Dr. Volpe highlighted the CT Bosniak classification of renal cysts, the aim of which is to classify renal cysts according to the risk of malignancy:
- Bosniak I: these are simple, benign cysts with a 0-2% risk of malignancy. These cysts are hairline-thin walled, without septations, calcifications or solid components. They are the same density as water, with no enhancement with contrast. There is no need to follow these cysts.
- Bosniak II: these are also benign cysts with a 0-5% chance of malignancy. These may contain a few hairline thin septa, fine calcifications in the cyst wall or septations, and are uniformly high-attenuated lesions <3 cm. These cysts have sharp margins without contrast enhancement and there is no need for follow-up imaging.
- Bosniak IIF: these are low risk cysts with a 17-25% risk of malignancy and more hairline-thin septa than Bosniak II cysts. They have minimal enhancement, minimal thickening, and calcifications. There is no enhancing soft tissue and are totally intrarenal and well marginated non-enhancing high attenuation lesions ≥3 cm in size. These cysts are observed and followed expectantly.
- Bosniak III: these are indeterminate cysts with a 30-54% risk of malignancy with thickened irregular walls or septa. These cysts do enhance and the recommendation is for surgical excision.
- Bosniak IV: these are malignant cysts with 90-100% risk of malignancy. They have enhancing soft-tissue components and the recommendation is for surgical excision.
The role of percutaneous biopsy for characterization of cystic renal masses has recently been addressed in a systematic review and meta-analysis1. Whereas the estimate for sensitivity of solid renal masses is 99.1%, it is only 83.6% for cystic renal masses. As such, the EAU guidelines state “core biopsies have low diagnostic yield for cystic renal masses and should not be recommended in these cases unless areas with a solid pattern are present (Bosniak IV cysts)”.
Dr. Volpe concluded with several take-home messages:
- The Bosniak classification remains the standard for characterization of cystic masses
- CT is the cross-sectional imaging of choice
- MRI is indicated if CT is not possible or inconclusive
- Percutaneous biopsy is not recommended
Presented by: Alessandro Volpe, MD, University of Eastern Piedmont Hospital, Maggiore Della Carita Hospital, Novara, Italy
Written by: Zachary Klaassen, MD, MSc – Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, Twitter: @zklaassen_md, at the 16th Meeting of the European Section of Oncological Urology, #ESOU19, January 18-20, 2019, Prague, Czech Republic
1. Marconi L, Debastani S, Lam TB, et al. Systematic review and Meta-analysis of Diagnostic Accuracy of Percutaneous Renal Tumour Biopsy. Eur Urol 2016 Apr;69(4):660-673.
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