After the imaging work-up, the patient underwent ultrasound guided Tru-Cut biopsy, followed by the complete excision of the mass laparoscopically.  

Histopathological diagnosis: Epithelioid gastrointestinal stromal tumor (GIST) low grade, encased by a thin layer of serosa. Tumor size 5 x 4 x 4 cm. Mitotic count 0/150 HPF. Proliferation index approximately 5%. Negative for tumor necrosis.

Immunohistochemistry: The tumor cells show a uniform positivity for vimentin and CD117.   S100 also shows a uniform but weaker positivity limited to cytoplasm.  CK AE1/3, CD34, SMA and desmin show a negative reaction.  Ki-67 stains about 5% of the tumor cells.  A single layer of flattened mesothelial cells is highlighted by CK AE1/3 and HBME-1.  Large spaces with albuminous fluid show no endothelial lining.