Initial Management of Indeterminate Renal Lesions in a Statewide Collaborative: A MUSIC-KIDNEY Analysis.

PURPOSE: Renal masses can be characterized as "indeterminate" due to lack of differentiating imaging characteristics. Optimal management of indeterminate renal lesions remains nebulous and poorly defined. We assess management of indeterminate renal lesions within the MUSIC-KIDNEY (Michigan Urological Surgery Improvement Collaborative-Kidney mass: Identifying and Defining Necessary Evaluation and therapY) collaborative. MATERIALS AND METHODS: Each renal mass is classified as suspicious, benign, or indeterminate based on radiologist and urologist assessment. Objectives were to assess initial management of indeterminate renal lesions and the impact of additional imaging and biopsy on characterization prior to treatment. RESULTS: Of 2,109 patients, 444 (21.1%) had indeterminate renal lesions on their initial imaging, which included CT without contrast (36.2%), CT with contrast (54.1%), and MRI (9.7%). Eighty-nine patients (20.0%) underwent additional imaging within 90 days, 8.3% (37/444) underwent renal mass biopsy, and 3.6% (16/444) had reimaging and renal mass biopsy. Additional imaging reclassified 58.1% (61/105) of indeterminate renal lesions as suspicious and 21.0% (22/105) as benign, with only 20.9% (22/105) remaining indeterminate. Renal mass biopsy yielded a definitive diagnosis for 87%. Treatment was performed for 149 indeterminate renal lesions (33.6%), including 117 without reimaging and 123 without renal mass biopsy. At surgery for indeterminate renal lesions, benign pathology was more common in patients who did not have repeat imaging (9.9%) than in those who did (6.7%); for ≤4 cm indeterminate renal lesions, these rates were 11.8% and 4.3%. CONCLUSIONS: About 33% of patients diagnosed with an indeterminate renal lesion underwent immediate treatment without subsequent imaging or renal mass biopsy, with a 10% rate of nonmalignant pathology. This highlights a quality improvement opportunity for patients with cT1 renal masses: confirmation that the lesion is suspicious for renal cell carcinoma based on high-quality, multiphase, cross-sectional imaging and/or histopathological features prior to surgery, even if obtaining subsequent follow-up imaging and/or renal mass biopsy is necessary. When performed, these steps lead to reclassification in 79% and 87% of indeterminate renal lesions, respectively.