Are Hemorrhagic Cysts Hyperintense Enough on T1-Weighted MRI to Be Distinguished From Renal Cell Carcinomas? A Retrospective Analysis of 204 Patients

Abstract

<b>OBJECTIVE.</b> The purpose of this study was to evaluate the utility of T1- and T2-weighted MRI signal-intensity ratios and signal-intensity SDs of renal lesions to determine the feasibility of distinguishing between simple cysts, hemorrhagic renal cysts, clear cell renal cell carcinoma (RCC), and papillary RCC. <b>MATERIALS AND METHODS.</b> Pathology records of 53 cases of papillary RCCs between 1 and 5 cm in size were included. Thirty-eight pathology-proven clear cell RCCs, 54 simple renal cysts seen on abdominal MRI, and 59 hemorrhagic renal cysts seen on abdominal MRI were identified. Lesion location and size, T1- and T2-weighted signal intensity, and corresponding SD values for each renal lesion and psoas muscle (from which lesion-to-muscle ratios were calculated) were collected. <b>RESULTS.</b> Analysis revealed a statistically significant difference (<i>p</i> < 0.001) in T1-weighted lesion-to-muscle signal-intensity ratios between simple cysts (mean ± standard error, 0.54 ± 0.05), clear cell RCCs (0.86 ± 0.06), papillary RCCs (1.17 ± 0.05), and hemorrhagic renal cysts (1.95 ± 0.04). The T2-weighted lesion-to-muscle signal-intensity ratios showed a statistically significant difference between all lesion types (<i>p</i> < 0.02) except between hemorrhagic renal cysts and papillary RCCs, where the difference approached significance (<i>p</i> = 0.075). ROC analysis showed an optimal cutoff of T1-weighted lesion-to-muscle signal-intensity ratio of 1.39 to differentiate hemorrhagic cysts (above this value) from RCCs (below this value). Corresponding sensitivity and specificity were 91.2% and 74.6%, respectively. <b>CONCLUSION.</b> T1-weighted lesion-to-muscle signal-intensity ratio is a useful measure to discriminate mildly hyperintense RCCs from more hyperintense hemorrhagic cysts when contrast enhancement is unavailable.