Background: This study aimed to identify clear cell renal cell carcinoma (ccRCC) histopathological grade and differentiate it from fat-poor angiomyolipoma (AML). This was achieved through contrast-enhanced magnetic resonance (MR) T1 mapping with intravenous low-dose gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA).
Methods: In total, 56 consecutive patients received MR scanning between January 2016 and December 2018 using the pre- and post- contrast-enhanced T1 mapping sequences with low-dose Gd-DTPA (0.036 mmol/kg). RCCs were pathologically proven in 40 patients after surgery and graded according to the International Society of Urological Pathology (ISUP) classification system. Ten AMLs were pathologically proven by surgery histopathology and six AMLs were diagnosed by magnetic resonance imaging (MRI). Patients were followed up for more than half a year. The mean T1 values of the renal lesion and ipsilateral normal renal parenchyma were measured before and after Gd-DTPA administration (T1p and T1e). The reduction of T1 value (T1d) and the ratio of its reduction (T1d %) were calculated and compared.
Results: In 40 ccRCCs, higher-grade [International Society of Urologic Pathology (ISUP) grade 3 and 4] and lower-grade (ISUP grade 1 and 2) ccRCCs were noted in 13 and 27 patients, respectively. The mean T1p was 1,514.8±139.4 ms and the mean T1d was 907.7±193.7 ms in the higher-grade ccRCCs, which were significantly higher than in the lower-grade ccRCCs (T1p =1,251.7±151.5 ms and T1d =648.5±218.2 ms, respectively; P<0.001). Fat-poor AMLs had higher T1p (1,677.3±104.8 ms) and T1e (865.6±251.5 ms) as compared to ccRCCs (P<0.001). Combined T1p + T1d showed the highest area under the curve (AUC) (0.912) in the differentiation of higher-grade ccRCCs from lower-grade ccRCCs (P=0.010). Combined T1p + T1e had the highest AUC (0.956) in the differentiation between ccRCCs and fat-poor AMLs (P=0.010). All T1 mapping metrics could discriminate between normal renal parenchyma and renal lesions (P<0.001). No significant difference was found in the T1p and T1e at different parts of the ipsilateral normal renal parenchyma. Interobserver agreement for quantitative longitudinal relaxation time in the T1 maps was excellent.
Conclusions: Contrast-enhanced T1 mapping with low-dose Gd-DTPA may provide a more reliable and accurate approach in identifying ccRCCs histopathological grade and differentiating ccRCCs from fat-poor AMLs.
Keywords: Magnetic resonance imaging (MRI); angiomyolipoma (AML); gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA); image enhancement; kidney neoplasms; radiologic technology.
2020 Quantitative Imaging in Medicine and Surgery. All rights reserved.