Lower limits of detection using magnetic resonance imaging for solid components in cystic renal neoplasms

OBJECTIVES We determined the positive predictive value (PPV) for malignancy in complex renal cysts with focal nodular enhancement seen on magnetic resonance imaging (MRI). METHODS A surgical database was reviewed to identify all patients having both a preoperative 3 dimensional (3D) renal MRI and a radical or partial nephrectomy from January 2000 through April 2004 at our hospital. A group of 21 patients were identified with focal nodular enhancement within cystic renal masses. Pathologic correlation was made in each case. RESULTS We performed 286 nephrectomies during the study period. Of these patients, 159 (56%) had a preoperative MRI studies. There were 21 of 159 (13%) patients with complex cystic lesions that displayed focal nodular enhancement, 14 of which (67%) measured 10 turn or larger in size. Twenty (95%) of the 21 lesions were renal cell carcinoma. The single, benign lesion was a cystic nephroma. Fuhrman grade 1 or grade 2 cancers were found in the majority of patients (80%), and there were no grade 4 cancers. Fifteen patients had a preoperative computerized tomography (CT) scan as well and nodular enhancement was suspected in only 4 patients (27%). MRI findings upgraded these lesions in 11 patients (73%). CONCLUSIONS The demonstration of solid enhancing nodular components with high-resolution 3D MRI provides excellent positive predictive value for diagnosing neoplastic cystic renal lesions, including a large percentage 10 mm or larger in size. Our experience suggests a 95% likelihood that cystic renal lesions with focal nodular enhancement are malignant. We recommend that such lesions be considered malignant.