, 13%). In addition, although the majority of IFPs expressed CD34, 6 of 44 (14%) were negative. No associated dysplasia or malignancy was seen. IFPs represent a diverse set of submucosal-based lesions that commonly extend into the mucosa, making them amenable to endoscopic biopsy. Although their classic histologic features of perivascular onion skinning and predominance of eosinophils are well described, they may alternatively present with a short fascicular growth pattern, a sparse number of eosinophils, and prominent hyalinization.