Anterior Triangle of the Neck

• The anterior triangle of the neck is studied in Year 2, Semester 1.
• The anterior triangle's boundaries, content, and subdivisions need to be demonstrated.
• The location and course of major vessels and nerves in the neck need to be described.
• The anatomical features and development of the thyroid gland need to be described.
• The blood supply of the thyroid needs to be identified.
• The course and clinical significance of the laryngeal nerves need to be described.
• The location of the parathyroid glands needs to be described.
• The carotid sheath, its arteries, and contents need to be identified.
• The location of the carotid pulse needs to be located.
• A laryngotomy and tracheotomy need to be compared and contrasted.
• The cervical sympathetic trunk and vagus nerve in the neck need to be described.

Anterior vs Posterior Triangle

• Anterior triangle structures course between the head and thorax
• Posterior triangle structures course between the neck/thorax and upper limb

Deep Cervical Fascia

• Deep cervical fascia layers include subcutaneous, skin, platysma, investing, pretracheal, carotid sheath, alar and prevertebral
• Anterior is a layer in the deep cervical fascia
• Recall is important for understanding deep cervical fascia layers.
• The investing layer is the outermost layer of the deep cervical fascia.
• The superior view of the transverse section is seen at the C7 vertebra level.

Muscular Triangles of Neck

• For description, the neck is divided into anterior and posterior triangles by the sternocleidomastoid muscle.

Hyoid Bone

• The hyoid bone features greater and lesser horns, and a body.

• Muscles connect to the hyoid bone

• Hyoid bone is at level C3

• Superior thyroid notch is at level C4

• Cricoid cartilage is at level C6

Anterior Triangle Subdivisions

• Anterior to the sternocleidomastoid muscle(SCM), the anterior triangle can be further divided by the digastric and omohyoid muscles.
• The anterior triangle subdivisions, include submandibular, submental, carotid, and muscular triangles.

Suprahyoid Muscles

• Suprahyoid muscles include the digastric, stylohyoid, mylohyoid and geniohyoid
• Digastric has anterior and posterior bellies.
• The origin of the digastric muscle is the digastric notch on the mastoid.
• The digastric muscle runs through the fibrous hyoid sling, with a synovial sheath.
• The digastric muscle inserts at the digastric fossa in the mandible.
• The anterior belly of the digastric muscle has a nerve supply from the nerve to mylohyoid (CN V).
• The posterior belly of the digastric muscle has a nerve supply from the facial nerve (CN VII).
• The stylohyoid muscle originates from the styloid process to the hyoid bone.
• The insertion of the stylohyoid muscle splits to lie over the digastric sling.
• The nerve to the stylohyoid muscle is the facial nerve (CN VII).
• The mylohyoid has a mylohyoid line attachment on the mandible.
• Mylohyoid attaches to the midline raphe and body of the hyoid.
• Nerve to the mylohyoid is Vc
• The geniohyoid attaches to the inferior mental spines of the mandible and the body of the hyoid.
• C1 fibers hitchhike along with the hypoglossal to reach the geniohyoid.

Infrahyoid muscles

• Infrahyoid muscles include the sternohyoid, omohyoid, thyrohyoid and sternothyroid.
• The sternohyoid runs from the hyoid (body) to the sternum and clavicle.
• The laryngeal prominence protrudes between the sternohyoid muscle.
• The nerve supply to the sternohyoid is via the ansa cervicalis.
• The omohyoid muscle has superior and inferior bellies and originates from the hyoid bone.
• The intermediate tendon of the omohyoid lies deep to the SCM, running over the internal jugular vein, with a fascial sling from deep investing fascia.
• The insertion for the omohyoid transverse scapular ligament.
• The nerve supply to the omohyoid via the ansa cervicalis.
• The thyrohyoid runs from the hyoid (greater horn) to the thyroid cartilage on the oblique line.
• The nerve supply to the thyrohyoid comes C1 fibers that hitchhike along with hypoglossal.
• The sternothyroid originates at the posterior manubrium (sternum).
• The sternothyroid inserts at the thyroid cartilage on the oblique line.
• Nerve supply to the sternothyroid comes from the ansa cervicalis, specifically C2/C3 fibers.

Ansa Cervicalis

• Ansa Cervicalis originates from the cervical plexus.
• C1 fibers hitchhike on hypoglossus while others supply geniohyoid and thyrohyoid directly.
• The remaining C1 fibers form the descendens hypoglossi.
• C2 and C3 fibers form the descendens cervicalis.
• The ansa cervicalis is formed by two descendens joining to form a loop in the anterior carotid fascia.
• Remaining strap muscles are supplied from lateral aspect, segmentally from inferior to superior.

Vessels

• The right common carotid artery (CCA) originates from the brachiocephalic trunk, posterior to the right sternoclavicular joint.
• The left common carotid artery (CCA) begins in the thorax as a direct branch of the arch of the aorta.
• Near the superior edge of the thyroid cartilage at C3/C4, each CCA divides into two terminal branches: the external carotid artery (ECA) and the internal carotid artery (ICA).

Carotid Sheath

• Carotid Sheath is a column of fascia that surrounds the common carotid artery, the internal carotid artery, the internal jugular vein, and the vagus nerve.

Carotid System

• The carotid pulse is found in the anterior triangle
• The carotid sinus is a dilatation at the proximal part of the ICA at the bifurcation.
• The Carotid Sinus contains receptors that monitor changes in blood pressure.
• The Carotid Sinus is innervated by a branch of the glossopharyngeal nerve (IX CN).
• "SALFOPS" is a mnemonic to remember the branches of the external carotid artery Superior thyroid, Ascending pharyngeal, Lingual, Facial, Occipital, Posterior auricular, Superficial temporal

Internal Jugular Vein (IJV)

• The internal jugular vein begins as a dilated continuation of the sigmoid sinus (dural venous sinus).
• The initial dilated part is also known as the superior bulb of the jugular vein.
• The internal jugular vein exits the skull via the jugular foramen along with cranial nerves IX, X, and XI, and enters the carotid sheath.
• The IJV joins with the subclavian vein to form the brachiocephalic vein.
• Tributaries to the IJV include inferior petrosal sinus, facial, lingual, pharyngeal, occipital, superior thyroid, and middle thyroid veins.

Nerves

• Facial nerve (VII CN), Accessory nerve (XI CN), Glossopharyngeal nerve (IX CN), Hypoglossal nerve (XII CN), Vagus nerve (X CN) are all mentioned in this presentation and could be found in the anterior triangle

Thyroid and Parathyroid Glands

• The thyroid and parathyroid glands are located in the anterior neck.
• The thyroid gland has a right lobe, left lobe, and isthmus.
• The parathyroid glands are located on the posterior aspect of the thyroid gland.

Blood Supply to the Thyroid

• The thyroid gland receives blood supply from the superior and inferior thyroid arteries.
• The superior thyroid artery and vein, an anterior glandular branch, middle thyroid vein are all connected to the thyroid
• The inferior thyroid artery and thyrocervical trunk are connected to the thyroid
• Right and left recurrent laryngeal nerves are also next to these structures

Nearby Nerves

• The superior thyroid artery courses nearby (but not necessarily to) the external laryngeal nerve of Vagus nerve
• The inferior thyroid artery courses nearby (but not necessarily to) the recurrent laryngeal nerve.
• The anatomy of these two nerves and their relationship to the nearby vessels can be variable.

Cervical Sympathetic Trunk

• The cervical sympathetic trunk runs is continuous with the thoracic trunk, crosses the neck of the first rib, posterior to the carotid sheath, and on the prevertebral fascia.
• The cervical sympathetic trunk has 3 cervical ganglia: superior, middle, and inferior.
• The superior cervical ganglion is located at the C1 and C2 vertebral level, and branches pass to C1 to C4 spinal nerves.
• The middle cervical ganglion is located at the level of the C6 vertebra, and branches pass to C5 and C6 spinal nerves.
• The inferior cervical ganglion is named as the stellate ganglion (if merged with the T1 ganglion) and branches pass to C7 to T1 spinal nerves.

Lymph Nodes

• Lymph Nodes in the superficial cervical chain are Occipital, Mastoid(posterior auricular), Pre-auricular and parotid, Submandibular, Submental
• Lymph Nodes in the deep cervical chain are Jugulodigastric, Jugulo-omohyoid

Clinical Applications

• Cricothyroidotomy (Laryngotomy): a tube is inserted in the interval between the cricoid cartilage and thyroid cartilage.
• Tracheotomy: a tracheal tube is inserted between the 2nd and 4th tracheal rings.
• Tracheostomy tube is inserted into incision after retracting infrahyoid muscles and incising isthmus of thyroid