What is the Bosniak classification system for cystic renal lesions?
The Bosniak classification system utilizes specific CT or MR imaging features to help classify cystic renal lesions into those that are likely benign (and do not require surgical resection) from those that are likely malignant (and thus require surgical resection).
Bosniak Classification System for Cystic Renal Lesions
| CATEGORY | IMAGING FEATURES | MANAGEMENT |
|---|---|---|
| I: simple cyst | Fluid attenuation (CT) Fluid signal intensity (MRI) Thin smooth wall No enhancement | 100% benign No further follow-up |
| II: minimally complex cyst | Fine calcifications or a short segment of slightly thickened calcification (CT) Few thin internal septations without enhancement Homogeneously hyperattenuating (>20 HU) and nonenhancing but ≤ 3 cm and not fully intrarenal (CT) Increased T1-weighted signal intensity or slightly decreased T2-weighted signal intensity relative to simple fluid but nonenhancing (MRI) | 100% benign No further follow-up |
| IIF: probable minimally complex cyst | Small nodular calcifications (CT) Multiple thin internal septations without enhancement Minimal smooth thickening of wall or internal septations Homogeneously hyperattenuating (>20 HU) and nonenhancing but either ≤ 3 cm and fully intrarenal or >3 cm (CT) | 95% benign Follow-up imaging |
| III: probable cystic renal neoplasm | Thick or irregular walls or internal septations with enhancement | >50% malignant Surgical resection |
| IV: cystic renal neoplasm | Solid nodular components with enhancement | >95% malignant Surgical resection |
