Your doctor will want your small abdominal aortic aneurysm to be followed with a watchful-waiting approach: serial imaging to see if the bulge is getting bigger.
The latest investigation (a meta-analysis) reveals that the smallest abdominal aortic aneurysms often do not seem to get significantly larger over many years. Full details are in the Feb. 27, 2013 issue of JAMA.
Thus, it may seem wiser to limit follow-up imaging to every several years, even though the survival rate of an AAA rupture is 20 percent, says the report.
A “small” abdominal aortic aneurysm has a diameter less than 5.5 cm; smaller means lower risk of rupture, indicating surveillance only rather than surgery. Most AAAs grow at a slow rate, adds the JAMA report.
However, growth rate does vary from patient to patient. The paper also notes that the intervals between ultrasound follow-ups depend on size of aneurysm; and that optimal time intervals have not been established.
The study was led by Simon G. Thompson, D.Sc., from the University of Cambridge, England. He and his team set out to determine rates at which the small abdominal aortic aneurysm grew to 5.5 cm. The meta-analysis involved 18 studies and over 15,000 patients (the vast majority being men) with small aneurysms.
For every 0.5 cm increase in baseline AAA diameter, a 0.59 mm per year increase in diameter resulted. In men, every 0.5 cm increase in baseline diameter resulted in an increased rupture rate of a factor of 1.9.
If a man had a 3 cm AAA, the average time period to develop a 10 percent chance of reaching 5.5 cm was 7.4 years. For a 4 cm and 5 cm AAA, it was 3.2 years, and then eight months, respectively.
To put the rupture risk in men under 1 percent, the estimated imaging frequency came in at 8.5 years for a 3 cm abdominal aortic aneurysm, and 17 months for a 5 cm dilation.
Absolute rates of growth were similar for both genders. But women had a four-fold greater risk for rupture for all sizes, plus reached a risk of rupture greater than 1 percent in a much shorter period of time than men did.
So how often should patients with an abdominal aortic aneurysm get imaged?
The paper states that follow-up intervals vary quite a bit, but the smaller the AAA, the longer the intervals between imaging.
For example, the surveillance interval for 3 to 4.4 cm is one year. For 4.5 to 5.4 cm, it’s three months. These surveillance intervals apply to England’s current screening program.
The paper notes that surveillance intervals for men “could be extended to 3 years for AAAs measuring 3.0 to 3.9 cm, 2 years for 4.0 to 4.4 cm, and yearly for 4.5 to 5.4 cm.”
This would put rupture risk at less than 1 percent. For an American patient with a 3 cm dilation, the above protocol would drop the average number of imaging scans from about 15 to seven.
More research is needed for women as far as ideal interval times between follow-ups for an abdominal aortic aneurysm of 4.5 to 5.4 cm.
Cost effectiveness of following an abdominal aortic aneurysm needs to be assessed, as well as different types of surveillance policies. Reducing imaging frequency would cut surveillance costs, yet also increase patient anxiety and rupture rates. In turn, costs related to emergency surgery would rise.