Cystic renal lesions are common, increasing in prevalence with the patient’s age. 

The Bosniak classification system for CT evaluation of renal cysts is helpful in determining both malignant risk and required followup / treatment.

Hypoattenuating cysts characterized as homogeneous thin-walled, non-enhancing fluid-attenuation lesions are classified on Bosniak category I (simple renal cysts), and are rarely problematic when encountered incidentally at contrast-enhanced CT.