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 1I
- simple cyst
- imperceptible wall, rounded
- work-up: none
- percentage malignant: ~0%
Bosniak 2II
- minimally complex
- a few thin <1 mm septa or thin calcifications (thickness not measurable);
- non-enhancing high-attenuation (due to proteinaceous or haemorrhagic contents) renal lesions <3 cm
- these lesions are generally well marginated
- work-up: none
- percentage malignant: ~0%
Bosniak 2FIIF
- minimally complex
- increased number of septa, minimally thickened with nodular or thick calcifications
- there may be perceived (but not measurable) enhancement of hairline-thin smooth septa
- minimal thickening of the wall with perceivable enhancement
- hyperdense cyst >3 cm diameter, mostly intrarenal (less than 25% of wall visible); no enhancement
- requiring follow-up (the 'F' in 2F is for 'follow'): needs ultrasound/CT/MRI follow up - no strict rules on the time frame but reasonable at 6 months
- percentage malignant: ~5% 6
Bosniak 3III
- indeterminate
- thick, nodular multiple septa or wall with measurable enhancement
- treatment/work-up: partial nephrectomy or radiofrequency ablation in elderly or poor surgical candidates
- percentage malignant: ~55% 6
Bosniak 4IV
- clearly malignant
- solid mass with a large cystic or a necrotic component
- treatment: partial or total nephrectomy
- percentage malignant: ~100%
History and etymology
It is named after Morton A Bosniak (1929-2016), who was professor emeritus in radiology at New York University (NYU) Langone School of Medicine 9,10.
-<p>The <strong>Bosniak classification system of renal cystic masses</strong> 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.</p><h4>Classification</h4><h6>Bosniak 1</h6><ul><li>simple cyst<ul>- +<p>The <strong>Bosniak classification system of renal cystic masses</strong> 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.</p><h4>Classification</h4><h6>Bosniak I</h6><ul><li>simple cyst<ul>
-</li></ul><h6>Bosniak 2</h6><ul><li>minimally complex<ul>- +</li></ul><h6>Bosniak II</h6><ul><li>minimally complex<ul>
-</li></ul><h6>Bosniak 2F</h6><ul><li>minimally complex<ul>- +</li></ul><h6>Bosniak IIF</h6><ul><li>minimally complex<ul>
-</li></ul><h6>Bosniak 3</h6><ul><li>indeterminate<ul>- +</li></ul><h6>Bosniak III</h6><ul><li>indeterminate<ul>
-</li></ul><h6>Bosniak 4</h6><ul><li>clearly malignant<ul>- +</li></ul><h6>Bosniak IV</h6><ul><li>clearly malignant<ul>
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