Aortic Aneurysm and Dissection
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Direct answer
An aneurysm is a localised abnormal dilatation of a vessel wall; a true aneurysm involves all three layers, whereas a false aneurysm is a contained haematoma communicating with the lumen. The clinically dominant forms are the abdominal atherosclerotic aneurysm — an infrarenal dilatation of elderly male smokers that ruptures into the retroperitoneum — and aortic dissection, in which blood splits a media weakened by cystic medial degeneration, usually within 10 cm of the aortic valve in a hypertensive or Marfan patient. Syphilitic aneurysm of the ascending aorta and berry aneurysms complete the examinable set.
What you must remember
- Abdominal aortic aneurysm: atherosclerosis, smoking, male sex, older age and hypertension; typically infrarenal, presenting with a pulsatile abdominal mass and back pain; rupture causes pain with hypotension — repair is guided by size and symptoms per current guidance.
- Aortic dissection: hypertension is the strongest risk factor; cystic medial degeneration (loss and fragmentation of elastic laminae with mucoid pools) is the substrate, notably in Marfan syndrome (fibrillin-1), Ehlers-Danlos type IV and bicuspid aortic valve.
- Course of dissection: an intimal tear lets blood into a false channel within the media; it may rupture outward (haemopericardium or haemothorax), extend to branch arteries, or cause acute aortic regurgitation when proximal.
- Stanford classification: type A involves the ascending aorta — emergency surgery; type B is confined to the descending aorta beyond the left subclavian, managed medically unless complicated.
- Clinical picture: abrupt tearing chest or interscapular pain, unequal limb pulses and pressures, and a widened mediastinum; CT angiography confirms; transoesophageal echocardiography is an alternative.
- Syphilitic aortitis: tertiary syphilis causes obliterative endarteritis of the vasa vasorum of the thoracic ascending aorta, producing tree-bark wrinkling, aneurysm, aortic regurgitation and coronary ostial stenosis.
- Berry aneurysm: congenital medial defects at circle of Willis branch points, aggravated by hypertension and associated with polycystic kidney disease, coarctation and Ehlers-Danlos; rupture gives subarachnoid haemorrhage.
Common confusion
Dissection is not aneurysm rupture: in dissection the wall splits within the media through an intimal tear, whereas aneurysm rupture is transmural bursting of a dilated segment. Equally tested is mycotic (infected) aneurysm from septic emboli — bacterial despite the name — versus the sterile, thoracic syphilitic aneurysm. Remember that abdominal aneurysms accompany atherosclerosis while syphilitic aneurysms spare the abdomen and involve the ascending aorta and arch.
Exam-focused takeaway
Stems describe an elderly smoker with a pulsatile abdominal mass collapsing (ruptured abdominal aneurysm), or a hypertensive man with tearing back pain, absent femoral pulse and widened mediastinum (type A dissection). Young tall patients with lens or skeletal features point to Marfan. Questions ask the layer defect in berry aneurysm, the vasa vasorum lesion of syphilis, or which Stanford type needs surgery. Link risk factor to segment: atherosclerosis — infrarenal; syphilis — ascending; dissection — near the valve.
Frequently asked questions
What is the difference between a true and a false aneurysm?
A true aneurysm is bounded by all three wall layers; a false one is a pulsating haematoma outside the wall communicating with the lumen, often after trauma.
What causes cystic medial degeneration?
Ageing-related or genetic weakening of the aortic media — elastic fragmentation with mucoid change — classically severe in Marfan syndrome.
What distinguishes Stanford type A from type B dissection?
Type A involves the ascending aorta and demands urgent surgery because of tamponade and regurgitation risk; type B is distal to the left subclavian and is usually managed medically.
Why does syphilitic aneurysm affect the ascending aorta?
Treponemal obliterative endarteritis of the vasa vasorum starves the thoracic media, producing tree-bark scarring and aneurysm.
With which conditions are berry aneurysms associated?
Hypertension, adult polycystic kidney disease, coarctation and Ehlers-Danlos syndrome; rupture causes thunderclap headache from subarachnoid haemorrhage.