Bosniak Cyst: Classification and Management
Understanding the imaging report and the risk associated with each category
Quick answer
The Bosniak classification assesses, on a scale from I to IV, the risk of malignancy of a complex kidney cyst detected on imaging. It helps determine whether simple surveillance is sufficient or whether further tests (biopsy, treatment) are needed.
What is the Bosniak classification?
The Bosniak classification is a system used in imaging to assess the risk of malignancy of a complex kidney cyst, on a scale from I to IV. It helps determine whether simple surveillance is sufficient or whether further tests are needed.
The different categories
Bosniak I and II: benign cysts, no particular surveillance required in the vast majority of cases. Bosniak IIF: intermediate category requiring regular surveillance. Bosniak III: significant risk of malignancy. Bosniak IV: lesion highly suspicious for malignancy.
What should be done after a Bosniak III or IV result?
These categories warrant a discussion with a urologist or an interventional radiologist to assess the options: close surveillance, percutaneous biopsy, or treatment depending on the case.
Frequently asked questions
Is a Bosniak IIF cyst a cancer?
Is the Bosniak classification always 100% reliable?
Diagnosis, cryoablation, radiofrequency, follow-up: everything about the management of kidney tumours.
Related pages
A kidney tumour: what are the options?
Cryoablation can sometimes be considered for a small kidney tumour, depending on its size, location and kidney function. See the page on kidney tumour ablation.
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Written by the Radiology team at Cochin Hospital AP-HP, Université Paris Cité. Medically reviewed by a radiologist of the department. Last updated: August 2026.