Introduction

Detection of small renal masses (SRM) is increasing with the use of cross-sectional imaging, although many incidental lesions have negligible metastatic potential. Among common malignant masses, clear cell renal cell carcinoma (ccRCC) 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 (mpMRI) in the diagnosis of clear cell histology.

Methods

Patients with cT1a masses who underwent mpMRI (T2-, chemical shift T1-, and contrast-enhanced T1-weighted imaging) 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 (ccLS, 1-5): 1) definitely not, 2) probably not, 3) equivocal, 4) probably, and 5) definitely. Receiver operating characteristic (ROC) analysis determined the accuracy of ccRCC versus 'all other' histologies, and inter-observer agreement was calculated with a weighted &[kappa] statistic.

Results

In total, 110 patients with 121 cT1a renal masses were identified. Mean tumor size was 2.4cm and 50% were ccRCC. Figure 1 summarizes classification of the entire cohort. Defining ccRCC as ccLS 4-5 lesions demonstrated overall mean accuracy of 79%, sensitivity of 78%, specificity of 80%, positive predictive value (PPV) of 80%, and negative predictive value (NPV) of 80%. Including ccLS 3 lesions changed the mean accuracy to 77%, sensitivity to 95%, specificity to 58%, PPV to 70%, and NPV to 93%. ROC analysis calculated an area under the curve (AUC) range from 0.82-0.92 for the seven radiologists, and inter-observer agreement was moderate to good with a mean &[kappa] of 0.53. Of ccLS 4-5, 4.5% and 1.7% were false positive oncocytoma and angiomyolipoma, respectively, while 6% of ccRCC was false negative ccLS 1-2.

Conclusions

mpMRI can reasonably identify ccRCC histology in cT1a renal masses, and may reduce the number of patients who undergo routine biopsy of SRM. Standardization of imaging protocols and reporting criteria are needed to improve inter-observer reliability, and prospective studies are required to validate these findings.

Funding

Partially funded by grant 5RO1CA154475