Kidney cyst simple
Informed by recognized medical guidance
Overview
A kidney cyst is a fluid-filled sac that forms on or inside one or both kidneys. A 'simple' kidney cyst is the most common type and is usually harmless. It has a thin wall and contains clear fluid, much like a water balloon. Most simple cysts don't cause problems and are often found by chance during scans for other reasons.
Key facts
- Simple kidney cysts are very common, especially after age 50.
- They are almost always non-cancerous (benign).
- They rarely cause symptoms and usually don't need treatment.
- If a cyst grows large, it may cause pain or other issues.
Yes, simple kidney cysts are common. Around 1 in 5 people have one by age 50, and up to 1 in 3 people over 70 have at least one.
Simple kidney cysts become more common with age. They can affect anyone, but are most often seen in older adults. Men and women get them about equally.
Symptoms
- Sudden, severe pain in the side or back that comes on quickly.
- Blood in the urine – seen as pink, red, or brown urine.
- Fever, chills, or shaking (could be a sign of infection in the cyst).
- ⚠Pain that gets worse over a few days and does not go away with rest.
- ⚠A bulge or lump in the abdomen that feels hard or grows quickly.
Common symptoms
- Most simple kidney cysts cause no symptoms at all.
- If a cyst grows large (usually over 5 centimetres), it may cause a dull ache or pain in the side, back, or upper abdomen.
- Some people feel a sense of fullness or pressure in the tummy area.
Symptoms in children
- Simple kidney cysts are rare in children. When they occur, they are usually found by chance and are not harmful.
- Most children with simple cysts have no symptoms.
Symptoms in older adults
- Older adults are more likely to have larger or multiple cysts. Symptoms are still uncommon.
- If symptoms occur, they may include back or side pain, or a lump felt in the abdomen.
Causes
Main causes
- The exact cause of simple kidney cysts is not fully understood.
- They are thought to develop from tiny outpouchings (diverticula) in the kidney tubules that fill with fluid and then seal off.
Risk factors
- Age – the risk increases significantly after age 40.
- Being male – men are slightly more likely to develop them.
- Having high blood pressure or chronic kidney disease may increase the chance.
- Family history – very rarely, multiple cysts can run in families, but simple cysts are usually not inherited.
When to see a doctor
See a doctor urgently if:
- Sudden, severe pain in the side or back.
- Blood in your urine.
- Fever with back pain (possible infection).
Book a routine appointment if:
- If you have a dull ache or pain in your side that lasts more than a few weeks.
- If you feel a lump or fullness in your tummy.
- If you have a scan that shows a cyst – your doctor may want to monitor it.
Diagnosis
Simple kidney cysts are usually found by chance when an imaging scan is done for another reason. The most common scans used are ultrasound, CT, or MRI. A simple cyst has a very typical appearance on these scans – round, thin-walled, and filled with clear fluid.
Tests that may be done
- Ultrasound scan – uses sound waves to create pictures of the kidneys.
- CT scan (computed tomography) – gives detailed cross-section images.
- MRI scan (magnetic resonance imaging) – uses magnets and radio waves to make detailed images.
What to expect at your appointment
If a cyst is found, your doctor will review the scan images. For a simple cyst, no further tests are usually needed. If the cyst looks unusual, you may be asked to have another scan in a few months. In rare cases, a doctor may recommend a urine test or blood test to check kidney function, but this is not routine for simple cysts.
Treatment
Simple kidney cysts rarely need treatment. If a cyst is large and causing pain or other problems, there are options to reduce its size. Treatment is only considered when symptoms are bothersome.
Self-care at home
- If you have mild discomfort, over-the-counter pain relievers like paracetamol or ibuprofen may help. Always follow the dose instructions on the packet and check with a pharmacist if you have other health conditions.
- Apply a warm compress to the area to ease mild pain.
Medical treatments
If pain is significant, a doctor may suggest draining the cyst with a fine needle (aspiration). This is done using ultrasound guidance. After draining, a special solution (a sclerosing agent) may be injected to help prevent the cyst from refilling. This is a minor procedure usually done as an outpatient.
When is surgery considered?
Surgery is rarely needed. If a cyst is very large or does not respond to drainage, a procedure called laparoscopic deroofing may be considered. This is keyhole surgery to remove part of the cyst wall so the fluid drains away. This is only done in selected cases and after discussion with a specialist.
Living with this condition
Most people with simple kidney cysts live normally without any problems. You do not need to change your daily routine. If you have a large cyst, you may want to avoid heavy lifting or contact sports that could cause trauma to the area.
Lifestyle tips
- Stay well hydrated by drinking plenty of water.
- Maintain a healthy weight to reduce pressure on your kidneys.
- If you have high blood pressure, work with your doctor to keep it under control.
Diet and exercise
No special diet is needed for simple kidney cysts. A balanced diet with plenty of fruits, vegetables, and whole grains is good for overall kidney health. Regular moderate exercise, like walking or swimming, is safe and healthy.
Mental health and emotional wellbeing
Finding out you have a kidney cyst can cause worry, even though it is usually harmless. If you feel anxious, talk to your doctor or a counsellor. Most cysts do not affect kidney function or cause long-term harm.
Prevention
There is no known way to prevent simple kidney cysts. They develop naturally with age and are not caused by lifestyle factors.
Complications
If left untreated
- Simple kidney cysts rarely lead to complications. If a cyst becomes infected, it can cause fever and pain, but this is uncommon.
- Very large cysts can press on nearby organs, causing discomfort or rarely interfering with kidney function.
- Rupture: The cyst may burst, causing sudden sharp pain, but this usually heals on its own.
Long-term outlook
The outlook for simple kidney cysts is excellent. They are almost always benign and do not turn into cancer. Most people never experience any symptoms. If treatment is needed, it is simple and effective. You can usually live a full, healthy life without any restrictions.
Find support
Local organisations
- Kidney Care UK ↗ · UK
Helplines
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: July 16, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.