Kidney Cysts: Symptoms, Causes, Diagnosis, and Treatment Options

Oct 10

10 min read

Updated: 7 days ago

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 17, 2026

A kidney cyst is a round, fluid-filled pouch that forms on or in the kidney. The most common type, a simple kidney cyst, is not cancer and usually causes no symptoms or kidney damage. These cysts are found by chance on imaging tests for other conditions and become more common with age, especially in men. If a cyst grows large, it can cause back pain, fever, or stomach pain. Treatment is often not needed, but symptomatic cysts can be drained and sealed or surgically removed [1] [2].

Quick Answer: What is a kidney cyst?

A kidney cyst is a round or oval fluid-filled pouch that forms on or in the kidneys. The most common type, a simple kidney cyst, is not cancer and usually does not harm kidney function. Risk increases with age, and cysts are often found incidentally on imaging. Treatment is needed only for symptoms, by draining or surgical removal. [1] [2]

What the research says

Simple kidney cysts become more common with age and grow slowly. In 743 patients who had an ultrasound for microscopic blood in the urine, cysts were found in 4.3% of those aged 29 or younger, rising to 15.3% at 30 to 39, 21.8% at 40 to 49, 23.3% at 50 to 59 and 32.6% at 60 or older, and men tended to have a higher incidence than women. In 55 patients followed for more than 3 years, the average maximum cyst diameter grew about 4.2% per year, and the authors suggested that most simple cysts can be followed at intervals of more than 10 years once diagnosed (Marumo et al., International Journal of Urology, 2003 [3]).
Imaging categories help predict cancer risk. A systematic review and meta-analysis of 35 studies (2,578 cystic kidney lesions) of the Bosniak CT classification found pooled malignancy rates of 3.2% for Bosniak I, 6% for II, 6.7% for IIF, 55.1% for III and 91% for IV. The authors concluded that the classification is an accurate tool for stratifying risk and that follow-up should be considered for Bosniak II and IIF cysts (Sevcenco et al., European Radiology, 2017 [4]).
Draining a symptomatic cyst and sealing it works for most people. A systematic review of 57 studies (4,071 patients) of needle aspiration with sclerotherapy found 87.7% had treatment success, defined as more than a 50% reduction in cyst size and complete resolution of symptoms. Minor, temporary complications occurred in 11.2% and major complications in fewer than 0.1% (4 patients). The authors called it a safe and effective first-line therapy, though the best sealing agent, volume and dwell time are not yet defined (Brown et al., Abdominal Radiology, 2021 [5]).

What Is a Kidney Cyst?

A kidney cyst is a round or oval fluid-filled pouch with a well-defined outline. Kidney cysts typically grow on the surface of a kidney. Some may develop inside the kidney. Often, kidney cysts are a type called simple kidney cysts. Simple kidney cysts are not cancer and typically cause few problems.

It helps to understand how simple kidney cysts differ from other kinds of kidney cysts. The table below compares the main types.

Cyst type	What it is	Cancer risk	Kidney function
Simple kidney cyst	Single round fluid-filled pouch, often on the kidney surface	Not cancer	Usually no harm to function
Polycystic kidney disease cysts	Multiple cysts linked to a disease	Not cancer	Can impair how well kidneys work
Complex cyst	Cyst with irregular features	Needs watching for changes that could be cancer	Depends on features

Simple kidney cysts are not the same as cysts that form with polycystic kidney disease. Simple cysts also differ from complex cysts. Complex cysts need to be watched for changes that could be cancer.

It is not clear what causes simple kidney cysts. Often, one cyst occurs on the surface of a kidney. But more than one cyst can appear on one or both kidneys. Simple kidney cysts are often found during an imaging test for another condition. Treatment usually is not needed unless simple cysts cause symptoms [1].

Symptoms of Kidney Cysts

Simple kidney cysts typically do not cause symptoms. But if a simple kidney cyst grows large enough, symptoms may include dull pain in the back or side, fever if a cyst becomes infected, and upper stomach pain [1].

Symptom	When it appears
Dull pain in the back or side	When a cyst grows large enough
Fever	If a cyst becomes infected
Upper stomach pain	When a cyst grows large enough
No symptoms at all	Most common: cysts are often found by chance

When to See a Doctor

Make an appointment with a healthcare professional if you have symptoms of a kidney cyst.

What Causes Kidney Cysts?

It is not clear what causes simple kidney cysts. One theory suggests that kidney cysts develop when the surface layer of the kidney weakens and forms a pouch. The pouch then fills with fluid, detaches, and develops into a cyst [1].

Risk Factors

The risk of having simple kidney cysts increases as you get older. But they can occur at any age. Simple kidney cysts are more common in men [1].

Risk factor	Detail
Older age	Risk increases as you get older
Age range	Can occur at any age
Male sex	More common in men

Complications

Kidney cysts may sometimes lead to complications. The table below summarizes the three main complications and what they cause [1].

Complication	What happens
Infected cyst	A kidney cyst may become infected, causing fever and pain
Burst cyst	A burst cyst causes severe pain in the back or side; sometimes blood in the urine
Blocked urine flow	A cyst that blocks the typical flow of urine may lead to kidney swelling

How Kidney Cysts Are Diagnosed

Tests and procedures used to diagnose simple kidney cysts include imaging tests and kidney function tests.

Imaging tests. MRI, CT, and ultrasound are imaging tests that are often used to diagnose simple kidney cysts. Imaging tests can help show whether a kidney mass is a cyst or a tumor.
Kidney function tests. Testing a sample of your blood may reveal whether a kidney cyst is affecting how well your kidney works.

Diagnostic test	What it does
MRI	Imaging test that helps show whether a kidney mass is a cyst or a tumor
CT	Imaging test that helps show whether a kidney mass is a cyst or a tumor
Ultrasound	Imaging test that helps show whether a kidney mass is a cyst or a tumor
Kidney function (blood) test	Reveals whether a cyst is affecting how well your kidney works

Kidney Cyst Treatment Options

Treatment May Not Be Needed

If a simple kidney cyst causes no symptoms and does not affect kidney function, you may not need treatment. Instead, your healthcare professional may recommend that you have imaging tests, such as ultrasounds, over time to see whether your kidney cyst changes. If your kidney cyst changes and causes symptoms, you may choose to have treatment at that time [2].

Treatments for Cysts That Cause Symptoms

If a simple kidney cyst is causing symptoms, your healthcare professional may recommend treatment. The two main options are draining the cyst or surgically removing it.

Piercing and draining the cyst, then filling it with a solution. To shrink the cyst, a long, thin needle is inserted through your skin and through the wall of the kidney cyst. The fluid is drained from the cyst and a solution is injected into the empty space to prevent the cyst from reforming. The solution causes scarring and helps prevent the cyst from filling with fluid again. Alcohol or a chemical compound may be used as the solution.
Surgery to remove the cyst. A large cyst that is causing symptoms may require surgery. To access the cyst, a surgeon makes several small cuts in your skin and inserts special tools and a small video camera. While watching a video monitor in the operating room, the surgeon guides the tools to the kidney and uses them to drain the fluid from the cyst. Then the walls of the cyst are cut or burned away. Surgery is rarely performed for simple cysts. The procedure is more often used for complex cysts with changes that may be cancer.

Treatment option	How it works	When it is used
Watchful waiting with imaging	Ultrasounds over time to watch for changes	No symptoms, kidney function unaffected
Piercing, draining, and filling	Needle drains fluid; alcohol or chemical solution injected to prevent refilling	Cyst causing symptoms
Surgery to remove the cyst	Small cuts, tools and video camera; fluid drained, walls cut or burned away	Large cyst causing symptoms; more often used for complex cysts that may be cancer

Some procedures to treat a kidney cyst may require a brief hospital stay.

Coping and Preparing for Your Appointment

A simple kidney cyst found during an imaging test for another disease or condition may concern you. Talk with your healthcare professional about what having a simple kidney cyst means for your health. Gathering information may put your mind at ease and help you feel more in control of your situation [2].

What You Can Do

Before meeting with your healthcare professional, prepare a list of questions to ask, such as:

How big is the kidney cyst?
Is the kidney cyst new or has it been visible on other scans?
Is the kidney cyst likely to grow?
Can the kidney cyst hurt my kidney?
I have these unexplained symptoms. Could they be caused by a kidney cyst?
Does the kidney cyst need to be removed?
What are my treatment options?
What are the potential risks of each treatment option?
What symptoms may indicate the kidney cyst is growing?
Should I see a specialist?
Are there any restrictions that I need to follow?
Do you have any printed material that I can take with me? What websites do you recommend?
Will I need a follow-up visit?

Don't hesitate to ask other questions as they occur to you during your appointment.

What to Expect From Your Doctor

Your healthcare professional is likely to ask you a number of questions, such as:

Do you have any symptoms?
If so, how long have you experienced symptoms?
Have your symptoms gotten worse over time?
Do you have any blood in your urine?
Have you had pain in your back or sides?
Have you had a fever or chills?
Do you have any other medical conditions?
What medications, vitamins or supplements do you take?

Appointment preparation item	Details to prepare
Cyst history	Size, whether new or seen on earlier scans, likelihood of growth
Symptoms	Blood in urine, back or side pain, fever or chills, symptom duration and changes
Health history	Other medical conditions, medications, vitamins, supplements
Questions list	Treatment options, risks, restrictions, specialist referral, follow-up

Bottom Line

A kidney cyst is a round, fluid-filled pouch on or in the kidney. The most common type, a simple kidney cyst, is not cancer and usually causes no symptoms or kidney damage. These cysts become more common with age and are more frequent in men. Most are discovered by chance during imaging for another condition.

When a cyst grows large enough, it can cause dull back or side pain, upper stomach pain, or fever if infected. The three complications to watch for are an infected cyst, a burst cyst, and blocked urine flow. Diagnosis relies on MRI, CT, or ultrasound imaging plus a blood test of kidney function. The good news is that treatment is often not needed. Simple cysts that cause no symptoms can simply be monitored with periodic ultrasounds. When symptoms develop, effective options include draining the cyst and sealing it with a solution, or surgical removal.

Your next step: if you were told you have a kidney cyst or you have pain in your back or side, schedule an appointment with your healthcare professional. Bring your imaging results, note your symptoms, and use the question list above to make the most of your visit.

Frequently Asked Questions

What is a kidney cyst?

A kidney cyst is a round or oval fluid-filled pouch with a well-defined outline that forms on or in the kidneys. They typically grow on the surface of a kidney, though some develop inside the kidney. The most common type is a simple kidney cyst.

Is a kidney cyst cancer?

No. Simple kidney cysts are not cancer and typically cause few problems. They are different from complex cysts, which need to be watched for changes that could be cancer, and from the cysts that form with polycystic kidney disease.

Do kidney cysts cause symptoms?

Simple kidney cysts typically do not cause symptoms. But if a cyst grows large enough, it may cause dull pain in the back or side, fever if the cyst becomes infected, or upper stomach pain.

What causes simple kidney cysts?

It is not clear what causes simple kidney cysts. One theory suggests they develop when the surface layer of the kidney weakens and forms a pouch that fills with fluid, detaches, and develops into a cyst.

Who is at risk of kidney cysts?

The risk of simple kidney cysts increases with age, though they can occur at any age. They are more common in men.

Can kidney cysts cause complications?

Yes. A cyst may become infected, causing fever and pain. A burst cyst causes severe pain in the back or side and sometimes blood in the urine. A cyst that blocks the typical flow of urine may lead to kidney swelling.

How are kidney cysts diagnosed?

Imaging tests such as MRI, CT, and ultrasound are often used to diagnose simple kidney cysts and show whether a kidney mass is a cyst or a tumor. A blood test of kidney function may reveal whether a cyst is affecting how well your kidney works.

Do kidney cysts need treatment?

Not always. If a simple kidney cyst causes no symptoms and does not affect kidney function, you may not need treatment. Your healthcare professional may instead recommend imaging tests, such as ultrasounds, over time to see whether the cyst changes.

How is a symptomatic kidney cyst treated?

Options include piercing and draining the cyst with a long, thin needle, then filling it with a solution such as alcohol or a chemical compound that causes scarring to prevent refilling. Surgery is an option for large cysts causing symptoms, where the fluid is drained and the cyst walls are cut or burned away.

Is surgery common for kidney cysts?

No. Surgery is rarely performed for simple cysts. It is more often used for complex cysts with changes that may be cancer.

References

Mayo Clinic Staff. Kidney cysts: symptoms and causes. Mayo Clinic. June 4, 2026. https://www.mayoclinic.org/diseases-conditions/kidney-cysts/symptoms-causes/syc-20374134
Mayo Clinic Staff. Kidney cysts: diagnosis and treatment. Mayo Clinic. June 4, 2026. https://www.mayoclinic.org/diseases-conditions/kidney-cysts/diagnosis-treatment/drc-20374138
Marumo K, Horiguchi Y, Nakagawa K, et al. Incidence and growth pattern of simple cysts of the kidney in patients with asymptomatic microscopic hematuria. International Journal of Urology. 2003;10(2):63-67. PMID: 12588599. DOI: 10.1046/j.1442-2042.2003.00577.x
Sevcenco S, Spick C, Helbich TH, et al. Malignancy rates and diagnostic performance of the Bosniak classification for the diagnosis of cystic renal lesions in computed tomography: a systematic review and meta-analysis. European Radiology. 2017;27(6):2239-2247. PMID: 27761710. DOI: 10.1007/s00330-016-4631-9
Brown D, Nalagatla S, Stonier T, et al. Radiologically guided percutaneous aspiration and sclerotherapy of symptomatic simple renal cysts: a systematic review of outcomes. Abdominal Radiology. 2021;46(6):2875-2890. PMID: 33544165. DOI: 10.1007/s00261-021-02953-9

Medical disclaimer

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. The clinical information in this guide reflects source material accessed in October 2026.