Cystic renal masses: A reevaluation of the usefulness of the Bosniak classification system

Rationale and Objectives. We evaluated the utility of the Bosniak system for classifying cystic renal masses on computed tomography (CT) scans. Methods. The CT scans of 20 patients with 24 cystic renal masses that were subsequently surgically removed or biopsied were reviewed retrospectively. Masses were categorized using the Bosniak system and were correlated with the pathology results. Results. The final pathology results of the cystic renal masses were as follows: Seven of seven category I lesions were benign, one of five category II lesions was benign, zero of four category III lesions were benign, and zero of six category IV lesions were benign. Neither of two unclassifiable cystic lesions were benign. The average enhancement of lesions in categories II, III, and IV was 6.3, 2.3, and 27.6 Hounsfield units (H), respectively. The two uncategorizable lesions had a mean enhancement of 26.8 H. Conclusion. The results of our study serve to underscore some limitations of the Bosniak classification system because most of our category II and all of our category III lesions were malignant, suggesting that minimally complex cystic renal masses may contain malignant cells. Contrast enhancement of less than 10 H was demonstrated in lesions in categories II and III.