Small abdominal aortic aneurysm: surveillance
The case
A 67-year-old man attends his GP after an abdominal ultrasound performed for gallstones incidentally showed an infra-renal aortic diameter of 3.8 cm. He is an ex-smoker (40 pack-years, stopped 5 years ago) with treated hypertension (blood pressure today 128/76 mmHg) and hypercholesterolaemia on a statin. He has no abdominal or back pain, syncope or limb ischaemia. The abdomen is soft and non-tender with no palpable mass. Haemoglobin is 145 g/L (130–170) and creatinine 88 micromol/L (60–110). What is the single best next step in management?
Options
- ARepeat ultrasound in 12 months and manage cardiovascular risk
- BUrgent CT angiogram for endovascular repair planning
- CRefer to vascular surgery now because it is over 3.5 cm
- DDischarge without imaging because it is under 4 cm
- EStart a beta-blocker and repeat ultrasound in 6 months
Think it through before you read on. Which single option is best, and why are the other four wrong?
Show the answer and explanation
Answer
A. Repeat ultrasound in 12 months and manage cardiovascular risk
Why this is the right answer
An abdominal aortic aneurysm (AAA) is an aortic diameter of 3.0 cm or more. At 3.8 cm this aneurysm is small. The yearly rupture risk below 4.0 cm is very low (under 1%), and repair carries its own mortality, so operating now would do more harm than good.
Small aneurysms grow slowly, on average 2 to 3 mm per year, and the growth rate rises with size. Surveillance intervals are set by diameter and vary a little between vascular units. For an aneurysm under 4 cm, a repeat ultrasound at 12 months is the usual advice (some units stretch this to 2 or 3 years for the smallest aneurysms); 4.0 to 4.9 cm is scanned every 6 to 12 months; and 5.0 to 5.4 cm every 3 to 6 months. Ultrasound is the surveillance test because it is accurate, cheap and involves no radiation or contrast.
Referral for elective repair is made when the aneurysm reaches 5.5 cm in men (5.0 cm in women), grows more than 1 cm in a year, or becomes symptomatic. Any abdominal or back pain in a patient with a known AAA is a possible rupture and needs immediate assessment.
While he is under surveillance, cardiovascular risk control is the most useful intervention. He should stay off cigarettes (smoking is the strongest driver of expansion), continue his statin and antihypertensive, and take antiplatelet therapy if there is other vascular disease. The Australian and New Zealand Society for Vascular Surgery endorses this approach.
He should be told the diagnosis clearly, including the symptoms of rupture and the reason he must not miss surveillance scans.
Why the other options are wrong
- B
CT angiography is for planning repair of large or symptomatic aneurysms; it adds radiation and contrast risk for no benefit here.
- C
Repair is considered at 5.5 cm in men, rapid growth, or symptoms; 3.8 cm needs surveillance, not surgery.
- D
Small aneurysms grow; discharging him risks a missed enlargement to a dangerous size.
- E
Beta-blockers have not been shown to slow AAA growth, and 6-monthly scans are more than a 3.8 cm aneurysm needs.
High-yield takeaway
AAA under 4 cm: ultrasound in 12 months plus aggressive risk factor control; refer for repair at 5.5 cm in men, growth over 1 cm/year, or symptoms.
Reference: Society for Vascular Surgery Practice Guidelines on the Care of Patients with an AAA (referenced by ANZSVS) (2018)
Common questions
How often should a 3.8 cm aneurysm be scanned?
Every 12 months by ultrasound, with the interval shortening as the aneurysm grows.
When is an aortic aneurysm repaired?
At 5.5 cm in men (5.0 cm in women), if it grows more than 1 cm in a year, or if it becomes symptomatic.
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