Bosniak

v2019AJR

Bosniak Classification of Renal Cysts

Classifies renal cystic lesions based on CT and MRI features. Septation, wall characteristics and enhancement patterns determine Bosniak I-IV category.

Septa

Wall

Enhancement

Solid component

Select all features

References

Silverman SG, et al. Bosniak Classification of Cystic Renal Masses, Version 2019: An Update Proposal and Needs Assessment. Radiology 2019;292(2):475-488.
Israel GM, Bosniak MA. An update of the Bosniak renal cyst classification system. Urology 2005;66(3):484-488.

This classification system is intended for clinical decision support. Final diagnosis and treatment decisions rest with the clinician.

Categories

ISimple cyst0% malignancy

Thin-walled, homogeneous water density, no enhancement

Thin (<2mm) smooth wall
Homogeneous water density (-9 to +20 HU)
No enhancement
No septa

Management: Benign — no follow-up needed

IIMinimally complicated cyst0% malignancy

Thin septa, thin calcification, hyperdense cyst (<3cm)

1-3 thin (<2mm) septa
Thin/short calcification
No septal/wall enhancement
Hyperdense cyst <3cm (>=70 HU)

Management: Benign — no follow-up needed

IIFRequires follow-up5-10% malignancy

Minimally suspicious features — surveillance needed

>=4 thin septa
Minimally thickened (3mm) smooth septa/wall
Minimal enhancement
Hyperdense cyst >=3cm

Management: Follow-up: 6 months, then annually (5 years)

IIIIndeterminate40-60% malignancy

Thickened irregular wall/septa or measurable enhancement

Thickened (>=4mm) irregular wall/septa
Measurable enhancement (>=20 HU increase)
Wall/septal irregularity

Management: Surgery or active surveillance

IVMalignant>80% malignancy

Cystic mass with enhancing solid component

Enhancing solid component (nodule)
Solid component >=4mm
Convex contour
Enhancing tissue independent of septa/wall

Management: Surgery (partial/radical nephrectomy)