Aortic dissection happens when a tear forms in the inner layer of the aorta, the body’s largest blood vessel, allowing blood to force its way between the layers of the vessel wall. About 5 people per 100,000 experience one each year, and hypertension is the single biggest driver, accounting for an estimated 53% to 58% of all cases. The causes range from long-term conditions like high blood pressure and genetic disorders to sudden triggers like cocaine use or extreme physical exertion.
How the Aortic Wall Tears Apart
The aorta has three layers: an inner lining, a thick muscular middle layer, and a tough outer shell. A dissection typically starts as a small tear in the inner lining. Blood under high pressure rushes through that tear and splits the middle layer apart, creating a second channel called a false lumen. A thin flap of tissue now separates the normal blood flow path from this new, abnormal one.
That flap can extend in either direction along the aorta, sometimes propagating within minutes. If the blood in the false channel breaks back into the true channel further downstream, it creates additional openings. If it instead ruptures outward through the remaining outer wall, the result is a complete aortic rupture, which is often fatal. In some cases, the process works in reverse: a small bleed within the wall itself weakens the middle layer first, and the inner lining tears open afterward.
High Blood Pressure: The Leading Cause
Between 67% and 77% of people who develop an aortic dissection have hypertension. The mechanism is straightforward: chronically elevated blood pressure batters the aortic wall with every heartbeat, gradually weakening its structure. Over years, this stress can also cause the ascending aorta to widen. Once the aorta dilates beyond about 4.5 centimeters in diameter, the risk of dissection climbs sharply, because a wider vessel means thinner walls under even greater tension.
Population-level data from large studies in Japan and the UK estimate that if hypertension were eliminated entirely, more than half of all aortic dissections would never occur. That makes blood pressure control the single most impactful preventive measure for this condition.
Genetic and Connective Tissue Disorders
Inherited conditions account for roughly 14% to 22% of thoracic aortic dissections. These disorders weaken the structural proteins that give the aortic wall its strength and flexibility.
Marfan syndrome is the most common genetic cause, responsible for about 5% of all aortic dissections and the leading cause in people under 40. It results from a mutation affecting fibrillin, a protein essential for connective tissue. The aortic wall in people with Marfan syndrome shows loss of smooth muscle cells, disorganized elastic fibers, and excess collagen, all of which make the wall prone to splitting.
Loeys-Dietz syndrome is rarer but more aggressive. It disrupts a signaling pathway involved in blood vessel maintenance, leading to weakened elastic fibers, aortic dilation, and dissection at younger ages than Marfan syndrome. Aortic root enlargement has been reported in children as young as six.
Vascular Ehlers-Danlos syndrome (the vascular type, previously called type IV) involves a mutation in the gene for type III collagen. Unlike other forms of the condition, the vascular type carries a high risk of spontaneous aortic tears and arterial rupture. Dissection can occur without the aorta being significantly enlarged beforehand, making it harder to predict and screen for.
Some lesser-known genetic variants also carry risk. Mutations in genes like ACTA2 can cause dissection at aortic diameters below 4.5 centimeters, which falls under the threshold that would normally trigger concern. People with PRKG1 mutations can present with dissections in their late teens. Current guidelines recommend genetic testing for anyone with an aortic aneurysm or dissection, along with screening of their first-degree relatives.
Bicuspid Aortic Valve
A bicuspid aortic valve, where two of the valve’s three leaflets are fused together, is the most common congenital heart defect, present in roughly 1% to 2% of the population. It accounts for up to 15% of aortic dissections. The valve abnormality itself isn’t what causes the tear. Rather, the same developmental issue that produces the abnormal valve also weakens the aortic wall, making it prone to dilation and dissection over time.
The risk tracks closely with aortic size. Dissection probability starts climbing meaningfully once the ascending aorta reaches about 5.0 centimeters in diameter. Preventive surgical replacement of the ascending aorta is typically considered at that threshold for people with bicuspid valves, particularly at specialized centers. Current guidelines also recommend that all first-degree relatives of someone with a bicuspid valve and a dilated aorta be screened with imaging.
Cocaine and Stimulant Drugs
Cocaine is a potent vasoconstrictor, meaning it causes blood vessels to clamp down and blood pressure to spike dramatically within minutes. That sudden surge in pressure generates intense shear stress on the inner aortic wall, enough to initiate a tear. The combination of an abrupt blood pressure spike and direct vascular toxicity makes cocaine one of the most dangerous acute triggers for dissection, particularly in younger people who might not have other risk factors.
Other stimulant drugs that raise blood pressure and heart rate rapidly carry similar risks, though cocaine is the best documented in clinical literature.
Extreme Physical Exertion
Heavy weightlifting and similar intense activities have been linked to acute aortic dissection, particularly when they involve straining against a closed airway (the kind of breath-holding grunt common during a heavy lift). This dramatically increases pressure inside the chest and, by extension, on the aortic wall.
A review of 31 cases of exertion-related dissection found that nearly all occurred in men, with an average age of 47 and a mean aortic diameter of 4.63 centimeters. That diameter is mildly enlarged but not large enough to have triggered surgical intervention under standard guidelines. Only about 10% had a family history of aortic disease. The mortality rate was 32%, though those who reached surgery had an 83% survival rate. The takeaway is that even moderate, undiagnosed aortic enlargement can make the aorta vulnerable during moments of extreme exertion.
Inflammatory Conditions
Chronic inflammation of the aorta, called aortitis, can weaken the vessel wall and set the stage for dissection. Several autoimmune and inflammatory conditions are known to cause aortitis, with giant cell arteritis and Takayasu arteritis being the two most commonly implicated. Both primarily affect the aorta and its major branches, causing thickening, scarring, and eventual weakening of the wall.
Other inflammatory conditions linked to aortitis include Behçet disease, lupus, rheumatoid arthritis, ankylosing spondylitis, and sarcoidosis. The inflammatory damage can lead to aneurysm formation, narrowing, or both, and any of these changes raise the risk of eventual tearing.
Pregnancy
Women with pre-existing aortic conditions face an elevated dissection risk during and shortly after pregnancy. Hormonal changes alter the structure of connective tissue in the vessel wall, while the increased blood volume and cardiac output of pregnancy place additional mechanical stress on the aorta. Most pregnancy-related dissections occur in the third trimester or within the first 12 weeks after delivery. Women with known aortic enlargement, Marfan syndrome, or other connective tissue disorders are monitored with aortic imaging throughout pregnancy and into the postpartum period.
Type A vs. Type B: Location Matters
Aortic dissections are classified by where they occur because location determines both the danger and the treatment approach. The Stanford system divides them into two types. Type A involves the ascending aorta (the section closest to the heart) and is the more dangerous form, occurring at an estimated rate of 3.0 per 100,000 people per year. Type B is limited to the descending aorta, occurring at about 1.6 per 100,000 per year.
Type A dissections almost always require emergency surgery because they can quickly compromise blood flow to the heart, brain, or both. Type B dissections are more often managed with blood pressure control and close monitoring, though some require intervention. In-hospital death rates reflect this difference: roughly 1.0 per 100,000 per year for Type A versus 0.3 per 100,000 for Type B.