Primary Multifocal Hepatic Gastrointestinal Stromal Tumor Mimicking Metastatic Disease: A Diagnostic Challenge With PET-CT and Histopathological Correlation.

Primary hepatic gastrointestinal stromal tumor (PHGIST) is an exceptionally rare extra-gastrointestinal stromal tumor arising within the liver. It poses a significant diagnostic challenge because hepatic involvement in gastrointestinal stromal tumor (GIST) is more commonly metastatic. Multifocal primary hepatic presentation is even less frequently described. We report a case of a 62-year-old male presenting with constitutional symptoms, wherein contrast-enhanced computed tomography (CECT), magnetic resonance imaging (MRI), and PET-CT revealed multiple lobulated solid lesions involving the right lobe of the liver, associated with mild circumferential thickening of the gastroesophageal junction (GEJ). The lesions demonstrated internal septations, mural nodules, diffusion restriction, subtle wall enhancement, and fluorodeoxyglucose (FDG) avidity, initially raising concern for metastatic disease in the liver. However, histopathological examination of ultrasound-guided liver biopsy revealed a spindle cell neoplasm arranged in sheets and fascicles, with tumor cells showing strong diffuse CD117 positivity on immunohistochemistry. A separate upper gastrointestinal endoscopy-guided biopsy from the GIST demonstrated only mild hyperplasia without evidence of dysplasia or malignancy. The combined radiologic and pathologic findings favored a diagnosis of primary multifocal hepatic GIST. On follow-up PET-CT scan after imatinib therapy, the patient showed a complete/near complete metabolic response. This report expands the imaging spectrum of PHGIST and emphasizes the importance of radiologic-pathologic correlation in distinguishing this rare lesion from metastatic liver disease.