Fig. 4

Upstaging of cystic lesion on contrast-enhanced CT and CEUS due to greater special resolution. Contrast enhanced CT (4a) showing a smaller hyperdense cyst (long arrow) classified by readers as Bosniak II by one reader and IIF by the other in a 75 year old man. Adjacent to this is a large simple cyst (Bosniak I) (short arrow). On CEUS (4b), the smaller cyst (long arrow) shows enhancing internal septa and a solid component invisible on the CT that resulted in a Bosniak III classification. The larger cyst (short arrow) demonstrates internal features such as septations and wall irregularity that were also not visible on the CT. This illustrates the greater spatial resolution of CEUS compared to CT, and may explain why applying the Bosniak criteria to CEUS leads to upstaging