Imaging of pancreatic metastases from renal cell carcinoma

Background: To describe the main imaging characteristics of pancreatic metastases from renal cell carcinoma (RCC) with particular attention to CT features, underlining possible criteria for a differential diagnosis. Methods: 15 patients have been included in this study. 14 patients underwent multislice CT with triphasic acquisition (unenhanced, pancreatic parenchymal and portal venous phases). In 9 cases a delayed phase (120 sec) was also acquired. 5 patients underwent MRI, before and after administration of gadolinium. Results: The mean time interval between nephrectomy and recurrence was 7.5 years (range 1-17 years). On CT metastases avidly enhanced in the parenchymal phase and then demonstrated a significant wash-out, approaching isodensity to the normal pancreatic parenchyma in the portal phase. In the portal phase 20 of the 25 lesions found in the arterial phase were recognizable. On non-enhanced scans, only 13 of the 25 lesions were detected. On MRI, with the limitations due to the paucity of cases, the metastatic foci appeared hypointense to normal pancreatic tissue on T1-weighted images, and hyperintense on T2- and diffusion-weighted images. After gadolinium, the behaviour was similar to that reported for CT, except for one patient in whom two metastatic foci presented a signal intensity almost isointense to the surrounding parenchyma, accompanied also by an unusual lowering of the signal on DWI (diffusion-weighted imaging) with high b-values. Compared to CT, with MRI the lesions appeared all detectable even on non-enhanced acquisitions. Conclusion: Renal Cell Carcinomas require a prolonged CT or MRI follow-up. In patients with RCC history, an early arterial or a pancreatic parenchymal phase is always mandatory, as pancreatic metastases typically present themselves as hypervascular lesions. This behavior is similar to that of neuroendocrine tumors, while the other primary pancreatic tumors tend to be hypovascular.