Abstract
A 63-year-old man was admitted to our hospital with the chief complaint of constipation. A rectal digital examination revealed an elastic hard mass located in the posterior wall of the rectum. Colonoscopy showed a submucosal tumor measuring 60 mm in diameter in the lower rectum above the dentate line, near the anal canal. Dynamic CT revealed a rectal tumor measuring 61×59mm in size displacing the lower rectum forward. There was no evidence of either lymph node or distant metastasis. MRI showed the membrane-covered tumor extending to the levator ani muscle bilaterally. A biopsy specimen was positive for CD34 and c-kit (CD117). The Ki-67/MIB-1 index of the tumor cells was 10.7%. Based on the findings, the tumor was diagnosed as a rectal GIST. The patient desired anal preservation, therefore, preoperative imatinib mesylate (IM) therapy was selected. IM was administered at the dose of 400 mg once daily. After 6 months of IM therapy, CT and MRI revealed a decrease of the maximal diameter of the tumor to 45 mm (33% reduction). Seven months after the initial diagnosis, laparoscopic inter-sphincteric resection (ISR) was performed, including partial external sphincter resection and temporary ileostomy, and the anal sphincter muscle was successfully preserved.
