42 AORTIC DISEASE
# Aortic Disease
The aorta carries the entire cardiac output, so when it dilates, dissects or ruptures the consequences are catastrophic. Aortic disease is high-yield in MRCS Part A because the same anatomical landmarks, embryological origins and pathological mechanisms reappear across vascular, anatomy and pathology SBAs.
👩⚕️ Anchor concept: AAA = loss of elastin from the media (wall bulges out); dissection = intimal tear (blood burrows between the layers). Confusing the two is the commonest trap on this topic.
Detailed notes
Anatomy of the aorta
The aorta is divided into four continuous segments:
➡ Ascending aorta — arises from the left ventricle at the aortic valve; gives off only the right and left coronary arteries.
➡ Aortic arch — three great branches in this order: brachiocephalic trunk → left common carotid → left subclavian artery.
➡ Descending thoracic aorta — begins distal to the left subclavian and runs in the posterior mediastinum.
➡ Abdominal aorta — begins as the aorta pierces the aortic hiatus of the diaphragm at T12 and ends by bifurcating into the common iliac arteries at L4 (level of the umbilicus).
The aortic hiatus also transmits the thoracic duct and azygos vein — a classic anatomy SBA pairing.
Abdominal branches (vertebral levels)
A reliable mnemonic: each unpaired midline branch supplies the gut region named for its embryological origin.
| Branch | Level | Supplies |
|---|---|---|
| Coeliac trunk | T12 | Foregut (lower oesophagus to mid-duodenum, liver, spleen, pancreas) |
| Superior mesenteric artery (SMA) | L1 | Midgut (mid-duodenum to two-thirds along transverse colon) |
| Renal arteries | L2 | Kidneys |
| Inferior mesenteric artery (IMA) | L3 | Hindgut (distal transverse colon to upper rectum) |
| Aortic bifurcation | L4 | Into common iliac arteries |
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Types of aneurysm (definitions you must not confuse)
A true aneurysm is a permanent dilatation of an artery to >1.5× its normal diameter, involving all three layers of the wall.
| Type | Mechanism | Classic example |
|---|---|---|
| Fusiform | Atherosclerotic medial degeneration | Abdominal aortic aneurysm |
| Saccular (berry) | Congenital weakness at branch points | Circle of Willis |
| Dissecting | Intimal tear, false lumen within the media | Aortic dissection |
| Mycotic | Infective destruction (often from endocarditis) | Salmonella, Staphylococcus |
| Pseudoaneurysm | Wall disruption, haematoma contained by adventitia/surrounding tissue | Post-catheterisation femoral pseudoaneurysm |
👩⚕️ Examiners love to mix the mechanism of one aneurysm type with the location of another. Always match mechanism to type, not site.
Abdominal aortic aneurysm (AAA)
The vast majority (>95%) of AAAs are infrarenal — distal to the renal arteries. The infrarenal aorta has fewer vasa vasorum and lower elastin content, predisposing it to medial degeneration.
Risk factors: male sex, age >65, smoking (single strongest modifiable risk factor), hypertension, family history, connective tissue disease (Marfan, Ehlers–Danlos).
Screening (UK NAAASP): single abdominal ultrasound for all men aged 65. Women are not screened — AAA is roughly six times more common in men.
Management thresholds:
| AAA diameter | Plan |
|---|---|
| <3 cm | Normal — no follow-up |
| 3.0–4.4 cm | Yearly USS |
| 4.5–5.4 cm | 3-monthly USS |
| ≥5.5 cm, symptomatic, or rapid growth (>1 cm/year) | Refer for repair |
Repair options:
- Open repair — preferred in younger, fitter patients; durable, but higher perioperative mortality.
- EVAR (endovascular aneurysm repair) — preferred in older/comorbid patients or unsuitable for open surgery; lower early mortality but requires lifelong surveillance for endoleak and graft migration.
Ruptured AAA
The classic triad: sudden severe back/abdominal pain + hypotension + pulsatile expansile abdominal mass. Any elderly man with this triad goes straight to theatre — imaging delays kill.
Permissive hypotension is the resuscitation principle: aim for a systolic BP of ~90 mmHg, just enough to perfuse the brain and kidneys but low enough that the contained retroperitoneal haematoma is not blown out by aggressive fluid resuscitation.
Trash foot / blue toe syndrome
After aortic instrumentation (EVAR, angiography) or from a partially thrombosed AAA, cholesterol microemboli showering into digital arteries cause patchy distal ischaemia. The macro-circulation remains intact, so peripheral pulses stay palpable — the classic discriminator from acute large-vessel embolism.
Aortic dissection
A tear in the intima allows pulsatile blood to track into the media, creating a false lumen. Propagation can occlude branches (coronary, carotid, renal, spinal, iliac) and rupture into the pericardium causing tamponade.
Stanford classification (the one that matters for exams):
| Stanford A | Stanford B | |
|---|---|---|
| Site | Ascending aorta (± arch) | Distal to left subclavian (descending only) |
| Management | Emergency surgical repair | Medical first — strict BP/HR control (IV labetalol) |
| Risks | Tamponade, AR, MI, stroke | Visceral/limb malperfusion, paraplegia |
Risk factors: hypertension (commonest), Marfan syndrome, Turner syndrome, bicuspid aortic valve, pregnancy (3rd trimester), atherosclerosis, cocaine, trauma.
Presentation: sudden tearing chest pain radiating to the back, often with inter-arm BP difference >20 mmHg and a widened mediastinum on CXR. New early-diastolic murmur suggests aortic regurgitation from a Stanford A.
Investigation: CT angiography is gold standard in the stable patient. TOE (transoesophageal echo) is useful at the bedside in the unstable or peri-arrest patient and intraoperatively.
Complications to memorise: cardiac tamponade, aortic regurgitation, MI (right coronary occlusion), stroke (carotid involvement), paraplegia (artery of Adamkiewicz), renal failure, lower-limb ischaemia.
Traumatic aortic injury
In rapid deceleration (RTA, fall from height) the aorta tears at the isthmus, just distal to the left subclavian — the point where the mobile arch meets the descending aorta tethered by the ligamentum arteriosum.
CXR clues: widened mediastinum (>8 cm), loss of aortic knob, left apical cap, depressed left main bronchus, deviated NG tube. CT angiography confirms the diagnosis.
Aortic coarctation
Congenital narrowing, typically just distal to the left subclavian artery near the ligamentum arteriosum.
➡ Associations: Turner syndrome, bicuspid aortic valve, berry aneurysms.
➡ Clinical signs: hypertension in the upper limbs, low BP and weak/delayed femoral pulses in the lower limbs (radio-femoral delay).
➡ CXR: rib notching (from dilated intercostal collateral arteries eroding the inferior rib surfaces) and a "figure-3" sign.
Inflammatory aortic disease
| Takayasu arteritis | Giant cell arteritis | |
|---|---|---|
| Vessel | Large (aorta + branches) | Medium/large (extracranial branches of carotid) |
| Classic patient | Young Asian women (<40) | Women >50, often with polymyalgia rheumatica |
| Features | Absent/diminished arm pulses ("pulseless disease"), arm claudication, BP discrepancy | Temporal headache, jaw claudication, scalp tenderness, visual loss |
| Bloods | ESR ↑ | ESR markedly ↑ |
| Treatment | High-dose steroids | High-dose steroids urgently to prevent blindness |
[Image: MCQs banner]
Test yourself
Which pathological process best describes the initial event in an AAA in a 65-year-old hypertensive smoker?
- ((Loss of elastic fibres from the media::☑️ Medial degeneration with elastin loss is the primary event in AAA.))
- ((Intimal tear with false lumen formation::Describes aortic dissection, not aneurysm.))
- ((Atherosclerotic plaque rupture::Contributes but is not the initial process; rupture causes ACS or stroke.))
- ((Infective destruction of the arterial wall::Describes a mycotic aneurysm.))
- ((Cystic medial necrosis::Associated with thoracic aneurysms in Marfan/connective tissue disease.))
👩⚕️ AAA = elastin loss in the media; dissection = intimal tear. Never mix these up.
A 36-week-pregnant tall woman with a family history of sudden death develops sharp chest pain. Most likely diagnosis?
- ((Aortic dissection::☑️ Marfan habitus plus 3rd-trimester pregnancy is a classic Stanford A trigger.))
- ((Acute myocardial infarction::Possible but tall stature + late pregnancy strongly favours dissection.))
- ((Pulmonary embolism::Pleuritic pain and dyspnoea, not tearing chest pain.))
- ((Pre-eclampsia::Hypertension and proteinuria — not acute chest pain.))
- ((Spontaneous pneumothorax::Tall habitus is a risk but presents with pleuritic pain and breathlessness.))
An elderly man has tearing chest pain radiating to the back with a BP difference between arms. Most likely diagnosis?
- ((Aortic dissection::☑️ Tearing pain to the back with inter-arm BP discrepancy is the textbook triad.))
- ((Acute myocardial infarction::Crushing central pain, no inter-arm BP difference.))
- ((Pulmonary embolism::Pleuritic chest pain and dyspnoea.))
- ((Tension pneumothorax::Respiratory distress and tracheal deviation.))
- ((Oesophageal rupture::Severe pain after vomiting, no BP discrepancy.))
Aortic dissection with widened mediastinum on CXR. Most likely type?
- ((Stanford Type A::☑️ Involves the ascending aorta — widens the upper mediastinum and needs emergency surgery.))
- ((Stanford Type B::Descending only, distal to left subclavian — medical management first.))
- ((DeBakey Type III::Equivalent to Stanford B; descending aorta only.))
- ((Traumatic aortic transection::Question specifies dissection, not trauma.))
👩⚕️ A = Ascending = Axe (surgery). B = Below subclavian = Beta-blocker (medical).
What is the gold-standard investigation for aortic dissection?
- ((Chest X-ray::May show widened mediastinum but not diagnostic.))
- ((Transoesophageal echocardiography::Bedside option in unstable patients; not first-line gold standard.))
- ((CT angiography of the thoracic aorta::☑️ Fast, accurate and defines extent — gold standard in stable patients.))
- ((MRI::Excellent sensitivity but impractical in the acute setting.))
- ((Conventional angiography::Historic; replaced by CTA.))
Which is NOT a recognised risk factor for aortic dissection?
- ((Diabetes mellitus::☑️ Not a recognised risk factor — diabetes actually appears slightly protective.))
- ((Atherosclerosis::Weakens the aortic wall.))
- ((Smoking::Major vascular risk factor.))
- ((Hypertension::Strongest and most common risk factor.))
- ((Marfan syndrome::Classic connective tissue association for Stanford A.))
A smoker post-EVAR develops "trash foot" but has palpable peripheral pulses. Most likely cause?
- ((Thrombosed EVAR::Would cause acute limb ischaemia with absent pulses.))
- ((Popliteal aneurysm::Causes distal embolisation but unrelated to EVAR.))
- ((Atrial fibrillation::Larger emboli lodge at bifurcations with absent distal pulses.))
- ((Cholesterol microemboli from the aneurysm/plaque::☑️ Microemboli lodge in digital arteries; macro-circulation intact so pulses palpable.))
- ((Peripheral arterial disease::Would cause absent pulses, not palpable pulses with blue toes.))
👩⚕️ Palpable pulses + blue toes = micro-embolic (cholesterol). Absent pulses + blue toes = macro-embolic (e.g. AF).
A 70-year-old with a partially thrombosed AAA develops a sudden blue big toe, with absent distal pulses. Most likely cause?
- ((Acute embolism from the aneurysm::☑️ A partially thrombosed AAA is a classic source of macro-emboli.))
- ((Chronic peripheral arterial disease::Gradual claudication, not sudden blue toe.))
- ((Small vessel disease::Tends to cause ulcers, not acute ischaemia.))
- ((Buerger disease::Young male smokers with corkscrew collaterals.))
- ((Raynaud phenomenon::Episodic bilateral colour change, not unilateral.))
A 65-year-old diabetic presents with a blackened, gangrenous big toe. Most likely pathology?
- ((Iliofemoral atherosclerosis::☑️ Most common cause of chronic limb ischaemia and dry gangrene in elderly diabetics.))
- ((Acute embolism::Sudden pain, no time for collaterals — not chronic gangrene.))
- ((Small vessel disease::Causes ulcers more than frank gangrene.))
- ((Buerger disease::Young male smokers, corkscrew collaterals.))
- ((Takayasu arteritis::Young Asian women, large-vessel arm symptoms.))
A patient in an RTA has a widened mediastinum on CXR. Which part of the aorta is most likely injured?
- ((Ascending aorta::Less commonly injured in deceleration.))
- ((Aortic arch::Relatively mobile and less vulnerable.))
- ((Aortic isthmus (proximal descending)::☑️ Tethered by the ligamentum arteriosum — shears in deceleration.))
- ((Abdominal aorta::Rarely injured in thoracic trauma.))
- ((Aortic root::Protected within the pericardium.))
👩⚕️ The ligamentum arteriosum is the embryological remnant of the ductus arteriosus — it fixes the descending aorta and is the reason the isthmus shears in deceleration injury.
A stable 24-year-old has chest trauma and a widened mediastinum on CXR. Next step?
- ((Echocardiogram::Useful but not first-line for thoracic aortic trauma.))
- ((ECG::Important but won't diagnose aortic injury.))
- ((Ultrasound::Not the investigation of choice for thoracic aorta.))
- ((CT chest angiography::☑️ Gold standard in the stable trauma patient with suspected aortic injury.))
- ((Diagnostic peritoneal lavage::Assesses intra-abdominal bleeding, not the thoracic aorta.))
An asymptomatic 70-year-old has an incidental AAA measuring 4.7 cm. Best management?
- ((Surveillance with 3-monthly ultrasound::☑️ 4.5–5.4 cm AAAs are surveilled 3-monthly; repair triggered at ≥5.5 cm, symptoms, or rapid growth.))
- ((Open AAA repair::Reserved for ≥5.5 cm, symptomatic or rapidly growing in fit patients.))
- ((EVAR::Same thresholds as open — preferred for unfit patients or favourable anatomy.))
- ((Endovascular embolisation::Not used for AAA.))
- ((Urgent CT::Not required if already characterised on USS and asymptomatic.))
Which best describes the cause of a saccular (berry) aneurysm?
- ((Atherosclerotic degeneration::Causes fusiform aneurysms such as AAA.))
- ((Congenital weakness at arterial branch points::☑️ Berry aneurysms classically arise at branch points of the Circle of Willis.))
- ((Intimal tear with blood between wall layers::Describes a dissecting aneurysm.))
- ((Infective destruction of the wall::Describes a mycotic aneurysm.))
- ((Trauma to the arterial wall::Causes pseudoaneurysm, not a true saccular aneurysm.))
👩⚕️ Berry aneurysms are associated with polycystic kidney disease, Ehlers–Danlos, and coarctation of the aorta — classic SBA links.
Revision summary
➡ Aortic arch branches in order: brachiocephalic → left common carotid → left subclavian.
➡ Vertebral levels: coeliac T12, SMA L1, renal L2, IMA L3, bifurcation L4. Aorta enters abdomen via aortic hiatus at T12 (with thoracic duct and azygos vein).
➡ AAA = elastin loss in media; dissection = intimal tear.
➡ AAA screening: single USS for men at 65. Repair if ≥5.5 cm, symptomatic, or growing >1 cm/year.
➡ Surveillance: <3 cm none; 3–4.4 cm yearly; 4.5–5.4 cm 3-monthly.
➡ Ruptured AAA triad: back/abdo pain + hypotension + pulsatile mass → straight to theatre, permissive hypotension (SBP ~90).
➡ Stanford A = ascending = surgery; Stanford B = below subclavian = BP control (labetalol).
➡ Dissection risk: HTN (commonest), Marfan, Turner, bicuspid valve, pregnancy.
➡ Investigation of choice: CT angiography; TOE if unstable/bedside.
➡ Traumatic aortic injury: at the isthmus, tethered by ligamentum arteriosum.
➡ Coarctation: HTN in arms, weak femorals (radio-femoral delay), rib notching, associated with Turner's and bicuspid valve.
➡ Takayasu: young Asian women, pulseless disease. GCA: women >50, temporal headache, jaw claudication, ESR ↑↑.
➡ Trash foot with palpable pulses = cholesterol microemboli; absent pulses + blue toe = macroembolus.