Primary Rectal Perineurioma: A Rare Incidental Finding

Perineurioma is a rare benign peripheral nerve sheath tumor which can occur intraneurally or uncommonly in the extraneural soft tissues. The majority of the perineuriomas of the gastrointestinal tract occur distal to the splenic flexure as polypoid pedunculated or sessile lesions. Lesions are often discovered incidentally during routine colonoscopy for cancer screening. Diagnosis is mainly histological with the majority of the cases showing mucosal/submucosal bland spindle cell proliferation with expression of perineurial markers. We report a rare case of rectal perineurioma in a 42-year-old female who presented with the complaint of intermittent episodes of painless rectal bleed associated with defecation. A pedunculated polypoid lesion in the rectum measuring 12 mm in greatest dimension was seen on colonoscopy. The patient underwent endoscopic mucosal resection of the mass. Microscopically, the lesion showed proliferation of spindle cells with oval-to-spindle nuclei, bland chromatin, and moderate amount of pale to eosinophilic cytoplasm with indistinct cell borders. Overlying mucosa showed hyperplastic crypt epithelium. Spindle cells were positive for epithelial membrane antigen and CD 34 and negative for S100, with low Ki-67 marked cycling cell population (<1.0%) and negative Progesterone receptor (PR) and CD 117, these features confirming the diagnosis of perineurioma.