Colonic Perineurioma Presenting as a Small Subepithelial Lesion With Distinctive Endoscopic Findings.

A 59-year-old man with a history of colorectal polypectomy underwent a screening colonoscopy. A 5-mm reddish lesion was identified in the sigmoid colon. The lesion had a smooth surface without erosion or ulceration and appeared slightly elevated with well-demarcated margins. Magnifying narrow-band imaging revealed dilated round pits, reduced crypt density, and arborizing vessels in the central area. Cold snare polypectomy was performed for diagnostic and therapeutic purposes. Histopathological examination demonstrated proliferation of bland spindle cells with oval nuclei in the lamina propria. Immunohistochemistry showed positivity for vimentin and GLUT-1, weak epithelial membrane antigen expression, and negativity for S-100, SMA, c-kit, and CD34, with a Ki-67 index of <1%. These findings were consistent with colonic perineurioma, a rare benign peripheral nerve sheath tumor composed of perineurial cells. This case highlights that colonic perineurioma should be considered in the differential diagnosis of small subepithelial lesions detected during colonoscopy. Reduced crypt density and arborizing vessels may provide subtle clues; however, definitive diagnosis requires histopathological and immunohistochemical evaluation.