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 mm 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.
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