Purpose Detection of small renal masses is increasing with the use of cross-sectional imaging, although many incidental lesions have negligible metastatic potential. Among malignant masses, clear cell renal cell carcinoma is the most prevalent and aggressive subtype, and a method to identify such histology would aid in risk stratification. Our goal was to evaluate a likelihood scale for multiparametric magnetic resonance imaging in the diagnosis of clear cell histology. Methods Patients with cT1a masses who underwent MRI and partial or radical nephrectomy from December 2011 to July 2015 were retrospectively reviewed. Seven radiologists with different levels of experience and blinded to final pathology independently reviewed studies based on a predefined algorithm, and applied a clear cell likelihood score: 1) definitely not, 2) probably not, 3) equivocal, 4) probably, and 5) definitely. Binary classification determined the accuracy of clear cell versus ‘all other’ histologies, and inter-observer agreement was calculated with a weighted κ statistic. Results In total, 110 patients with 121 masses were identified. Mean tumor size was 2.4 cm and 50% were clear cell. Defining clear cell as scores ≥4 demonstrated sensitivity and specificity of 78% and 80%, respectively, while scores ≥3 were 95% and 58%, respectively. Inter-observer agreement was moderate to good, with a mean κ of 0.53. Conclusions A clear cell likelihood score with MRI can reasonably identify clear cell histology in small renal masses, and may reduce the number of diagnostic renal mass biopsies. Standardization of imaging protocols and reporting criteria are needed to improve inter-observer reliability.

Purpose To determine the diagnostic performance and inter-reader agreement of a standardized diagnostic algorithm for determining the histologic type of small (<=4cm) renal masses (SRM) with multiparametric magnetic resonance imaging (MRI). Materials and Methods This single-center, retrospective, HIPAA-compliant, IRB-approved study included 103 patients with 109 SRM, resected between December 2011 and July 2015. The requirement for informed consent was waived. Pre-surgical renal MRIs were reviewed by 7 radiologists with diverse experience. Eleven MRI features were assessed and a standardized diagnostic algorithm used to determine the most likely histologic diagnosis, which was compared to histopathology after surgery. Inter-reader variability was tested with Cohen’s κ. Regression models using MRI features were used to predict the histopathologic diagnosis with 5% significance level. Results Clear-cell (ccRCC) and papillary type renal cell carcinomas (pRCC) were diagnosed with respective sensitivities of 85% (47/55) and 80% (20/25), and specificities of 76% (41/54) and 94% (79/84). Inter-reader agreement was moderate-to-substantial (ccRCC, κ=0.58; pRCC, κ=0.73). Signal intensity of the lesion on T2-weighted images (T2W) and degree of contrast enhancement during corticomedullary phase (CE) were independent predictors of ccRCC (T2W OR: 3.19 CI95%: [1.4, 7.1], p=0.003; CE OR: 4.45 [1.8, 10.8], p<0.001) and pRCC (CE OR: 0.053 [0.02, 0.2], p<0.001), both with substantial inter-reader agreement (T2W, κ=0.69; CE, κ=0.71). Lower performance was observed for chromophobe histology, oncocytomas, and minimal-fat angiomyolipomas, [ranges, sensitivity=14%(1/7)–67%(4/6), specificity=97%(100/103)–99%(101/102)], with fair-to-moderate inter-reader agreement (κ=0.23–0.43). Segmental enhancement inversion was an independent predictor of oncocytomas (OR: 16.21 [1.0, 275.4], p=0.049), with moderate inter-reader agreement (κ=0.49). Conclusion The proposed standardized MRI-based diagnostic algorithm had a diagnostic accuracy of 81% (88/109) and 91% (99/109) for the diagnosis of ccRCC and pRCC, respectively, while achieving moderate to substantial inter-reader agreement among 7 radiologists.

Although with low morbidity, in comparison to extirpation and conventional thermal ablation technologies, irreversible electroporation has suboptimal short-term local disease control results in this series of small, low complexity tumors. Larger series and longer follow-up will determine the durability of this modality.

Chest x-rays are a low yield diagnostic tool for detecting pulmonary metastasis in patients treated for T1a renal cel carcinoma. Treatment mode does not appear to influence the need for chest x-ray surveillance.