S1812 A Solitary Sigmoid Perineurioma in an Otherwise Healthy 30-Year-Old Male

INTRODUCTION: Colorectal perineuriomas are rare benign fibroblastic polyps of the colon that comprise only 0.1% to 0.46% of polyps found on colonoscopy and usually present as a sessile polyp distal to the splenic flexure. We report a case of sessile sigmoid perineurioma in a young healthy male. CASE DESCRIPTION/METHODS: A 30-year-old male with chronic constipation presented for a diagnostic colonoscopy. He suffered severe constipation despite the use of over the counter laxatives. Family history was significant for a paternal uncle who was diagnosed with colon cancer at age 40. The patient underwent colonoscopy at our gastroenterology clinic and was found to have a 3-4 mm sessile polyp in the sigmoid colon (Figure 1). The rectum showed a 3 × 3 cm patch with biopsy results significant for fragments of an ulcer, believed to be from chronic constipation. The pathology report of the sigmoid polyp showed a perineurioma. Histology showed a poorly circumscribed proliferation of uniform, spindled cells in the lamina with eosinophilic cytoplasm with absence of ganglion cells, pleomorphism, mitotic figures and necrosis (Figure 2). Immunohistochemical staining was negative for S100 (Figure 3), ruling out Schwann cell hamartoma and ganglioneuroma. DISCUSSION: Perineuriomas are peripheral nerve sheath tumors composed of bland spindle cells with ovoid nuclei in a whorling appearance. Nuclear pleomorphism, mitotic activity and necrosis are often absent. Immunohistochemistry is often strongly positive for Glucose Transporter -1 (GLUT-1), Claudin-1, and less specifically for Epithelial Membrane Antigen (EMA). BRAF V600E mutations are found in 63% of these polyps. Perineuriomas comprise 0.1% to 0.46% of colonic polyps and are often found incidentally in asymptomatic patients. They can appear pedunculated or serrated. If they are mucosal, the differential includes ganglioneuromas, schwannomas, neuromas, neurofibroma, or Schwann cell hamartomas; if submucosal, it may be schwannoma versus a gastrointestinal stromal tumor (GIST). GIST is important to rule out given its malignant potential, but they tend to be larger with an average size of 20 mm. Perineuriomas are often around 4 mm. GIST may show hyperchromasia and mitotic activity. There have not been any case control or cohort studies to assess the risk of malignant potential especially in polyps positive for BRAF V600E mutations. While these polyps are regarded as benign, it is prudent to rule out other tumors that have malignant potential.Figure 1.: 4 mm sessile polyp in sigmoid colon.Figure 2.: Spindle cells in the lesion (arrow).Figure 3.: Spindle cells negative for S100 stain (arrow).