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Bosniak classification system of renal cystic masses (version 2005)

Changed by Amir Rezaee, 12 Aug 2015
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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, 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 but requiring follow-up
    • increased number of septa, minimally thickened or enhancing septawith nodular or wall
    • thick calcifications
    • but no measurable contrast  enhancement enhancing 
    • hyperdense cyst, i.e.
      • >3 cm diameter, mostly intrarenal (less than 25% of wall visible); no enhancement
    • workrequiring 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
    • indeterminate thick, thicknodular multiple septa or multiple septations, septal nodularitywall ,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%
  • -<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, imperceptible wall, rounded</li>
  • +<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>
  • +<li>imperceptible wall, rounded</li>
  • -</ul><h6>Bosniak 2</h6><ul>
  • -<li>minimally complex, a few thin (&lt;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</li>
  • +</ul>
  • +</li></ul><h6>Bosniak 2</h6><ul><li>minimally complex<ul>
  • +<li>a few thin &lt;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>
  • -</ul><h6>Bosniak 2F</h6><ul>
  • -<li>minimally complex but requiring follow-up</li>
  • -<li>increased number of septa, minimally thickened or enhancing septa or wall</li>
  • -<li>thick calcifications</li>
  • -<li>hyperdense cyst, i.e.<ul><li>&gt;3 cm diameter, mostly intrarenal (less than 25% of wall visible); no enhancement</li></ul>
  • -</li>
  • -<li>work-up: needs ultrasound/CT follow up - no strict rules on the time frame but could do at around 6 months.</li>
  • +</ul>
  • +</li></ul><h6>Bosniak 2F</h6><ul><li>minimally complex<ul>
  • +<li>increased number of septa, minimally thickened with nodular or thick calcifications</li>
  • +<li>but no measurable contrast  enhancement enhancing </li>
  • +<li>hyperdense cyst &gt;3 cm diameter, mostly intrarenal (less than 25% of wall visible); no enhancement</li>
  • +<li>requiring follow-up: needs ultrasound/CT follow up - no strict rules on the time frame but could do at around 6 months.</li>
  • -</ul><h6>Bosniak 3</h6><ul>
  • -<li>indeterminate, thick or multiple septations, septal nodularity, hyperdense on CT (see 2F)</li>
  • +</ul>
  • +</li></ul><h6>Bosniak 3</h6><ul><li>indeterminate<ul>
  • +<li> thick, nodular multiple septa or wall ,with measurable enhancement, hyperdense on CT (see 2F)</li>
  • -</ul><h6>Bosniak 4</h6><ul>
  • -<li>clearly malignant, solid mass with a large cystic or a necrotic component</li>
  • +</ul>
  • +</li></ul><h6>Bosniak 4</h6><ul><li>clearly malignant<ul>
  • +<li>solid mass with a large cystic or a necrotic component</li>
  • -</ul>
  • +</ul>
  • +</li></ul>

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