Aortic Anatomy

 
Objectives
 
At the completion of this chapter the user will be able to:
 
  • Discuss the Normal Anatomy of the Aorta
  • Describe the Echocardiographic Views and Evaluation of the Aorta
  • Discuss the Echocardiographic Findings in Aortic Aneurysm, Dissection and Atherosclerosis
  • Evaluate Other Aortic Diseases
  • Describe Common Artifacts found in Aortic Scans
Introduction
 

Echocardiographic evaluation of the intrathoracic aorta by transesophageal echocardiography has been useful for the rapid and accurate diagnosis of primary or secondary aortic pathology.  The severity and the etiology of the aortic pathology can be quickly diagnosed and treated. 

Almost the entire intrathoracic aorta can be visualized with transesophageal echocardiography whereas transthoracic echocardiography has limited views.  Transthoracic echocardiography permits only limited views of the ascending aorta, the distal descending aorta.  Intraoperatively, epiaortic echocardiography provides a useful complement to transesophageal echocardiography for interrogation of the ascending aorta and proximal aortic arch.

While other diagnostic modalities (MRI, CT) are accurate in defining aortic pathology, diganosis by transesophageal echocardiography may be more efficient and practical to obtain.  In addition to an aortic evaluation, interrogation of the heart for the primary etiology or secondarily effects of the aortic pathology adds to the advantages of transesophageal echocardiography.

Diseases of the Aorta
Atherosclerotic
     Aneurysm
     Athetheroembolic Disease
     Rupture
     Pseudoaneurysm
     Penetrating Ulcer
     Dissection
     Intramural Hematoma
Non-Atheroclerotic
     Cystic Medial Necrosis
     Aneurysm
     Aortic Dissection
     Intramural Hematoma
     Anuloaortic Ectasia
Inflammatory/Infectious
     Takayasu Arteritis
     Giant Cell Arteritis
     Endocarditis
Miscellaneous
     Trauma
     Intraluminal Thrombus
     Poststenotic Dilation
     Hypertension
     Aortic Insufficiency
     Aortic Insufficiency/Stenosis
     Iatrogenic Injury
Normal Anatomy & Function
 
The aorta is the major structure that distributes blood ejected from the aortic valve.  The aorta has six primary segments: aortic annulus, sinuses of Valsalva, sinotubular junction, ascending aorta, aortic arch, descending aorta, and abdominal aorta.  The aortic root consists of the the aortic annulus, the sinuses of Valsalva and the sinotubuluar junction. The aortic annulus forms from the junction of the left ventricular outflow tract and the proximal ascending aorta.  The aortic annulus also forms the annular ring for the aortic valve.  The aortic annulus is part of the fibrous skeleton of the heart and is contiguous with the anterior mitral valve leaflet and perimembranous septum.  The aortic annular diameter is 13 ± 1 mm/M2 and is relatively resistant to dilation. The diameter of the sinuses of valsalva is normally 19 ± 1 mm/M2.  The sinotubular junction is 15 ± 1 mm/M2. 
 
Aortic Anatomy
*Annulus
*Sinuses of Valsalva
*Sinotubular Junction
  Ascending Aorta
  Aortic Arch
  Descending Aorta
  Abdominal Aorta
*Aortic Root
Normal Aortic Anatomy
In a tricuspid aortic valve has three sinuses of Valsalva.  A classic bicuspid aortic valve has two sinuses of Valsalva. The sinuses of Valsalva are named by the normal origin of the coronary arteries: left coronary cusp (LCC), right coronary cusp (RCC), and non-coronary cusp (NCC).   The left main coronary artery ostia is usually visible by transthoracic or transesophageal echocardiography.  The right coronary artery ostia usually originates closer to the sinotubuluar junction.
Sinuses of Valsalva
Left Coronary Cusp (LCC)
Right Coronary Cusp (RCC)
Non-Coronary Cusp (NCC)
 
script
script
LMCA
RCA

The geometry of the sinotubular junction is important for the normal function of the aortic valve apparatus.  The aortic valve cusps insert from the aortic annulus to the sinotubular junction.  Dilation of the sinotubular junction causes the aortic cusps and aortic valve leaflets to be displaced away from the center of the aortic valve causing loss of coaptation of the leaflets resulting in aortic insufficiency. 
Normal STJ Diameter
Dilated STJ
 
 
The ascending aorta is the section of aorta from the sinotubular junction to the innominate (brachiocephalic) artery.  The diameter of the ascending aorta is uniform and is the same as the sinotubular junction, 15 ± 2 mm/M2.
 
The aortic arch extends from the brachiocephalic artery to the left subclavian artery and ligamentum arteriosum (aortic isthmus).  The three branches of the aortic arch are the innominate (brachiocephalic), left carotid, and left subclavian artery.  Anatomic variants of the branches and their origins can occur.  The major branches are often visible from the transthoracic as well as the transesophageal approach.  The aortic arch is of similar diameter to the ascending aorta, 15 ± 2 mm/M2.
 
The descending aorta extends from the left subclavian artery origin and the ligamentum arteriosum to the femoral arteries.  The descending aorta is further dived into the intrathoracic and abdominal aorta.  The descending aorta tapers slightly to 13 ± 2 mm/M2.
The walls of the aorta include the intima, media, and adventia layers.  The intima is the endothelial lined layer that regulates vasomotor tone, participates in the coagulation cascade and mediates immunologic and inflammatory responses.  The medial layer is the muscular layer that provides the vasomotor tone and is the thickest (80%) part of the aortic wall.  The adventitial layer is a loosely defined layer that contains collagen, lymphatics, and the vasa vasorum (arterial supply to the aortic wall). 
Aortic Wall Layers