Simple renal cysts¹ is also called stage I renal cysts. They are small cysts with liquid or semisolid fluid and round or oval in shape. Most cysts are discovered incidentally during imaging tests for other conditions and have no symptoms or impact on kidney function.
These cysts may be diagnosed using abdominal ultrasound, a CT scan, or an MRI. They seldom require treatment.
However, if they are unusually large, they can cause pain or block the flow of urine, which may require sclerotherapy.² This means inserting a long needle through the skin into the cyst, draining out the fluid, and injecting an alcohol solution that helps keep the cyst from filling up again.
Large cysts may require surgery, typically performed laparoscopically under general anesthesia. These surgeries often require a one- or two-day hospital stay.
Simple renal cysts increase in frequency with age and are more common in men than women. Nearly 1 in 5 people over 50 years old have simple kidney cysts, and this may be a low figure as so many have no symptoms and are discovered only incidentally.
One lead theory for the cause of simple renal cysts is a subclinical kidney injury that may go unnoticed at the time and is only detected when the cyst has grown to a detectable size.
Simple renal cysts are considered large if they start causing problems. They range in size from the size of a pea to as large as a golf ball. The average size, however, is 5 to 10 mm.
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A large renal cyst can cause symptoms, including dull pain in the back, side, or stomach. Pain can also be caused if a cyst bursts. In rare cases, cysts can get infected, causing fever, pain, and tenderness.
Large kidney cysts may also block the normal flow of blood or urine through the kidneys. This can lead to swelling of the kidneys and can also result in blood in the urine and frequent urination.
After treatment with sclerotherapy or surgery, full recovery is expected. Antibiotics may be used if an infection is suspected.
You should not be particularly concerned if you are diagnosed with simple renal cysts and have no symptoms. In most cases, the cysts will continue to have no symptoms. In fact, small, simple renal cysts aren’t even considered a contraindication for kidney donation.
However, doctors will typically do imaging tests to better look at kidney cysts because, in some cases, there may be something else going on. Doctors may consider a diameter greater than 3 cm worthy of a follow-up. Your doctor may also take a blood or urine sample to check kidney function.
Cysts are also potentially of concern if you have chronic kidney disease and/or have been on dialysis. Dialysis can increase the number and size of cysts. This has been recognized as a risk factor for cancer.
You should also be concerned if you have a family history of polycystic kidney disease.
Polycystic kidney disease³ (PKD) is a chronic genetic condition that causes numerous fluid-filled cysts to grow in the kidneys. These may cause damage to the kidneys or replace kidney tissue, leading to reduced kidney function. PKD is the fourth leading cause of kidney failure.
PKD can be distinguished from simple cysts by the size and number of the cysts. It is also possible to develop cysts in the liver, pancreas, spleen, large bowel, and ovaries. It can even affect the brain or heart. PKD symptoms, which typically show up in one’s 30s or 40s, include:
Blood in the urine
Recurring bladder and/or kidney infections
High blood pressure (simple cysts can also be associated with an elevated risk of hypertension)
Increase in the abdomen’s size
Back or side pain
Pounding or fluttering in the chest, affecting about 25% of PKD patients
If you have a family history and reach 40 without showing cysts in your kidneys, you probably do not have PKD. There is no cure for PKD, but it can be managed by controlling blood pressure, drinking more fluids, taking over-the-counter medication, and leading a healthy lifestyle. People with PKD should not consume caffeinated beverages.
Most people with kidney cysts do not have PKD.
Very rarely, a form of recessive PKD may occur in very young children. This is called autosomal recessive PKD and is often fatal in the first few months of life. It is extremely rare, and there is currently no treatment.
PKD can increase the risk of pregnancy complications, specifically pre-eclampsia or toxemia. People with PKD and high blood pressure should be monitored carefully while pregnant. If you have a family history of PKD and wish to start a family, you might consider genetic counseling to know your child’s risk.
Acquired cystic kidney disease⁴ (ACKD) happens in kidneys with long-term damage. In fact, 90% of people on dialysis for eight years or more will develop ACKD. However, it is not caused by dialysis but by the underlying kidney failure that necessitates dialysis.
People with ACKD have cysts only in the kidneys and typically do not have enlarged kidneys.
Unlike PKD, ACKD often has no symptoms, although it can lead to blood in the urine, infection of the cysts, or an increased risk of cancer. However, cancer associated with ACKD generally does not extend beyond the kidneys and has a better outlook than other renal cancers.
ACKD is typically not treated as it causes no further problems, although antibiotics may be given if there is an infection. Sclerotherapy may be used if a cyst is causing pain. After a transplant, the cysts generally vanish in the damaged kidneys, indicating that they may be caused by the strain on weak kidneys as they try to function.
However, if they do not, there is a risk of renal cancer, which may indicate the kidneys’ removal. ACKD is considered a strong risk factor for renal carcinoma.
While most renal cysts are harmless and do not get worse over time, your doctor may recommend ongoing monitoring to ensure they do not start to grow.
Also, people with simple renal cysts are at higher risk of hypertension and should get their blood pressure checked regularly. It is unknown how cysts impact hypertension, but as it seems to happen with both simple cysts and PKD, it appears to be related to the cysts’ presence.
If you have high blood pressure, it is crucial to keep it under control, typically with a low-sodium diet and medication.
These simple cysts will never cause a problem. However, it is still vital to monitor them if they start growing (in which case sclerotherapy may be recommended) or show signs of turning into tumors. The latter is rare unless you have chronic kidney disease.
You should immediately see a doctor if you find blood in your urine. A urinary tract or kidney infection most often causes this. If you are over 40, it could indicate a large cyst interfering with the flow of blood or urine in your kidneys.
Dull pain in the back or side indicates that you should see a doctor. If you also have a fever, this suggests a kidney infection and should be taken seriously. You will probably need antibiotics.
If you are known to have kidney cysts, your doctor may recommend imaging tests at intervals or regular tests to monitor kidney function. If you have a family history of PKD and have these symptoms, you should talk to a doctor immediately.
Small, simple kidney cysts are common in older populations. A large cyst is not a measure of size but of the issues caused by the cyst, which might include pain, urinary blockage resulting in kidney swelling, or blood in the urine. Cysts can also become infected.
However, most simple kidney cysts have no symptoms or issues, and many may go undetected unless abdominal imaging is done for other purposes.
You should always seek medical care if you see blood in your urine or have pain in your back and side, especially if accompanied by a fever. This can indicate a kidney infection, which needs immediate treatment. People with a family history of PKD need to be particularly careful.
Simple kidney cysts | NIH: National Institute of Diabetes and Digestive and Kidney Diseases
Polycystic kidney disease | National Kidney Foundation
Acquired cystic kidney disease | NIH: National Institute of Diabetes and Digestive and Kidney Diseases
Simple kidney cysts | National Kidney Foundation