Table 1.

Imaging findings and Bosniak classification (adapted from references 1, 5, 6 and 9).

Type	Imaging features without contrast	Contrast enhancement features
I	Water density (0–20 HU), thin margins, sharp delineation with the renal parenchyma, thin and smooth walls, homogeneous	No contrast enhancement
II	Presence of one or few thin septations, small and fine calcifications; hyperdense cysts measuring up to 3.0 cm (60–70 HU)	No contrast enhancement, or no measurable or perceptible enhancement of septa
IIF	More complex lesions which cannot be included in category II or III. Multiple septa. Walls or septa with nodular or irregular calcifications	Absent, dubious or hair-like enhancement
	Hyperdense cysts > 3.0 cm or with only 25% of their walls visible (exophytic)
III	Thick-walled cystic lesion, septum irregularity and heterogeneous septum and wall and/or contents. Gross and irregular calcifications with measurable enhancement	Wall or septum enhancement
IV	Lesions with all the findings of category III, and solid component, soft parts, independent of finding of wall or septa	Enhancement of wall and/or solid component(s)