External Carotid Artery Anatomy

• The neck's main vessels include the common, external, and internal carotid arteries, as well as the internal jugular vein.

External Carotid Artery

• It begins at the split of the common carotid artery, close to the hyoid bone's greater horn.
• It initially runs somewhat medially before ascending in front of the internal carotid artery.
• It passes deep to the digastric and stylohyoid muscles' posterior belly.
• Perforates the parotid fascia's deep lamina and enters the gland.
• Divides into the maxillary and superficial temporal arteries within the parotid gland, behind the mandible's neck.
• At its start, positioned against the pharynx's side wall, where the internal carotid artery soon takes over.
• Within the parotid gland, it remains separate from the internal carotid due to the gland's deep part and pharyngeal structures.
• The facial vein crosses it, with the hypoglossal nerve in between.
• Except at its origin, it lies in front of the sternocleidomastoid muscle's anterior border.
• Surface marking: A line from the common carotid's bifurcation near the hyoid bone's greater horn, passing behind the mandible's angle to a point just in front of the ear's tragus.
• Surgical Approach: Can be accessed by ligating the facial vein and cutting the carotid sheath in front of the upper part of sternocleidomastoid before it enters the parotid gland.
• The hypoglossal nerve must be protected during surgery.
• Gives off six branches before entering the parotid gland: three from the front, two from the back, and one deep (medial).
• Branches from the front: superior thyroid, lingual, and facial arteries.
• Branches from the back: occipital and posterior auricular arteries.
• Medial branch: ascending pharyngeal artery.

External Carotid Artery Branches

• Superior Thyroid Artery: Arises at the start of the external carotid and goes almost straight down to the thyroid gland's upper pole.
• The external laryngeal nerve runs close behind it, alongside the larynx.
• The main branch, the superior laryngeal artery, pierces the thyrohyoid membrane with the internal laryngeal nerve.
• Lingual Artery: Originates from the external carotid's front, above the superior thyroid.
• Forms a short upward loop and then runs forward along the upper border of the hyoid bone's greater horn, deep to the hyoglossus muscle.
• Accompanied by the deep lingual vein
• The hypoglossal nerve and its accompanying vein cross it
• Facial Artery: Arises from the external carotid's front, above the lingual artery.
• Runs upward on the superior constrictor, deep to the digastric and stylohyoid muscles, and then deep to the submandibular salivary gland.
• Gives off a tonsillar branch to the tonsil and soft palate as it lies on the superior constrictor muscle.
• Makes an S-bend, curling down over the submandibular gland and up over the mandible.
• Gives off the submental artery just before crossing the mandible's inferior border
• Occipital Artery: Arises from the external carotid's back, level with the facial artery.
• Courses along the lower border of the digastric's posterior belly, grooving the skull base at the occipitomastoid suture.
• Passes through the posterior triangle's apex to supply the back of the scalp.
• Gives off two branches to the sternocleidomastoid muscle.
• Posterior Auricular Artery: Arises above the digastric muscle, sometimes within the parotid gland.
• Runs up superficial to the styloid process across the upper border of the digastric
• Supplies the skin over the mastoid process.
• Ascending Pharyngeal Artery: Arises just above the start of the external carotid, from its deep side.
• Runs up along the pharynx's side wall in front of the prevertebral fascia, deep to the internal carotid artery.
• Supplies the pharyngeal wall and soft palate and sends meningeal branches through nearby foramina.

Internal Carotid Artery

• Arises from the common carotid's bifurcation and continues upward within the carotid sheath.
• Shows a slight bulge at its start, called the carotid sinus.
• The arterial wall is thin at the carotid sinus, and its baroreceptors are supplied by the glossopharyngeal nerve's carotid sinus branch.
• The carotid body is a small yellowish-grey structure behind the common carotid artery's bifurcation.
• Contains chemoreceptors for respiratory reflexes and has the highest blood flow of any organ relative to its size.
• Has no branches in the neck and goes straight up in the carotid sheath beside the pharynx to the carotid canal in the skull base.
• Behind it, the sympathetic trunk and pharyngeal veins are located
• The superior laryngeal branch of the vagus crosses obliquely behind it.
• The internal jugular vein is lateral, with the vagus nerve deeply placed between the artery and vein.
• It is crossed by the lingual and facial veins, the occipital artery, and the hypoglossal nerve superficially near its origin.
• Surface marking: A line from the common carotid artery's bifurcation near the hyoid bone's greater horn to the head of the mandible.
• Surgical approach: Exposed by retracting the upper part of sternocleidomastoid backwards, ligating the facial vein, and cutting the carotid sheath.

Internal Jugular Vein

• Emerges from the jugular bulb at the jugular foramen's posterior compartment.
• It lies on the lateral mass of the atlas, crossed by the accessory nerve.
• Receives the inferior petrosal sinus as its first tributary, just below the skull base.
• Passes down to the lateral side of the internal carotid artery within the carotid sheath, with the vagus nerve between the vein and arteries.
• Deep cervical lymph nodes are closely adjacent to the vein.
• The thoracic duct crosses behind the left vein at the level of the C7 vertebra.
• Tributaries below the inferior petrosal sinus: pharyngeal plexus, facial, lingual, and superior and middle thyroid veins.
• Surface marking: A line from the ear's lobule to the clavicle's sternal end.
• Catheterization: Can be cannulated for central venous line insertion; approached from 5 cm above the clavicle at the posterior border of sternocleidomastoid.

Triangles of the Neck

• Posterior Triangle:
  • Boundaries: Sternocleidomastoid, trapezius, clavicle.
  • Contents: Arteries, veins, cervical plexus branches, brachial plexus trunks, omohyoid, lymph nodes.
• Anterior Triangle:
  • Boundaries: Sternocleidomastoid, mandible, midline.
  • Subdivisions: Carotid, digastric, submental, and muscular triangles.

Subdivisions of Anterior Triangle

• Carotid Triangle:
  • Boundaries: Sternocleidomastoid, posterior belly of digastric, superior belly of omohyoid.
  • Contents: Carotid artery bifurcation and external carotid branches; hypoglossal and laryngeal nerves; lymph nodes.
• Digastric Triangle:
  • Boundaries: Mandible, anterior and posterior bellies of digastric.
  • Contents: Submandibular gland and lymph nodes; facial, submental, and mylohyoid vessels; hypoglossal and mylohyoid nerves.
• Submental Triangle:
  • Boundaries: Anterior belly of digastric, body of hyoid bone, midline.
  • Contents: Anterior jugular vein; lymph nodes.
• Muscular Triangle:
  • Boundaries: Sternocleidomastoid, superior belly of omohyoid, midline from hyoid bone to jugular notch.
  • Contents: Part of larynx and thyroid gland; lymph nodes.

The external carotid artery originates from the common carotid artery near the hyoid bone. It ascends anterior to the internal carotid artery, passing deep to specific muscles before entering the parotid gland. Within the gland, it divides into the maxillary and superficial temporal arteries.