Overview
Kidney cysts are fluid-filled sacs that form in or on the kidneys. Simple cysts are the most common type — they are almost always benign and rarely cause problems. Polycystic kidney disease (PKD) is a genetic condition causing multiple cysts to grow progressively and can lead to kidney failure. Most simple cysts need no treatment.
How common is it?
Simple kidney cysts are very common, affecting around 25% of adults over 40 and 50% of adults over 50. Autosomal dominant PKD (ADPKD) affects approximately 1 in 400 to 1,000 people and is one of the most common inherited conditions.
Causes and risk factors
Simple cysts arise from abnormal tubular dilatation during development or ageing. PKD is caused by mutations in the PKD1 or PKD2 genes disrupting normal kidney structure.
Common risk factors
- Simple cysts: ageing, possibly tubule obstruction
- ADPKD: autosomal dominant mutation in PKD1 (chromosome 16) or PKD2 (chromosome 4)
- Autosomal recessive PKD (ARPKD): rarer, more severe, presents in infancy
- Acquired cystic disease in dialysis patients
- Tuberous sclerosis and Von Hippel-Lindau disease (associated complex cysts)
Symptoms
- Most simple cysts: no symptoms (found incidentally on imaging)
- Back or flank pain if cyst is large or infected
- Blood in urine if cyst bleeds
- ADPKD: gradually developing hypertension, loin pain, haematuria, urinary infections, abdominal fullness, declining kidney function over decades
- ADPKD: associated liver cysts, intracranial aneurysms, and heart valve abnormalities
When to see a doctor
Simple cysts require no urgent review if they appear clearly benign on ultrasound. PKD requires regular nephrology follow-up. Seek urgent assessment for severe pain, fever (infection), or blood in urine.
Diagnosis
Ultrasound is the first-line investigation. CT or MRI for complex or uncertain cysts. Bosniak classification guides management of complex renal cysts. Genetic testing for PKD. GFR monitoring in PKD.
Treatments
Watchful waiting
Simple cysts with no suspicious features need no treatment, only monitoring with repeat ultrasound in 1 to 2 years to confirm stability.
Aspiration and sclerotherapy
Drainage of a symptomatic simple cyst with sclerotherapy (alcohol injection) to prevent recurrence. Performed under ultrasound guidance.
Tolvaptan for ADPKD
A vasopressin V2 receptor antagonist that slows kidney cyst growth and preserves GFR in rapidly progressing ADPKD. Licensed in the UK for adults at risk of rapid progression. Liver function monitoring required.
Blood pressure control and renal protection
Tight BP control (target under 130/80) with ACE inhibitors or ARBs slows kidney function decline in ADPKD.
Self-care and lifestyle
- Maintain good hydration (some evidence high fluid intake slows cyst growth in ADPKD)
- Avoid NSAIDs and nephrotoxic medications
- PKD: regular BP monitoring at home
- Genetic counselling for PKD families before family planning
Prevention
Simple cysts cannot be prevented. Genetic testing allows ADPKD to be identified before symptoms develop, enabling early blood pressure control to slow progression.