Aortic Dissection

Overview
  • Aortic Dissection is the result of dissection of blood between or potentially through the layers of the vascular wall. In most cases this is a catastrophic illness and results in a medical emergency or death.
Etiology
  • Overview
    • The ultimate cause of Aortic Dissection is a structural weakening of the vascular wall, especially the tunica media. Consequently, disease processes which result in vascular weakening increase the risk of dissection incidence whereas others which cause inflammatory scarring within the wall tend to reduce the incidence.
  • Inducers
    • Chronic hypertension is a clear risk factor especially among elderly men between (60-70yo)
    • Marfan Syndrome is a clear risk factor and tends to result in dissections among younger patients
  • Protectors
Pathology
  • Overview
    • The pathological basis for the medial weakening which predisposes vasculature to dissection is still being understood. In the case of Marfan Syndrome, the morphological phenomenon of "Cystic Medial Degeneration (CMD)" is thought to be the causative pathology. Mild CMD is also seen in some hypertensive patients; however, in many cases there is no obvious preexisting pathological basis for aortic weakening in hypertensive individuals.
  • Cystic Medial Degeneration (CMD)
    • Recall that the tunica media of elastic arteries like the aorta are composed of alternative elastic and collagenous layers (See: Arterial Histology). CMD is characterized by degeneration and fragmentation of these layers along with the development of small, cystic spaces between them. These morphological phenomenon likely represent significant weakening of the aortic tunica media, thus predisposing patients to dissections.
Pathogenesis
  • Initiation
    • Aortic Dissections are ultimately initiated by tears of the tunica intima and dissection of blood into the tunica media. Dissections usually begin in the ascending aorta, where sheer stress is the highest, or in the descending thoracic aorta. Once dissection occurs, it often spreads through the aortic layers either proximally, distally, or both.
  • Spread
    • Proximal spread can result in involvement of the aortic root and thus initiate dysfunction of the aortic valve. Distal spread can extend up to the iliac or femoral arteries. In some cases distally dissected blood can re-dissect back through the tunica intima creating a second vascular channel for flow of blood, termed a "Double-barrel Aorta".
Classification
  • Type A: Type A tears involve the ascending aorta regardless of their point of origin and may or may not involve the descending aorta
  • Type B: Type B tears involve only the descending aorta and do not involve any part of the ascending aorta
Clinical Consequences
  • Overview
    • The initial symptoms of aortic dissection are intense chest pain which often radiates to the back and moves downward if the dissection progresses through the descending aorta. Depending on how the dissection evolves the clinical consequences can vary.
  • Rupture
    • Rupture of the dissection through the remaining layers of the aorta results in major hemorrhage and is the most common cause of death
    • Ruptures into the intrapleural space can cause hemothorax
    • Ruptures into the pericardium can result in hemopericardium and cardiac tamponade
    • Ruptures into the peritoneum can cause hemoperitoneum
  • Extension
    • Extension into aortic root can result in aortic regurgitation
    • Extension into coronary arteries can result in myocardial infarction
    • Extension into the carotid arteries can result in stroke
    • Extension into the subclavian artery can result in diminished peripheral pulses
A Magnetic Resonance Angiogram of a Stanford Type B Aortic Dissection. Source: Radiopedia