Thoracic Aortic Dissection

• Dissection of the thoracic aorta

Incidence

• Aortic dissection = Most common catastrophe of Aorta (more common than AAA)
• M > F (3:1)
• Peak age: 50-65; (75% occur in pts aged 40-70yrs)

Classification

Aetiology

• Marfans, Ehlers-Danlos & other connective tissue diseases
• HTN can propagate dissection
• Atherosclerosis
• Iatrogenic injury (e.g. Catheter, Open heart procedures)
• Blunt chest trauma
• Can be associated with Pregnancy

Clinical

• Chest pain
• Ripping / tearing/ sudden onset
• Neck, jaw, interscapular pain
• Pain tends to be felt anteriorly in ascending dissection & posterior interscapular in descending dissection
• Neurological Sx / stroke Sx / limb paraesthesia, pain or weakness – in 20%
• BP differential of > 20mmHg
• Renal failure, acute mesenteric occlusion & lower extremity arterial occlusion may occur
• If the dissection involves the pericardial space, tamponade may result
• Occlusion of coronary arteries may also occur
• Aortic root involvement is also associated with prolapse of the Aortic valve

Pathology

• 90% occur within 10cm of the Aortic valve
• Tear in the intimal layer → Formation & propagation of subintimal haematoma
• Cystic Medial Necrosis
• Hallmark change associated with dissection, esp. in Marfan’s
• Degenerative changes in the media leading to breakdown of the collagen, elastin and smooth muscle
• Medial degeneration predisposes to rupture of Vasa Vasorum → Intramural haematoma formation → Dissection

Investigations

• ECG
  • 8% of pts with type A dissections have ST elevation (none with type B)
• CXR
  • Normal in up to 50%
  • Widened mediastinum (> 8cm on PA CXR)
  • Abnormal (blunted) Aortic knuckle
  • Left Apical Cap
• Angiography
  • Accurate Dx in 95% (historically the gold standard)
• CT
  • Helical / multiplanar CT = Replacing angiography as the test of choice
  • Sensitivity 83-94%, specificity 87-100%
• Echo
  • Transthoracic – Sensitivity 80%, specificity 90%
  • Transoesophageal – Sensitivity 97-99%, specificity 97-100%
• MRI
  • Sensitivity >90%, specificity >95%

Management

• Type A: Surgery → Dacron graft
• Type B: Medical therapy → Control of BP (β-blockers)
• But ≈ 20% will require surgery for organ ischaemia

Prognosis / Natural Hx:

• If untreated, Acute Type A → 33% die within 24/24, 50% die in 48/24; 70% by 1/52
• 2-week mortality ≈ 75% in pts with undiagnosed Ascending Aortic dissection
• After surgery
  • Operative mortality: 5-15%
  • 5YS Open surgery 50%
• Type B risks: 3% Paraplegia, 34% Renal failure, 7% Bowel ischaemia, 4.7% CVA

Follow-up

• For Type B dissection, 20% develop aneurysmal dilation of the aorta, therefore yearly imaging surveillance advised