Triangles of the Neck Dr. April R. Hatcher arich3@uky.edu MN212 323-4907 Fascia's of the Neck Fascial layers of the neck Investing fascia Pretracheal fascia IF pTF Carotid sheath CS Prevertebral fascia pVF IF CS pTF pVF Fascial layers of the neck Superficial to deep: Investing fascia –encircles the cervical region Anterior Pretracheal fascia- has muscular and visceral components *Note that the part of the pretracheal fascia that covers the posterior surface of the pharyngeal muscles is called the buccopharyngeal fascia (dashed green line) Posterior Fascial layers of the neck in cross-section Superficial to deep: Prevertebral fascia surrounds the musculature of around the vertebral column The carotid sheath includes the internal jugular vein, common carotid artery, and vagus nerve (CN X) Anterior Prevertebral muscles include longus capitis and longus colli. The various fascial planes between the compartments of the neck provide ideal pathways for the spread of infection from the oral cavity down into the thorax. One of the most important fascial planes is the retropharyngeal space (“Danger Space”). It is located between prevertebral fascia and the buccopharyngeal fascia and contains loose areolar tissue. This space communicates with the superior mediastinum, and gives a route for infection to spread from the neck to the thorax. Triangles of the neck The sternocleidomastoid muscle passes obliquely from the sternum and clavicle to the mastoid process and occipital bone. The sternocleidomastoid can be used to divide each side of the neck into: - anterior triangle - posterior triangle SCM A P P Regions of the Neck-Right Anterior Oblique View Anatomical Borders of the Posterior Triangle The boundaries of the posterior triangles are: Anterior boundary: the posterior border of sternocleidomastoid muscle Posterior boundary: anterior border of trapezius muscle. Base: superior border of the clavicle bone Roof: investing layer of deep cervical fascia Floor: prevertebral fascia covering the splenius capitis, levator scapulae, and scalene muscles Boundaries of the Posterior Triangle-Left Side (Lateral View) Anatomical Borders of the Anterior Triangle The boundaries of the anterior triangle are: Posterior boundary: the anterior border of the sternocleidomastoid muscle Superior boundary: the inferior border of the mandible bone. Anterior boundary: the median line of the neck Boundaries of the Anterior Triangle-Anterior View Hyoid Bone One of the more unique bones in the body, the hyoid bone is different in that it doesn’t directly articulate with any other bones. Instead, it is attached only by surrounding muscles and ligaments. The hyoid bone is found in the anterior midline of the neck between the mandible and thyroid cartilage. There are two groupings of muscles that have an attachment on the hyoid bone. These muscles are often categorized by the location of their muscle bellies relative to the hyoid bone. Those muscles found superior to the hyoid bone are referred to as suprahyoid muscles, while those below it are known as the infrahyoid muscles. Hyoid Bone-Oblique Left Lateral View Hyoid bone Suprahyoid & Infrahyoid Muscles-Anterior View Suprahyoid Muscles The muscles found superior to the hyoid bone are the: 1. Digastric muscle • Anterior belly • Posterior belly Anterior belly Mylohyoid Posterior belly Hyoid bone Stylohyoid 2. Stylohyoid 3. Mylohyoid 4. Geniohyoid (on next slide) Supra- & Infrahyoid Muscles-Anterior View Digastric Suprahyoid Muscles In this illustration showing us a superior view of the oral floor muscles, note that the majority of the tongue (except the most anterior portion) has been removed, revealing the floor of the mouth. This image allows us to see the hyoid bone from a superior view, as well as two of the suprahyoid muscles-the geniohyoid and the mylohyoid. Geniohyoid Mylohyoid 4. Geniohyoid Muscle: Found just deep to the mylohyoid muscle, it is located along the floor of the oral cavity Hyoid bone Stylohyoid Muscles of Oral Floor-Mandible & Hyoid Bone (Superior View) Suprahyoid Muscles When the suprahyoid muscles simultaneously contract, the hyoid bone is pulled upward. Stylohyoid Digastric, posterior belly As a result, the larynx is pulled up by its connection to the hyoid, the thyrohyoid membrane. This occurs during swallowing, allowing the epiglottis to cover the opening into the larynx (discussed in more detail later). Digastric, anterior belly Mylohyoid Suprahyoid & Infrahyoid Muscles-Left Lateral View Infrahyoid Muscles Muscles found inferior to the hyoid bone are called infrahyoid muscles. These can be further subdivided by their location into subgroups of either superficial or deep infrahyoids. Superficial Infrahyoid Muscles -Sternohyoid -Omohyoid (superior & Superficial Deep Hyoid bone Thyrohyoid Sternohyoid Omohyoid, inferior belly) Sternothyroid Deep Infrahyoid Muscles -Sternothyroid -Thyrohyoid Supra- & Infrahyoid Muscles-Anterior View superior and inferior belly Infrahyoid Muscles When the infrahyoid muscles contract as a group they both depress and stabilize the hyoid bone so that the contraction of the suprahyoids functions as accessory depressors of the mandible. Thyrohyoid Sternothyroid Omohyoid, Sternohyoid superior and inferior belly Suprahyoid & Infrahyoid Muscles-Left Side (Left Lateral View) Subdivisions of the Anterior Triangle The anterior triangle on the right and left sides can be divided into four smaller triangles: -Digastric triangle (2) -Submental triangle (1) -Carotid triangle (2) -Muscular triangle (2) Digastric triangles Submental triangle Carotid triangles Muscular triangles Anterior Triangle & It’s Subdivisions-Anterior View Dashed line indicates midline of neck Anterior Triangle – Digastric Triangle Anterior bellies of the digastric muscle Digastric triangle (paired) Superior boundary – the mandible Lower border of the mandible Inferior boundary - posterior belly of digastric Medial boundary – anterior belly of digastric Posterior bellies of the digastric muscles Floor - mylohyoid Contents: • stylohyoid muscle • facial artery and vein • submandibular gland • submandibular lymph nodes Digastric Triangles & Bordering StructuresAnterior View Anterior Triangle – Digastric Triangle Digastric Triangles Facial artery Some of the key structures found in this area below the body of the mandible include the facial artery. This is a branch off of the external carotid artery, and as its name implies it is primarily responsible for supplying oxygenated blood to the superficial structures of the face. Also present are a pair of salivary glands, which are conveniently called the submandibular glands. Found beneath the floor of the mouth, these are major producers of saliva (accounting for ~70% of our total salivary output while we are eating). Submandibular gland Contents of the Digastric TriangleLeft Lateral View Divisions of Anterior TriangleDigastric Triangle (Anterior View) Anterior Triangle – Submental Triangle Mental foramina Mylohyoid muscle Submental triangle Hyoid bone As its name suggests, the submental triangel lies just inferior to the two mental foramina, which are openings in the mandible that allow neurovascular structures to pass through. The boundaries of this triangle are: Lateral: bounded by the anterior bellies of digastric muscle Superior: inferior border of the mandible Inferior: body of the hyoid bone Floor: mylohyoid muscle Contents: submental lymph nodes To the left we can also see that the floor of the submental division is formed by the mylohyoid muscle (one of the suprahyoid muscles). This muscle contributes to the floor of the oral cavity. Structures of the Anterior Neck-Submental Triangle (Anterior View) Anterior Triangle – Carotid Triangle The carotid triangle is that portion of the anterior triangle bounded laterally by the anterior sternocleidomastoid, medially by the superior belly of omohyoid, and superiorly by the posterior digastric muscle. Some of the most notable neurovascular structures located inside the carotid triangle include (but are not limited to) those listed below: 1. 2. 3. 4. 5. 6. Common carotid artery bifurcation into internal/external carotid arteries Carotid sinus Carotid body Internal jugular vein Vagus nerve Hypoglossal nerve (CN XII) Internal jugular vein Hypoglossal n. (CN XII) Vagus n. (CN X) Common Carotid artery Carotid Triangle-Right Side (Right Lateral View) Anterior Triangle – Carotid Triangle The common carotid artery terminates by bifurcating into the internal and external carotid aa. – The external carotid has branches in the region of the head and neck, while the internal carotid artery has no branches until it emerges in the cranial cavity Clinical Correlation Internal carotid aa. Carotid stenosis, or carotid artery disease, results from plaque accumulation (atherosclerosis) in the carotid arteries. This decreases blood supply to the brain and increases the risk for stroke. External carotid aa. Arteries of the Anterior Triangle-Left Lateral View Anterior Triangle – Carotid Triangle The internal carotid exhibits an initial swelling called the carotid sinus – It is a baroreceptor that helps to regulate blood pressure The carotid body is a small mass of vascular tissue located at the bifurcation of the common carotid into the external/internal carotid arteries (carotid body location indicated, actual structure not visible) – Lies close to the carotid sinus – It is a chemoreceptor, responding to CO2 levels in the blood to increase respiration if levels get too high Carotid body Carotid sinus – The carotid body and sinus are innervated by the Glossopharyngeal nerve (CN IX) Arteries of the Anterior Triangle-Left Lateral View Anterior Triangle – Muscular Triangle Boundaries: • Median line of the neck • Anterior border of the sternocleidomastoid • Superior belly of the omohyoid Muscular Triangle-Anterior View Anterior Triangle – Muscular Triangle Boundaries: • Median line of the neck • Anterior border of the sternocleidomastoid • Superior belly of the omohyoid Contents: • infrahyoid muscles • larynx • thyroid gland and parathyroid glands • Trachea • esophagus Muscular Triangle-Anterior View Anterior Triangle: Structures of the Muscular Triangle The thyroid gland is composed of two lobes connected by an isthmus. It overlies the 2nd and 3rd tracheal rings. A pyramidal lobe (remnant of embryonic development) may be present. It is associated with metabolic regulation and is easily palpable. Blood supply is by the superior thyroid artery (external carotid artery) and inferior thyroid artery of the thyrocervical artery (subclavian artery). Thyroid gland Venous drainage is by multiple veins draining into internal jugular vein and brachiocephalic vein. Recurrent laryngeal nerves travel posterior to the thyroid gland. Larynx, Hyoid, and Thyroid Gland-Anterior View Arterial supply of the neck Superficial temporal a. Maxillary a. External carotid a. Internal carotid a. Facial a. Lingual a. Superior thyroid a. Common carotid a. Note that posterior auricular, occipital, and ascending pharyngeal arteries are also branches of the external carotid artery. These are smaller branches that arise posteriorly. Arteries of the Anterior Triangle-Left Lateral View Six branches arise from the anterior (3) and posterior (3) aspects of the external carotid a.: The first branch (5) is anterior, the superior thyroid a., bringing blood to the superior aspect of each lobe of the thyroid gland. It also gives rise to the superior laryngeal a. that supplies the larynx. The second branch is posterior, the ascending pharyngeal a. sending branches to the pharynx and prevertebral mm. The third branch (6) is anterior, the lingual a., that supplies the muscles of the tongue. It passes deep to the hyoglossus m. and becomes the deep lingual a. 1=internal jugular v. 2=common carotid a. 3=internal carotid a. The fourth branch (7) is also anterior, the facial a. that hooks around the inferior border of the mandible to ascend on the face. The fifth branch is posterior, the occipital a. that passes back to supply the posterior scalp. The sixth branch (8) is also posterior, the posterior auricular a. that supplies the adjacent parotid gland and scalp. Terminal branches: 9-Maxillary (deep face) 10-Superficial temporal Stole Man Papa’s Fat Only Little Apple Some Venous Drainage of the Neck The venous blood from the superficial muscles in the head, as well as from the skin covering them, is collectively drained first through a superficial drainage network before moving down through deeper veins. In this illustration we can trace the path of some of these veins. The five notable superficial veins are shown first, followed by the primary deep vein in this region. Superficial temporal v. Superficial Veins Maxillary v. -Facial v. -Superficial temporal v. -Maxillary v. (has deep portion too, drains back to retromandibular vein -Retromandibular v. -External jugular v. -Anterior jugular v. Internal jugular v. External jugular v. Anterior jugular v. Deep Veins -Internal jugular v. Note that most of the superficial veins drain back to the deeper internal jugular vein while the external jugular vein drains to the subclavian vein Veins of the Neck-Left Side (Lateral View) Retromandibular vein The retromandibular vein is formed by the maxillary vein and superficial temporal vein deep within the parotid gland. Parotid gland Parotid duct It forms an inverted “Y” which has branches that drain into both the external jugular vein and internal jugular vein. Its branches receive multiple tributaries from the face, neck and posterior side of the head. Retromandibular vein Sternocleidomastoid External jugular v. Internal jugular v. Innervation of the Neck The cervical plexus supplies both motor and sensory innervation to the structures of the neck. 1. Sensory branches (C2-C4) SENSORY MOTOR 1. Supraclavicular 2. Transverse cervical 3. Great auricular 4. Lesser occipital 2. Motor branches (C1-C3) to most infrahyoid muscles and one suprahyoid 1. Ansa cervicalis 3. Phrenic nerve (C3, C4, C5) to diahragm For schematic purposes only, sensory nerves are illustrated on one side of the cervical spine, while nerves supplying motor innervation are on the opposite. Phrenic nerve Diagram-Sensory & Motor Nerve Fibers of Cervical Plexus Innervation of the Neck-Sensory The cervical plexus and its sensory branches exit posterior to the sternocleidomastoid in an area called Erb’s point. Erb’s Point Sternocleidomastoid Convergence of Nerves at Erb’s Point-Right Lateral View A cervical plexus block involves blocking the transmission of nerve impulses as a result of an injection of a local anesthetic into the cervical plexus at Erb’s point. Innervation of the Neck-Sensory The superficial skin covering the majority of the anterior & lateral sides of the neck receives sensory innvervation via fibers from the cervical plexus. The illustration on the bottom left depicts the different areas of skin in this region. The areas colored in light green and gray correspond to the branches of the cervical plexus. Innervation of the face is from cranial nerve V, the Trigeminal nerve. Supraclavicular nn. Transverse cervical n. Great auricular n. Lesser occipital n. Lesser occipital n. Trigeminal n. Great auricular n. Lesser occipital n. Erb’s Point Great auricular n. Transverse cervical n. Sensory Innervation to Skin of Head/NeckLeft Lateral View Supraclavicular nn. Supraclavicular nn. Transverse cervical n. Convergence of Nerves at Erb’s Point-Left Lateral View 1. dorsal ramus of C2 (greater occipital) 2. dorsal rami C3-5 3. lesser occipital (C2) 4. great auricular (C2/3) 5. transverse cervical (C2/3) 6. supraclavicular nn. (C3/4) Branches of ansa cervicalis supply motor innervation to three of the four infrahyoid muscles: omohyoid, sternohyoid, & the sternothyroid muscles. Innervation of the Infrahyoid Muscles The thyrohyoid muscle is instead supplied by fibers from the ventral root of the spinal nerve C1. After exiting the spine, the C1 branch travels anteriorly from the spine by passing parallel to the hypoglossal nerve (CN XII). Hypoglossal Nerve (CN XII) Ansa cervicalis: Geniohyoid Supplied by C1 -Superior root of ansa cervicalis (C1) C1 -Inferior root of ansa cervicalis (C2, C3) -Thyrohyoid -Omohyoid -Sternohyoid Infrahyoid muscles supplied by ansa cervicalis NOTE: a portion of C1 also innervates the suprahyoid muscle, geniohyoid. -Sternothyroid Motor Innervation of the NeckLeft Lateral View superior root Root of Neck Sternocleidomastoid The posterior triangle is further subdivided into two smaller triangles by the inferior belly of the omohyoid into an occipital triangle and a supraclavicular triangle Contents of the posterior triangle: • spinal accessory nerve (CN XI) • cutaneous branches of the cervical plexus superior belly of the omohyoid • inferior belly of the omohyoid • thyrocervical trunk • subclavian a./v. (in supraclavicular triangle) clavicle inferior belly of the omohyoid The root of the neck is that area immediately above the thoracic inlet. There are 3 muscles in this area: - the anterior scalene extends from the anterior tubercles of the cervical vertebrae down onto the scalene tubercle of R1. - the middle scalene attaches to R1 behind the groove for the subclavian a. - the posterior scalene attaches inferiorly to R2 and is often located behind, or fused with, the middle scalene. The subclavian can be divided into 3 parts: - the first part of the subclavian a. extends from its origin to the medial border of the anterior scalene giving rise to the following branches: - vertebral a. (a) ascending to enter the transverse foramen of C6 to eventually enter the cranial cavity via the foramen magnum - the thyrocervical trunk (b) which in turn gives rise to three branches: - inferior thyroid a. (c) - suprascapular a. (d) -transverse (superficial) cervical a. (e) - the internal thoracic artery (f) Branches of the subclavian artery The vertebral artery is the first branch off the subclavian artery. It is deeply located where it passes through transverse foramina on its way to the brain. Thyrocervical trunk: supplies blood to the thyroid, neck and shoulder. • Inferior thyroid artery • Transverse cervical • Ascending cervical • Suprascapular Subclavian artery continued… -the second part is that portion of the subclavian found posterior to the anterior scalene. This region gives rise to the costocervical trunk which in turn gives rise to the superior intercostal a. supplying the 1st and 2nd intercostal spaces and the deep cervical a. which supplies muscles of the back of the neck. - the third part of the subclavian extends from the lateral border of the anterior scalene to the distal border of the first rib. It has no branches arising from it. Hyoid Thyroid Regional group of superficial lymph nodes: 1. occipital 2. mastoid (retroauricular) 3. parotid 4. buccal 5. submandibular 6. submental 7. superficial cervical 8. laryngeal 9. tracheal Lymph from these regional nodes drains to the deep cervical lymph nodes located alongside the internal jugular vein (blue chain of nodes in this diagram). The circles highlight the deep lymph nodes in the neck located along the length of the internal jugular vein. Submental nodes (under the chin) → submandibular nodes (along the jaw line and below)→ Submentalsubmandibular deep cervical lymph nodes (in the neck)→ jugular trunks → right lymphatic duct and thoracic duct Deep lymph nodes along the length of the internal jugular vein - Jugulodigastric node (a deep node): relatively constant node located where the digastric muscle crosses the internal jugular vein. Receives drainage from palatine tonsil, pharynx and posterior part of tongue.
