AAA Flashcards
What is AAA?
A permament and irreversible localised dilatation of the abdominal aorta by more than 50% of its normal diameter.
What size is it normally? And what does it increase to?
The abdominal aorta is normally 2cm so an AAA is classed as >3cm.
Where (else) can aortic aneurysms occur?
Majority of aortic aneurysms are abdominal but some can be thoracic and can also extend to affect the iliac, femoral and popliteal arteries
Where do 90% of AAA occur?
Infrarenally - below level of kidneys
What different types of aneurysm can you have?
fusiform (most AAAs) or sac-like (e.g. Berry aneurysms).
What is a true aneurysm?
A true aneurysm involves all layers of the arterial wall.
What is false aneurysm?
False aneurysms (pseudoaneurysms) involve a collection of blood in the outer layer only (adventitia) which communicates with the lumen.
What does incidence increase with?
Incidence increases with age.
How common is?
Present in 3% of population >50y
More in male or female?
M 3x>F and in 1/4 of male children of an affected individual
What ethnicity is more common in?
Rarely affects African/Hispanic, low prevalence in Asians, mainly affects Caucasians
Who is it most common in?
8:1 smokers
Who is it less common in?
Less common in diabetics
Aetiology
- Atherosclerosis - new evidence suggests this is not the only factor and that there is also a distinct arterial pathology
- Trauma
- Infection e.g. mycotic aneurysm in endocarditis, tertiary syphilis
- Connective tissue disorders (e.g. Marfan’s, Ehlers-Danlos)
- Inflammatory e.g. Takayasu’s aortitis
What is the pathophysiology?
AAA results from a failure of the major structural proteins of the aorta – elastin and collagen. The mechanism is not fully understood but it is to do with proteolysis or degradation of the proteins. The elimination of elastin from the tunica media means the aortic wall is more susceptible to the influence of blood pressure. The diameter of the aorta gradually decreases distally and infrarenally it contains less elastin which means the mechanical tension is higher. This is why abdominal aneurysms are more common than thoracic.
What are the risk factors?
• Smoking – 8x more likely • Male • Family history – 15% of first degree releatives will also develop an AAA; probably strong genetic links • Age • HTN • Hyperlipidaemia • COPD DM seems to decrease the risk
What are the symptoms?
- Most are asymptomatic and found on routine abdo exam
- As it expands it may cause:
- Epigastric pain radiating to back
- Pulsating sensations in abdomen
- Pain in chest, lower back or scrotum – due to pressure on nearby structures; back pain may be due to erosion of vertebral bodies
What are the signs?
• Pulsatile abdominal swelling • Aortic bruits Ruptured AAA may present with: • Pain in abdomen, back or loin – may be sudden and severe • Hypotension • Pulsatile and expansile abdominal mass • Syncope, shock or collapse Sudden death
What investigations?
Blood tests
ECG
Imaging – USS/ CT/ MRI angiography
What would you look for on blood tests?
- FBC, clotting, renal function, liver function
- Cross-match if surgery planned
- ESR/CRP if inflammatory cause suspected
What do you see on USS/ CT/ MRI angiography?
1. USS • Used for initial assessment and follow-up • Can assess to accuracy of 3mm 2. CT • Assesses in more anatomical detail • If with contrast then can show rupture 3. MRI angiography Put in two cannulas; call a vascular surgeon and anaesthetist; treat with ORh –ve blood; keep systolic BP <100mmHg; take blood for amylase, Hb, crossmatch
What conservative management?
- For asymptomatic AAAs where risk of repair is higher than risk of not treating
- Modify and treat risk factors
- Treat underlying causes e.g. infection
- Regular monitoring
- DVLA must be notified of aneurysms >6cm. >6.5cm disqualifies person from driving.
What medical treatments?
- To treat risk factors and underlying causes
- Some evidence that some drugs may reduce diameter of small aneurysms e.g. doxycycline, roxithromycin, ACE-I, losartan, statins, low-dose aspirin
What surgical managements?
• Indicated for all aneurysms >5.5cm, rupture, rapid expansion or onset of sinister symptoms
Open repair. EVAR (Endovascular aneurysm repair)
• Stent-graft system through femoral arteries
Less invasive but failure of graft can occur
What differentials?
Acute abdomen e.g. cholecystitis, appendicitis, bowel obstruction, pancreatitis, pyelonephritis. If TAA then other causes of chest pain e.g. MI, PE
What is the prognosis?
Overall mortality for elective surgery repair is 2.4%.
Increasing size = increasing risk of rupture.
1 in 3 patients with rupture reach hospital alive and 20% of those that do don’t reach theatre.
What are the complications?
Aortic dissection
Rupture
Ureterohydronephrosis – due to compression of the ureters
Distal embolization leading to limb ischaemia – mirco-embolic lower limb infarcts with palpable pedal pulses suggest popliteal or abdominal aneurysm
Retroperitoneal fibrosis or inflammation
How do you manage aortic dissection?
- Tear in inner wall of aorta allows blood to flow between layers of aorta forcing the layers apart
- Severe characteristic chest/abdominal pain (depending on location of dissection described as ‘tearing’)
- Type A (70%) in ascending aorta and Type B elsewhere
- Associated with other symptoms of decreased blood supply to organs
- Medical emergency – can lead to aortic rupture and death
- Usually in patients with hypertension, aortic aneurysm or disorders which affect blood vessel wall integrity
- Diagnosis made using medical imaging
- Surgery is used to treat Type A dissections
- Emergency blood pressure lowering medication given for descending/abdominal aorta dissections
