S3970 Mucosal Schwann Cell Hamartoma of the Colon: A Rare Finding on Colonoscopy

Introduction: Mucosal Schwann cell hamartoma (MSCH) is a rare but benign lesion, often found incidentally within the recto-sigmoid colon during screening or surveillance colonoscopies. Histologically, MSCH polyps demonstrates proliferation of Schwann cells in the lamina propria. Unlike other neural tumors of the gastrointestinal tract, MSCH is not associated with inherited syndromes and is considered benign. Case Description/Methods: A 66-year-old man with a history of tubulo-villous and sessile serrated adenomas presented for routine surveillance colonoscopy. Colonoscopy revealed several small polyps distributed throughout the colon. Notably, a 3 mm sessile polyp was identified in the sigmoid colon and removed in its entirety using cold jumbo forceps. Histologic evaluation showed a well-circumscribed proliferation of bland spindle cells in the lamina propria, with elongated nuclei and no atypia or mitoses. Immunohistochemistry demonstrated positivity for S100 protein and was negative for epithelial membrane antigen (EMA). These findings were consistent with mucosal Schwann cell hamartoma. Discussion: MSCH is an uncommon but benign histologic diagnosis, most frequently seen in the rectosigmoid colon during routine colonoscopies. The key to diagnosis lies in histopathology and immunohistochemical staining, particularly the presence of S100 positivity and the absence of other markers. It is important to distinguish MSCH from gastrointestinal stromal tumors and neurofibromas, as these conditions differ in both treatment approach and prognosis. Once MSCH is completely removed, it is typically considered cured, and no further workup or changes to routine surveillance are usually necessary.