Benign Solitary Fibroma of the Kidney with Hepatic Metastasis: A Case Report

Background: Solitary Fibrous Tumor (SFT) is a rare fibroblastic mesenchymal neoplasm. Primary renal involvement is infrequent and generally regarded as benign. Distant metastasis from histologically benign renal SFT is rare and is frequently overlooked or misdiagnosed. Case Presentation: 66-year-old woman was incidentally discovered to have a left renal mass on routine screening. Contrast-enhanced computed tomography demonstrated an irregular, 82 × 73 × 71 mm mass arising from the lower pole of the left kidney. Concurrent arterial-phase imaging revealed multiple hyperenhancing hepatic nodules. The pre-operative impression was “left renal carcinoma with abnormal hepatic perfusion.” However, histopathologic evaluation of the nephrectomy specimen established a benign SFT. Four months postoperatively, arterial-phase CT confirmed mild enlargement of the hepatic nodules. Two years later, contrast-enhanced MRI confirmed multiple hepatocellular nodules, and at three years, followup CT demonstrated further substantial enlargement. Percutaneous liver biopsy established the definitive diagnosis of metastatic solitary fibrous tumor. Conclusion: Even when an SFT is histologically classified as benign, the possibility of hepatic metastasis is not excluded if abnormal enhancing hepatic lesions are present. Long-term, close imaging surveillance is therefore mandatory. Early detection and timely intervention are expected to improve prognosis.