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Health condition · Clinically reviewed

Aneurysms, from silent finding to a clear repair plan.

Most aneurysms are silent. Modern UK vascular, neurovascular and cardiothoracic teams use size, shape, growth and family history to decide between surveillance, endovascular repair and open surgery.

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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, ESVS, ESC, NHS AAA screening and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK vascular, neurovascular and cardiothoracic practice including EVAR, TEVAR, coiling and flow diversion.

Key facts

Aneurysms at a glance.

The essentials in plain English. What an aneurysm is, where they occur and how modern UK teams decide when to repair.

  • What it is

    An aneurysm is a focal, permanent dilatation of an artery to more than 1.5 times its normal diameter, with weakening of the wall.

  • Where they occur

    Intracranial (Circle of Willis), thoracic aorta, abdominal aorta, iliac, femoral, popliteal, splenic, renal, hepatic, mesenteric and carotid or vertebral arteries.

  • Main risks

    Smoking, hypertension, atherosclerosis, family history and connective tissue disorders such as Marfan, Loeys-Dietz, Ehlers-Danlos and ADPKD.

  • Why they matter

    Silent until they rupture, dissect, thrombose or embolise. Ruptured aortic and intracranial aneurysms carry very high mortality.

  • NHS AAA screening

    All men in England are invited for a one-off ultrasound at age 65 to look for an abdominal aortic aneurysm.

  • How they are treated

    Cardiovascular risk optimisation, surveillance for small aneurysms, endovascular repair (EVAR, TEVAR, coiling, flow diversion) or open surgery.

Types by location

Where aneurysms form and how each behaves.

Location shapes risk. Aortic aneurysms rupture, popliteal ones thrombose and embolise, cerebral ones bleed. The plan follows the pattern.

  • Intracranial aneurysm

    Most arise on the Circle of Willis, with the middle cerebral, anterior communicating and posterior communicating arteries the commonest sites. Rupture causes subarachnoid haemorrhage.

  • Thoracic aortic aneurysm

    Ascending disease is often linked to Marfan, bicuspid aortic valve and Loeys-Dietz. Descending disease is usually atherosclerotic. Aortic dissection is a related emergency.

  • Abdominal aortic aneurysm

    The commonest large-artery aneurysm. NHS AAA screening invites men at 65. Elective repair is usually offered at 5.5 cm or above in men.

  • Iliac, femoral and popliteal

    Popliteal aneurysms are bilateral in around half of cases and around 40 per cent have a concurrent AAA. Thrombosis and embolism outweigh rupture.

  • Visceral aneurysms

    Splenic, renal, hepatic and mesenteric. Splenic aneurysms carry a particular risk of rupture in the third trimester of pregnancy.

  • Mycotic and cervical

    Infectious aneurysms follow endocarditis or bacteraemia. Extracranial carotid and vertebral aneurysms can present with stroke, cranial nerve palsy or a pulsatile neck mass.

How the diagnosis is made

From incidental finding to a definitive plan.

The steps a UK vascular, neurovascular or cardiothoracic team will normally follow, in order.

  1. 01

    Assessing

    Clinical assessment

    History, family history, cardiovascular risk profile and a focused vascular and neurological examination.

  2. 02

    Assessing

    Ultrasound

    First-line for abdominal aortic, femoral and popliteal aneurysms. Fast, radiation-free and used in NHS AAA screening.

  3. 03

    Assessing

    CT angiography

    The workhorse for aortic, visceral and peripheral aneurysms. Defines size, shape, extent and planning for repair.

  4. 04

    Confirming

    MR angiography

    Radiation-free alternative for surveillance, intracranial imaging and patients who cannot have iodinated contrast.

  5. 05

    Confirming

    Catheter angiography

    Reserved for detailed planning of complex endovascular repair or when non-invasive imaging is inconclusive.

  6. 06

    Preparing

    Family cascade screening

    First-degree relatives are offered imaging when a heritable or familial pattern is suspected.

  7. 07

    Preparing

    Genetic testing

    Considered in suspected Marfan, Loeys-Dietz, vascular Ehlers-Danlos or ADPKD, and in early or unusual aneurysm patterns.

Typical timeline: from incidental finding to a settled surveillance or repair plan in weeks.

Symptoms

What aneurysms actually feel like.

Most give no warning. When they do, the pattern of pain, pulsation or neurological deficit points to the site and the risk.

  • Often silent

    Most aneurysms cause no symptoms and are found incidentally on scans done for other reasons.

  • Pulsatile abdominal mass

    A tender or expansile mass in the midline abdomen can be the only sign of a sizeable AAA.

  • Back, flank or abdominal pain

    New severe pain in a known aortic aneurysm suggests expansion, contained leak or rupture and needs emergency care.

  • Thunderclap headache

    Sudden, worst-ever headache raises concern for a ruptured intracranial aneurysm and subarachnoid haemorrhage.

  • Cold, painful leg

    Popliteal aneurysms often present with limb-threatening thrombosis or distal embolisation rather than rupture.

  • Hoarseness or dysphagia

    A large thoracic aortic aneurysm can compress the recurrent laryngeal nerve or oesophagus.

  • Cranial nerve palsy

    A posterior communicating artery aneurysm can press on the third cranial nerve, causing a dilated pupil and eyelid droop.

  • Red flag - sudden severe pain

    Tearing chest or back pain, syncope or collapse suggests dissection or rupture. Call 999 immediately.

Treatment

How aneurysms are treated in the UK.

Cardiovascular risk optimisation for everyone, surveillance for small aneurysms, and endovascular or open repair when size, symptoms or morphology cross the threshold.

  • Cardiovascular risk optimisation

    Smoking cessation is the single most effective intervention. Add a statin, control blood pressure below 140/90 and use antiplatelet therapy when indicated.

  • Surveillance imaging

    Small aneurysms are monitored with ultrasound, CT or MR at intervals set by size and growth rate rather than repaired straight away.

  • EVAR for AAA

    Endovascular aneurysm repair delivers a stent-graft through the femoral arteries. Standard for most infrarenal AAAs at or above 5.5 cm in men.

  • TEVAR for thoracic aneurysms

    Thoracic endovascular repair for descending thoracic aortic aneurysms, complicated Type B dissections and selected traumatic injuries.

  • FEVAR and BEVAR

    Fenestrated and branched grafts for juxtarenal and thoracoabdominal aneurysms where standard EVAR would cover vital branch vessels.

  • Cerebral aneurysm coiling

    Endovascular coiling packs the sac with platinum coils through a microcatheter. Flow diverters such as Pipeline reconstruct the parent artery for wide-neck aneurysms.

  • Open surgical repair

    Aortic graft replacement or surgical clipping for young patients, complex anatomy, connective tissue disease and many ruptured aneurysms.

  • Emergency care for rupture

    Permissive hypotension, major haemorrhage protocol, rapid CT and immediate endovascular or open repair in a vascular or neurosurgical centre.

Multidisciplinary care

Aneurysm care is a team sport.

Complex aneurysms are discussed at a multidisciplinary meeting that brings together vascular surgery, cardiothoracic surgery, neurosurgery, interventional radiology, cardiology, genetics and anaesthetics. The team weighs size, morphology, symptoms, comorbidity and patient preference before recommending surveillance, endovascular repair or open surgery.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, 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, vascular surgeon or neurosurgical team knows your scans and history and can tell you which parts apply to you. If in doubt, get seen.

  • NICE NG156. Abdominal aortic aneurysm: diagnosis and management.

  • European Society for Vascular Surgery (ESVS). Clinical practice guidelines on aortic, peripheral and visceral aneurysms.

  • European Society of Cardiology (ESC). Guidelines on the diagnosis and treatment of aortic diseases.

  • NHS AAA Screening Programme. Standard operating procedures and clinical guidance.

  • Royal College of Radiologists and BSNR. Standards for management of unruptured intracranial aneurysms.

Red flags

When an aneurysm needs urgent attention.

Small, stable aneurysms are safely watched. Rupture, dissection, acute limb ischaemia and infected aneurysms are true emergencies.

  • Ruptured abdominal aortic aneurysm

    Sudden severe abdominal or back pain, collapse and a pulsatile mass. Call 999. Mortality is very high without immediate repair.

  • Aortic dissection

    Tearing chest or interscapular pain, blood pressure difference between arms and possible neurological or limb symptoms. Emergency CT aorta and vascular referral.

  • Ruptured intracranial aneurysm

    Thunderclap headache, neck stiffness, photophobia, reduced consciousness or seizure. Emergency CT head and neurosurgical referral.

  • Acute limb ischaemia

    Painful, pale, pulseless, paraesthetic, paralysed and perishingly cold limb, often from a thrombosed popliteal aneurysm. Vascular emergency.

  • Mycotic aneurysm

    Fever, back pain and positive blood cultures, often with a history of endocarditis or sepsis. Needs urgent imaging and combined vascular and infection team input.

  • Rapidly growing aneurysm

    Growth of more than 1 cm per year, or a new symptom in a previously stable aneurysm, warrants urgent specialist review.

  • Splenic aneurysm in pregnancy

    Risk of rupture rises in the third trimester and carries very high maternal and foetal mortality. Elective repair is often advised before pregnancy.

  • Connective tissue disease

    Marfan, Loeys-Dietz or vascular Ehlers-Danlos syndromes need earlier surgical thresholds and lifelong specialist follow-up.

  • Family history of aneurysm

    A first-degree relative with an aortic or intracranial aneurysm is an indication to discuss cascade screening with a vascular or neurovascular team.

Living with it

A watched aneurysm is a treatable one.

Four things that make the biggest difference year on year. Stop smoking, control blood pressure, keep every scan and talk to your family.

A quiet reminder

Small habits, kept up, change outcomes.

Daily blood pressure medication and a steady blood pressure log matter more than any single hospital appointment.

  1. 01 Stop smoking

    Smoking cessation first

    Nothing else matches the impact of quitting smoking on aneurysm growth, rupture risk and cardiovascular outcomes.

  2. 02 Numbers

    Keep blood pressure controlled

    Aim for under 140/90, or tighter targets set by your specialist, and take medicines regularly rather than only when you feel unwell.

  3. 03 Surveillance

    Never miss a scan

    Small aneurysms are safest when watched. Diarise every scan and let your team know if new pain, breathlessness or headache develops.

  4. 04 Family

    Talk to your relatives

    First-degree relatives may benefit from screening. A short conversation can lead to an ultrasound or MRA that finds a problem early.

Frequently asked

Everything we get asked about aneurysms.

Quick answers on screening, size thresholds, EVAR, TEVAR, coiling and what to do when a family member is affected.

  • What is an aneurysm?

    An aneurysm is a focal weakening and permanent dilatation of an artery. Common sites include the abdominal aorta, thoracic aorta, brain arteries at the Circle of Willis and the popliteal, femoral and visceral arteries. Most are silent until they rupture, dissect, thrombose or embolise.

  • What causes aneurysms?

    Atherosclerosis, hypertension and smoking drive most aortic and peripheral aneurysms. Family history matters, and connective tissue disorders such as Marfan, Loeys-Dietz, vascular Ehlers-Danlos and ADPKD account for a smaller but important group. Infection, trauma and inflammatory arteritis are less common causes.

  • How are aneurysms found?

    Many are picked up incidentally on scans done for other reasons. In England, men are invited for a one-off abdominal aortic ultrasound at age 65. Symptomatic patients or those with a family history are investigated with ultrasound, CT angiography or MR angiography, and sometimes catheter angiography for detailed planning.

  • When does an aneurysm need surgery?

    Repair is usually offered for infrarenal abdominal aortic aneurysms at or above 5.5 cm in men, ascending thoracic aneurysms above 5.5 cm and descending thoracic aneurysms above 6.0 cm, with lower thresholds in Marfan, bicuspid aortic valve, Loeys-Dietz and other high-risk groups. Cerebral aneurysm thresholds depend on size, location, morphology and patient factors.

  • What is EVAR and how does it differ from open repair?

    EVAR is endovascular aneurysm repair. A stent-graft is delivered through small groin incisions under X-ray guidance and lines the aorta from inside. Recovery is faster than open surgery but lifelong imaging follow-up is required. Open repair replaces the diseased segment with a graft through an abdominal or chest incision and is preferred in complex anatomy, younger patients and many ruptures.

  • What happens if a brain aneurysm ruptures?

    A ruptured cerebral aneurysm causes a subarachnoid haemorrhage, presenting with sudden thunderclap headache, vomiting, neck stiffness and often reduced consciousness. It is a neurosurgical emergency needing immediate CT, transfer to a neurosurgical centre and either endovascular coiling or surgical clipping to secure the aneurysm and prevent rebleeding.

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