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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