Multilocular cystic renal cell carcinoma: Clinicopathological features and preoperative prediction using multiphase computed tomography

OBJECTIVE To analyse the clinicopathological and radiological features of multilocular cystic renal cell carcinoma (MCRCC) and to determine the preoperative factors differentiating MCRCC from other cystic RCC (CRCC). PATIENTS AND METHODS The medical records of 53 patients with complex cystic renal masses evaluated by multiphase computed tomography (CT), surgically removed and confirmed as sporadic RCC were reviewed. Of these 53 patients, 23 were classified as having MCRCC and 30 as other CRCCs, defined as RCCs with extensive cystic change or cystic necrosis. Another 22 patients were treated for complex cystic renal masses presumed to be RCC and diagnosed as having benign cyst. RESULTS Benign cysts and MCRCCs were significantly more likely to be of Bosniak classification III than other CRCCs (77% vs 61% vs 27%, P= 0.001). The mean Hounsfield unit (HU) during the corticomedullary phase (CMP) was significantly higher in other CRCCs, with HU ≥38 having 83% sensitivity and 80% specificity for predicting other CRCCs. In a multiple regression model, Bosniak classification and mean HU during CMP were independent factors predictive of other CRCCs. In the 41 patients with masses >4 cm in diameter, the combination of Bosniak classification IV and HU ≥38 during CMP showed 63% sensitivity, 96% specificity, 91% positive predictive value and 80% negative predictive value, yielding 2% false-positive and 15% false-negative rates. CONCLUSIONS The mean HU during CMP and Bosniak classification can differentiate MCRCC from other CRCCs. This could help in selecting an appropriate surgical method, such as nephron-sparing surgery, for complex cystic renal masses >4 cm.