Anal canal gastrointestinal stromal tumors: case report and literature review.

Gastrointestinal stromal tumors (GIST) are an uncommon group of tumors of mesenchymal origin. GIST of the anal canal is extremely rare. At present, only 10 cases of c-kit positive anal GIST have been reported in the literature. There is no widely accepted treatment approach for this neoplasia. Literature is sparse on imaging evaluation of anal canal GIST, usually described as a lesion in the intersphincteric space. We describe the case of a 73-year-old man with a mass in the anal canal, and no other symptoms. Endoanal ultrasound and magnetic resonance imaging showed a well circumscribed solid nodule in the intersphincteric space. The patient was treated by local excision. Gross pathological examination showed a 7 cm × 3.5 cm × 3 cm mass, and histological examination showed a proliferation of spindle cells, with prominent nuclear palisading. The mitotic count was of 12 mitoses/50 HPF. The tumor was positive for KIT protein, CD34 and vimentin in the majority of cells, and negative for desmin and S100. A diagnosis of GIST, with high risk aggressive behavior was made. An abdomino-perineal resection was discussed, but refused. The follow-up included clinical evaluation and anal ultrasound. After 5 years the patient is well, with maintained continence and no evidence of local recurrence.