Aortic Dissection

Aortic dissection is a tear in the inner layer of the aortic wall that allows pulsatile blood to enter and split the layers of the media, creating a second, false channel within the wall. It is an acute, life-threatening condition: the false lumen can extend along the aorta, occlude branch vessels and cause organ malperfusion, rupture into surrounding spaces, or extend into the aortic root and the pericardium. Classification by the anatomical site of involvement underpins how dissection is described and triaged (Nienaber et al., 2016).

Definition

Aortic dissection is the separation of the layers of the aortic wall by blood entering the media through an intimal tear, producing a true and a false lumen along a variable length of the aorta.

Scope

This topic covers the definition, anatomical classification (Stanford and DeBakey systems), mechanisms, presentation patterns, and natural history of acute and chronic aortic dissection. It draws on registry data describing how dissection presents and behaves. It is reference-educational and does not provide individualized diagnostic or treatment recommendations.

Key concepts

• Intimal tear and entry point
• True and false lumen
• Stanford type A and type B
• DeBakey types I, II, and III
• Branch-vessel malperfusion
• Acute versus chronic dissection
• Aortic rupture and tamponade

Mechanisms

Dissection begins when an intimal tear, often arising in a region of medial weakness or high wall stress, allows blood under arterial pressure to enter the media and cleave it longitudinally into true and false lumens. Propagation of the false lumen can shear off the origins of branch vessels and cause static or dynamic obstruction with downstream malperfusion of the brain, viscera, kidneys, or limbs; proximal extension can disrupt the aortic valve or rupture into the pericardium. Hypertension, pre-existing medial degeneration, aneurysm, and heritable connective-tissue disorders are the principal predisposing conditions (Nienaber et al., 2016; Hagan et al., 2000).

Clinical relevance

Aortic dissection is a reference example of an acute aortic syndrome in which anatomical classification governs how the condition is described and risk-stratified. Type A dissection (involving the ascending aorta) and type B dissection (confined to the descending aorta) follow different natural histories, and registry and guideline statements summarise these patterns; such descriptions characterise the evidence and are not a substitute for emergency clinical evaluation, which is time-critical (Hagan et al., 2000; Isselbacher et al., 2022).

Epidemiology

Acute aortic dissection is uncommon relative to other cardiovascular emergencies but carries high early mortality, particularly for ascending (type A) involvement, where untreated risk rises steeply in the first hours and days. The International Registry of Acute Aortic Dissection (IRAD) documented the typical presentation as abrupt, severe chest or back pain in older, frequently hypertensive patients, and characterised the predominance of type A involvement and its outcomes (Hagan et al., 2000). Hypertension is the most common associated condition, and heritable aortopathy accounts for a notable share of younger cases (Nienaber et al., 2016).

History

Surgical and anatomical interest in dissecting aneurysms grew through the twentieth century, and the DeBakey and Stanford classifications, based on the extent and origin of the dissection, became the durable framework for describing the condition. The founding of the International Registry of Acute Aortic Dissection around the turn of the century then provided large-scale data on presentation and outcomes, refining the modern understanding of the disease (Hagan et al., 2000; Nienaber et al., 2016).

Debates

How should uncomplicated type B dissection be characterised and followed?

Whether and when an uncomplicated descending (type B) dissection warrants closer intervention versus surveillance depends on features such as aortic diameter, false-lumen behaviour, and malperfusion, and the optimal stratification remains an area of active evidence synthesis.

Seminal works

• nienaber-2016
• hagan-2000
• isselbacher-2022

Frequently asked questions

What is the difference between Stanford type A and type B dissection?

Type A dissection involves the ascending aorta (regardless of where the tear starts), whereas type B is confined to the aorta beyond the left subclavian artery. The two are classified separately because they tend to follow different natural histories.

Why is aortic dissection considered an emergency?

Blood entering the wall can rapidly extend, block branch arteries, disrupt the aortic valve, or rupture, and early mortality is high, especially when the ascending aorta is involved.