Bosniak classification system of renal cystic masses (version 2005)
Updates to Article Attributes
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.
Usage
The Bosniak classification is widely used by radiologists and urologists for addressing the clinical problem assessing renal cysts 3. It was last updated in 2005 12. A Bosniak classification, version 2019 11 has been proposed to increase the accuracy and include MRI features but does not yet (c. 2021) have widespread validation.
Although practised by some, the use of ultrasonography to characterise the Bosniak classification remains controversial. Originally, it was felt that ultrasound was not adequate for the task as it was incapable of showing neovascularisation (cf. contrast-enhanced CT/MRI), however newer studies looking at contrast-enhanced USultrasound, suggest that this impediment is no longer true. There is also evidence that ultrasound has a higher sensitivity for intralesional septa than either CT or MRI 8,13.
Classification
Bosniak I
- benign simple cyst
- hairline-thin wall of ≤2 mm
- water density
- no septa, calcifications, or solid components
- no enhancement
- work-up: none
- percentage malignant: ~0% ref
Bosniak II
- benign cyst - "minimally complex"
- few hairline thin <1 mm septa or thin calcifications (thickness not measurable)
- perceived enhancement
- non-enhancing high-attenuation (due to proteinaceous or haemorrhagic contents) renal lesions <3 cm
- generally well marginated
- work-up: none
- percentage malignant: ~0% ref
Bosniak IIF
- minimally complex
- multiple hairline thin septa or minimally smooth thickened walls or septa
- perceived but no measurable enhancement of wall or septa
- calcification can be present and may be thick and nodular
- generally well marginated
- high-attenuation lesion >3 cm diameter, totally intrarenal (<25% of wall visible); no enhancement
- requiring follow-up (F for follow-up): needs ultrasound/CT/MRI follow up - no strict rules on the time frame but reasonable at 6 months, 12 months then annually for 5 years 3
- percentage malignant: ~5% 6
Bosniak III
- indeterminate cystic mass
- thickened irregular or smooth walls or septa with measurable enhancement
- treatment/work-up: partial nephrectomy or radiofrequency ablation in poor surgical candidates ref
- percentage malignant: ~55% 6
Bosniak IV
- clearly malignant cystic mass
- Bosniak III criteria + enhancing soft tissue components adjacent to but independent of wall or septum
- treatment: partial or total nephrectomy
- percentage malignant: ~100% ref
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>Usage</h4><p>The Bosniak classification is widely used by radiologists and urologists for addressing the clinical problem assessing renal cysts <sup>3</sup>. It was last updated in 2005 <sup>12</sup>. A <a href="/articles/bosniak-classification-of-cystic-renal-masses-version-2019">Bosniak classification, version 2019</a> <sup>11</sup> has been proposed to increase the accuracy and include MRI features but does not yet (c. 2021) have widespread validation.</p><p>Although practised by some, the use of ultrasonography to characterise the Bosniak classification remains controversial. Originally, it was felt that ultrasound was not adequate for the task as it was incapable of showing neovascularisation (cf. contrast-enhanced CT/MRI), however newer studies looking at <a href="/articles/contrast-enhanced-ultrasound-2">contrast-enhanced US</a>, suggest that this impediment is no longer true. There is also evidence that ultrasound has a higher sensitivity for intralesional septa than either CT or MRI <sup>8,13</sup>.</p><h4>Classification</h4><h6>Bosniak I</h6><ul><li>benign 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>Usage</h4><p>The Bosniak classification is widely used by radiologists and urologists for addressing the clinical problem assessing renal cysts <sup>3</sup>. It was last updated in 2005 <sup>12</sup>. A <a href="/articles/bosniak-classification-of-cystic-renal-masses-version-2019">Bosniak classification, version 2019</a> <sup>11</sup> has been proposed to increase the accuracy and include MRI features but does not yet (c. 2021) have widespread validation.</p><p>Although practised by some, the use of ultrasonography to characterise the Bosniak classification remains controversial. Originally, it was felt that ultrasound was not adequate for the task as it was incapable of showing neovascularisation (cf. contrast-enhanced CT/MRI), however newer studies looking at <a href="/articles/contrast-enhanced-ultrasound-2">contrast-enhanced ultrasound</a>, suggest that this impediment is no longer true. There is also evidence that ultrasound has a higher sensitivity for intralesional septa than either CT or MRI <sup>8,13</sup>.</p><h4>Classification</h4><h6>Bosniak I</h6><ul><li>benign simple cyst<ul>
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