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 a 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 or thin calcifications ( thickness not measurable); 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
- increased number of septa, minimally thickened with nodular or thick calcifications
- but no measurable contrast enhancement enhancing
- hyperdense cyst >3 cm diameter, mostly intrarenal (less than 25% of wall visible); no enhancement
- requiring follow-up: needs ultrasound/CT follow up - no strict rules on the time frame but could do at around 6 months.
- percentage malignant: ~ 5% 6
Bosniak 3
- indeterminate
- thick, nodular multiple septa or wall ,with measurable enhancement, 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>a few thin <1 mm septa or thin calcifications <span style="line-height:13.8666658401489px">( thickness not measurable</span><span style="line-height:13.8666658401489px">)</span>; 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</li>- +<li>a few thin <1 mm septa or thin calcifications ( thickness not measurable); 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</li>
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