M01.02.044 Arterial Supply

The head and neck receive their primary blood supply through the carotid arteries (common, internal, and external) and the vertebral arteries. Understanding the anatomy, branches, and clinical correlations of these arteries is vital for success in USMLE Step 1 and clinical practice.

Anatomy of Arterial Supply

1. Carotid Arteries

Common Carotid Arteries

• Right Origin: Arises from the bifurcation of the brachiocephalic trunk.
• Left Origin: Arises directly from the aortic arch.
• Course: Both ascend the neck lateral to the trachea and esophagus without branching.
• Bifurcation: At the level of the thyroid cartilage (C4) in the carotid triangle, splitting into:
  • Internal Carotid Artery (no branches in the neck).
  • External Carotid Artery (supplies extracranial structures).

Carotid Sinus and Body

• Carotid Sinus: Contains baroreceptors for blood pressure regulation.
• Carotid Body: Contains chemoreceptors for detecting blood oxygen levels.

Clinical Note: External pressure on the carotid sinus may cause carotid sinus hypersensitivity, leading to bradycardia, hypotension, and syncope.

2. External Carotid Artery

Supplies extracranial structures via the following major branches:

Clinical Note:

• Scalp injuries can result in excessive bleeding due to dense vascular anastomoses and tightly bound arterial walls.
• Extradural hematoma is caused by rupture of the middle meningeal artery (branch of the maxillary artery).

3. Internal Carotid Artery

• Path: Enters the cranial cavity via the carotid canal in the temporal bone.
• Supplies: Brain, eyes, and forehead.
• Clinical Correlation:
  • Turbulent blood flow in the carotid sinus can predispose to atherosclerosis.
  • Severe cases may require carotid endarterectomy to restore blood flow.

4. Vertebral Arteries

• Origin: Arise from the subclavian arteries.
• Course: Ascend through the foramina transversarium of cervical vertebrae.
• Termination: Enter the cranium via the foramen magnum and form the basilar artery.
• Function: Supplies the brain.

5. Additional Arteries of the Neck

These branches arise from the thyrocervical trunk of the subclavian artery:

Clinical Correlations

1. Carotid Sinus Hypersensitivity

• Pathophysiology: Overactive baroreceptors lead to bradycardia and hypotension.
• Precaution: Avoid palpating the carotid sinus in sensitive individuals.

2. Extradural Hematoma

• Cause: Fracture at the pterion damaging the middle meningeal artery.
• Symptoms: Increased intracranial pressure, nausea, seizures.
• Treatment: Burr holes or craniotomy in severe cases.

3. Atherosclerosis of the Carotid Artery

• Risk Area: Turbulent flow at the carotid bifurcation.
• Outcome: Neurological deficits or stroke if blood flow is occluded.
• Diagnosis and Treatment: Doppler study and carotid endarterectomy.

Key Points to Remember

1. Common Carotid Arteries bifurcate at C4 to form the internal and external carotid arteries.
2. External Carotid Artery branches supply the face, scalp, and extracranial neck structures.
3. Internal Carotid Artery is a major supplier of the brain, entering through the carotid canal.
4. The vertebral arteries form the basilar artery and supply the posterior brain.
5. Clinical conditions like carotid sinus hypersensitivity and atherosclerosis have high USMLE relevance.

Question

Bibliography

• TeachMeSeries Ltd. (2024). “Arterial Supply of the Head and Neck.”
• Gray’s Anatomy: The Anatomical Basis of Clinical Practice.
• Netter, F. H. “Atlas of Human Anatomy.”