Imaging and Management of Incidental Renal Lesions

Table 1

Cystic renal lesions.

Type	Definition	US	CT	MRI	Percentage of malignancy	Management
Benign	Bosniak class I; simple cyst not containing septa or calcification; no enhancement	(i) Anechoic; (ii) Thin, smooth walls; (iii) Posterior acoustic enhancement	(i) Near water density (<10 HU); (ii) Homogeneous density; (iii) No enhancement	(i) Sharp, well-defined walls; (ii) Signal characteristics of water; (iii) No enhancement	~0%	No intervention
	Bosniak class II; cystic lesion containing thin septa or fine calcifications; no enhancement	(i) Hypoechoic; (ii) Iso- or hyperechoic < 3 cm	(i) Hypodense; (ii) Hyperdense < 3 cm	(i) T1 hypointense; T2 hyperintense; (ii) T1 hyperintense; T2 hypointense; (<3 cm)
Minimally complex	Bosniak class IIF; (i) Multiple septa; (ii) Perceived (not measurable) enhancement; (iii) Calcifications	(i) Hypoechoic; (ii) Iso- or hyperechoic > 3 cm	(i) Hypodense; (ii) Hyperdense > 3 cm	(i) T1 hypointense; T2 hyperintense; (ii) T1 hyperintense; T2 hypointense; (>3 cm)	5%	Follow-up
Indeterminate and malignant	Bosniak class III; (i) Thickened irregular wall or septa; (ii) Thick calcifications; (iii) Measurable enhancement				55%	Histologic diagnosis and eventual surgical removal
	Bosniak class IV; (i) Bosniak class III parameters and solid nodular components				100%	Surgical removal