Double-echo gradient chemical shift MR imaging fails to differentiate minimal fat renal angiomyolipomas from other homogeneous solid renal tumors.

ABSTRACT

OBJECTIVES: The purpose of this retrospective study was to evaluate the diagnostic performance of double-echo gradient chemical shift (GRE) magnetic resonance (MR) imaging for the differentiation of angiomyolipomas with minimal fat (mfAML) from other homogeneous solid renal tumors. METHODS: Between 2005 and 2010 in two institutions, all histologically proven homogenous solid renal tumors imaged with computed tomography and MR imaging, including GRE sequences, have been retrospectively selected. A total of 118 patients (mean age 61 years; range 20-87) with 119 tumors were included. Two readers measured independently the signal intensity (SI) on GRE images and calculated SI index (SII) and tumor-to-spleen ratio (TSR) on in-phase and opposed-phase images. Intra- and interreader agreement was obtained. Cut-off values were derived from the receiver operating characteristic (ROC) curve analysis. RESULTS: Twelve mfAMLs in 11 patients were identified (mean size 2.8cm; range 1.2-3.5), and 107 non-AML tumors (3.2cm; 1-7.8) in 107 patients. The intraobserver reproducibility of SII and TSR was excellent with an intraclass correlation coefficient equal to 0.99 [0.98-0.99]. The coefficient of correlation between the readers was 0.99. The mean values of TSR for mfAMLs and non-mfAMLs were -7.0±22.8 versus -8.2±21.2 for reader 1 and -6.7±22.8 versus -8.4±20.9 for reader 2 respectively. No significant difference was noticed between the two groups for SII (p=0.98) and TSR (p=0.86). Only 1 out of 12 mfAMLs and 11 of 107 non-AML tumors presented with a TSR inferior to -30% (p=0.83). CONCLUSION: In a routine practice, GRE sequences cannot be a confident tool to differentiate renal mfAMLs from other homogeneous solid renal tumors.