Kidney cysts are fluid-filled sacs that can form on the kidneys. Most kidney cysts are not dangerous and may not cause symptoms. However, in rare cases, kidney cysts may be cancerous.

Kidney cysts are common, and it is rare for them to become cancerous. People do not typically need treatment for them.

If a kidney cyst contains any solid material or abnormal growth, doctors may monitor it for signs of cancer. If a cyst appears cancerous or causes unwanted symptoms, doctors may suggest surgery to remove it.

This article looks at what kidney cysts are, how doctors classify different cysts, diagnosis, and treatment options.

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Kidney cysts are sacs filled with fluid that form in the kidneys. In most cases, kidney cysts are harmless, do not cause any symptoms, and do not require treatment.

People may only become aware of a kidney cyst if they have an imaging test that shows the kidneys.

It is common for cysts to form on the kidneys. Doctors will diagnose around 40% of people who have imaging tests of the kidneys with kidney cysts.

Doctors sometimes call straightforward cysts “simple kidney cysts” or “simple renal cysts.” Simple kidney cysts are typically round or oval and can range from pea-size to golf ball-size.

People who have a genetic condition called polycystic kidney disease (PKD) may have multiple cysts that can impair their kidney function.

Learn more about kidney cysts here.

It is possible for kidney cysts to be cancerous. However, it is rare for simple kidney cysts to be cancerous.

If a kidney cyst is complex, it may appear to have a thicker outer wall or contain solid material rather than fluid. If a person has a complex kidney cyst, a doctor may order extra imaging tests, such as a pelvic ultrasound, to help them tell if a cyst is cancerous.

Doctors use a system called a Bosniak scale to classify kidney cysts, outlined below.

Bosniak class 1 cyst

  • thin, fluid-filled cyst
  • no solid material or calcification (buildup of calcium)
  • no inner dividing wall, called a septa
  • benign, simple kidney cyst

Bosniak class 2 cyst

  • thin septa
  • some calcification
  • cyst measures 3 centimeters (cm) or less
  • benign cyst

Bosniak class 2F cyst

  • thicker wall or multiple septa
  • thicker calcification
  • cyst measures more than 3 cm
  • low risk of being cancerous

Bosniak class 3 cyst

  • thickened or irregular walls or septa
  • cyst has enhancement, which means it has blood flow within it
  • higher possibility of being cancerous

Bosniak class 4 cyst

  • cyst contains abnormal tissue growth
  • cyst has enhancement
  • higher possibility of being cancerous

Experts do not know the cause of kidney cysts.

Kidney cysts are more common in older adults, and roughly one-third of people above the age of 70 years may have at least one kidney cyst.

If a person has multiple clusters of kidney cysts, it may be due to the genetic condition PKD.

If a kidney cyst causes no symptoms, doctors may discover it during imaging tests for another health issue. If a person has symptoms, or to confirm a diagnosis, doctors may order the following imaging tests:

If a doctor suspects any kidney problems, they may also take blood and urine tests to check kidney function.

A 2020 study cites the following treatment protocol for kidney cysts:

  • Bosniak stage 1 and 2 cysts are benign and do not require a follow-up or treatment.
  • Bosniak stage 2F cysts have a low, though possible, risk of being cancerous. Doctors will monitor the cyst with imaging scans, such as CT scans or ultrasounds.
  • Bosniak stage 3 and 4 cysts have a higher possibility of being cancerous. A person may require surgery to remove the cyst.

If surgery is not an option due to other medical conditions or health issues, doctors will continue to monitor the cyst with imaging scans.

If simple kidney cysts are causing symptoms, such as pain or blocking the flow of blood or urine, a person may need treatment. This may include:


Using an ultrasound to guide them, a doctor inserts a needle through the skin into the cyst. This allows the doctor to drain the cyst and inject an alcohol solution that hardens inside the cyst. This means the cyst is less likely to refill with fluid.

Sclerotherapy is typically an outpatient procedure done under local anesthetic.


Laparoscopy is also known as keyhole surgery. A surgeon makes a small incision to access the cysts. They then insert a laparoscope, which is a thin tube with a light and camera at the end of it.

A surgeon will drain the cyst before cutting or burning away the outer layer. A person will receive general anesthetic and may stay in the hospital for 1–2 days.

Learn more about keyhole surgery here.

A person may have kidney cysts that do not cause symptoms or health issues.

If symptoms do occur, a person will need to contact a doctor. Symptoms of kidney cysts include:

  • pain or discomfort, which could be due to a cyst pressing on organs or bones
  • fever or abdominal tenderness, which could be a sign of infection
  • change in urinating patterns
  • blood in the urine, if a kidney cyst bursts
  • high blood pressure

According to research, it is rare for simple kidney cysts to become cancerous. In a 2021 study of 61 people with simple kidney cysts, a follow-up 14 years later found that only two cases had developed into kidney cancer.

If a person has kidney cysts, regular imaging tests can help monitor the cyst, so doctors can identify any changes early on.

If a cyst is cancerous, early treatment with surgical removal of the cyst can significantly improve the outlook.

Kidney cysts are fluid-filled sacs that form on the kidneys. Kidney cysts are common in older adults and typically cause no symptoms or health issues.

A person may discover they have a kidney cyst through an imaging scan for another health condition. Large kidney cysts may cause symptoms such as pain, tenderness, or fever.

If kidney cysts cause symptoms, a person may need medical procedures to drain or remove the cysts.

In rare cases, kidney cysts can be cancerous. If a person has a cancerous kidney cyst, they may need surgery to remove the cyst.