Retrospective comparison of complex cystic renal lesions which are found with computed tomography (CT) and were controlled with contrast enhanced ultrasound (CEUS).

All subjects receive an contrast enhanced CT due to different clinical indications. When a complex cystic renal lesion is found an evaluation with CEUS is performed. The CEUS protocol included a native baseline examination of both kidneys. After a bolus injection of 1.5 ml SonoVue (Bracco, Milano, Italy) an examination of the affected kidneys is performed over a time period of at least three minutes. An optional dose will be given when the initial examination is not conclusive, e. g. when the arterial phase is partly missed. When both examinations are done the lesions were classified using the Bosniak classification system and a comparison of both methods will be done.

Inclusion Criteria:

• Finding of a complex cystic renal lesion

Exclusion Criteria:

• age < 18 y, gravity

All patients undergoing a CT procedure.