Simple Renal Cyst: Symptoms, Causes & Treatment

A simple renal cyst is a round sac filled with clear fluid that forms on the surface of or inside the kidney. It is one of the most common kidney findings and becomes more frequent with age, present in a large proportion of older adults. It is entirely different from inherited polycystic kidney disease, which fills both kidneys with many cysts.

In the vast majority of cases a simple cyst is benign and causes no symptoms, discovered incidentally during abdominal imaging done for another reason. Most need no treatment, only reassurance and simple follow-up. Rarely, a cyst grows large enough to press on nearby tissue or cause pain, infection, or bleeding, and only then is intervention considered. Doctors use the Bosniak classification to distinguish benign simple cysts from complex cysts that need closer monitoring.

• Usually no symptoms and found incidentally.
• Flank or back pain if the cyst grows.
• Fever and pain if the cyst becomes infected.
• Blood in the urine, rarely.

• The exact cause is unclear; it is thought to relate to blockage of small kidney tubules.
• Occurrence increases naturally with age.

• Abdominal ultrasound.
• CT or MRI when needed to assess a complex cyst.
• The Bosniak classification to grade the cyst's risk.

Monitoring

• Most simple cysts need no treatment, only reassurance and periodic follow-up.

Intervention when needed

• Fluid drainage with a sclerosing agent, or laparoscopic removal for large symptomatic cysts.
• Antibiotics if infected.

This content is educational and does not replace consulting a urologist or nephrologist.

• Cyst infection.
• Bleeding inside the cyst.
• Pressure on the kidney or partial obstruction, rarely.

• There is no specific prevention since it is age-related.
• Regular follow-up and blood-pressure control support overall kidney health.