Classification

Dissections are classified by their location of origin and how far along they extend in the aorta. There are two important classification systems of dissection, the DeBakey and Stanford classifications (Table 1; Fig. 3). Dissections are also classified by their duration. Acute dissections are those of less than 2 weeks’ duration after the onset of symptoms; chronic dissections are those that have been present for longer than 2 weeks.

Table 1 Classification of Aortic Dissections

Figure 3 The DeBakey (A) and Stanford (B) classification systems of aortic dissection.

Signs and Symptoms

Dissections typically manifest between the fifth and seventh decades of life, with a male preponderance. Patients typically present with the acute onset of pain, which occurs in up to 96% of cases. Pain is often most severe at its onset and described as a tearing, ripping, or stabbing sensation. Often, the pain is migratory, a crucial component of the history, reflecting propagation of the dissection. Involvement of the ascending aorta results in anterior chest or neck pain, with intrascapular or subscapular pain from involvement of the descending thoracic aorta, and lower back and left flank pain from thoracoabdominal aortic involvement. Hypertension on presentation is common, more so in distal dissection, although hypotension can be seen if complications have developed, particularly in proximal dissections. The dissection may compromise flow to the great vessels and lead to pulse deficits; these can be transient, because the dissection flap can oscillate. Actual blood pressure may not be appreciated if the arm used has compromise of the brachial circulation (pseudohypotension).

If the dissection involves the aortic root, commissural involvement of the aortic valve can lead to aortic regurgitation. Dilation of the root and aortic annulus, without leaflet involvement, can also lead to aortic valve regurgitation. A diastolic murmur is evident in these cases. Dissections can involve the ostia of the coronary arteries, resulting in acute myocardial ischemia and infarction (2%-3% of cases). The right coronary artery ostium is more commonly affected than the left main. The dissection can extend proximally into the pericardial space, resulting in pericardial effusion and tamponade, a common mechanism of syncope and hypotension in dissection. A pericardial friction rub can be a clue to the presence of hemopericardium. Rupture into the pericardial space represents the most common mode of death in patients with aortic dissection. Acute lower extremity, renal, or mesenteric ischemia can be seen in descending aortic dissections. Focal neurologic deficits can occur with involvement of the great vessels. Compromise of spinal artery perfusion may result in paraparesis. Whereas chest pain and pulse deficits are usually described, it is important to recognize that less than 20% of patients present with these findings. Therefore, a high clinical suspicion for dissection is paramount.

Diagnostic Testing

The chest radiograph may be normal in cases of dissection. A well-recognized finding is mediastinal widening, present in about 60% of cases. Rupture into the pleural or pericardial space manifests as pleural effusions or an enlarged cardiac silhouette; the latter may also be present because of chronic aortic regurgitation. The electrocardiogram can be normal but often shows nonspecific ST-T wave changes. Involvement of the coronary artery ostia can result in ST-segment elevation, representing an acute myocardial injury pattern. Transthoracic echocardiography can on occasion identify a proximal or even distal dissection flap. Even if a flap is not seen, the presence of aortic dilation, aortic regurgitation, or an unexplained pericardial effusion can be important clues in the diagnostic consideration of dissection in a patient with chest pain. More definitive diagnostic modalities include transesophageal echocardiography (TEE), computed tomography (CT), and magnetic resonance angiography (MRA; Fig. 4). Each has relative advantages and disadvantages, but all have excellent sensitivity and specificity (Table 2).

Figure 4 Magnetic resonance angiography of a large ascending aortic aneurysm with a proximal (type A) dissection.

There is a dissection flap extending from the aortic sinuses to the arch.

Table 2 Comparison of Imaging Modalities for Aortic Dissection

Angiography is less commonly used for the primary diagnosis of aortic dissection. The choice of test is often dependent on expedited availability and expertise at the center in which the patient is evaluated. An important caveat is that in most patients, more than one test may be required. If clinical suspicion is high enough and the initial test is negative or equivocal, consideration should be given to performing another confirmatory test.