Aortic dissection pathophysiology

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Aortic dissection Microchapters

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Case #1


Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2] Sahar Memar Montazerin, M.D.[3]

Overview

Aortic dissection begins as a tear in the aortic wall in > 95% of patients. The tear is usually transverse, extends through the intima and halfway through the media and involves ~50% of the aortic circumference. Two thirds of dissections originate in the ascending aorta, and 20% are in the proximal descending aorta.

Pathophysiology

Normal Anatomy of the Aorta

As with all other arteries, the aorta is made up of three layers. The layer that is in direct contact with the flow of blood is the tunica intima, commonly called the intima. This layer is made up of mainly endothelial cells. Just deep to this layer is the tunica media, known as the media. This middle layer is made up of smooth muscle cells and elastic tissue. The outermost layer (furthest from the flow of blood) is known as the tunica adventitia or the adventitia. This layer is composed of connective tissue.
Blood penetrates the intima and enters the media layer.

Pathogenesis

Initial Intimal Tear

  • Aortic dissection begins as a tear in the aortic wall in > 95% of patients.
  • It is usually transverse, extends through the intima and halfway through the media and involves ~50% of the aortic circumference.

Location of Dissections

Propagation of the Intimal Tear

In an aortic dissection, blood penetrates the intima and enters the media layer. The high pressure rips the tissue of the media apart, allowing more blood to enter. This can propagate along the length of the aorta for a variable distance, dissecting either towards or away from the heart or both.

Once a tear develops, blood then passes into the media, and a false lumen is dissected in the outer layer of aortic media involving ~50% of the aortic circumference. This false lumen can enlarge, and compress the true lumen, as well as extend proximally or distally and occlude aortic branches. For some unknown reason, the right lateral wall of the ascending aorta is the most common site for dissection. The right coronary artery can become occluded as a result of this propagation.

Separating the false lumen from the true lumen is a layer of intimal tissue. This tissue is known as the intimal flap. As blood flows down the false lumen, it may cause secondary tears in the intima. Through these secondary tears, the blood can re-enter the true lumen.

Aortic Dissection in the Absence of an Intimal Tear

In about 13% of aortic dissections, there is no evidence of an intimal tear. It is believed that in these cases the inciting event is an intramural hematoma (caused by hemorrhage within the media). Since there is no direct connection between the true lumen and the false lumen in these cases, it is difficult to diagnose an aortic dissection by aortography if the etiology is an intramural hematoma. An aortic dissection secondary to an intramural hematoma should be treated the same as one caused by an intimal tear.

An aortic intramural hematoma can form when the vasa vasorum ruptures into the aortic wall. This is distinguished from dissection by the lack of an intimal tear. This disorder parallels aortic dissection in terms of prognosis when the ascending aorta or aortic arch is involved, and rapid surgical intervention is indicated. Involvement of the descending aorta, however, carries a better prognosis than dissection, and outcome tends to be similar with medical or surgical therapy.

Genetics

Genes involved in the pathogenesis of aortic dissection include:[1][2]

Associated Conditions

Conditions associated with aortic dissection include:[1]

Gross Pathology

Images shown below are courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology

  • Dissecting Aneurysm: Gross very good example dissected channel has been opened.
    Dissecting Aneurysm: Gross very good example dissected channel has been opened.
  • Dissecting Aneurysm: Gross external view good appearance from adventitia.
    Dissecting Aneurysm: Gross external view good appearance from adventitia.
  • Dissecting Aneurysm: Gross opened false channel.
    Dissecting Aneurysm: Gross opened false channel.

Microscopic Pathology

[3]

References

  1. ↑ 1.0 1.1 Pinard, Amélie; Jones, Gregory T.; Milewicz, Dianna M. (2019). "Genetics of Thoracic and Abdominal Aortic Diseases". Circulation Research. 124 (4): 588–606. doi:10.1161/CIRCRESAHA.118.312436. ISSN 0009-7330.
  2. ↑ Verhagen, Judith M.A.; Kempers, Marlies; Cozijnsen, Luc; Bouma, Berto J.; Duijnhouwer, Anthonie L.; Post, Jan G.; Hilhorst-Hofstee, Yvonne; Bekkers, Sebastiaan C.A.M.; Kerstjens-Frederikse, Wilhelmina S.; van Brakel, Thomas J.; Lambermon, Eric; Wessels, Marja W.; Loeys, Bart L.; Roos-Hesselink, Jolien W.; van de Laar, Ingrid M.B.H. (2018). "Expert consensus recommendations on the cardiogenetic care for patients with thoracic aortic disease and their first-degree relatives". International Journal of Cardiology. 258: 243–248. doi:10.1016/j.ijcard.2018.01.145. ISSN 0167-5273.
  3. ↑ Case courtesy of Wikimedia Commons

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