What are the differences between an aortic aneurysm and an aortic dissection?

Aortic Aneurysm vs. Aortic Dissection: Key Differences

An aortic aneurysm is a permanent dilation involving all three intact layers of the aortic wall, while an aortic dissection is a disruption of the media layer with bleeding within and along the aortic wall—these are fundamentally different pathologies that can occur independently of each other. 1

Structural Differences

Aortic Aneurysm

• Involves all three intact wall layers (intima, media, and adventitia), though these layers may become severely attenuated in large aneurysms 1
• Defined as permanent dilation exceeding 50% of the expected normal diameter, or more than 2 standard deviations above the mean 1
• The aortic wall remains continuous without separation of layers 1
• Results from medial degeneration with fragmentation of elastic fibers, accumulation of proteoglycans, and smooth muscle cell loss 1

Aortic Dissection

• Involves disruption of the media layer with an intimal tear that creates a false lumen for blood flow between the intima and media 1
• At least one layer of the aortic wall is disrupted, distinguishing it from aneurysmal disease 1
• Blood flows within and along the aortic wall rather than causing uniform dilation 1, 2
• Can occur in a normal-caliber aorta without any aneurysmal dilation present 1, 2

Clinical Presentation and Timing

Aortic Aneurysm

• Typically asymptomatic and discovered incidentally 1, 3
• Chronic, progressive disease that develops over years 1
• Risk of rupture increases with size: aneurysms 6.0-6.5 cm carry a 7% annual rupture risk 1
• Growth rate >1 cm per year indicates higher rupture risk 1

Aortic Dissection

• Acute presentation in 80% of cases with sudden, extremely severe pain 3
• Represents an acute aortic syndrome requiring immediate intervention 1
• Life-threatening emergency with high mortality if untreated 1, 2
• Can progress to rupture, malperfusion syndrome, or organ ischemia 1, 2

Critical Distinction in Terminology

The term "dissecting aortic aneurysm" is often used incorrectly and should be reserved only for cases where a dissection occurs within an already aneurysmal aorta. 1 These are two separate entities:

• An aneurysm may exist without dissection 1
• A dissection may occur without an aneurysm being present 1, 2
• When both coexist, the risk of aortic rupture increases significantly in both proximal and distal segments 4

Management Implications

Aortic Aneurysm

• Surveillance imaging at regular intervals based on size and growth rate 1
• Elective surgical repair typically recommended at 5.5 cm for ascending thoracic aneurysms 1
• Medical management focuses on blood pressure control and risk factor modification 1

Aortic Dissection

• Urgent surgical consultation required immediately upon diagnosis or high suspicion 2
• Type A dissections (involving ascending aorta) require emergency surgery 2, 5
• Type B dissections (not involving ascending aorta) are managed medically unless complications develop 2, 5
• Immediate medical management targets heart rate ≤60 bpm and systolic blood pressure <120 mmHg 2

Common Pitfall to Avoid

Do not assume that all aortic pathology involves both aneurysm and dissection. These are distinct processes with different pathophysiology, natural history, and treatment approaches. A patient can have a large aneurysm without dissection, or an acute dissection in a normal-caliber aorta. 1