Granular cell tumor of the rectum: a case report and review of the literature.

A 47-year-old Japanese woman with a 5-year history of alcoholism was admitted to the Ryukyu University Hospital for the treatment of the alcoholism. For evaluation of observed changes in her bowel habits, she underwent colonoscopy, which revealed seven small polyps spread throughout the entire large intestine. Six of the polyps were in the colon; one was an adenoma and five were hyperplastic polyps. The remaining polyp, in the rectum, was an 8-mm submucosal tumor. Pathological analysis of a biopsy of the lesion in the rectum indicated a possible diagnosis of adenocarcinoma. Endoscopic ultrasonography (EUS) demonstrated a submucosal hypoechoic nodule, involving the mucosa and the muscularis propria. Subsequently, the patient underwent a radical low anterior resection of rectum. The lesion was a submucosal tumor with ulceration. The tumor consisted of granular tumor cells which were positive for S-100 protein, neuron-specific enolase, and periodic acid schiff (PAS) stain, but negative for desmin and vimentin. Granular cell tumor is rare in the gastrointestinal tract. As a result, such tumors can be misinterpreted to indicate a possible malignancy on either a biopsy or EUS.