Residency · Residency · Vascular Surgery

Acute Aortic Syndromes: Dissection, Intramural Hematoma, and Penetrating Ulcer

Overview

Acute aortic syndromes (AAS) represent a group of emergency conditions affecting the aorta, including aortic dissection, intramural hematoma (IMH), and penetrating atherosclerotic ulcer (PAU). These conditions share several key features: they typically present with an acute onset of severe pain, involve disruption of the aortic wall, and carry a risk of rupture or malperfusion. The combined incidence of these syndromes is approximately 30 to 40 cases per million people per year. Prompt diagnosis and management are crucial, as mortality for untreated type A aortic dissection increases by 1 to 2 percent per hour.

Aortic Dissection

Pathophysiology

Aortic dissection begins with a tear in the intimal layer of the aorta, allowing blood to enter the media and create a false lumen. This false lumen can propagate distally along the aorta and sometimes proximally as well. The true lumen may become compressed by the expanding false lumen, leading to malperfusion of branch vessels. The initial site of intimal disruption is called the entry tear, while re-entry tears are additional points where the true and false lumens communicate.

Classification Systems

The Stanford classification is the most commonly used system. It divides dissections into two types: Type A involves the ascending aorta regardless of the site of origin and requires emergency open cardiac surgery. Type B involves only the descending aorta distal to the left subclavian artery and is primarily managed by vascular surgery.

The DeBakey classification further subdivides dissections into three types: Type I originates in the ascending aorta and propagates to the descending aorta; Type II is confined to the ascending aorta; and Type III originates in the descending aorta, with IIIa limited to the thoracic aorta and IIIb extending below the diaphragm.

Risk Factors

Hypertension is the most important modifiable risk factor, present in 70 to 80 percent of cases. Connective tissue disorders such as Marfan syndrome, Ehlers-Danlos type IV, and Loeys-Dietz syndrome increase susceptibility. A bicuspid aortic valve is associated with ascending aortic dissection. Other risk factors include pre-existing aortic aneurysm, prior cardiac or aortic surgery, cocaine use, pregnancy—especially in the third trimester—and iatrogenic causes such as catheterization, cardiac surgery, or thoracic endovascular aortic repair (TEVAR).

Clinical Presentation

Patients typically present with severe, sudden-onset chest or back pain described as "tearing" or "ripping." Type A dissections usually cause anterior chest pain, while Type B dissections cause interscapular back pain. The pain may migrate as the dissection propagates. Hypertension is the most common hemodynamic finding, but hypotension may occur and suggests complications such as rupture, cardiac tamponade, or severe malperfusion. Pulse deficits occur in 15 to 30 percent of cases. An aortic regurgitation murmur may be heard in Type A dissections. Various malperfusion syndromes can develop depending on which branch vessels are involved.

Malperfusion Syndromes

Malperfusion can affect multiple organ systems. Coronary artery involvement, usually of the right coronary artery, can cause myocardial infarction, typically an inferior MI. Cerebral malperfusion may result in stroke due to carotid artery involvement. Spinal cord ischemia can cause paraplegia. Mesenteric ischemia leads to bowel ischemia, while renal malperfusion causes acute kidney injury and refractory hypertension. Extremity ischemia manifests as acute limb ischemia.

<image>Diagram of Stanford and DeBakey classification systems for aortic dissection showing the aorta from root to bifurcation, with colored zones indicating Type A/B (Stanford) and Types I, II, III (DeBakey), and arrows showing dissection flap propagation and common malperfusion territories</image>

Diagnosis

Computed tomography angiography (CTA) is the gold standard for diagnosing aortic dissection, with sensitivity and specificity exceeding 95 percent. CTA reveals the intimal flap, distinguishes the true and false lumens, defines the extent of dissection, and assesses branch vessel involvement, malperfusion, and rupture. Transesophageal echocardiography (TEE) is useful in unstable patients who cannot undergo CT and provides excellent visualization of the ascending aorta. Magnetic resonance angiography (MRA) is highly accurate but impractical in emergency settings. D-dimer levels are elevated in nearly all acute dissections, and a normal D-dimer has a high negative predictive value. Chest X-ray may show a widened mediastinum but is only 60 to 70 percent sensitive.

Type B Aortic Dissection Management

Uncomplicated Type B Dissection

Medical management is the cornerstone of treatment for uncomplicated type B dissections. The primary goal is anti-impulse therapy, which reduces the rate of rise of aortic pressure (dP/dt). Intravenous beta-blockers such as esmolol or labetalol are first-line agents, targeting a heart rate below 60 beats per minute and systolic blood pressure between 100 and 120 mmHg. If blood pressure remains uncontrolled with beta-blockers alone, vasodilators like nitroprusside or nicardipine may be added, but vasodilators should never be given before beta-blockers because reflex tachycardia can worsen the dissection. Pain control with intravenous morphine or fentanyl is essential, as pain drives sympathetic activation. Patients require intensive care unit monitoring. With optimal medical therapy, in-hospital mortality ranges from 5 to 10 percent. Long-term management includes oral antihypertensives and serial imaging with CTA at 1, 3, 6, and 12 months, then annually.

Complicated Type B Dissection

Complicated type B dissections are defined by the presence of malperfusion (visceral, renal, or limb), rupture or impending rupture, refractory pain despite optimal medical therapy, rapid aortic expansion greater than 4 mm in the acute phase, or refractory hypertension. Thoracic endovascular aortic repair (TEVAR) is the primary treatment for these cases. TEVAR covers the primary entry tear, redirecting blood flow into the true lumen, promoting false lumen thrombosis, and facilitating aortic remodeling. Malperfusion often resolves after coverage of the entry tear, but additional procedures such as branch vessel stenting or fenestration may be required. Despite treatment, mortality for complicated type B dissections remains high at 20 to 30 percent.

Preemptive TEVAR for Uncomplicated Type B Dissection

The INSTEAD-XL trial compared TEVAR plus best medical therapy (BMT) to BMT alone in uncomplicated type B dissections. At five years, TEVAR plus BMT improved aorta-specific survival and delayed disease progression, although no overall mortality benefit was seen at two years. The ADSORB trial demonstrated improved false lumen thrombosis and aortic remodeling with TEVAR. There is ongoing debate about whether uncomplicated type B dissections should be treated with TEVAR during the subacute phase (2 to 6 weeks) to prevent late aneurysmal degeneration. Proponents argue that TEVAR prevents late dilation and promotes remodeling, while opponents note that medical therapy is effective in most patients and that TEVAR carries procedural risks. The current trend favors preemptive TEVAR in selected patients, particularly younger individuals with a large false lumen, partial thrombosis, or anatomy favorable for remodeling.

<image>CT angiography of acute type B aortic dissection in axial and sagittal views showing the intimal flap separating the true lumen (smaller, anterolateral) from the false lumen (larger, posterolateral), with annotations indicating the entry tear site distal to the left subclavian artery and branch vessel origins from each lumen</image>

Intramural Hematoma (IMH)

Definition

Intramural hematoma is characterized by hemorrhage within the aortic media without an identifiable intimal tear or flow in a false lumen. It may result from rupture of the vasa vasorum within the aortic wall. Many consider IMH to be a precursor or variant of classic aortic dissection.

Diagnosis

On CTA, IMH appears as a crescent-shaped thickening of the aortic wall greater than 5 mm without flow in the thickened region. Non-contrast CT shows a hyperdense crescent corresponding to acute blood. Contrast-enhanced images lack an intimal flap or false lumen flow. MRI demonstrates a T1-weighted hyperintense signal in the wall due to methemoglobin.

Classification and Management

Type A IMH, involving the ascending aorta, requires emergent surgical repair similar to type A dissection because 30 to 40 percent progress to dissection or rupture if untreated. Type B IMH, involving the descending aorta, is initially managed medically. Most cases resolve with medical therapy as the hematoma resorbs, but some progress to classic dissection, PAU, or aneurysm formation. Complications such as rupture or progression warrant TEVAR or surgery. Serial imaging is essential; regression is a favorable sign, while progression or development of PAU indicates the need for intervention.

Penetrating Atherosclerotic Ulcer (PAU)

Definition

PAU is an ulceration of an atherosclerotic plaque that penetrates through the internal elastic lamina into the media. It typically occurs in elderly, hypertensive patients with extensive atherosclerosis and is most common in the mid-to-distal descending thoracic aorta.

Natural History

PAUs can lead to intramural hematoma, pseudoaneurysm formation, limited aortic dissection that usually does not propagate extensively, and aortic rupture. They are more prone to rupture than classic dissections, with rupture rates between 10 and 40 percent.

Diagnosis

CTA reveals a crater-like outpouching in the aortic wall, often accompanied by an associated intramural hematoma. The aorta is often heavily calcified, with focal contrast collection beyond the expected lumen.

Management

Asymptomatic, small PAUs are managed medically with surveillance. Symptomatic, enlarging, or complicated PAUs are treated with TEVAR, which is often feasible due to the focal nature of the lesion allowing for a short endograft. PAU-associated pseudoaneurysms also require TEVAR. Open surgical repair is reserved for cases with anatomy unsuitable for endovascular treatment.

Chronic Aortic Dissection

Chronic aortic dissection is defined as dissection present more than 14 days after onset. The false lumen may thrombose completely, which is favorable, or remain patent with ongoing perfusion through re-entry tears. It may also undergo aneurysmal degeneration, which is an indication for repair when the aortic diameter reaches 5.5 to 6.0 cm. Surveillance with serial CTA every 6 to 12 months is standard. Late interventions, including TEVAR or open repair, are performed for aneurysmal degeneration, malperfusion, or progressive expansion.

Clinical Pearls

It is essential to initiate beta-blockers before administering vasodilators because isolated vasodilation can cause reflex tachycardia, which worsens the dissection. Type B dissections complicated by malperfusion require intervention, typically TEVAR. A normal D-dimer level effectively rules out acute aortic dissection due to its high negative predictive value. Intramural hematoma should not be dismissed as benign since it can progress to classic dissection. Penetrating atherosclerotic ulcers are more prone to rupture than classic dissections, especially in the descending aorta. The use of preemptive TEVAR for uncomplicated type B dissection is an evolving approach, with careful patient selection being crucial. In type B dissection, the goal of TEVAR is to cover the primary entry tear, promote expansion of the true lumen, and achieve thrombosis of the false lumen.

References

• Erbel R, et al. 2014 ESC Guidelines on the Diagnosis and Treatment of Aortic Diseases. Eur Heart J. 2014;35(41):2873-2926.
• Nienaber CA, et al. Randomized comparison of strategies for type B aortic dissection: the INSTEAD-XL trial. Circulation. 2013;127(24):2369-2376.
• Brunkwall J, et al. Acute onset non-A non-B aortic dissection: the ADSORB trial. Eur J Vasc Endovasc Surg. 2012;44(1):31-36.
• Evangelista A, et al. Intramural hematoma of the aorta. Lancet. 2023;401:735-748.
• Nathan S, et al. Penetrating atherosclerotic ulcers of the thoracic aorta. J Vasc Surg. 2021;73(1):282-290.

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