Renal cysts are abnormal fluid-filled sacs within the kidney that can occur at any age. Approximately 1 in every 3 adults over the age of 50 has a renal cyst, with a higher prevalence in males. Renal cysts can be characterized by morphology (simple versus complex), malignant potential (Bosniak classification), or etiology of cysts (congenital or acquired).

Simple renal cysts are common renal lesions (70%); the majority are benign, and further imaging is not required.  

The most common form of cystic renal disease is due to autosomal dominant polycystic kidney disease (PKD) and accounts for 8%-10% of all causes of end-stage renal disease. The develoment of renal cysts has also been associated with diuretic use as well as some medications.

The presentation of renal cysts varies based on the cause, and physical examination may reveal a palpable flank or abdominal mass. Radiographic findings of a thick irregular wall, thick septations, or multilocular findings are concerning for malignancy.