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Health condition · Clinically reviewed

Kidney cysts, from simple to inherited, and what actually needs treatment.

Most kidney cysts are harmless. Some are not. A clear framework, from Bosniak I simple cysts to ADPKD, is what tells them apart.

A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE, KDIGO, the Renal Association and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice including Bosniak classification, tolvaptan for ADPKD and cascade family testing.

Key facts

Kidney cysts at a glance.

The essentials, in plain English. What the different cysts are, how common they are, and how they are managed in the UK today.

  • What they are

    Fluid-filled sacs on or in the kidney. Simple cysts are benign and very common. Complex or inherited cystic disease is different, and specialist commissioned.

  • How common

    Simple cysts are found in roughly 40 per cent of adults over 60 on scans. ADPKD affects about 1 in 400 to 1 in 1,000 people.

  • Types you will hear

    Simple (Bosniak I), complex (Bosniak II to IV), ADPKD, ARPKD, medullary sponge kidney, and acquired cystic disease from long dialysis.

  • Bosniak matters

    The Bosniak classification stratifies cyst complexity on CT or MRI and drives whether observation or specialist commissioned surgery is right.

  • ADPKD is inherited

    The most common inherited kidney disease. PKD1 and PKD2 mutations drive progressive cyst growth, hypertension and often kidney failure.

  • Treatment ladder

    Simple cysts need reassurance. ADPKD benefits from blood pressure control and, for eligible patients, tolvaptan through a specialist commissioned service.

Why this guide matters

Not every cyst is the same story.

Three ideas that shape everything else on this page and stop harmless findings turning into unnecessary worry.

  • Simple cysts are usually benign

    Bosniak I cysts on a scan mean reassurance, not surveillance. Most people never need another test for them.

  • Complex cysts deserve staging

    Bosniak III and IV cysts carry a real cancer risk. They belong in specialist urology, not primary care follow-up.

  • ADPKD is a whole-body condition

    Blood pressure, hepatic cysts, aneurysm risk, family screening and tolvaptan eligibility all sit under specialist commissioned nephrology.

How the diagnosis is made

From incidental scan to a settled plan.

The typical UK pathway, in order. Ultrasound and blood pressure first, cross-sectional imaging if needed, and specialist input for anything complex or inherited.

  1. 01

    Assessing

    History and family tree

    A careful family history matters. ADPKD, ARPKD, tuberous sclerosis and Von Hippel-Lindau all cluster in families and change what happens next.

  2. 02

    Assessing

    Blood pressure and urine

    Early hypertension is often the first sign of ADPKD. A urine dip for blood and protein and a baseline creatinine and eGFR anchor the picture.

  3. 03

    Assessing

    Renal ultrasound

    The workhorse for screening, surveillance and first look. Cheap, radiation-free and highly sensitive for cysts over 1cm.

  4. 04

    Confirming

    CT or MRI with Bosniak

    When a cyst looks complex, contrast-enhanced imaging classifies it as Bosniak I to IV and guides specialist commissioned decisions.

  5. 05

    Confirming

    Nephrology and urology referral

    ADPKD, ARPKD and Bosniak III or IV cysts need a specialist opinion. Tuberous sclerosis and VHL sit under specialist commissioned care.

  6. 06

    Preparing

    Genetic testing when appropriate

    PKD1, PKD2, PKHD1 and wider gene panels through a specialist commissioned genetics service confirm the diagnosis and support cascade testing.

  7. 07

    Preparing

    Aneurysm and extra-renal screening

    For selected ADPKD patients and families, intracranial aneurysm screening and hepatic cyst review are arranged through specialist commissioned services.

Typical timeline: a first scan to a specialist plan in weeks, not months.

Symptoms

What kidney cysts can feel like.

Most simple cysts are silent. In ADPKD, the picture is broader, from early hypertension to loin pain, blood in the urine and infection.

  • No symptoms at all

    Most simple cysts and early ADPKD are silent. Many are found by chance on a scan done for something else.

  • Loin or flank pain

    A dull ache in the flank or back is common in ADPKD as kidneys enlarge. Sharp pain can mean bleeding into a cyst or a stone.

  • Blood in the urine

    Visible or microscopic haematuria can follow a cyst bleed, a stone or infection. It always deserves review.

  • High blood pressure

    Often the earliest ADPKD sign, sometimes years before kidney function drops. Early control protects the kidneys.

  • Recurrent urinary infection

    ADPKD cysts can harbour infection. Fevers, loin pain and rigors in a known cystic kidney need urgent specialist input.

  • Kidney stones

    More common in ADPKD and medullary sponge kidney. Presents with colicky loin pain and blood in the urine.

  • Palpable kidneys or a fullness

    In advanced ADPKD, enlarged kidneys and liver cysts can be felt in the abdomen and cause bloating or early fullness.

  • Red flag features

    Sudden severe headache, fever with loin pain, or a rapidly enlarging mass. Any of these need same-day medical review.

Treatment

How kidney cysts are treated in the UK.

Reassurance for simple cysts, staged surgery for complex ones, and a full nephrology package for ADPKD, including tolvaptan for eligible patients.

  • Observation for simple cysts

    Bosniak I cysts need reassurance and, occasionally, a repeat scan. No drainage, no surgery, no follow-up in most cases.

  • Bosniak-guided surgery

    Bosniak III and IV cysts carry a real risk of malignancy and are managed through specialist commissioned urology, often with partial nephrectomy.

  • Blood pressure control

    For ADPKD, an ACE inhibitor or ARB is first line, targeting a lower blood pressure than the general population, under specialist guidance.

  • Tolvaptan for ADPKD

    A V2 receptor antagonist that slows kidney enlargement and function decline. NICE-approved and delivered through a specialist commissioned ADPKD clinic.

  • Hydration and lifestyle

    Generous water intake, moderate salt and moderate protein, and weight control. Small changes that add up over decades of disease.

  • Infection and stone management

    Cyst and pyelonephritis infections often need lipophilic antibiotics and specialist input. Stones follow standard urology pathways.

  • Aneurysm screening

    For ADPKD patients with a family history of intracranial aneurysm or symptoms, MRA screening is arranged through specialist commissioned neuroradiology.

  • Dialysis and kidney transplant

    When ADPKD reaches end-stage kidney failure, dialysis and transplant are delivered through specialist commissioned renal services.

What this guide is based on

The sources behind every claim on this page.

UK national guidance, international nephrology standards and the Bosniak imaging classification, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or specialist knows your history and imaging and can tell you which parts apply to you. If in doubt, get seen.

  • KDIGO. Autosomal Dominant Polycystic Kidney Disease (ADPKD) Executive Conclusions.

  • NICE. Tolvaptan for treating autosomal dominant polycystic kidney disease (TA358).

  • Renal Association / UK Kidney Association clinical practice guidelines.

  • Bosniak MA. The Bosniak renal cyst classification (updated 2019).

Red flags

When cysts need urgent attention.

Most simple cysts are safely watched from primary care. These are the situations that are not, and where a specialist opinion is needed sooner rather than later.

  • Sudden severe headache

    In someone with ADPKD or a family history, a thunderclap headache can be a ruptured intracranial aneurysm. Call 999 or go to A&E.

  • Fever with loin pain

    Cyst infection or pyelonephritis in a cystic kidney can escalate quickly. Same-day GP or emergency review is warranted.

  • Rapidly enlarging mass or heavy bleed

    A rapidly growing renal mass or heavy visible haematuria needs urgent specialist review to exclude malignancy or a large cyst bleed.

  • Bosniak III or IV cyst on imaging

    Complex cysts have a meaningful cancer risk and belong in specialist commissioned urology, not routine follow-up.

  • Falling kidney function in ADPKD

    A drop in eGFR, new proteinuria, or uncontrolled hypertension in known ADPKD deserves a nephrology review, not watchful waiting.

  • Pregnancy in ADPKD

    Blood pressure and pre-eclampsia risk are higher. Care is coordinated between obstetrics and nephrology through specialist services.

  • Family history of ADPKD

    First-degree relatives deserve counselling and, where appropriate, cascade screening through a specialist commissioned genetics service.

  • ARPKD in a newborn or child

    A serious paediatric disease with respiratory and renal complications. Managed entirely through specialist commissioned paediatric nephrology.

  • Tuberous sclerosis or VHL features

    Skin lesions, seizures, retinal changes or a family history point to syndromes with distinct surveillance and specialist commissioned pathways.

Living with it

A manageable condition, with a clear plan.

Four things that make the biggest difference day to day for people with kidney cysts and ADPKD, from reassurance to family conversations.

A quiet reminder

Little habits, kept up for decades, do the real work.

In slowly progressive kidney disease, the wins are quiet and cumulative. Blood pressure, hydration and follow-up beat any single heroic intervention.

  1. 01 Reassure

    Simple cysts are usually nothing

    If your scan says Bosniak I, that is genuinely good news. No treatment, no diet, no follow-up for most people.

  2. 02 Protect

    Look after your blood pressure

    In ADPKD, blood pressure is the single biggest lever you can pull. Home monitoring, salt awareness and staying on your medication all matter.

  3. 03 Hydrate

    Drink generously, unless told not to

    Most people with ADPKD are advised to drink freely, aiming for pale urine. Your specialist will tell you if fluid restriction applies.

  4. 04 Family

    Talk to your relatives

    ADPKD runs in families. A gentle conversation about screening can prevent decades of unrecognised hypertension in a sibling or child.

Frequently asked

Everything we get asked about kidney cysts.

Quick answers on simple cysts, Bosniak grading, ADPKD, tolvaptan and family screening.

  • Are kidney cysts dangerous?

    Most are not. Simple Bosniak I cysts are benign and need no treatment. Complex cysts (Bosniak III and IV) carry a cancer risk and go through specialist urology, and inherited cystic disease such as ADPKD needs specialist nephrology follow-up.

  • What is ADPKD?

    Autosomal dominant polycystic kidney disease is the most common inherited kidney disease. Mutations in PKD1 or PKD2 cause progressive cyst growth in both kidneys, high blood pressure, and around half of people reach end-stage kidney failure by age 60. It runs in families and each child of an affected parent has a 50 per cent chance of inheriting it.

  • What is tolvaptan and who is it for?

    Tolvaptan is a vasopressin V2 receptor antagonist that slows cyst growth and kidney function decline in ADPKD. NICE approved it in 2015 for adults with rapidly progressing disease at chronic kidney disease stage 2 to 4. It is delivered through a specialist commissioned ADPKD clinic and needs careful liver-function monitoring.

  • Should my children be screened for ADPKD?

    Guidance generally avoids routine imaging screening in young children because it can affect insurance and cause anxiety, and there is no treatment before adulthood. Blood pressure checks from adolescence, and formal screening from around age 18, are usually recommended, arranged through a specialist commissioned service.

  • What does Bosniak I to IV mean?

    The Bosniak classification grades cyst complexity on contrast CT or MRI. Bosniak I is a simple, benign cyst. Bosniak II is minimally complex. IIF needs surveillance. III and IV have progressively higher rates of cancer and typically go through specialist commissioned urology for surgical assessment.

  • Can kidney cysts cause pain?

    Simple cysts rarely cause pain. In ADPKD, chronic flank pain, cyst haemorrhage, infection or kidney stones can all cause discomfort. Sudden severe pain, fever or heavy bleeding needs same-day medical review through your GP, out-of-hours service or emergency department.

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