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Table 1 The five categories of renal cysts, divided on the basis of imaging appearance

From: CT and MR imaging of cystic renal lesions

Bosniak category Wall Septa Calcifications Enhancing nodularity
I Thin
Non-enhancing
- - -
II Thin
Non-enhancing
Few
Thin
Fine or slightly thickened -
II-Fa Minimal thickening
Perceived enhancement
Several
Minimal thickening
Perceived enhancement
Irregular or nodular -
IIIb Irregularly thick
Measurable enhancement
Several
Irregularly thick
Measurable enhancement
Variable -
IV Irregularly thick
Measurable enhancement
Several
Minimal thickening
Measurable enhancement
Variable Wall and/or septa
  1. aThis category includes complicated (< 3 cm) cysts
  2. bThis category includes complicated (> 3 cm) cysts