1535 A Rare Case of Rectosigmoid Mucosal Schwann Cell Hamartoma

Abstract

INTRODUCTION: Colorectal polyps of mesenchymal origin are rare. Mucosal Schwann cell hamartomas have a pure proliferation of Schwann cells in the lamina propria and show immunoreactivity to S-100 protein. To our knowledge, only 11 cases have been reported in the literature since it was first described in 2009. CASE DESCRIPTION/METHODS: We present a case of a 50-year-old African-American female who presented to us for routine screening colonoscopy. Her past medical history was only significant for a prolactinoma for which she was on cabergoline. The patient had no personal or family history of neural lesions or inherited syndromes such as NF1, Cowden syndrome or MEN 2B. The colonoscopy revealed a 2 mm polyp in the cecum and a 3 mm sized rectosigmoid polyp which were resected and sent to pathology. The cecal polyp showed a tubular adenoma. The pathology report for the rectosigmoid polyp was consistent with spindle-shaped lesional cells with immunohistochemical staining strongly positive for S-100. They did not have immunoreactivity for epithelial membrane antigen (EMA). Hence, supporting the diagnosis for Schwann cell hamartoma. The patient was made aware of pathology findings and reassured. DISCUSSION: Mucosal Schwann Cell Hamartoma is a rare and benign lesion that forms in the colon. It usually arises in older adults. The specific risk factors of Mucosal Schwann Cell Hamartoma are unknown. Most patients are asymptomatic however rectal schwannoma may cause symptoms such as obstruction, bleeding, and tenesmus. They are often found incidentally in the distal colon during a colonoscopy. These tumors are poorly circumscribed, with short fascicles of uniform spindle cells replacing the colonic lamina propria, especially the superficial lamina propria, and separating and entrapping the crypts. These tumors involve the mucosa but never the submucosa. Although the histological differential diagnosis of a mucosal Schwann-cell hamartoma can include a gastrointestinal stromal tumor (GIST), neurofibroma, mucosal neuroma, ganglioneuroma, or mucosal schwannoma, a mucosal Schwann-cell hamartoma is composed of single Schwann cells without other cells, such as axons or fibroblasts, and is uniformly stained for S-100. These cells do not have immunoreactivity for c-Kit, CD34, glial fibrillary acidic protein, epithelial membrane antigen (EMA), smooth muscle actin, or neurofilament protein (NFP). Due to the benign nature of Mucosal Schwann Cell Hamartoma, they do not generally require any treatment.