Renal cysts

Bosniak classification:

Grade	Description	Rate of malignancy	Follow-up
I	Simple benign cysts with hairline-thin walls. No septations, calcifications or solid components. No enhancing soft tissue components.	~0%	None None at all
II	Benign cystic lesions. The cysts may have hairline-thin septations with fine calcifications in the walls. Minimal enhancement of the hairline-thin smooth wall may be seen. No enhancing soft tissue components are present. Non-enhancing high-attenuation cysts <3cm in size are included.	~0%	None Really, none
IIF	Complex cysts requiring follow-up imaging. These cysts are more complex and do not fit into category II or III. These cysts have an increased number of hairline septations or mild thickening of the wall and/or septations. No enhancing soft tissue components are present.	~5%	1-2 years
III	Indeterminate masses. The cystic lesions have thickened walls and septations that are irregular. The cyst walls or septations demonstrate enhancement.	~50%	Biopsy
IV	Malignant cystic masses. Thick and irregular walls and septations may be present but enhancing soft tissue components are seen, independent of wall of septal enhancement.	~100%	Consider excision