A kidney cyst is a round, fluid-filled pouch that forms on or inside the kidneys. The most common type is called a “simple kidney cyst.” These simple cysts are generally harmless, non-cancerous, and do not interfere with the kidney’s ability to filter waste from the blood. The exact reason why they form is not entirely understood, but they become increasingly common as people get older. It is important to distinguish simple kidney cysts from complex cysts or from polycystic kidney disease, which is a genetic condition that causes many cysts to grow and can impair kidney function.
Most people with simple kidney cysts have no symptoms at all. In fact, these cysts are almost always discovered incidentally when a person is having an imaging test—like an ultrasound or a CT scan—for a completely different medical reason. Because they are typically small and asymptomatic, they usually do not require any treatment or medical intervention. Occasionally, if a simple cyst grows very large, it might cause a dull ache in the back or side, or upper stomach pain, but this is uncommon.
An MRI is a highly sensitive and non-invasive imaging test that is incredibly useful for evaluating kidney cysts. It provides exceptional detail of the kidney’s structure and the fluid inside the cyst. Doctors use MRI to confidently classify the cyst, easily distinguishing a harmless simple cyst (which has a thin wall and clear fluid ) from a complex cyst (which might have thick walls or solid areas that require closer monitoring). This detailed imaging ensures an accurate diagnosis and reassures patients when a cyst is simple and benign.
References
1.Kidney cysts – Symptoms and causes. Mayo Clinic. Published February 11, 2026. Accessed March 4, 2026. https://www.mayoclinic.org/diseases-conditions/kidney-cysts/symptoms-causes/syc-20374134
2.Simple Kidney Cysts. National Institute of Diabetes and Digestive and Kidney Diseases. Accessed March 4, 2026. https://www.niddk.nih.gov/health-information/kidney-disease/simple-kidney-cysts
3.Kidney Cysts (Renal Cysts ) – Diagnosis, Evaluation and Treatment. RadiologyInfo.org. Published March 11, 2024. Accessed March 4, 2026. https://www.radiologyinfo.org/en/info/renal-cyst
