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Bosniak renal cyst classification

Dr Yuranga Weerakkody and Dr Frank Gaillard et al.

The Bosniak classification system for CT evaluation of renal cysts is helpful in determining both malignant risk and required followup / treatment.

Bosniak 1

simple cyst, anechoic, imperceptable wall, rounded
work up : nil
% malignant : ~ 0

Bosniak 2

minimally complex, single thin (< 1mm) septations, thin Ca++; non-enhancing high-attenuation (due to to proteinaceous or hemorrhagic fluid) renal lesions of less than 3 cm are also included in this category; these lesions are generally well marginated.
work up : nil
% malignant : ~ 0

Bosniak 2F

minimally complex but requiring follow up.
increased number of septa, minimally thickened or enhancing septa or wall
thick Ca++,
hyperdense cyst that is:
- > 3 cm diameter, mostly intrarenal (less than 25% of wall visible); no enhancement
work up : needs ultrasound / CT follow up
% malignant : ~ 25 %⁶

Bosniak 3

indeterminate, thick or multiple septations, mural nodule, hyperdense on CT (see 2F)
treatment / work up : partial nephrectomy or RF ablation in elderly / poor surgical risk
% malignant : ~ 54%⁶

Bosniak 4