Imaging findings in fumarate hydratase-deficient renal cell carcinoma: a case series of 11 patients.

PURPOSE: Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) is a rare and aggressive RCC subtype defined in the 2022 WHO classification. This study aimed to describe its imaging and clinicopathological features.

METHODS

A retrospective analysis was conducted on 11 patients (12 tumors)　diagnosed with FH-deficient RCC between 2015 and 2024 across multiple institutions. Clinical data, imaging findings (CT, MRI, [18F] fluorodeoxyglucose (FDG) -PET/CT), and histopathological results were reviewed.

RESULTS

The median age at diagnosis was 54 years (range: 35-81), with a male predominance (64%). At presentation, distant metastases were observed in 27% of patients. Based on contrast-enhanced CT findings, tumors were morphologically classified into three types: cystic-predominant (n = 5), solid-predominant (n = 4), and purely solid (n = 3). The dynamic enhancement pattern of the solid components showed progressive enhancement in 54.5% and mild corticomedullary enhancement with delayed washout in 45.5%, suggesting vascular heterogeneity. MRI showed high signal intensity of cystic components on both T1WI and T2WI, suggestive of hemorrhage. Solid components exhibited restricted diffusion on DWI in all cases, with a median ADC value of 0.88 (range: 0.77-1.18) × 10⁻³ mm²/s. On FDG-PET/CT, solid components demonstrated elevated FDG uptake (median SUVmax: 7.25; range: 6.81-10.10). Among nine cases with available follow-up data, three (33%) developed recurrence within two years after surgery.

CONCLUSION

FH-deficient RCC has a high risk of metastasis and recurrence, requiring strict follow-up. Although definitive diagnosis relies on immunohistochemistry, imaging features-such as mixed cystic-solid morphology, hemorrhagic cysts, and, compared with clear cell RCC, lower enhancement, restricted diffusion, and higher FDG uptake-may serve as important diagnostic clues that facilitate accurate pathological diagnosis and management.