Extragastrointestinal Stromal Tumor Presenting as Omental Cyst.

INTRODUCTION: Extragastrointestinal stromal tumors (EGIST) are rarer counterparts of gastrointestinal stromal tumors (GIST) in omentum, mesentery, and retroperitoneum. CASE REPORT: Hereby, authors present a 47-year-old man with abdominal mass whose abdominal CT scan revealed a large septated cystic mass measuring 16 cm in largest diameter. The mass was aspirated and resected by laparotomy. Pathologic examination exhibited a mesenchymal spindle cell neoplasm which was immunohistochemically reactive for CD117 and SMA. Thus, the diagnosis of extragastrointestinal stromal tumor was made. DISCUSSION: A cystic EGIST in omentum falls in the differential diagnoses of omental cystic lesions which include omental cyst, mesenteric teratoma, cystic mesothelioma, cystic spindle cell tumors, pseudomyxoma peritonei, pancreatic pseudocyst, and complicated ascites. Therefore, proper diagnosis of cystic GIST is of great importance in respect to different behavior, management, and complications in comparison to its mimickers and GI counterparts.