Gastrointestinal stromal tumor arising from anorectum: correlation of imprint cytology and radiologic imaging.

The diagnosis of gastrointestinal stromal tumor (GIST) is generally established on histopathologic examination of surgical specimens. Gastrointestinal stromal tumor comprises a heterogenous group of neoplasms of the gastrointestinal tract previously referred to as leiomyomas, leiomyosarcomas, or schwannomas. Gastrointestinal stromal tumor arising from anorectum is a rare instance. We report a case of GIST for the correlation of imaging and cytologic features with immunocytochemical staining. A computed tomography and magnetic resonance imaging confirmed a 2-cm tumor growing into the rectal lumen. The central portion of the tumor showed T1-weighted imaging of low signal and suspected central necrosis by the T2-weighted imaging of high signal. Imprint cytology from excised tumors showed isolated or loosely aggregated spindle cells with scanty and fibrillary cytoplasmic processes, nuclear pleomorphism, fine granular chromatin, and irregular nuclear margins. Epithelioid tumor cells showed grooves with abundant cytoplasm and several round nucleoli. Both c-kit and CD34 antigen were positive with strong and diffuse stainability in smears as well as paraffin sections by immunoperoxidase staining. We suggest that the combined use of imaging diagnosis and cytology with immunocytochemical staining are useful initial diagnosis of GIST.