18F-FDG PET/CT Manifestations of a Gastrointestinal Stromal Tumor Presenting With Predominant Hepatic and Peritoneal Metastases

A 70-year-old man presented with abdominal pain. Contrast-enhanced CT demonstrated multiple large space-occupying lesions in the liver. An 18F-FDG PET/CT scan was subsequently performed to identify the primary tumor, revealing extensive hepatic and peritoneal metastases. Histopathologic examination ultimately confirmed the diagnosis of a gastrointestinal stromal tumor (GIST). GIST typically presents as a primary solid mass arising from the stomach or other parts of the gastrointestinal tract. In this case, however, the predominant imaging findings were multiple hepatic metastases and extensive peritoneal dissemination, with the primary tumor being less conspicuous.