Analysis of predictive factors for the malignancy in Bosniak category IIF renal cysts

Abstract

Purpose: To evaluate the clinical features associated with malignancy in category IIF renal cysts and to determine the optimal length of follow-up for them.Materials and Methods: Radiological and clinical informations were retrospectively searched for Bosniak IIF lesions in computed tomographic (CT) reports from January 1996 to January 2011. 78 adult patients with unenhanced and contrast material-enhanced CT results and with lesions either surgically resected or with 1 year or more of surveillance were included. Renal cyst progression to category III in follow-up studies was defined as an increase in complexity of cyst. I monitored radiologic changes and progression of renal cysts during the follow-up period, and analyzed the pathologic results of those patients who were treated surgically. Results: 21 patients without radiological progression underwent the operation on their own account and of 57 patients under surveillance, five patients (8.8%) showed evidence of progression to category III, with a median time to progression of 9 months (6-26). There was no significant difference in age, gender, cyst size, change in cyst size, multiple septa, wall thickness, calcification, or hyperdensity between the progressive and non-progressive group. Of five patients with radiologic progression, three patients underwent the operation; two patients (66.7%) showed malignancy, whereas of 21 patients without radiological progression underwent the operation; four patients (19.0%) showed malignancy. All six patients reported as malignancy were pT1 renal cell carcinomas and showed no recurrence during postoperative median follow-up of 20 months (4-35). Of 24 patients who underwent the operation, the malignant group showed a significantly older age than the benign group (p=0.035), but the hyperdensity was the sole significant predictive factor for malignancy (OR 13.000, 95% CI 1.201 to 140.734; p=0.035). Conclusions: It is hard to decide the optimal length of follow-up for Bosniak IIF lesions because of variable time to progression, but those with hyperdensity would need more close surveillance because of high risk of malignancy.