Analysis of Radiologic Findings to Predict the Histology of the Small Renal Tumors: A Retrospective Study / 대한비뇨기과학회지

ABSTRACT

PURPOSE: Recently, incidental small renal tumors detected by computerized tomography(CT) or ultrasonography(US) have been increasing. Differentiation between the small renal cell carcinoma and benign tumorous lesions is often difficult. To reduce the unnecessary surgical interventions for these small renal tumors, we anayzed the radiologic findings of surgically removed small renal tumors(less than 3cm in diameter) and evaluated whether radiologic studies would predict their histologic findings. MATERIALS AND METHODS: Radiologic findings of 28 renal cell carcinomas(RCC), 7 angiomyolipomas(AML), 4 cysts including 2 multilocular cysts and 1 oncocytoma were analyzed, retrospectively. Density, contour, and heterogenity of the tumors on CT were evaluated, while echogenecity, posttumoral enhancement, peritumoral hypoechoic rim, and intratumoral cystic change on US were evaluated. RESULTS: Tiny fat density on CT was found in 4 of 7 AMLs and 1 of 28 RCCs. On US, 3 of 6 AMLs and 1 of 24 RCCs showed marked hyperechogenecity identical to the renal sinus fat. AMLs showed fat density in 4 of 7(57.1%) on CT and marked hyperechogenecity in 5 of 7(71.4%) on US, respectively. Two AMLs which showed hypoechogenecity and no fat density had less than 5% of fat on histologic examination while others had more than 30% of fat. All AMLs, oncocytoma and most RCCs(73%) showed exophytically out-bulging growth pattern while all benign cysts showed endophytic growth. Posttumoral sonic enhancement was found in 3 of 4 cysts and 1 of 24 RCCs. Peritumoral hypoechoic rim and intratumoral cystic changes were identified in 8 of 24(33%) and 7 of 24(29%) RCCs, respectively, while no such findings were detected in other tumors and cysts. CONCLUSIONS: Fat density on CT or marked hyperechogenecity identical to renal sinus fat on US strongly suggest angiomyolipoma, whereas endophytic growth pattern and posttumoral enhancement on US favor benign cyst. In the meantime, absence of above findings combined with peritumoral halo and/or intratumoral cystic change indicate renal cell carcinoma which should be explored.