MRI for differentiation of renal cell carcinoma with sarcomatoid component from other renal tumor types.

Abstract

To investigate the usefulness of MRI for detection of sarcomatoid renal cell carcinoma (SRCC) components within RCC and differentiation from other renal tumors. Two observers independently interpreted T2-weighted images of 10 patients with pathologically confirmed RCCs with SRCC and 131 with non-SRCC renal tumors, with special reference to conspicuously low signal intensity (SI) areas (T2LIA) compared to the renal cortex. SRCC probability was classified as (1) definitely non-SRCC, no T2LIA; (2) probably non-SRCC, <1cm T2LIA; (3) low probability of SRCC, homogeneous tumor with 1-3cm T2LIA; (4) probably SRCC, heterogeneous tumor with 1-3cm T2LIA; and (5) definitely SRCC, >3cm T2LIA, multiple >1cm T2LIAs, or showing disruption of the pseudocapsule. The observers used chemical shift imaging to exclude the area representing hemorrhage or hemosiderin deposition from T2LIA. Scores of 4/5 were regarded as positive for evaluating the accuracy and area under the receiver operating characteristic curve. The SI ratio of the lowest SI in the tumor to that of the renal cortex in the 1 and ≥2 score groups was compared using Mann-Whitney's U test. Sensitivity, specificity, accuracy, and positive and negative predictive values were 90%, 95%, 94%, 56%, and 99%, respectively, and area under the receiver operating characteristic curve was 0.93. The mean SI ratio of the lowest SI in the tumor to that of the renal cortex was significantly lower in the ≥2 score group (0.58) than in the 1 score group (1.36). MRI predicted RCC with SRCC with a moderate positive predictive value and a high negative predictive value.