Early colonic perineurioma: a report of 11 cases.

Colonic perineurioma has been depicted as characterized by a mucosal proliferation of monomorphic spindle perineurial cells leading to an evident separation, distortion, and entrapment of colonic crypts. The authors, however, believe that a sizable subset of the cases differ in that they display only a limited perineurial proliferation leading to only mild crypt separation without crypt entrapment. This morphological variant (early perineurioma) has not yet been documented. The authors herein present the clinicopathological and immunohistochemical features of 11 cases. Polyp size ranged from 2 to 4 mm, and 8 (73%) were located in the sigmoid. Histologically, they revealed small, frequently noncontiguous nests or bundles of uniform round to oval cells, causing slight separation of parallel or mildly distorted crypts, which displayed a serrated/hyperplastic architecture in 8 (73%) cases. Immunostaining for perineurial markers showed strong expression for claudin-1, GLUT-1, and collagen type IV and weak reactivity for epithelial membrane antigen. In conclusion, early perineurioma is a morphological variant of colonic perineurioma in which the perineurial proliferation is limited and consequently more difficult to recognize. Using perineurial markers is helpful in reaching an accurate diagnosis.