Diagnostic Accuracy of Multiparametric Magnetic Resonance Imaging to Identify Clear Cell Renal Cell Carcinoma in cT1a Renal Masses

Abstract

Purpose: The 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. 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.

Materials and methods: We retrospectively reviewed the records of patients with cT1a masses who underwent magnetic resonance imaging and partial or radical nephrectomy from December 2011 to July 2015. Seven radiologists with different levels of experience who were blinded to final pathology findings independently reviewed studies based on a predefined algorithm. They applied a clear cell likelihood score, including 1-definitely not, 2-probably not, 3-equivocal, 4-probably and 5-definitely. Binary classification was used to determine the accuracy of clear cell vs all other histologies. Interobserver agreement was calculated with the weighted κ statistic.

Results: A total of 110 patients with 121 masses were identified. Mean tumor size was 2.4 cm and 50% of the lesions were clear cell. Defining clear cell as scores of 4 or greater demonstrated 78% sensitivity and 80% specificity while scores of 3 or greater showed 95% sensitivity and 58% specificity. Interobserver agreement was moderate to good with a mean κ of 0.53.

Conclusions: A clear cell likelihood score used with magnetic resonance imaging can reasonably identify clear cell histology in small renal masses and may decrease the number of diagnostic renal mass biopsies. Standardization of imaging protocols and reporting criteria is needed to improve interobserver reliability.

Keywords: carcinoma; histology; kidney neoplasms; magnetic resonance imaging; neoplasm metastasis; renal cell.

Figure 1

Multiparametric MRI algorithm for small renal masses. ccRCC- clear cell renal cell carcinoma. chrRCC- chromophobe renal cell carcinoma. pRCC- papillary renal cell carcinoma. ONCO- oncocytoma. AML- angiomyolipoma. SI- signal intensity. Reprinted from Radiologic Clinics of North America, Volume 55, Issue 2, Kay FU and Pedrosa I, “Imaging of Solid Renal Masses,” pg 243–258, Copyright 2017, with permission from Elsevier.

Figure 2

Histologic distribution of the entire cohort by clear cell likelihood score. Tumors that could not be assessed are not shown.

Figure 3

Binary classification of the seven readers defining clear cell RCC as ccLS 4–5. RCC- renal cell carcinoma. ccLS- clear cell likelihood score.

Figure 4

Receiver operating characteristic curves of the seven readers defining ccRCC and ccLS 4–5. RCC- renal cell carcinoma. ccLS- clear cell likelihood score.