How do aortic dissection and aortic aneurysm differ in pathophysiology, clinical presentation, diagnosis, and management?

Aortic Dissection vs. Aortic Aneurysm: Key Differences

Aortic dissection and aortic aneurysm are fundamentally different pathologic processes—dissection involves a tear in the aortic intima creating a false lumen between vessel wall layers, while aneurysm is a permanent localized dilation of the aortic wall without layer separation. 1

Pathophysiology

Aortic Dissection

• Occurs when an intimal tear allows blood to enter and separate the layers of the aortic wall, creating a true lumen and false lumen 1
• The dissection process can propagate along the length of the aorta, with blood infiltrating between the separated layers 1, 2
• Expansion rate is dramatically faster than aneurysms: 5-20 mm within 1-3 years for communicating dissections 1
• Medial degeneration from compromised vasa vasorum nutrition and smooth muscle cell necrosis creates vulnerability to shear stress 1

Aortic Aneurysm

• Represents permanent, localized dilation of the aortic wall exceeding normal diameter by >50% (typically >3.5-3.8 cm depending on location) 1
• Atherosclerosis is the primary cause, present in >90% of cases, leading to intimal thickening, fibrosis, and calcification 1
• Expansion rate is much slower: 2-3 mm/year for non-communicating lesions 1
• The dilated segment maintains intact wall layers (unless rupture occurs) 1

Clinical Presentation

Aortic Dissection

• Abrupt onset of severe pain (present in 90% of cases) with maximum intensity at the very beginning—this is the hallmark distinguishing feature 1, 3, 4
• Pain quality is sharp or stabbing (51-64%), not necessarily the classic "tearing" description 5, 4
• Location predicts dissection type: retrosternal pain indicates Type A (ascending aorta), while interscapular/back pain indicates Type B (descending aorta) 1, 3, 5
• Up to 20% present with syncope without pain 1, 3, 4
• Associated findings include pulse deficits, blood pressure differentials between arms (>20 mmHg), new aortic regurgitation murmur, and neurologic deficits 3, 5, 4
• Typical patient: male in his 60s with hypertension history 1, 3, 4

Aortic Aneurysm

• Initially asymptomatic and discovered incidentally in most cases 2
• Symptoms develop only when the aneurysm expands sufficiently to compress surrounding structures or threatens rupture 1, 2
• Pain, when present, builds gradually rather than abruptly 2
• Hypertension is the dominant risk factor (present in 85% of ruptured aneurysms) 1

Critical Clinical Distinction

The key differentiating feature is pain onset pattern: dissection causes instantaneous maximum-intensity pain, while aneurysm-related pain (if present) develops gradually. 1, 3, 4 This distinction is crucial because misdiagnosing dissection as acute coronary syndrome and administering thrombolytics can be catastrophic 3.

Common Pitfall to Avoid

• Pain resolution does NOT exclude acute dissection—up to 6.4% of dissections present without pain, particularly in older patients, those on steroids, and Marfan syndrome patients 5, 4
• Re-emergence or change in pain location indicates dissection propagation and requires immediate re-evaluation 4

Diagnosis

Imaging Approach

• Both conditions require definitive imaging with CT angiography, TEE, or MRI 3, 6
• For suspected dissection, proceed directly to imaging even if pain has resolved or D-dimer is negative 3, 5, 4
• D-dimer >0.5 µg/mL has 91-100% sensitivity for dissection but should not be used to rule it out 3, 5

Imaging Findings

• Dissection shows intimal flap separating true and false lumens on cross-sectional imaging 6, 2
• Aneurysm shows uniform dilation of all wall layers without intimal flap 6, 2

Management Differences

Acute Aortic Dissection

• Type A dissection (involving ascending aorta): Emergent surgical repair is mandatory to prevent rupture, tamponade, and death 1, 3
• Surgery involves composite graft implantation in the ascending aorta with or without coronary reimplantation 1
• Type B dissection (descending aorta only): Initial medical management unless complications develop (intractable pain, rapid expansion, malperfusion, rupture signs) 1, 3
• Immediate blood pressure control: target systolic 100-120 mmHg and heart rate ≤60 bpm using IV beta-blockers first-line 3
• Add sodium nitroprusside only after adequate beta-blockade 3
• Untreated acute dissection carries 1-2% mortality per hour 4

Aortic Aneurysm

• Indications for intervention are based on diameter thresholds and expansion rate, not acute symptoms 1
• Thoracic aneurysms: intervention typically at 5.5 cm (or 5.0 cm in Marfan syndrome) 1
• Surgical approach involves elective graft replacement of the aneurysmal segment 1
• Medical management focuses on blood pressure control and risk factor modification to slow expansion 1

Special Consideration: Coexistence

When dissection occurs in a pre-existing aneurysm, rupture risk increases dramatically at both the aneurysm site and the intimal tear location 7. This combination should be considered a surgical emergency even for Type B dissections 1.