Benign hybrid perineurioma-schwannoma in the colon. A case report.

A 48-year-old man of Haitian descent presented with progressive constipation, hematochezia, and weight loss. Colonoscopy and computed tomography scan revealed an obstructing colonic mass, causing intussusception and pneumatosis of the descending/upper sigmoid colon and necessitating an emergency left hemicolectomy. Gross examination revealed a 4.9-cm obstructing mass in the sigmoid colon extending through the muscularis propria. Histologically, the lesional cells were bland, spindled, with tapered and often wavy nuclei set in a loose fibromyxoid stroma. Focally, the lesional cells displayed whorling or storiform growth pattern mixed with spindle wavy cells. In many areas, the cells had bipolar cytoplasmic processes. Immunohistochemistry revealed patchy positivity for epithelial membrane antigen, CD34, vimentin, diffuse positivity for S-100, and negativity for CD117, cytokeratin (AE1/AE3), ALK1, desmin, smooth muscle actin, neuronal nuclei antigen (NeuN), and neurofilament protein. The morphology and immunohistochemical findings were consistent with hybrid perineurioma-schwannoma. Electron microscopic examination revealed the characteristic features of perineuriomal and schwannomatous differentiation. Based upon the histopathology, immunophenotype, and ultrastructure, this tumor was classified as a benign hybrid perineurioma-schwannoma, a counterpart to the tumor described in the soft tissue. This is the first case report of hybrid perineurioma-schwannoma in the colon.