A renal cyst is a fluid-filled mass in the kidney. Renal cysts are very common and at least 50 percent of 50 year-olds have one renal cyst. Fortunately, most renal cysts are benign and do not even require urologic care. This is very different from a renal mass, which most often refers to a solid tumor (benign or cancerous) of the kidney.
The risk of malignancy for a renal cyst is related to its “complexity.” A “simple” cyst is like a water balloon – a thin walled, fluid filled sac. These cysts can get very large but are 100% benign and do not require urologic intervention. A “complex” cyst has either septations (multiple compartments), calcifications or a nodular, solid component. The more complex a cyst, the more likely it is to be malignant.
Most renal cysts are managed by observation, or monitoring with ultrasound. Rarely cysts can cause symptoms (discomfort or pain) or raise suspicion of cancer and require treatment. Your kidney cancer expert at Johns Hopkins can determine the risk of malignancy related to your cyst and discuss management options.