Differentiation between renal cell carcinoma metastases to the pancreas and pancreatic neuroendocrine tumors in patients with renal cell carcinoma on CT or MRI.

Purpose: To determine whether renal cell carcinoma metastases (RCC-Mets) to the pancreas can be differentiated from pancreatic neuroendocrine tumors (PNETs) in patients with RCC on CT or MRI at presentation.

Methods: This retrospective study included patients with biopsy-proven RCC-Mets (n = 102) or PNETs (n = 32) at diagnosis or after nephrectomy for RCC. Inter-observer agreement (Cohen kappa) was assessed in 95 patients with independent reads by two radiologists, with discrepancies resolved by consensus for final analysis. The remaining 39 cases underwent consensus reads by two different radiologists for final analysis. The CT/MRI images were reviewed for number, size, regional distribution, parenchymal location (exophytic or intrapancreatic), contrast-enhancement, and enhancement pattern of pancreatic lesions in the available phases. Statistical tests were conducted using two sample t-tests and Pearson's chi-squared test for numeric and categorical variables respectively.

Results: The study group comprised of 134 patients (90 males) with 265 lesions (229 RCC-Mets and 36 PNETs). Patients with PNETs were significantly younger (62 ± 12 years vs. 67 ± 9 years, p = 0.013). Inter-observer agreement for CT/MRI features was excellent across multiple imaging variables (k = 0.86-1.00). Most PNETs were single lesions (88 vs. 63%, p = 0.008), smaller in size (14 mm vs. 23 mm, p = 0.042), more common in the body and tail (81 vs. 57%, p = 0.01), showed homogeneous contrast enhancement (64-79% vs. 39-49%, p < 0.01-0.03), less T1-hypointense (80 vs. 99%, p = 0.002) and more DWI hyperintense (71 vs. 58%, p < 0.001) compared to RCC-Mets.

Conclusion: PNETs are typically single, occur in distal pancreas, and enhance homogeneously compared to RCC-Mets which are often multiple, occur in the proximal pancreas, and enhance heterogeneously.