3071 A Rare Case of Colonic Mucosal Schwann Cell Hammartoma That Mimics a Regular Polyp

Abstract

INTRODUCTION: Mucosal Schwann cell hammartomas are considered benign and were rarely reported as an incidental finding during colonoscopies. There is a lack of data on outcomes and surveillance guidelines due to the rarity of these unusual polyps. Here we report a case of colonic mucosal Schwann cell hammartoma incidentally found in a patient with intermittent diarrhea to enhance recognition of this rare lesion. CASE DESCRIPTION/METHODS: A 70-year-old-male with history of venous thromboembolism in setting of Factor V Leiden mutation on rivaroxaban had presented to our gastroenterology clinic complaining of chronic intermittent diarrhea without pain, hematochezia, melena, upper GI symptoms, or weight loss. To further evaluate ongoing diarrhea, the patient had a colonoscopy that showed patchy erythematous mucosa of the sigmoid colon with a single polyp measuring 4 mm at the descending colon, which was removed with a cold snare. The polyp showed focal expansion of the lamina propria by a bland spindle cell proliferation (Schwann cells) with no evidence of atypia or mitotic figures. No ganglion cells were noted and by immunostaining the spindle cells were strongly immunoreactive for S100 (Figure 1). Neuron-specific enolase (NSE) and synaptophysin were negative supporting the absence of ganglion cells. The immunoprofile and morphology was consistent with a diagnosis of mucosal Schwann cell hamartoma. Random colon biopsies ruled out microscopic colitis. Follow up visits were suggestive that food intolerances were the likely cause of his intermittent diarrhea. DISCUSSION: Benign nerve sheath tumors are mostly seen in the stomach and are rare in the rest of the gastrointestinal tract. The differential diagnosis is wide including neurofibromas, perineuromas, ganglioneuromas, granular cell tumors, gastrointestinal stromal tumors, carcinoid, and leiomyoma. Although there are common histological features of neural tumors, the immunostaining pattern is necessary to differentiate them from one another. Due to its rare occurrence, the exact incidence and prevalence of mucosal Schwann cell hammartoma is unknown. This distinction is important as this lesion has no association with any inherited polyposis syndrome and has a benign clinical course.