CASE REPORT: A RARE ENCOUNTER – UNMASKING A RETROPERITONEAL GASTROINTESTINAL STROMAL TUMOR (GIST) IN A 37-YEAR-OLD MALE

Gastrointestinal stromal tumors (GISTs) are the most prevalent mesenchymal tumors of the gastrointestinal system.They arise from progenitor cells known as interstitial cells of Cajal,which are mainly found in the small intestine and stomach. Though they are far less common,extra-gastrointestinal stromal tumors (EGISTs) can develop in other areas,such as the retroperitoneum, mesentery and omentum. We present a rare case of a 37-year-old male with a retroperitoneal gastrointestinal stromal tumor (GIST),initially misdiagnosed as a retroperitoneal paraganglioma based on radiological findings.The patient presented with right-sided abdominal pain and distension.A contrast-enhanced CT (CECT) of the abdomen revealed a lobulated,hypervascular retroperitoneal mass with central necrosis and hemorrhage, suggestive of a paraganglioma. The patient underwent an excision biopsy of the lesion, and histopathological examination with immunohistochemistry confirmed the diagnosis of GIST, with positivity for CD117 and DOG1.The patient was treated with Imatinib postoperatively and showed clinical improvement.This case highlights the diagnostic challenges posed by retroperitoneal masses and the importance of corroborative histopathological and immunohistochemical analysis in establishing a definitive diagnosis.