Aortic Arch Anatomy

Question. Describe the arch of the aorta under the following headings:

1. Aortic arch Origin and course
2. Aortic arch Relations
3. Aortic arch Branches
4. Aortic arch Development and
5. Aortic arch Applied Anatomy.
6. Aortic arch Origin and course

Answer:

1. Aortic arch Origin and course:

• It is the continuation of the ascending aorta behind the right end of the sternal angle and lies behind the lower half of the manubrium sterni.
• It runs upward, backward, and to the left across the left side of the bifurcation of the trachea.
• It then passes downward behind the left bronchus, arching over the root of the left lung to end at the sternal angle (lower border of the 4th thoracic vertebra) by becoming continuous with the descending aorta.

Note: The arch of the aorta lies in the superior mediastinum. It begins and terminates at the same level, although it begins anteriorly and terminates posteriorly.

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2. Aortic arch Relations:

Posterior and to the right:

• Trachea (1)
• Esophagus (2)
• Left recurrent laryngeal nerve (3)
• Thoracic duct (4)
• Vertebral column (not)

Aortic arch Anterior and to the left:

• Left lung and pleura (not)
• Left phrenic nerve(2)
• Left vagus nerve (3)
• Left cardiac nerves (superior cervical cardiac branch of left sympathetic chain and inferior cardiac branch of the left vagus nerve) (4)
• Left superior intercostal vein (5)

Aortic arch Inferior:

• Left bronchus (1)
• Bifurcation of the pulmonary trunk (2)
• Ligamentum arteriosum (3)
• Left recurrent laryngeal nerve (4)
• Superficial cardiac plexus (5)

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Aortic arch Superior:

• Brachiocephalic trunk (1)
• Left common carotid artery (2)
• Left subclavian artery (3)
• Left brachiocephalic vein (4)
• Thymus (not)

3. Aortic arch Branches:

• Brachiocephalic trunk
• Left common carotid artery
• Left subclavian artery

4. Aortic arch Applied anatomy:

• Aortic knuckle: In the X-ray chest PA view, a bulb-like projection is seen at the left margin of the upper end of the cardiac shadow. It is formed by the distal part of the arch of aorta and is termed the aortic knuckle.
• Aneurysm of the arch of the aorta: It is a localized dilatation of the arch of the aorta. Clinically, it presents as a tracheal tug, a feeling of tugging sensation in the region of the supra sternal notch.

Question 3. Describe the development of the arch of the aorta in brief and associated congenital anomalies. 
Answer:

Arch Development:

The arch of the aorta develops at the end of 4th week of IUL from the following three sources:

• Left horn of aortic sinus: This forms the part of the arch of the aorta between the brachiocephalic trunk and the left common carotid artery.
• Left 4th aortic arch: This forms the part of the arch of the aorta between the left common carotid artery and ductus arterioles.
• Left dorsal aorta: This forms the rest of the arch up to the descending aorta.

Congenital anomalies:

Coarctation of the aorta:

It is congenital stenosis of the arch of the aorta distal to the origin of the left subclavian artery. It occurs due to defects in the tunica media followed by intimal proliferation. The coarctation of the aorta may be preductal or postductal.

• Product type: In this, narrowing/stenosis is just proximal to the opening of the ductus arterioles.
• Postductal type: In this, the narrowing/stenosis is just distal to the entrance of duct arterioles. The ducts arterioles is commonly obliterated in this type.

In the postductal type of coarctation of the aorta, extensive collateral circulation develops between the branches of subclavian arteries and those of the descending aorta. This includes the anastomoses between the anterior and posterior intercostal arteries.

Clinical presentation: The anterior and posterior intercostal arteries are enlarged greatly and produce a characteristic notching of the lower borders of the ribs.

Patent ductus arterioles (PDA):

During fetal life, the ducts arterioles (DA) is a short wide channel, which connects the beginning of the left pulmonary artery with the arch of the aorta just distal to the origin of the left subclavian artery. It shunts most of the blood from the right ventricle into the aorta, thus short-circuiting the lungs.

• Functionally, it is closed shortly (within about a week) after birth by the contraction of the smooth muscle of the DA.
• However, anatomically, it closed within about 2 months (8 weeks) through intimal proliferation mediated by bradykinin.
• The remnants of the ducts form a fibrous band called ligamentum arteriosum.
• The patent ducts arterioles occur if it fails to close. This leads to the shunting of blood from the aorta into the pulmonary circulation causing serious circulatory problems.

Note:

• Patent duct arterioles is the most common congenital anomaly of the great blood vessels occurring in about 8/10,000 births.
• Clinically, it presents progressive enlargement of the left ventricle and pulmonary hypertension.

Question 4. Give a brief account of descending thoracic aorta. 
Answer:

Thoracic Aorta Introduction:

• It is a continuation of the arch of the aorta and is located in the posterior mediastinum. It begins on the front of the left side of the lower border of the T4 vertebra.
• It descends downward with a slight inclination to the right and terminates in front of the lower border of the T12 vertebra where it continues as the abdominal aorta.

Thoracic aorta Branches:

• Posterior intercostal arteries on each side from the 3rd to 11th (9 pairs)
• Subcostal artery on each side
• Two left bronchial arteries
• Esophageal branches
• Pericardial branches
• Mediastinal branches
• Superior phrenic arteries