Acute aortic syndrome: aortic dissection and related emergencies explained

What is acute aortic syndrome?

Acute aortic syndrome (AAS) is not a single condition but a family of three related emergencies, all of which involve a disruption to the layers of the aortic wall. They share similar symptoms and require urgent hospital assessment, but they differ in their anatomy, natural history and treatment.

All three conditions are potentially life-threatening. They are most common in older adults with high blood pressure, atherosclerosis or connective tissue disorders. Aortic dissection is the most immediately dangerous and is the focus of this guide, with the other two conditions covered in detail below.

Aortic dissection: what happens inside the aorta

The aortic wall has three layers: the intima (inner), media (middle) and adventitia (outer). In an aortic dissection, a tear forms in the intima. Blood under arterial pressure forces its way through this tear and drives between the layers of the wall, splitting them apart as it travels. The split creates a new channel, called the false lumen, running alongside the original channel, the true lumen.

As the dissection extends, it can block the openings of arteries that branch off the aorta, cutting off blood supply to the kidneys, gut, spinal cord, arms or legs. This is called malperfusion and is one of the most serious complications. The outer wall of the aorta may also rupture, which is almost always fatal.

Classification: Type A and Type B

The most widely used classification system divides aortic dissections into two types based on whether the ascending aorta (the part closest to the heart) is involved. This distinction is critical because it determines whether emergency surgery is needed immediately.

The ESC 2024 guidelines introduced a new classification system called TEM, which adds detail about the localisation of the Entry tear and the presence of Malperfusion alongside the Type. This allows more precise risk stratification and guides treatment decisions for borderline cases.

Symptoms: what to look for

The hallmark symptom of aortic dissection is pain that is different from any pain the person has experienced before. Key features include:

• Onset: sudden and reaching maximum intensity almost instantaneously, sometimes described as "the worst pain of my life"
• Character: tearing, ripping or stabbing, often described as a sensation of something tearing apart inside the chest or back
• Location: anterior chest pain is more common with Type A; interscapular back pain is more common with Type B. Pain may migrate as the dissection extends
• Associated features: sweating, feeling faint, nausea, or a sense of impending doom

Aortic dissection can also present with features that mimic other conditions, which is one reason it is sometimes initially misdiagnosed. These include stroke-like symptoms (if the carotid arteries are involved), heart attack-like symptoms (if the coronary arteries are affected), pulse deficits (a difference in pulse or blood pressure between the two arms or legs), and sudden onset of aortic regurgitation (a heart murmur causing breathlessness).

Diagnosis

In the emergency setting, diagnosis is made with a CT angiogram of the chest, abdomen and pelvis with contrast. Modern CT scanners can image the entire aorta in under a minute and will show the intimal flap, the extent of the dissection, involvement of branch vessels, and any signs of rupture or pericardial bleeding.

The ESC 2024 guidelines recommend a structured approach called the aortic dissection detection risk score (ADD-RS), which assesses high-risk conditions (such as Marfan syndrome or known aortic disease), high-risk pain features (sudden onset, tearing character), and high-risk examination features (pulse deficit, blood pressure difference between arms, aortic regurgitation murmur). A high score prompts immediate CT imaging.

A chest X-ray may show a widened mediastinum (the shadow of the aorta appears enlarged), but a normal chest X-ray does not exclude dissection. Blood tests including D-dimer, troponin and full blood count are taken but are not diagnostic alone.

Emergency treatment: Type A dissection

Treatment: Type B dissection

Intramural haematoma (IMH)

Intramural haematoma occurs when small blood vessels within the aortic wall (the vasa vasorum) rupture, causing bleeding within the media layer without a visible tear in the intima. On CT scan, it appears as a crescent-shaped or circumferential thickening of the aortic wall without contrast enhancement (because blood cannot flow into the haematoma from outside).

IMH carries a significant risk of progression to classical dissection (approximately 28 to 47%) or rupture (up to 45% in some series). Management follows the same Type A / Type B logic as dissection:

• Type A IMH: emergency surgery is recommended. Untreated Type A IMH has a medical mortality of approximately 40 to 56%. The operation is similar to Type A dissection repair
• Type B IMH: initially managed medically with strict blood pressure control. Close imaging surveillance is essential. TEVAR is indicated if the haematoma progresses, the aortic diameter increases beyond 50 mm, wall thickness exceeds 11 mm, or a penetrating ulcer develops within the haematoma

Some Type B IMH cases resolve spontaneously with medical treatment alone. This is more likely in patients with a smaller initial aortic diameter and thinner haematoma. Long-term surveillance imaging is required regardless of initial outcome, as a proportion develop aneurysmal dilatation of the affected segment over years.

Penetrating atherosclerotic ulcer (PAU)

A penetrating atherosclerotic ulcer forms when a plaque in the aortic wall erodes through the intima and penetrates into the media or beyond. PAU most commonly affects the descending thoracic aorta in older patients with extensive atherosclerosis. On CT, it appears as a contrast-filled crater projecting into the aortic wall.

PAU can be an incidental finding on a scan done for another reason, or it can present acutely with pain similar to dissection. Management depends on symptoms and imaging features:

• Asymptomatic PAU: surveillance with regular CT imaging is generally appropriate, with intervention reserved for growth or development of symptoms
• Symptomatic PAU: TEVAR is the preferred treatment. TEVAR for PAU has a 30-day mortality of approximately 5% in published series, with 1-year survival around 91% at specialist centres
• Intervention thresholds: ESC and international guidelines suggest considering TEVAR for asymptomatic PAU with a ulcer diameter above 20 mm, a neck deeper than 10 mm, or associated periaortic haematoma or pleural effusion

Chronic aortic dissection: long-term management

Any aortic dissection that persists beyond 30 days is classified as chronic. Many patients who survive a Type B dissection will have a false lumen that remains at least partially open for months or years after the acute event. This is not immediately dangerous, but it requires lifelong surveillance.

The main risk of chronic dissection is progressive dilatation. Over years, the weakened outer wall of the false lumen can expand, eventually creating a chronic thoracoabdominal aortic aneurysm. If the aorta reaches a diameter of 5.5 to 6 cm, TEVAR or open surgery is typically considered.

All patients with a history of aortic dissection, whether treated initially with surgery, TEVAR or medical management alone, require:

• Lifelong antihypertensive medication to keep blood pressure below 130/80 mmHg
• Regular CT angiography surveillance, typically at 1, 3, 6 and 12 months after the acute event, and then annually if stable
• Genetic counselling if a connective tissue disorder is suspected
• Counselling to avoid strenuous isometric exercise (such as heavy weightlifting) and contact sports
• Prompt reporting of any new or changing chest, back or abdominal pain to their medical team

Risk factors and prevention

The most important modifiable risk factor for all forms of acute aortic syndrome is uncontrolled high blood pressure. Long-term hypertension is present in the majority of patients with dissection. Treating blood pressure consistently and effectively is the single most important thing that can reduce the risk of an acute aortic event.

Other important risk factors include:

• Connective tissue disorders: Marfan syndrome, Loeys-Dietz syndrome and Ehlers-Danlos syndrome predispose to dissection, often at a younger age and at smaller aortic diameters. Anyone with a confirmed or suspected connective tissue disorder should have regular aortic surveillance imaging and be under the care of a specialist
• Bicuspid aortic valve: present in approximately 1 to 2% of the population and associated with aortic dilatation and increased dissection risk
• Known aortic aneurysm: a pre-existing aneurysm significantly increases the risk of dissection
• Smoking: increases the risk of atherosclerosis and aortic wall disease
• Cocaine and amphetamine use: cause extreme acute hypertension and have been associated with aortic dissection, particularly in younger people
• Family history: a first-degree relative with aortic dissection or aneurysm warrants imaging surveillance

What to do next

If you or a family member have survived an aortic dissection and want to understand your follow-up plan, or if you have risk factors for aortic disease and want a specialist assessment, a private vascular consultation can provide a prompt and thorough review. This includes assessment of surveillance imaging, blood pressure management and an honest discussion of long-term risk.

If you have a family history of aortic dissection or a known connective tissue disorder, speak to your GP about referral for aortic screening. Early identification of aortic dilatation allows intervention before an acute event occurs.