Approach to a patient with a 7.6cm AAA

Things were livened around 11am up by a call from the ultrasonographer. A man in his late 60s year had undergone an abdominal ultrasound at the request of the consultant haematologist, with a view to confirming his impression of splenomegaly. The ultrasonographer instead found a 7.6cm aneurysm, and wanted me to make a plan.

I decided to go and see the patient in the room, and asked the nurses to get some obs on him. He was symptom free, comfortable at rest and his obs were stable. He had back pain for the past 12 months, which was relieved by leaning forward. There was no leg pain. This seemed consistent with spinal stenosis. There had been no recent progression.

His PMH showed COPD as well as RAEB (refractory anaemia with excessive blasts), with a generally poor exercise tolerance of a few metres. Poor exercise tolerance, low platelets, chronic anaemia…surely not the best candidate for surgery? Where are the guidelines for this scenario?

It turns out there is a lack of data in this field. “Guidelines for the treatment of abdominal aortic aneurysms: Report of a subcommittee of the Joint Council of the American Association for Vascular Surgery and Society for Vascular Surgery”, notes this, and offers the following:

Decision making involved in selecting patients for AAA repair is influenced primarily by estimates of (1) aneurysm rupture risk, (2) elective operative mortality risk, (3) life expectancy, and (4) patient preference. In the absence of truly accurate data regarding many of these variables, decision making is often a complex and uncertain process. It is increasingly recognized that patient preference, after a complete review of options and anticipated results (true informed consent), must be a very important component in this decision-making process.

What is the rupture risk? The same paper offers the following. Bear in mind the normal abdominal aorta has a diameter of 2cm, and 3cm and above defines an aneurysm.

AAA diameter (cm) Rupture risk (%/y)
<4 0
4-5 0.5-5
5-6 3-15
6-7 10-20
7-8 20-40
>8 30-50

Interestingly, although AAAs are twice as common in men than in women, women are at 4 times the risk of rupture compared to men, and a greater proportion of female ruptures are fatal. The 5.5cm diameter cut off for elective surgery in the UK was originally designed for men, and this number should perhaps be lower in women.

What were my patient’s risk factors for AAA? I had always been taught that it was basically the atheroscelerotic risk factors, with an emphasis on smoking and hypertension. Then there were the medical school favourites like Ehlors Danlos and Marfan’s. I have found out today that diabetes is protective against AAA, and that there is no association with cholesterol levels. This suggests that the disease process is not simply atherosclerosis. In addition, COPD is an independent risk factor from smoking.

I thought back to the non rupture complications of AAA, and remembered about the microemboli that can be thrown off. Our patient had perfectly good pulses bilaterally, and no evidence of emboli in the feet.

At this stage, I was stuck with an anxious man who has just been told he has a large blood vessel in his abdomen that could burst at any second as well as two medical students and a nurse looking at me expectantly. My belief in guardian angels was restored when my bleep went off. I was delighted to hear the voice of my SHO, who had thought to bleep me just to see what’s up. The vascular reg came down to discuss it with the patient, and an urgent outpatient appointment was arranged to go through his options more fully once he had more time to reflect.


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