In this article, we report the case of a 40-year-old woman with a sessile polyp of the rectosigmoid junction that underwent endoscopic resection. The resected specimen showed spindle cell proliferation with eosinophilic cytoplasm between mucosal crypts, mimicking mucosal prolapse syndrome. However, these were immunohistochemically positive for S-100, indicating neural cell origin. As neural polypoid lesion of the rectum, neurofibroma, perineurioma, schwannoma, and mucosal Schwann cell hamartoma were in the differential diagnosis. Histology and additional immunohistochemistry confirmed mucosal Schwann cell hamartoma. Mucosal Schwann cell hamartoma of the rectosigmoid junction or rectum can be a histological mimic of mucosal prolapse syndrome and other S-100 positive neural cell lesions; however, the lesion in the present case was correctly diagnosed with histology and immunohistochemistry.
Keywords: S-100; immunohistochemistry; mucosal Schwann cell hamartoma; polyp; rectosigmoid junction.