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JU INSIGHT Evolution of Bosniak IIF Renal Cysts and Impact of the 2019 Bosniak Classification
By: Félix Couture, MD, Centre Hospitalier de l’Université de Montréal, Quebec, Canada Centre Hospitalier Universitaire de Sherbrooke, Quebec, Canada; Sarah Hadj-Mimoune, MD, Centre Hospitalier Universitaire de Sherbrooke, Quebec, Canada; Stéphane Michael, MD, Centre Hospitalier de l’Université Laval, Quebec, Canada; Teodora Boblea Podasca, MD, Centre Hospitalier Universitaire de Sherbrooke, Quebec, Canada; Maxime Noël-Lamy, MD, Centre Hospitalier Universitaire de Sherbrooke, Quebec, Canada; Patrick O. Richard, MD, Centre Hospitalier Universitaire de Sherbrooke, Quebec, Canada | Posted on: 20 Apr 2023
Couture F, Hadj-Mimoune S, Michael S, Podasca TB, Noël-Lamy M, Richard PO. Evolution of Bosniak IIF renal cysts and impact of the 2019 Bosniak classification. J Urol. 2023;209(4):694-700.
Study Need and Importance
Bosniak IIF (BIIF) renal cysts currently require cumbersome radiological follow-up, given a risk of upgrading to more complex cysts traditionally reported at around 10%-15%. Recent studies have suggested that the risk of upgrading may be lower than previously thought. Also, the impact of the revised 2019 Bosniak classification on the diagnosis and follow-up of such lesions has yet to be assessed in a real-world population.
What We Found
Through a cohort of 181 BIIF renal cysts with a median follow-up of approximately 4 years, we identified only 4 radiological progressions (2%), of which only 1 was found to be a malignant cyst (see Table). No malignant or suspicious progression occurred beyond 36 months of follow-up. When applying the 2019 Bosniak classification to our cohort, we reduced the amount of initial BIIF diagnoses by 76%, without any detrimental impact on the diagnosis and follow-up of suspicious lesions.
Table. Radiological and Clinical Outcomes of Bosniak IIF Cysts
| Radiological evolution | |
|---|---|
| Cyst size | |
| Increased, No. (%) | 73 (45) |
| Size increase, median (IQR), mm | 4 (2-9) |
| Decreased, No. (%) | 63 (38) |
| Size decrease, median (IQR), mm | 3 (1-7) |
| Stable, No. (%) | 28 (17) |
| Cyst classification, No. (%) | |
| Stable BIIF | 140 (85) |
| Downgrade to BI | 2 (1.1) |
| Downgrade to BII | 16 (10) |
| Upgrade to BIII | 2 (1.1) |
| Upgrade to BIV | 2 (1.1) |
| Spontaneous involution | 1 (0.55) |
| Clinical outcomes | |
| Symptomatic cyst, No. (%) | |
| Pain | 1 (0.55) |
| Hematuria | 1 (0.55) |
| Surgical excision, No. (%) | |
| Partial nephrectomy | 3 (1.7) |
| Radical nephrectomy | 2 (1.1) |
| Benign pathology | 4 (2.2) |
| Malignant pathology | 1 (papillary type 1 RCC, F2, pT1a) |
| Abbreviations: B, Bosniak; IQR, interquartile range; RCC, renal cell carcinoma. | |
Limitations
Limitations include the lack of assessment of interobserver agreement between radiologists, as well as the varying imaging quality throughout the 18-year study period. A total of 55 patients were excluded because of insufficient follow-up. Given the retrospective nature of our study, there was no standardized follow-up protocol in our cohort.
Interpretation for Patient Care
Many renal cysts (76%) classified as BIIF using the previous Bosniak classification could be classified as Bosniak II using the 2019 classification and be spared from imaging follow-up, avoiding important costs, radiation, and patient anxiety. No BIIF cyst had a significant progression beyond 36 months, which may help physicians decide how long to pursue follow-up. The very low rate of upgrading in BIIF cysts (2%) should also guide the counseling of patients diagnosed with such lesions.
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