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Outcomes of Bosniak Classification Version 2019 Class IIF Cystic Renal Masses at Imaging Surveillance. AJR. American journal of roentgenology Shen, L., Yoon, L., Chung, B. I., Kamaya, A., Tse, J. R. 2022

Abstract

Background: Bosniak classification system version 2019 (v2019) recommends that class IIF masses undergo follow-up imaging at 6 months, 12 months, and then annually for 5 years. The frequency and timing of upgrade on follow-up imaging are incompletely understood. Purpose: To describe the temporal evolution of Bosniak v2019 class IIF cystic renal masses, with attention to outcomes at 6-month follow-up, time to class upgrade, and malignant histologic diagnoses. Methods: This retrospective study included 219 patients (91 women, 128 men; median age, 72 years) with 246 localized class IIF masses from January 2005 to June 2022. Patients underwent both a baseline and at least one follow-up renal-mass protocol contrast-enhanced CT or MRI. Two radiologists evaluated masses at all follow-up time points to categorize masses as downgraded (class I or II), stable (localized class IIF), or upgraded (class III or IV, solid, or =T3a, N1, or M1 disease); a third radiologist resolved discrepancies. Incidence rate of upgrade was determined. Histopathologic outcomes were assessed for resected masses. Results: Median follow-up was 28.4 months (IQR, 13.7-59.4 months). At 6-month follow-up, 5 (2%) masses were downgraded, 241 (98%) were stable, and none were upgraded. Based on final follow-up, 14 (6%) masses were downgraded, 223 (91%) were stable, and 9 (4%) were upgraded. All upgrade events entailed a class increase to III (n=7) or IV (n=2); no mass became solid or developed T3, N1, or M1 disease. Among the nine upgraded masses, median time to upgrade was 53.5 months (IQR, 23.2-63.7 months). Incidence rate of upgrade was 3.006 per 100,000 person-days (95% CI, 1.466-5.516). Ten masses were resected; histopathology was benign in six, and malignant in four. Of the four malignant masses, one was upgraded to class III after 15 months of preoperative follow-up imaging, and three remained class IIF on preoperative follow-up imaging. No resected malignant mass developed postoperative recurrence. Conclusion: Bosniak v2019 class IIF masses are unlikely to represent aggressive malignancy; only 4% were upgraded over time, and never on initial 6-month follow-up. Clinical Impact: The currently recommended initial 6-month follow-up imaging examination for class IIF masses is of questionable clinical utility.

View details for DOI 10.2214/AJR.22.28599

View details for PubMedID 36416398