Triangles of the Neck (corrected).pdf

INTRODUCTION The neck is a complex anatomical area that contains various muscles, nerves and blood vessels. To better understand the relationship between these structures, the neck can be divided into regions known as Triangles of the neck. The triangles of the neck are the topographic...

INTRODUCTION The neck is a complex anatomical area that contains various muscles, nerves and blood vessels. To better understand the relationship between these structures, the neck can be divided into regions known as Triangles of the neck. The triangles of the neck are the topographic areas of the neck bounded by the neck muscles The sternocleidomastoid muscle divides the neck into the two major neck triangles; - (1) anterior triangle (2) posterior triangle, each of them containing a few subdivision The triangles of the neck are important because of their contents, as they house all the neck structures (glands, nerves, vessels and lymph nodes).  ANTERIOR TRIANGLE The anterior triangle of the neck is a large triangular space on each side of the neck. It lies between the anterior border of sternocleidomastoid, lower border of mandible and the midline of neck. The apex of the anterior triangle is located downwards [at manubrium sternum] and its base is directed upward. BORDERS OF THE ANTERIOR TRIANGLE: ✔ Superior (Base): Inferior border of mandible ✔ Anterior: Median line of neck ✔ Posterior: Anterior margin of sternocleidomastoid ✔ Apex: Manubrium of Sternum Investing Fascia covers roof of the triangle while Visceral Fascia covers floor of the triangle CONTENTS: MUSCLES: Hyoid bone divides them into Suprahyoid and Infrahyoid muscles Suprahyoid Muscles: Digastric, Stylohyoid, Mylohyoid, Geniohyoid. Infrahyoid Muscles: Omohyoid, Sternohyoid, Thyrohyoid, Sternothyroid ARTERIES AND VEINS Within anterior triangle, common carotid artery bifurcates into external and internal carotid arteries. Internal Jugular vein: Responsible for venous drainage of head and neck.  CRANIAL NERVES Fascial nerve[VII] Glossopharyngeal[IX] Vagus nerve[X] Accessory nerve[XI] Hypoglossa nerveXII] LYMPH NODES  SUBDIVISIONS The anterior triangle is subdivided by the digastric muscle and superior belly of omohyoid muscle into: 1. Submental triangle (half only). 2. Digastric (submandibular) triangle. 3. Carotid triangle. 4. Muscular triangle.  Submental Triangle It is a median triangle on the front of neck below the chin and above the hyoid bone. It occupies the upper portions of the anterior triangle. Borders ✔ Inferior: Hyoid bone ✔ Medial: Midline of the neck ✔ Lateral: Anterior belly of digastric muscle. The floor of the submental triangle is formed by the mylohyoid muscle, which runs from the mandible to the hyoid bone. Contents ✔ Submental lymph nodes (filter lymph draining floor of mouth and parts of tongue) ✔ Small vein that unite to form anterior jugular veins  Submandibular (Digastric) Triangle It is named so because it is located between the two bellies of the digastric muscle and below the base of the mandible. Borders ✔ Superior: Lower border of mandible ✔ Anterior: Anterior belly of digastric ✔ Posterior: Posterior belly of digastric Roof is formed by investing layer of deep cervical fascia, which splits to enclose the submandibular salivary gland. Contents Contents in the anterior part of the triangle: 1. Submandibular salivary gland. 2. Submandibular lymph nodes. 3. Hypoglossal nerve. 4. Facial vein (lies superficial to the gland). 5. Facial artery (lies deep to the gland). 6. Submental artery. 7. Mylohyoid nerve and vessels.  Contents in the posterior part of the triangle: 1. External carotid artery. 2. Carotid sheath and its contents. 3. Structures passing between the external and internal carotid arteries Carotid Triangle It is so called because it contains all the three carotid arteries which are; common carotid, internal carotid, and external carotid. Borders ✔ Superiorly: Posterior belly of digastric supplemented by stylohyoid. ✔ Anteroinferiorly: Superior belly of omohyoid. ✔ Posteriorly: Anterior border of sternocleidomastoid. ✔ Roof is formed by investing layer of deep cervical fascia. ✔ Floor: It is formed by the following four muscles: 1. Thyrohyoid. 2. Hyoglossus. 3. Middle constrictor. 4. Inferior constrictor  Contents ✔ Common carotid artery (bifurcates into internal and external carotid arteries within the triangle) ✔ Internal jugular vein ✔ Vagus nerve ✔ Spinal accessory nerve ✔ Hypoglossal nerve  Muscular Triangle Located more inferiorly than other subdivisions of the anterior triangles Borders Superoposteriorly: Superior belly of the omohyoid Medially – Midline of the neck Inferoposteriorly – Anterior margin of sternocleidomastoid Contents ✔ Infrahyoid process ✔ Pharynx ✔ Thyroid and parathyroid gland  CLINICAL RELEVANCE Medical Uses of the Carotid Triangle In the carotid triangle, many of the vessels and nerves are relatively superficial, and so can be accessed by surgery. The carotid arteries, internal jugular vein, vagus and hypoglossal nerves are frequent targets of this surgical approach. The carotid triangle also contains the carotid sinus-a dilated portion of the common carotid and internal carotid arteries. It contains specific sensory cells, called Baroreceptors. The baroreceptors detect stretchas a measure of blood pressure. The glossopharyngeal nerve feeds this information to the brain, and this is used to regulate blood pressure.  POSTERIOR TRIANGLE The posterior triangle of the neck is located at posterolateral aspect of the neck. It is enclosed between the sternocleidomastoid and trapezius muscles Its apex is directed upwards and backwards towards the mastoid process and base downwards towards the clavicle. Borders ✔ Anterior: posterior border of sternocleidomastoid ✔ Posterior: anterior border of trapezius ✔ Inferior: Middle 1/3 of clavicle The roof is formed by investing layer of fascia and floor is formed by prevertebral fascia. Subdivisions The posterior triangle is subdivided into two parts by the inferior belly of the omohyoid, which crosses the lower part of the triangle obliquely upwards and forwards. 1. Occipital triangle 2. Subclavian(Supraclavicular triangle)  Occipital triangle It is located superior to omohyoid muscle. It is so named because it contains the occipital arteries Borders ✔ Anterior: Posterior margin of sternocleidomastoid ✔ Posterior: Anterior margin of trapezius ✔ Inferior: Inferior belly of omohyoid Contents ✔ Spinal accessory nerve ✔ 3rd and 4th cervical nerves providing branches to levator scapulae and trapezius muscles ✔ Dorsal scapular nerve (C5) ✔ Four cutaneous branches of cervical plexus (initial parts) ✔ Superficial transverse cervical artery ✔ Occipital artery.  Subclavian Triangle Located below the omohyoid. It is so named because it contains the subclavian artery. Borders ✔ Superior: Inferior belly of omohyoid ✔ Anterior: Posterior head of sternocleidomastoid ✔ Inferior: Clavicle Contents ✔ 3rd part of the subclavian artery ✔ Subclavian vein ✔ Terminal part of external jugular vein ✔ Trunks of brachial plexus ✔ Superficial (transverse) cervical, suprascapular, and dorsal scapular arteries ✔ Lymph nodes. CLINICAL RELEVANCE Cervical Plexus Nerve Block For anesthesia of the neck area, a cervical plexus block can be used. Local anaesthetic is injected along the posterior border of sternocleidomastoid at the junction of its superior and middle thirds. This junction is where the cutaneous branches of the cervical plexus emerge, known as the nerve point of the neck.