Should You Worry About a Cyst on Your Kidney?
Kidney cysts are fluid-filled sacs that can form on one or both kidneys. Most of the time, they are harmless and don’t cause symptoms. But in some cases, they may indicate underlying health problems. In this article, we’ll cover everything you need to know about a cyst on kidney, including causes, symptoms, diagnosis, treatment, and when you should seek help.
What is a kidney cyst?
A kidney cyst is a fluid-filled sac that forms in or on your kidney. It can be round or oval, usually filled with clear or yellowish fluid.
There are two types:
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Simple kidney cysts – Common, usually harmless, and often don’t cause symptoms.
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Complex kidney cysts – May have irregular walls or contain blood or solid material. These need closer monitoring.
You might have one cyst or several, and they can occur on one kidney or both.
How common are kidney cysts?
Very. By age 50, about half of all adults have at least one kidney cyst. Most are simple cysts and go unnoticed.
Are kidney cysts dangerous?
Most are not. Simple kidney cysts rarely cause problems and usually don’t turn into cancer. They often don’t affect kidney function, either.
Complex cysts, on the other hand, might carry a small risk of becoming cancerous. That’s why they’re watched more closely.
People with polycystic kidney disease (PKD), a genetic condition, can develop many cysts that damage kidney tissue over time. PKD is different from having a single or simple cyst.
What causes a cyst to form on the kidney?
The cause of simple kidney cysts isn’t clear. Some researchers believe cysts form when:
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Tubes in the kidneys become blocked
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Tissue weakens with age
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Fluid builds up in pockets that balloon out
You may be more likely to develop a kidney cyst if you are over 50, are male, have high blood pressure, or have a family history of kidney problems.
How Are Simple and Complex Kidney Cysts Different?
A simple cyst typically has a thin, smooth wall, contains clear fluid, has a very low risk of cancer, and rarely requires follow-up. In contrast, a complex cyst may have a thick or irregular wall, contain debris or blood, carry a slightly higher risk of cancer, and usually requires follow-up.
Your doctor may use the Bosniak classification system (explained below) to rate the complexity of a cyst.
What are the symptoms of a kidney cyst?
You may not feel anything at all. Most kidney cysts are asymptomatic.
But if a cyst grows or causes pressure, you might notice:
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A dull ache in your side or back
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Pain in your upper abdomen (can mimic kidney stone pain)
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Blood in your urine
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Frequent urination
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High blood pressure
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Fever or chills (if the cyst is infected)
If a cyst bursts or gets infected, symptoms can become more severe.
How are kidney cysts diagnosed?
Most are found by accident, during scans for other reasons. Your provider may use one or more of these tools:
1. Ultrasound
This uses sound waves to create images. It’s painless and often the first step.
2. CT scan
This provides a more detailed view than ultrasound. CT scans help distinguish between simple and complex cysts.
3. MRI
An MRI gives detailed images of soft tissues and may be used for further evaluation.
4. Blood and urine tests
These check kidney function and look for signs of infection or blood.
To check function and infection, urine may show proteinuria or protein/creatinine ratio changes
What is the Bosniak classification?
This system helps doctors decide whether a cyst is benign or potentially cancerous, based on how it looks on a CT or MRI:
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Bosniak I: Simple cyst, no risk
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Bosniak II: Mildly complex, still benign
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Bosniak IIF: Follow-up needed to confirm stability
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Bosniak III: Suspicious; surgery may be considered
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Bosniak IV: High risk of cancer; usually removed
Your doctor will explain what your score means and if monitoring or treatment is needed.
When do kidney cysts need treatment?
You may not need any treatment if the cyst is small and simple, you're not experiencing any symptoms, and your kidney function is normal. However, treatment may be necessary if the cyst is large and painful, starts bleeding or becomes infected, blocks the flow of urine, or appears suspicious on imaging tests.
What treatments are available for kidney cysts?
1. Watchful waiting
If the cyst is simple and not causing symptoms, your doctor may just monitor it over time.
2. Aspiration and sclerotherapy
A needle is inserted to drain the cyst. Then, a special solution is added to shrink it and reduce recurrence. It’s usually guided by ultrasound or CT.
3. Surgery
If the cyst is large or complex, laparoscopic surgery may be done. The cyst is drained or removed through small incisions. It’s a minimally invasive procedure with a quick recovery.
What is polycystic kidney disease (PKD)?
Polycystic kidney disease is an inherited condition where many cysts grow in both kidneys. Unlike simple cysts, these can enlarge the kidneys and eventually lead to kidney failure.
There are two main types:
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Autosomal dominant PKD (ADPKD) – The most common type. Symptoms usually begin between ages 30–50.
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Autosomal recessive PKD (ARPKD) – Rarer and often diagnosed in infancy or childhood.
Symptoms of polycystic kidney disease (PKD) may include high blood pressure, back or side pain, an enlarged abdomen, blood in the urine, kidney stones, frequent urinary tract infections, and progressive kidney failure. While there’s no cure, treatments can help slow the disease and manage these symptoms.
Can kidney cysts cause complications?
Yes, though complications are uncommon. Possible risks include:
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Infection, causing fever and pain
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Rupture, leading to sharp pain or bleeding
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Bleeding into the cyst
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Obstruction of urine flow
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Rarely, cancer in complex cysts
How can you support kidney health?
You can’t always prevent a cyst from forming, but you can protect your kidneys with these habits:
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Stay hydrated – Aim for 6–8 glasses of water a day.
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Control blood pressure – High blood pressure can damage kidneys over time.
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Limit alcohol and avoid smoking – These strain kidney function.
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Eat a kidney-friendly diet – Low in salt, processed food, and added sugars.
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Avoid overusing NSAIDs – Pain relievers like ibuprofen can harm kidneys in high doses.
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Get regular checkups – Especially if you have a family history of kidney disease.
When should you see a doctor?
Talk to your provider if you experience:
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Pain or pressure in your side
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Blood in your urine
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Trouble urinating
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High blood pressure that’s hard to control
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Fever or signs of infection
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A family history of PKD or kidney disease
Takeaway
Most kidney cysts are nothing to worry about—they’re common, usually harmless, and don’t need treatment. But some cysts, especially complex ones, may need follow-up to rule out problems like cancer or infection. If you have symptoms like pain, blood in your urine, or a family history of kidney issues, it’s important to get checked. With simple tests and regular monitoring, your doctor can guide you on whether treatment is needed. Taking care of your kidneys through healthy habits and checkups can help prevent complications.
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Related Resources
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What Size of Kidney Cyst Is Dangerous?
Understand when a kidney cyst might be cause for concern and what sizes doctors monitor closely. -
The Complete Guide to At-Home Kidney Function Tests
Learn how to track your kidney health at home using test strips and easy tools. -
Kidney Disease and Nail Changes
See how subtle nail changes can reflect kidney issues and when to take them seriously.
References
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Kidney Cysts: Causes, Symptoms, Treatment & Prevention. (2017, March 7). Retrieved July 30, 2025, from Cleveland Clinic website: https://my.clevelandclinic.org/health/diseases/14884-kidney-cysts
Polycystic kidney disease - Symptoms and causes. (2025). Retrieved July 30, 2025, from Mayo Clinic website: https://www.mayoclinic.org/diseases-conditions/polycystic-kidney-disease/symptoms-causes/syc-20352820
Silverman, S. G., Pedrosa, I., Ellis, J. H., Hindman, N. M., Schieda, N., Smith, A. D., … Davenport, M. S. (2019). Bosniak Classification of Cystic Renal Masses, Version 2019: An Update Proposal and Needs Assessment. Radiology, 292(2), 475–488. https://doi.org/10.1148/radiol.2019182646
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