Bosniak classification system of renal cystic masses (version 2005)
Updates to Article Attributes
The Bosniak classification system of renal cystic masses divides divides renal cystic masses into five categories based on imaging characteristics on contrast-enhanced CT. It helps predict a risk of malignancy and suggests 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 201911 has been proposed to increase the accuracy and include MRI features but does not yet (2022) 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 inadequate for the task as it was incapable of showing neovascularisation (cf. contrast-enhanced CT/MRI), however, newer studies looking at contrast-enhanced ultrasound, 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
The "official" Bosniak classification uses Roman numerals, not Arabic ones, for each category. The use of the term "grade", "stage", "group", "type", or similar for each category is technically incorrect. Version 2019 has switched from "category" to "class"11.
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% 17
Bosniak II
-
benign cyst - "minimally complex"
few hairlines 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: ~0-6% 17,18
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,
totallytotally intrarenal (<25% of wall visible);nono enhancementrequiring 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: ~5-26%6,19-21
Bosniak III
-
indeterminateindeterminate cystic massthickened irregular or smooth walls or septa with measurable enhancement
treatment/work-up: partial nephrectomy or radiofrequency ablation in poor surgical candidates 23,24
percentage malignant: ~55-72%6,17,19,22
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: ~91-100% 19,22
History and etymology
The Bosniak classification is named after Morton A Bosniak (1929-2016), who was professor emeritus in radiology at New York University (NYU) Langone School of Medicine. It was first published in 1986, introducing the 2F category in 1993, and revisions in 1997, 2005 and 2019 9,10,14-16.
-<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 helps predict a risk of malignancy and suggests 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 (2022) 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 inadequate 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><p>The "official" Bosniak classification uses <a href="/articles/numbers-units-and-operators">Roman numerals</a>, not Arabic ones, for each <strong>category</strong>. The use of the term "grade", "stage", "group", "type", or similar for each category is technically incorrect. Version 2019 has switched from "category" to "class" <sup>11</sup>.</p><h6>Bosniak I</h6><ul><li>-<p>benign simple cyst</p>-<ul>-<li><p>hairline-thin wall of ≤2 mm</p></li>-<li><p>water density</p></li>-<li><p>no septa, calcifications, or solid components</p></li>-<li><p>no enhancement</p></li>-<li><p>work-up: none</p></li>-<li><p>percentage malignant: ~0% <sup>17</sup></p></li>-</ul>-</li></ul><h6>Bosniak II</h6><ul><li>-<p>benign cyst - "minimally complex"</p>-<ul>-<li><p>few hairlines thin <1 mm septa or thin calcifications (thickness not measurable)</p></li>-<li><p>perceived enhancement</p></li>-<li><p>non-enhancing high-attenuation (due to proteinaceous or haemorrhagic contents) renal lesions <3 cm</p></li>-<li><p>generally well marginated</p></li>-<li><p>work-up: none</p></li>-<li><p>percentage malignant: ~0-6% <sup>17,18</sup></p></li>-</ul>-</li></ul><h6>Bosniak IIF</h6><ul><li>-<p>minimally complex</p>-<ul>-<li><p>multiple hairline thin septa or minimally smooth thickened walls or septa</p></li>-<li><p>perceived but no measurable enhancement of wall or septa</p></li>-<li><p>calcification can be present and may be thick and nodular</p></li>-<li><p>generally well marginated</p></li>-<li><p>high-attenuation lesion >3 cm diameter, totally intrarenal (<25% of wall visible); no enhancement</p></li>-<li><p>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 <sup>3</sup></p></li>-<li><p>percentage malignant: ~5-26% <sup>6,19-21</sup></p></li>-</ul>-</li></ul><h6>Bosniak III</h6><ul><li>-<p> indeterminate cystic mass</p>-<ul>-<li><p>thickened irregular or smooth walls or septa with measurable enhancement</p></li>-<li><p>treatment/work-up: partial nephrectomy or <a href="/articles/radiofrequency-ablation">radiofrequency ablation</a> in poor surgical candidates <sup>23,24</sup></p></li>-<li><p>percentage malignant: ~55-72% <sup>6,17,19,22</sup></p></li>-</ul>-</li></ul><h6>Bosniak IV</h6><ul><li>-<p>clearly malignant cystic mass</p>-<ul>-<li><p>Bosniak III criteria + enhancing soft tissue components adjacent to but independent of wall or septum</p></li>-<li><p>treatment: partial or total nephrectomy</p></li>-<li><p>percentage malignant: ~91-100% <sup>19,22</sup></p></li>-</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 helps predict a risk of malignancy and suggests either follow up or treatment.</p><h4>Usage</h4><p>The Bosniak classification is widely used by radiologists and urologists for 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 (2022) 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 inadequate 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><p>The "official" Bosniak classification uses <a href="/articles/numbers-units-and-operators">Roman numerals</a>, not Arabic ones, for each <strong>category</strong>. The use of the term "grade", "stage", "group", "type", or similar for each category is technically incorrect. Version 2019 has switched from "category" to "class" <sup>11</sup>.</p><h6>Bosniak I</h6><ul><li>
- +<p>benign simple cyst</p>
- +<ul>
- +<li><p>hairline-thin wall of ≤2 mm</p></li>
- +<li><p>water density</p></li>
- +<li><p>no septa, calcifications, or solid components</p></li>
- +<li><p>no enhancement</p></li>
- +<li><p>work-up: none</p></li>
- +<li><p>percentage malignant: ~0% <sup>17</sup></p></li>
- +</ul>
- +</li></ul><h6>Bosniak II</h6><ul><li>
- +<p>benign cyst - "minimally complex"</p>
- +<ul>
- +<li><p>few hairlines thin <1 mm septa or thin calcifications (thickness not measurable)</p></li>
- +<li><p>perceived enhancement</p></li>
- +<li><p>non-enhancing high-attenuation (due to proteinaceous or haemorrhagic contents) renal lesions <3 cm</p></li>
- +<li><p>generally well marginated</p></li>
- +<li><p>work-up: none</p></li>
- +<li><p>percentage malignant: ~0-6% <sup>17,18</sup></p></li>
- +</ul>
- +</li></ul><h6>Bosniak IIF</h6><ul><li>
- +<p>minimally complex</p>
- +<ul>
- +<li><p>multiple hairline thin septa or minimally smooth thickened walls or septa</p></li>
- +<li><p>perceived but no measurable enhancement of wall or septa</p></li>
- +<li><p>calcification can be present and may be thick and nodular</p></li>
- +<li><p>generally well marginated</p></li>
- +<li><p>high-attenuation lesion >3 cm diameter, totally intrarenal (<25% of wall visible); no enhancement</p></li>
- +<li><p>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 <sup>3</sup></p></li>
- +<li><p>percentage malignant: ~5-26% <sup>6,19-21</sup></p></li>
- +</ul>
- +</li></ul><h6>Bosniak III</h6><ul><li>
- +<p> indeterminate cystic mass</p>
- +<ul>
- +<li><p>thickened irregular or smooth walls or septa with measurable enhancement</p></li>
- +<li><p>treatment/work-up: partial nephrectomy or <a href="/articles/radiofrequency-ablation">radiofrequency ablation</a> in poor surgical candidates <sup>23,24</sup></p></li>
- +<li><p>percentage malignant: ~55-72% <sup>6,17,19,22</sup></p></li>
- +</ul>
- +</li></ul><h6>Bosniak IV</h6><ul><li>
- +<p>clearly malignant cystic mass</p>
- +<ul>
- +<li><p>Bosniak III criteria + enhancing soft tissue components adjacent to but independent of wall or septum</p></li>
- +<li><p>treatment: partial or total nephrectomy</p></li>
- +<li><p>percentage malignant: ~91-100% <sup>19,22</sup></p></li>
- +</ul>
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