Bosniak classification system of renal cystic masses (version 2005)
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The Bosniak classification system of renal cystic masses divides renal cystic masses into five categories based on imaging characteristics on contrast-enhanced CT. It is helpful in predicting risk of malignancy and suggesting either follow-up or treatment.
Classification
Bosniak 1
- simple cyst, imperceptible wall, rounded
- work-up: nil
- percentage malignant: ~0%
Bosniak 2
- minimally complex, a few thin (<1 mm) septa, thin calcifications; non-enhancing high-attenuation (due to to proteinaceous or haemorrhagic fluid) renal lesions of less than 3 cm are also included in this category; these lesions are generally well marginated
- work-up: nil
- percentage malignant: ~0%
Bosniak 2F
- minimally complex but requiring follow up
- increased number of septa, minimally thickened or enhancing septa or wall
- thick calcifications
- hyperdense cyst, i.e.:
- >3 cm diameter, mostly intrarenal (less than 25% of wall visible); no enhancement
- work-up: needs ultrasound/CT follow up - no strict rules on time frame but could do at around 6 months.
- percentage malignant:
~25~ 5% 6
Bosniak 3
- indeterminate, thick or multiple septations,
mural noduleseptal nodularity, hyperdense on CT (see 2F) - treatment/work-up: partial nephrectomy or radiofrequency ablation in elderly or poor surgical candidates
- percentage malignant: ~54% 6
Bosniak 4
- clearly malignant, solid mass with a large cystic or a necrotic component
- treatment: partial or total nephrectomy
- percentage malignant: ~100%
-<li>increased number of septa, minimally thickened or enhancing septa or wall </li>- +<li>increased number of septa, minimally thickened or enhancing septa or wall </li>
-<li>percentage malignant: ~25% <sup>6</sup>- +<li>percentage malignant: ~ 5% <sup>6</sup>
-<li>indeterminate, thick or multiple septations, mural nodule, hyperdense on CT (see 2F)</li>- +<li>indeterminate, thick or multiple septations, septal nodularity, hyperdense on CT (see 2F)</li>
-<li>clearly malignant, solid mass with a large cystic or a necrotic component </li>- +<li>clearly malignant, solid mass with a large cystic or a necrotic component</li>