A small aortic aneurysm has been found. What does surveillance mean?

The word aneurysm frightens people, and understandably so. Then the letter arrives saying the aneurysm is small, no treatment is needed, and you will be scanned again in a year. Both halves of that message are true, and this article explains why they fit together.

What an aneurysm is

The aorta is the main artery carrying blood from the heart. It passes down through the chest and abdomen before dividing to supply the legs. In the abdomen it is normally about 2 cm across. With age, and particularly with smoking, the wall can weaken and the artery stretches. Once it measures 3 cm or more we call it an abdominal aortic aneurysm, or AAA.

Most cause no symptoms at all. The concern is that a large aneurysm can rupture, which is a surgical emergency with a high death rate. The whole purpose of surveillance is to repair the aneurysm before that happens, and not a moment sooner than necessary.

How aneurysms are found

In England the NHS AAA screening programme invites all men registered with a GP in the year they turn 65 for a single ultrasound scan. Around 1 in 92 men screened have an aneurysm. Men are about six times more likely to have one than women, which is why women are not routinely screened. Men over 65 who missed their invitation can ask to be screened. The other common route is incidental discovery, when an aorta is measured on a CT or ultrasound done for an unrelated reason.

People at higher risk include current or former smokers, those with high blood pressure, and anyone whose parent, brother or sister has had an aneurysm. If a close relative has had one, it is reasonable to ask for a scan from your early sixties, or earlier if your relative was young when theirs was found.

Why small aneurysms are watched, not repaired

This is the question that matters most, and the evidence is clear. Two large randomised trials, the UK Small Aneurysm Trial and the American ADAM trial, compared early repair of aneurysms between 4 and 5.5 cm with surveillance until they reached 5.5 cm. Early surgery did not improve survival. Later trials of early keyhole repair found the same. The reason is simple arithmetic: below 5.5 cm the annual risk of rupture is small, on the order of 1% per year or less, while repair carries a real risk of death and complications. Operating early exposes people to that risk without a matching benefit.

NICE's 2020 guideline (NG156) therefore recommends considering repair only when an aneurysm is 5.5 cm or more, when it is growing by more than 1 cm in a year in an aneurysm already over 4 cm, or when it is causing symptoms such as abdominal or back pain or tenderness over the aneurysm. Anyone whose aneurysm reaches 5.5 cm should be seen by a vascular service within two weeks; those with smaller aneurysms within 12 weeks.

What surveillance involves

Surveillance is a repeat ultrasound scan of the abdomen. It takes about ten minutes, uses no radiation and gives the measurement on the spot. The interval depends on size:

• Small (3.0 to 4.4 cm): rescanned every year under the NHS screening programme; NICE allows up to two years for the smallest.
• Medium (4.5 to 5.4 cm): rescanned every three months.
• Large (5.5 cm or more): referred to a vascular surgeon to discuss repair.

Growth is slow and irregular. Small aneurysms typically grow by a few millimetres a year, and larger ones grow faster, which is why the scan interval shortens as the size increases. A pooled analysis of 18 studies found that a 3 cm aneurysm takes on average more than seven years to have even a 10% chance of reaching 5.5 cm, whereas a 5 cm aneurysm can reach it within a year. The scan schedule is built around those numbers so that the threshold is not missed between appointments.

Measurements are made from the inner wall to the inner wall, front to back, and different machines and operators can vary by a millimetre or two. A reading that appears to go down slightly, or jump, between scans is usually measurement variation rather than real change. The trend over several scans is what counts.

What you can do in the meantime

Smoking is the single strongest influence on aneurysm growth and rupture that you can change. Stopping slows growth and roughly halves the rupture risk compared with continuing. Blood pressure should be well controlled. Because an aneurysm is a sign of arterial disease generally, NICE recommends that people with an AAA are treated for their cardiovascular risk in the usual way, which for most means a statin and an antiplatelet. Normal exercise, including brisk walking, cycling and gym work, is safe and is positively encouraged; it keeps you fitter should an operation be needed later. There is no need to avoid lifting in daily life.

Driving and insurance

With a car or motorcycle licence you can continue to drive and need not inform the DVLA while the aneurysm is below 6 cm. You must tell the DVLA if it reaches 6 cm, and you must not drive at 6.5 cm or more until it has been successfully repaired. Bus, coach and lorry licence holders must notify the DVLA of an aneurysm of any size and must stop driving at 5.5 cm. You should declare the aneurysm to travel and health insurers.

When the time for repair comes

Repair is planned, not rushed. There are two approaches. Endovascular repair (EVAR) places a stent graft inside the aneurysm through small incisions in the groin; recovery is quick and hospital stay short, but the graft needs lifelong imaging follow-up and sometimes further procedures. Open repair replaces the aneurysm with a fabric graft through an abdominal incision; recovery is longer but the repair is durable and needs little follow-up. NICE suggests open repair for most people who are fit enough, with EVAR for those who are not, although anatomy, age and personal preference all come into the decision and it is made jointly with the patient after a CT scan and a fitness assessment.

Symptoms that must not wait

A known aneurysm with new, sudden, severe pain in the abdomen or back, particularly with feeling faint, sweaty or unwell, could mean the aneurysm is leaking. This is an emergency: call 999 and say you have an aortic aneurysm.

What happens at a private consultation

People come to me privately with an aneurysm for three main reasons: a scan report they want explained, a wish to be followed by the surgeon who would do the operation, or a strong family history and a request for a scan. The appointment covers your history and risk factors, a review of your imaging, a duplex measurement of the aorta where that is useful, and a plain explanation of where your aneurysm sits against the thresholds above. You leave with a written plan, a surveillance interval and a letter to your GP. If and when repair is needed, I carry it out.

Frequently asked questions

What counts as an abdominal aortic aneurysm?

The aorta is the main artery running from the heart through the chest and abdomen. In the abdomen it is normally around 2 cm across. A diameter of 3 cm or more is called an aneurysm. Most are found by the NHS screening programme, which invites men in the year they turn 65, or by chance on a scan done for something else.

Why is my aneurysm being monitored rather than repaired?

Because for aneurysms under 5.5 cm the risk of rupture each year is small, and trials have shown that operating early does not improve survival compared with careful surveillance. Repair carries its own risks, so it is reserved for the point at which the risk of rupture clearly exceeds the risk of the operation.

How often will I need a scan?

Small aneurysms (3.0 to 4.4 cm) are rescanned every one to two years depending on the programme, and medium aneurysms (4.5 to 5.4 cm) every three months. NICE sets out these intervals in its guideline NG156 and the NHS screening programme follows a similar schedule.

When is repair recommended?

NICE recommends considering repair when an aneurysm reaches 5.5 cm, when it is growing quickly (more than 1 cm in a year in an aneurysm over 4 cm), or when it causes symptoms. Anyone with an aneurysm of 5.5 cm or more should be seen by a vascular service within two weeks.

Can I still drive with an aneurysm?

With a car or motorcycle licence you can drive and do not need to tell the DVLA while the aneurysm is under 6 cm. You must tell the DVLA at 6 cm or more, and you must not drive at 6.5 cm or more until it has been repaired. Bus and lorry licence holders must notify the DVLA of any aneurysm and must stop driving at 5.5 cm.

What can I do to slow it down?

Stop smoking, which is the strongest modifiable factor in aneurysm growth and rupture. Keep blood pressure well controlled and take the statin and antiplatelet your doctor advises, which protect the rest of your arteries. Normal exercise is safe and encouraged.