The role of Bosniak classification in malignant tumor diagnosis: A single institution experience

To evaluate the clinical reliability of the Bosniak classification in Korea, and to identify independent predictors of malignancy in complicated renal cysts.

We reviewed the records of 368 patients with renal cysts between January 2001 and December 2014; 14 patients were excluded, due to interobserver variability in Bosniak classification between the radiologist and urologist. Clinical characteristics and radiologic findings of malignant cystic masses were analyzed, retrospectively.

In 324 surgically excised lesions from patients (n=312) with renal cysts, the percentages of malignancy in the different Bosniak classifications were as follows: category I, 1.0% (1 of 103); II, 3.8% (2 of 53); IIF, 17.1% (7 of 41); III, 38.0% (27 of 71); and IV, 82.1% (46 of 56). Mean age and lesion size were 59.88±11.9 years (180 men, 144 women) and 5.47±3.51 cm, respectively. Univariate analysis identified hypertension (p=0.011), a history of smoking (p=0.038), and obesity (p=0.015) as the strongest risk factors of malignancy. In a study of Bosniak category III patients, hypertension (p=0.018), lesion size (p<0.001), and difference of Hounsfield Unit (HU) (p=0.027) were the strongest risk factors of malignancy. Multivariate analysis identified lesion size as the strongest potential predictor of malignancy, followed by hypertension and difference of HU.

Risk factors of malignancy in complicated renal cyst patients were not different from those published previously. In Bosniak category III lesions, hypertension and lesion size were the strongest predictors of malignancy. Characteristically, the lesion size was smaller than in benign complicated renal cysts, in contrast with other categories.