2024_Triangles_MP.pdf

Triangles of the Neck Megan Perry, PhD Pronouns: she/her/hers [email protected] WHM 2003; 402-559-6493 Learning Objectives 1. Describe the layers, organization, and function of the cervical fascia. 2. Describe the boundaries of the posterior and anterior triangles of the neck. 3. Describe the a...

Triangles of the Neck Megan Perry, PhD Pronouns: she/her/hers [email protected] WHM 2003; 402-559-6493 Learning Objectives 1. Describe the layers, organization, and function of the cervical fascia. 2. Describe the boundaries of the posterior and anterior triangles of the neck. 3. Describe the anatomical relationships of the muscles and neurovascular structures of the posterior triangle. 4. Describe the anatomical relationships of the muscles and neurovascular structures of the anterior triangle. Overview of the Neck Transitional area between the base of the cranium and the clavicles. Conduit for structures passing between the head and trunk Relatively slender to allow flexibility to position the head and maximize the efficiency of the special senses. Thus, many important structures are crowded together and are vulnerable to injury. Major structures: Arterial blood supply to and venous drainage from the head Origin of the brachial plexus Thyroid/parathyroid glands, larynx, trachea, esophagus …and many more! Cervical Fascia Superficial cervical fascia (subcutaneous tissue) Deep to the skin; Contains platysma muscle Deep cervical fascia: 3 fascial layers 1. Investing layer; surrounds entire neck; encloses trapezius and SCM 2. Pretracheal layer: anterior neck; visceral part encloses thyroid, trachea, esophagus 3. Prevertebral layer: tubular sheath for vertebral column and muscles Carotid sheath and retropharyngeal space Carotid Sheath Blends anteriorly with investing and pretracheal layers and posteriorly with the prevertebral layer Contents: Common and Internal carotid arteries Internal jugular vein Vagus nerve (CN X) Retropharyngeal Space Potential space; permits movement of pharynx, esophagus, larynx and trachea during swallowing Boundaries: Anterior: Pretracheal layer Posterior: Prevertebral layer Lateral: Carotid sheath Communicates inferiorly with the mediastinum Infection spread in the neck Investing layer: inferiorly attached to the manubrium of the sternum, clavicles, and spines of the scapula. Infections between the investing layer and fascia of infrahyoids will usually not spread inferiorly If the infection occurs between the infrahyoids and the pretracheal fascia, it can spread into the thoracic cavity anterior to the pericardium. Infection spread in the neck Infections in the head may spread inferiorly posterior to the esophagus and enter the posterior mediastinum, or it may spread anterior to the trachea and enter the anterior mediastinum. Infections in the retropharyngeal space may also extend inferiorly into the superior mediastinum. Pus from an abscess posterior to the prevertebral layer may perforate the fascia and enter the retropharyngeal space, producing a bulge in the pharynx (retropharyngeal abscess). This abscess may cause difficulty in swallowing (dysphagia) and speaking (dysarthria). What are the triangles? Regional divisions of the neck based on bony and muscular landmarks Allows clear communication of anatomical relationships of structures in the neck Lateral cervical region = Posterior triangle Anterior cervical region = Anterior triangle Sternocleidomastoid divides the posterior and anterior triangles Unilateral Bilateral action action Torticollis Contraction or shortening of the SCM that produces lateral flexion of the neck toward the affected side and turning of the face away from the affected side. Common causes of congenital torticollis: fibrous tissue tumor in the SCM, injury during birth Spasmodic torticollis can occur in adults and can affect multiple muscles, commonly SCM and trapezius Posterior Triangle (lateral cervical region) Borders: Anterior: Posterior border of sternocleidomastoid Posterior: anterior border of trapezius Inferior: middle 1/3 of clavicle Semispinalis capitis Apex: superior meeting of SCM and trapezius Floor: muscles covered by prevertebral fascia 1. (Semispinalis capitis) Splenius capitis 2. Splenius capitis 3. Levator scapulae 4. Posterior scalene Levator scapulae 5. Middle scalene Posterior scalene 6. (Anterior scalene) Middle scalene Anterior scalene Inferior belly of omohyoid traverses Omohyoid (inferior belly) the posterior triangle Vessels of the posterior triangle Anterior scalene Occipital a. (not shown) Transverse cervical a. Dorsal scapular a. External jugular v. Subclavian a. Suprascapular a. Subclavian v. Transverse cervical a. Thyrocervical trunk Subclavian a. Dorsal scapular a. **Note the relationship of the subclavian vessels to the anterior scalene muscle** Suprascapular a. Subclavian v. Nerves of the posterior triangle Phrenic n. Anterior scalene Nerves of the posterior triangle COA Error: C5-T1 Anterior Triangle (anterior cervical region) Anterior Triangle Borders: Anterior: median line of neck Posterior: anterior border of sternocleidomastoid Superior: inferior border of mandible Apex: jugular notch in manubrium Floor: pharynx, larynx, and thyroid gland Anterior triangle Carotid Sub-triangles: Muscular Submental Submandibular Carotid Muscular Refer to COA Table 9.1 (9th Ed, p.1009) for a list of triangle contents Muscles of the anterior triangle Suprahyoid muscles Mylohyoid Anterior belly of digastric Elevate the hyoid and Stylohyoid larynx for swallowing and speaking Stylohyoid Mylohyoid Geniohyoid Intermediate Stylohyoid tendon of digastric Posterior Digastric Mylohyoid Geniohyoid Omohyoid belly of digastric (superior belly) Infrahyoid muscles Thyrohyoid Depress hyoid and larynx Sternohyoid during swallowing and speaking Omohyoid Omohyoid (inferior Sternohyoid belly) Sternothyroid Thyrohyoid Sternothyroid Vessels of the anterior triangle Carotid sheath contents: Common and internal carotid arteries Internal jugular vein Vagus nerve (CN X) Vessels of the anterior triangle Common carotid artery branches from: Brachiocephalic trunk (R) Aortic arch (L) Common carotid bifurcates approx. at the superior border of thyroid cartilage into internal and external carotid arteries. Carotid sinus: dilation of proximal ICA. Baroreceptor that reacts to changes in blood pressure. Carotid body: small tissue bundle lying on the bifurcation of common carotid. Chemoreceptor that monitors blood oxygen level. Innervated by carotid sinus nerve, branch of CN IX. Branches of external carotid artery 1. Ascending pharyngeal a. 2. Occipital a. 3. Posterior auricular a. 4. Superior thyroid a. → superior laryngeal a. 5. Lingual a. 6. Facial a. 7. Maxillary a. terminal branches 8. Superficial temporal a. of ECA Nerves of the anterior triangle Ansa cervicalis: nerve loop comprised of fibers Cutaneous innervation: transverse cervical nerve from C1-3 that lies on the anterior surface Motor to infrahyoid muscles: branches of ansa cervicalis of/embedded within the carotid sheath. Superior root: C1 and C2, joins then descends from hypoglossal n. (CN XII) Inferior root: C2 and C3 Hypoglossal n. (CN XII) Ansa cervicalis – superior root Ansa cervicalis – inferior root Vagus n. (CN X) Nerves of the anterior triangle – Cranial Nerves Traverses posterior triangle Branch supplying carotid sinus and body Traverses carotid & submandibular triangles; travels (C1 fibers only) briefly with superior root of ansa cervicalis. Within carotid sheath; pharyngeal, laryngeal and cardiac branches arise in the neck Thyroid and parathyroid glands Thyroid gland: secretes thyroid hormone and calcitonin Deep to sternothyroid and sternohyoid muscles Right and left lobes anterolateral to the larynx and trachea, connected by a narrow isthmus Common variant: Pyramidal lobe Blood supply: superior and inferior thyroid arteries Parathyroid glands: secrete parathormone (PTH) Posterior surface of each lobe of thyroid gland; external to its fibrous capsule Most people have 4 parathyroid glands Deep structures of the neck - arteries Ascending cervical artery Transverse cervical artery Suprascapular artery Inferior thyroid artery Dorsal scapular artery Thyrocervical trunk Deep structures of the neck - nerves Vagus nerves: pass anterior to the subclavian arteries and posterior to the brachiocephalic veins. Recurrent laryngeal nerves: supply most muscles of the larynx (R): loops around right subclavian artery (L): loops around arch of the aorta After looping around arteries, ascend in the tracheo-esophageal groove to the posteromedial aspect of the thyroid gland Right vagus Left vagus nerve nerve Left recurrent Right recurrent Right recurrent laryngeal nerve laryngeal nerve laryngeal nerve Deep structures of the neck - nerves Sympathetic trunks: Anterolateral to vertebral column 3 cervical sympathetic ganglia: superior, middle, and inferior. *Stellate ganglion: inferior cervical ganglion fused with 1st thoracic ganglion Lymphatics of the neck Lymph from superficial neck drains to superficial cervical lymph nodes, located along the external jugular vein. These nodes, along with lymph from deep neck tissues, drain to deep cervical lymph nodes, and then to the right lymphatic duct or the thoracic duct at the respective venous angles. Cervical plexus – reference images