What is an intramural aortic hematoma (Intramural Aortic Hematoma, IMH)?

From the Guidelines

Intramural aortic hematoma (IMH) is a condition where a hematoma develops in the media of the aortic wall in the absence of an intimal tear or false lumen.

Definition and Diagnosis

• IMH is diagnosed in the presence of a circular or crescent-shaped thickening of ≥ 7 mm of the aortic wall in the absence of detectable blood flow 1.
• Imaging criteria include crescentic or circular thickening of the aortic wall with maximal thickness greater than or equal to 7 mm on TEE without intimal flap or tear or longitudinal flow in the false lumen 1.
• The thickened wall has a higher tissue density than unenhanced blood on CT and is without enhancement after contrast on the CT/MR 1.

Clinical Presentation and Management

• Clinically, IMH most commonly occurs in the descending aorta and in older patients, with pain being a characteristic symptom 1.
• The natural history of IMH is variable, with the hematoma potentially resolving, converting to a classic dissection, or the aorta enlarging and potentially rupturing 1.
• IMH involving the ascending aorta has a high, early risk of complication and death with medical treatment alone, and surgery is usually indicated 1.
• Medical management of acute ascending IMH is associated with a high mortality rate, and timely diagnosis and treatment are crucial to improve outcomes 1.

Epidemiology and Risk Factors

• IMH occurs with approximately 10% of the frequency of aortic dissection, and can be seen in isolation or in conjunction with aortic dissection and penetrating aortic ulcer 1.
• Risk factors for IMH include hypertension, family history, and underlying collagen vascular disorders 1.
• The annual incidence of acute aortic syndrome, which includes IMH, is 2 to 4 cases/100,000, with higher prevalence in patients with genetic conditions that weaken the aortic wall 1.

From the Research

Definition and Characteristics of Intramural Aortic Hematoma (IMH)

• Intramural hematoma (IMH) is one of the acute aortic syndromes, originally noted as an 'aortic dissection without intimal tear' 2.
• IMH is characterized by bleeding into the media of the aortic wall without intimal disruption or the classic flap formation 3.
• It appears as an area of hyperattenuating crescentic thickening in the aortic wall that is best seen at nonenhanced computed tomography 4.
• The natural history of IMH is highly variable; it may resolve or progress to aneurysm, dissection, or rupture 4, 3.

Pathophysiology and Causes of IMH

• IMH was historically believed to originate from ruptured vasa vasorum in the aortic media without an intimal tear 2, 4.
• However, there are reports of small intimomedial tears identified prospectively at imaging or found at surgery in some cases of IMH, blurring the distinction between aortic dissection and IMH 2, 4.
• IMH may also arise from primary vasa vasorum hemorrhage within the aortic media or rupture of an atherosclerotic plaque 5.

Management and Treatment of IMH

• The management of IMH has been controversial, but guidelines recommend treating IMHs as classical aortic dissections: surgical repairs were indicated for type A IMHs; complicated acute type B IMHs were treated with endovascular or open repairs and uncomplicated type B IMHs were to be managed with antiimpulse therapy and close surveillance 2.
• Type B IMH should be managed with antiimpulse therapy, unless the patient has persistent pain or large ulcer-like projection 2.
• The optimal mode of management of patients with IMH (medical versus medical plus surgical) remains problematic due to the paucity of information available 5.