S3923 A Rare Colonic Perineurioma Discovered in Routine Screening

Introduction: Colonic perineuriomas are rare and benign peripheral nerve sheath tumors with an incidence of 0.1%-0.46% of all colonic polyps. They are usually found in the sigmoid colon or rectum incidentally during routine colorectal cancer screening. Histologically, they are characterized by spindle cells within the lamina propria. They are often sessile and small, and they may mimic hyperplastic or adenomatous polyps endoscopically. Diagnosis relies on histopathologic evaluation and immunohistochemical staining. Due to their rarity and non-specific appearance on endoscopy, they are frequently underrecognized. We present a case of colonic perineurioma of the sigmoid colon discovered during routine colonoscopy. Case Description/Methods: A 69-year-old woman with a family history of colon cancer presented for screening colonoscopy. Colonoscopy 3 years prior identified a 5 mm, protruding, sessile polyp in the ascending colon that was resected but not retrieved. A 4 mm, protruding, sessile polyp was resected and retrieved from the transverse colon with pathology negative for dysplasia. Repeat colonoscopy showed one 2 mm polyp in the cecum and one 10 mm polyp in the sigmoid colon. Pathologic examination of the cecal polyp was unremarkable, but the polyp in the sigmoid colon was identified as a perineurioma with benign spindle cells, positive for GLUT-1 and negative for S-100 and smooth muscle myosin on immunostains. Follow-up colonoscopy in 3 years was recommended. Discussion: Anatomically, the perineurium is the protective connective tissue that surrounds nerve fascicles. A perineurioma is a benign soft tissue neoplasm composed of the cells resembling the normal perineurium, and they can be found either intraneurally or in soft tissue. The soft tissue variant may present as a nodule growing under the skin, or they can less commonly affect visceral organs, as in this case of colonic perineurioma. They are occasionally identified during colonoscopy, often incidentally. They tend to have a sessile morphology and a size of less than 10 mm, and they are most often found in the distal colon and rectum. These tumors are likely underrecognized, since they may mimic adenomatous or hyperplastic polyps endoscopically or may evade detection entirely if they are submucosal. Accurate diagnosis requires microscopic and immunohistochemical analysis and is important in prescribing appropriate follow up for these benign lesions.