Granular cell tumor--a unique neoplasm of the internal anal sphincter: report of a case.

Granular cell tumors are rare, invariably benign, and often solitary tumors, which infrequently involve the gastrointestinal tract. We report the unique presentation of a granular cell tumor of the internal anal sphincter in a 75 year-old female. The tumor was detected during investigation of new rectal bleeding and was excised using a transanal approach and sphincter repair. At five-year follow-up the patient reported normal continence to stool and flatus and demonstrated no evidence of tumor recurrence. Immunohistochemical studies cite the Schwann neural cell as the origin of the granular cell tumor. Cytoplasmic features include acidophilic, p-aminosalicylic acid-positive, diastaseresistant granules. Granular cell tumors may be located anywhere in the body, but anorectal involvement is rare. In our own search of the world literature, no other cases were reported specifically to involve the anal sphincter. Granular cell tumors are usually detected incidentally but may be symptomatic, especially when the anorectal region is involved. Symptoms include perianal discomfort and bleeding. Adequate local excision is effective for both diagnosis and treatment of anorectal granular cell tumors. Careful follow-up should be performed after excision because of the risk of recurrence.