eng Science and Education Publishing American Journal of Medical Case Reports 2374-216X 2024-03-22 12 3 49 55 10.12691/ajmcr-12-3-6 AJMCR20241236 article Kristina Loukeris 1 Elmira Mostafidi Elmira.mostafidi@downstate.edu 1 Department of Pathology, SUNY Downstate Health Science University, Brooklyn, NY, USA Background: Here, we report a sigmoid mucosal Schwann cell hamartoma as an uncommon entity. Though unexpected, the pathologist should consider this among differential diagnoses and be able to distinguish the microscopic features when examining colorectal biopsies. Finally, we have reviewed the literature for similar cases reported over the past two decades. Case presentation: A 55-year-old woman was found to have a 5 mm sessile polyp during her screening colonoscopy. The microscopic study revealed colonic mucosa with ill-defined proliferation of uniform spindle-shaped cells arranged in a haphazard pattern within the lamina propria. All cells had elongated bland nuclei with eosinophilic cytoplasm and unclear cell borders. Edema and mild lymphoplasmacytic infiltration were noticed in the lamina propria. No nuclear atypia, necrosis, or mitosis was identified. On immunohistochemistry, Schwann cells showed diffuse and strong nuclear and cytoplasmic positivity for S-100 protein. CD117 (C-kit) and desmin were negative. Conclusion: Colorectal MSCH has a benign nature, and the lack of axons and strong immunoreactivity for S-100 protein can help distinguish MSCH from most similar entities. https://pubs.sciepub.com/ajmcr/12/3/6/ajmcr-12-3-6.pdf schwann cell hamartoma neurofibroma neuroma colorectal polyp