Bosniak category III renal lesions: likelihood of malignancy based on computed tomography findings

Bosniak introduced a classification of renal cysts based on imaging characteristics. Cystic renal changes are categorized determining their risk of malignancy and further management. However, defining the malignancy of category III lesions still remains a challenge and our aim was to evaluate the features of malignancy in computed tomography within this category.

The Vilnius University Hospital Santariškių Klinikos information system was retrospectively searched for computed tomography examinations in which Bosniak category III lesions were reported. Data of genetic disorders and history of malignancy were collected. Longest diameter, location, shape, amount and location of calcification, contrast enhancement of Bosniak category III lesions were evaluated. The relation between collected data and malignancy was estimated.

There were 73 patients with Bosniak category III lesions included and 43 cysts were surgically removed and histologically analyzed. Mean tumor size was significantly lower in malignant lesions. Mean enhancement in arterial and portovenous phase, change of mean enhancement in portovenous and native phases were significantly different between benign and malignant lesions. Significant differences in the contrast enhancement pattern was found: septa and capsular enhancement was detected in 28.6% (n = 12) of cases in malignant lesions, while only 4.8% (n = 2) benign lesions show the same enhancement pattern. Some other features showed tendencies to be more prevalent in malignant lesions, however, no significant differences were found.

The collected data and selected features do not allow us to reliably differentiate Bosniak category III cystic lesions as benign or malignant. Some of the criteria showed some tendencies, however, further studies are required to confirm these findings' potential.