S1648 A Colon Polyp from Outside the BOX—Schwann Cell Hamartomatous Polyp

Abstract

INTRODUCTION: A positive cologuard leads to a colonoscopy that can show typical polyps of the gastrointestinal (GI) mucosa. Still rare, GI tract nerve sheath tumors have become more common.1 Nerve sheath tumors are rare in the GI tract but common in skin and soft tissue.2 Some GI nerve sheath tumors have malignant potential or can be affiliated with inherited polyposis syndromes and require histological and immunostaining evaluation to differentiate the polyps. A variant of nerve sheath tumors is Schwann cell hamartoma, described in a large case series by Gibson and Hornick.3 CASE DESCRIPTION/METHODS: 70 year-old female with hypertensive and diabetic history had a colonoscopy for a positive Cologuard. Colonoscopy showed two 3-4 mm polyps in the ascending colon, removed by cold biopsy forceps, entire colon diverticulosis and internal hemorrhoids. Normal ileal mucosa and bleeding. Biopsied polyps showed hyperplastic polyp and Schwann cell hamartoma, staining S-100 positive and cytokeratin AE1/AE3 negative (Image 1,2). DISCUSSION: Polyps with neural histology have a differential diagnosis of schwannomas, neurofibromas, leiomyomas, perineuriomas, ganglioneuromas, and granular cell tumor.3,4 Neurofibromas, mucosal neuromas and ganglioneuroma lesions are often associated with Neurofibromatosis type 1, Multiple Endocrine Neoplasia Type 2b and Cowden syndrome respectively.2 Schwann cell hamartoma are GI Schwannomas that are not affiliated with inherited syndromes. 3,4 They are often both small polyps ranging from 1-6mm and left-sided colonic lesions specifically seen in the rectosigmoid colon. Grossly they are polypoid lesions and histologically show neural proliferation but absence of ganglion cells.2,3,4 All neuronal etiology polyps have diffuse proliferation of spindle cells in the lamina propria. All Schwann cell hamartomas stain strongly positive for S-100. They have no staining of neurofilament protein while the opposite is true for neurofibromas.2 It is important to distinguish schwannomas from Schwann cell hamartomas. Both stain positive for S-100, but schwannomas are typically found in the stomach and noted to have peripheral cuff-like lymphoid aggregates with germinal centers, composed exclusively of Schwann cells.2 It is important to differentiate neuronal histologic polyps to discern underlying malignancy or inherited syndrome. Importantly, Schwann cell hamartomas have all been described being discovered incidentally with benign clinical courses, consistent with what is seen in our patient.Figure 1.: Hematoxylin and eosin shows scattered proliferation of bland spindle cells in the lamina propria.Figure 2.: Immunohistochemical staining for S-100 displays a positivity of both nucleus and cytoplasm.