A Case of Gastrointestinal Stromal Tumor (GIST) of the Anal Canal

Abstract

We present a case of gastrointestinal stromal tumor (GIST) which appeared to have arisen from the internal sphincter muscle of anus. The patient was a woman in her sixties who presented to our hospital because of a sense of discomfort and a lump at the perineum. We palpated an elastic-hard tumor with the size of a walnut at the 11 o'clock direction in the subcutaneous structure in the vicinity of the anus. No changes on the skin surface were seen. Visual and digital examinations and anosigmoidoscopy revealed no abnormal findings on the mucosa and lumen of the anal canal and rectum. Imaging studies revealed a 30-mm well-circumscribed tumor showing iso-density to that of muscle in the perineal subcutaneous structure, but we could not determine from where the tumor had arisen. Percutaneous tumorectomy for the purpose of incision biopsy revealed that the tumor connected to the sphincter muscle of anus in the deep structure so that we had to divide and remove a part of the tissue at the tumorectomy. Histopathological diagnosis was GIST derived from the internal sphincter muscle of anus. The patient was considered to belong to a clinically high risk group of recurrence and she has been on adjuvant chemotherapy with imatinib. She is doing well without signs of recurrence, as of 14 months after the operation.