MR characteristics of mucinous tubular and spindle cell carcinoma (MTSCC) of the kidney: comparison with clear cell and papillary subtypes of renal cell carcinoma

Purpose To describe MR features of mucinous tubular spindle cell carcinoma (MTSCC) of the kidney that may help differentiate from clear cell renal cell carcinoma (ccRCC) and papillary RCC (pRCC). Methods 15 MTSCCs were retrospectively evaluated by MR with T2-weighted image without fat suppression (n = 15) and dynamic contrast-enhanced (DCE), fat-suppressed T1-weighted GRE (n = 11). Size-matched ccRCC (n = 30) and pRCC (n = 30) were evaluated as control. T2 ratio was calculated as the signal intensity (SI) ratio of the lesion to the renal cortex on T2W images. Enhancement ratio (ER) was calculated as (SIpost - SIpre)/(SIpre), where SIpre (SIpost) is the SI of the entire lesion on each phase of DCE images. Early nodular enhancement was subjectively evaluated in MTSCC. T2 ratio and ER were compared using the Mann-Whitney U test with Bonferroni correction. Results The mean value of T2 ratio was highest in ccRCC (1.24), followed by MTSCC (1.02), and pRCC (0.84). Difference of T2 ratio was significant between ccRCC and pRCC (p < 0.001), but not between MTSCC and ccRCC (p = 0.4) or between MTSCC and pRCC (p = 0.2). The mean ER of MTSCC, ccRCC and pRCC were 1.33, 1.53 and 0.38 in corticomedullary phase (CMP), 1.60, 1.61 and 0.69 in nephrographic phase (NGP) and 1.79, 1.35 and 0.77 in excretory phase (EP), respectively. ERs were significantly different between MTSCC and pRCC in CMP (p = 0.01), NGP (p = 0.003), and EP (p = 0.002). Early nodular enhancement was observed in 4/11 MTSCC (36%), 17/30 ccRCC (57%), and 2/30 pRCC (7%). Conclusions MTSCC has distinct MR features that can help differentiate from ccRCC and pRCC. MTSCC enhances more avidly compared to pRCC and shows gradual progressive enhancement.