Applied Anatomy of the Arch of Aorta
Patent Ductus Arteriosus (PDA)
Definition: Failure of the ductus arteriosus to close after birth, resulting in a persistent communication between the arch of the aorta (just distal to the left subclavian origin) and the left pulmonary artery.
Incidence: 1 in 3000 births; more common in premature infants; associated with congenital rubella.
Pathophysiology:
- After birth, systemic pressure > pulmonary pressure
- Blood shunts left to right (aorta → pulmonary artery) — reversed from fetal direction
- This causes volume overload of the pulmonary circulation → pulmonary hypertension
- Over time: Eisenmenger syndrome — pulmonary pressure exceeds systemic → shunt reverses (right to left) → cyanosis
Clinical Features:
- Continuous (machinery) murmur — at the left 2nd intercostal space, close to the sternal margin (Gibson’s murmur)
- Continuous thrill at the same site
- Wide pulse pressure (bounding pulses)
- Signs of left heart failure in large PDAs
Treatment:
- Medical: Indomethacin (prostaglandin synthetase inhibitor) → promotes closure in premature neonates
- Surgical/catheter: Ligation or clipping of PDA; catheter-based occlusion
Coarctation of the Aorta
Definition: Congenital narrowing (stenosis) of the aorta, most commonly at the aortic isthmus — the segment between the origin of the left subclavian artery and the insertion of the ductus arteriosus (ligamentum arteriosum).
Types:
| Type | Location | Ductus | Notes |
|---|---|---|---|
| Postductal (adult type) | Distal to ligamentum arteriosum | Closed | Collateral circulation develops; most common type |
| Preductal (infantile type) | Proximal to ductus | Patent | Ductus carries deoxygenated blood to lower body; presents early in life |
Clinical Features:
- Radiofemoral delay — pulse in femoral artery lags behind radial artery
- Hypertension in upper limbs; hypotension / absent pulses in lower limbs
- Headache, epistaxis (due to hypertension)
- Weakness of legs, claudication
- Rib notching (on chest X-ray) — notching of the inferior borders of ribs 3–8 due to tortuous, dilated posterior intercostal arteries forming collateral circulation
- Pulsating scapulae — visible pulsation due to enlarged subscapular arteries
- Reverse 3 sign (or E sign) on chest X-ray — indentation at the coarctation site flanked by pre- and post-stenotic dilatation
Collateral Circulation: Subclavian arteries → internal thoracic + costocervical arteries → posterior intercostal arteries (3rd–8th) → descending aorta below the coarctation. This is why ribs 3–8 are notched (1st and 2nd rib arteries are not intercostal in origin).
Treatment: Surgical resection and anastomosis; balloon dilatation with stenting.
Aneurysm of the Arch of Aorta
Definition: Pathological dilatation of the arch of the aorta.
Causes: Atherosclerosis, syphilis (classically), Marfan’s syndrome, trauma, cystic medial necrosis.
Effects — Compression of Adjacent Structures:
| Structure Compressed | Symptom |
|---|---|
| Trachea | Dyspnoea, stridor, tracheal tug |
| Left recurrent laryngeal nerve | Hoarseness (dysphonia) — bovine cough |
| Oesophagus | Dysphagia |
| Superior vena cava | SVC obstruction — oedema of face, neck, upper limbs |
| Sympathetic trunk | Horner’s syndrome (ptosis, miosis, anhidrosis, enophthalmos) |
| Left phrenic nerve | Diaphragmatic paralysis |
Tracheal tug: A downward tugging sensation felt in the suprasternal notch when the finger is placed there — due to transmission of aortic pulsation to the trachea via the coarctation or aneurysm. The aortic arch normally anchors the tracheal bifurcation — an aneurysm exaggerates this pull.
Aortic Knuckle
On a PA chest X-ray, the arch of the aorta produces a small bulge at the upper left margin of the cardiac shadow — called the aortic knuckle (aortic shadow / aortic nob).
- Becomes prominent in: old age (atherosclerotic unfolding of the arch), aortic aneurysm, hypertension
- Absent or unilateral: Aortic dissection, coarctation (small knuckle)
Dysphagia Lusoria
Definition: Dysphagia caused by an aberrant right subclavian artery arising as the fourth branch of the arch of aorta (instead of from the brachiocephalic trunk).
The aberrant artery passes posterior to the oesophagus (occasionally between oesophagus and trachea) → compresses the oesophagus posteriorly → intermittent dysphagia, worse with solids.
Incidence: ~0.5–1% of population; most are asymptomatic.
Left Recurrent Laryngeal Nerve — Surgical Importance
The left recurrent laryngeal nerve is at risk in:
- Surgery on the arch of aorta or descending thoracic aorta
- Left upper lobe pneumonectomy
- Oesophageal surgery
- Mediastinal lymph node dissection
- Aortic arch aneurysm (causing hoarseness before surgery)
Injury → ipsilateral vocal cord paralysis → hoarseness, bovine cough, aspiration risk.