Abdominal Aortic Aneurysm Flashcards
What is an aneurysm?
An aneurysm is defined as an abnormal dilatation of a blood vessel by more than 50% of its normal diameter.
What is an abdominal aortic aneurysm (AAA)?
An abdominal aortic aneurysm (AAA) is defined as a dilatation of the abdominal aorta greater than 3cm.
What are the causes of AAA?
The aetiology of abdominal aortic aneurysm is largely unknown.
Possible causes include atherosclerosis, trauma, infection, connective tissue disease (e.g. Marfan’s disease, Ehler’s Danlos, Loey Dietz), or inflammatory disease (e.g. Takayasu’s aortitis).
What are the risk factors of AAA?
Risk factors for AAA include smoking, hypertension, hyperlipidaemia, family history, male gender, and increasing age. Diabetes mellitus is a negative risk factor for AAA (the mechanism for this is still poorly understood).
What are the clinical features of AAA?
Note: signs and symptoms
Many abdominal aortic aneurysms are asymptomatic and are simply detected on incidental finding or screening.
Symptomatic patients with an AAA can present with:
- Abdominal pain
- Back or loin pain
- Distal embolisation producing limb ischaemia
- Aortoenteric fistula
A patient with a ruptured AAA may present with pain (abdominal, back, or loin) and a degree of shock or syncope.
What are the clinical features of AAA?
Note: clinical examination
On examination, a pulsatile mass can be felt in the abdomen (above the umbilical level), and rarely, signs of retroperitoneal haemorrhage may be evident.
Briefly describe the screening for AAA
In the UK, the national abdominal aortic aneurysm screening programme (NAAASP) offer an abdominal US scan for all men in their 65th year.
What is the benefit for screening for AAA?
Men screened for AAA have been shown to have an approximately 50% reduction in aneurysm-related mortality (albeit a limited influence on all-cause mortality), based on the Multicentre Aneurysm Screening Study.
What investigations should be ordered for AAA?
In the routine outpatient setting, any suspected AAA should be initially investigated by an ultrasound scan (USS).
Once an USS has confirmed this diagnosis, a follow-up CT scan with contrast is warranted when at threshold diameter of 5.5cm. This provides more anatomical details in order to determine suitability for endovascular procedures.
What is the threshold for surgical intervention for an AAA?
Any AAA less than 5.5cm can be monitored via Duplex USS.
Briefly describe the monitoring of AAA
Note: less than 5.5 cm
Any AAA less than 5.5cm can be monitored via Duplex USS, as surgery prior to this diameter provides no survival benefit either for open repair or endovascular repair
- 3.0-4.4cm: yearly ultrasound
- 4.5-5.4cm: 3-monthly ultrasound
What are the cardiovascular interventions advised for medical management of an AAA?
- Smoking cessation (reduces rate of expansion and risk of rupture)
- Improve blood pressure control
- Commence statin and aspirin therapy
- Weight loss and increased exercise
When should surgery be considered in a AAA?
Surgery should be considered for an AAA >5.5cm in diameter, AAA expanding at >1cm/year, or a symptomatic AAA in a patient who is otherwise fit.
In unfit patients, the AAA may be left until 6cm or more prior to repair, due to the significant risk of mortality from an elective repair compared to the risk of mortality if not repaired.
What are the 2 surgical interventions for AAA?
The main treatment options are open repair or endovascular repair.
Briefly describe the open repair of AAA
Open repair involves a midline laparotomy or long transverse incision, exposing the aorta, and clamping the aorta proximally and the iliac arteries distally, before the segment is then removed and replaced with a prosthetic graft.
Briefly describe the endovascular repair of AAA
Endovascular repair involves introducing a graft via the femoral arteries and fixing the stent across the aneurysm.
What is an important complication following endovascular repair?
Endovascular leaking.
Briefly describe endovascular leaking
An important complication for EVAR is endovascular leak, whereby an incomplete seal forms around the aneurysm resulting in blood leaking around the graft.
Endoleaks are often asymptomatic hence regular surveillance (usually ultrasound unless a complication is noted) is needed. If left untreated, the aneurysm can expand and subsequently rupture. As such, any aneurysm expansion following EVAR warrants investigation for endoleak.
What are the complications of AAA?
The main complication of AAA is rupture, as discussed below. Other less common complications include:
- Retroperitoneal leak
- Embolisation
- Aortoduodenal fistula
What differentials should be considered for AAA?
The main differential diagnosis in patients who present symptomatically is renal colic, due to presence of back pain with no other symptoms present.
Other abdominal pathology such as diverticulitis, inflammatory bowel disease, irritable bowel syndrome, GI haemorrhage, appendicitis, ovarian torsion or ovarian rupture, or splenic infarctions may also be possible differentials.
