Background: Gastrointestinal stromal tumors (GIST) are the most commonly seen mesenchymal tumors of stomach. They originate from interstitial cells of Cajal (ICC) or from stem cells that differentiate towards the ICC. Although the CT finding of malignant GIST is quite constant, pure cystic form of the disease can be seen rarely. In the present case we reported a patient with GIST
presented as huge cystic lesion initially diagnosed as cyst hydatid disease in liver and discussed the relevant literature on this topic.
Case Report: A 49 year old woman was referred to our clinic for the presence of huge hepatic cystic lesion At preoperative evaluation the patient was found to have 15X10 cm cystic lesion located in left lobe of liver. Since the patient lived in an area where the cyst hydatid disease was frequently
seen and the CT findings strongly suggested us, the preoperative diagnosis of patient was liver cyst hydatic disease. At operation a 15x10 cm sized cyst embedded in lesser sac beneath the left lobe of liver was found. The cyst was dissected completely off adjacent thin adhesions until the
lesser curvature of the stomach where the cyst was originated from was reached. Partial gastric wedge resection was performed with at least 2 cm margin. The postoperative diagnosis revealed that the tumor was positive for c-kit and the patient was diagnosed as gastric gastrointestinal
stromal tumor.
Conclusions: Since the surgical treatment of GIST is completely different than that of other bening cystic lesions the diagnosis of GIST should be kept in mind in deciding the surgical resections of intraabdominal cystic lesions.

Keywords: GIST, Stomach, cyst, Surgery