Bosniak classification system of renal cystic masses (version 2005)
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The Bosniak classification system for CT evaluation of renal cysts is helpful in determining both malignant risk and required follow-up and/or treatment.
Bosniak 1:
- simple cyst, imperceptible wall, rounded
- work up: nil
- % malignant: ~0%
Bosniak 2:
- minimally complex, a few thin (<
; 1mm;1 mm) septa, thin Ca++; 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
- % malignant: ~0%
Bosniak 2F:
- minimally complex but requiring follow up
- increased number of septa, minimally thickened or enhancing septa or wall
- thick Ca++
- hyperdense cyst, i.e.:
- >3 cm diameter, mostly intrarenal (less than 25% of wall visible); no enhancement
- work up: needs ultrasound/CT follow up - no strict rules on time frame but could do at around 6 months.
- % malignant: ~25%6
Bosniak 3:
- indeterminate, thick or multiple septations, mural nodule, hyperdense on CT (see 2F)
- treatment/work up: partial nephrectomy or RF ablation in elderly or poor surgical candidates
- % malignant: ~54%6
Bosniak 4:
- clearly malignant, solid mass with large cystic or necrotic component
- treatment: partial or total nephrectomy
- % malignant: ~100%
-<li>minimally complex, a few thin (< 1mm) septa, thin Ca++; 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>minimally complex, a few thin (<1 mm) septa, thin Ca++; 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>