Part 3 - Neck

• Bones of the Neck


  • Cervical Vertebrae
  • Atlas (C1)
  • Axis (C2)
  • Vertebra prominens (C7)

  
• Typical cervical vertebrae (C3-C6)


  • Small vertebral body (concave superiorly and convex inferiorly)
  • Large and triangular vertebral foramen
  • Transverse foramina in the transverse processes (where vertebral arteries run towards the head)
  • Superior facets of articular processes directed superoposteriorly
  • Inferior facets of articular processes directed inferoposteriorly
  • Short spinous processes

  
• Atlas (C1)

  • Ring-like and kidney shaped
  • Lacks a spinous process and body
  • Consists of 2 lateral masses connected by anterior and posterior arches
  • Concave superior articular facets receive the occipital condyles

  
• Axis (C2)

  • A peg-like dens projects superiorly from its body (odontoid process)
• Vertebra prominens (C7)


  • Has a long spinous process that is not bifid
  • Has large transverse processes but small transverse foramina

  
• Hyoid


  • Lies anteriorly at the level of C3 between mandible and thyroid cartilage
  • Has no articulations with any other bone
  • Suspended from the styloid process of temporal bones by the stylohyoid ligaments
  • Firmly bound to the thyroid cartilage

  
• Superficial Cervical Fascia


  • Layer of fatty connective tissue lying between the dermis of the skin and the investing layer of the deep cervical fascia
  • Thinner than superficial fascia in other regions of the body, especially anteriorly
  • Contains cutaneous nerves, blood and lymphatic vessels, superficial lymph nodes, variable amounts of fat, and the platysma muscle

  
• Cutaneous and superficial muscles of the neck


  • Platysma
  • Sternocleidomastoid (SCM)
  • Trapezius

  
• Platysma


  • Originates from the inferior border of mandible, inserts into the skin and subcutaneous tissue and the deep fascia covering superior parts of deltoid and pectoralis major
  • Innervated by the cervical branch of the facial nerve
  • Draws corners of mouth inferiorly and tenses skin of the neck

  
• Sternocleidomastoid (SCM)


  • Originates from the lateral surface of the mastoid process of the temporal bone and the lateral half of the superior nuchal ligament
  • Sternal head originates from the anterior surface of the manubrium of sternum, clavicular head originates from the superior surface of the medial third of the clavicle
  • Innervated by the spinal accessory nerve for motor function and by C3 & C4 for pain and proprioception
  • Unilateral contraction tilts the head to the same side, bilateral contraction extends the neck at the atlantooccipital joint, brings the chin to the manubrium, and thrusts the chin forward while the head is kept at the same level

  
• Trapezius


  • Originates from the medial third of the superior nuchal line, the external occipital protuberance, the nuchal ligament, and the spinous processes of C7-T12 vertebrae
  • Inserts onto the lateral third of the clavicle, the acromion, and the spine of the scapula
  • Innervated by the spinal accessory nerve for motor function and by C3 & C4 for pain and proprioception
  • Descending part elevates the scapulae, ascending part depresses the scapulae, all parts retract the scapulae, and the ascending and descending parts rotate the glenoid cavities superiorly

  
• Layers of deep cervical fascia


  • Investing
  • Pretracheal
  • Prevertebral
  • Carotid

  
• Investing layer of deep cervical fascia


  • Most superficial layer of deep fascia
  • Surrounds the entire neck deep to the skin and subcutaneous tissue
  • At the 4 corners of the neck, it splits into superficial and deep layers to enclose the trapezius and sternocleidomastoid muscles
  • Superior attachments: superior nuchal lines of occipital bone, mastoid processes of temporal bones, zygomatic arches, inferior border of mandible, hyoid bone, spinous processes of cervical vertebrae
  • Inferior attachments: manubrium of sternum, clavicles, acromions and spines of scapulae
  • Contains the sternocleidomastoid, trapezius, submandibular gland, and parotid gland
  • Continuous with the periosteum of C7 spinous process and with the nuchal ligament
  • Splits into 2 above the manubrium to enclose the sternocleidomastoid, with one layer attaching to the anterior and the other to the posterior surface of the manubrium, enclosing the suprasternal space

  
• Pretracheal layer of deep cervical fascia


  • Limited to the anterior part of the neck
  • Extends inferiorly from the hyoid to the thorax where it blends with the pericardium
  • Has a thin muscular part that encloses the infrahyoid muscles, and a visceral part that encloses the thyroid gland, trachea and oesophagus
  • Continuous posteriorly and superiorly with the buccopharyngeal fascia of the pharynx, and blends laterally with the carotid sheaths

  
• Prevertebral layer of deep cervical fascia


  • Forms a tubular sheath for the vertebral column and the muscles associated with it (longus colli, longus capitis, scalenes, deep cervical muscles)
  • Extends superiorly to the cranial base and inferiorly blends with the endothoracic fascia peripherally and fuses with the anterior longitudinal ligament centrally at the T3 vertebra
  • Continuous laterally with the axillary sheath

  
• Carotid layer of deep cervical fascia


  • Extends from the cranial base to the root of the neck
  • Communicates with the mediastinum and cranial base, allowing for the spread of infection and extravasated blood
  • Blends anteriorly with the investing and pretracheal layers and posteriorly with the prevertebral layer
  • Contains the common and internal carotid arteries, internal jugular vein, vagus nerve, carotid sinus nerve, sympathetic nerve fibers, and deep cervical lymph nodes

  
• Retropharyngeal space


  • Potential space consisting of loose connective tissue
  • Extends superiorly between the prevertebral layer (deep) and buccopharyngeal fascia (superficial), and inferiorly the buccopharyngeal fascia is continuous with the pretracheal layer

  
• Alar fascia


  • Subdivides the retropharyngeal space into anterior and posterior compartments
  • Attached along the midline of the buccopharyngeal fascia from the cranium to the C7 vertebral level, extending laterally and terminating in the carotid sheath
  • Closed superiorly by the cranial base and on each side by the carotid layer, opens inferiorly into the mediastinum
  • Allows movement of the pharynx, oesophagus, larynx and trachea

  
• If infection occurs between the investing layer and muscular part of pretracheal fascia


  Infection will not spread to mediastinum
• If infection occurs between the investing layer and visceral part of the pretracheal fascia


  Infection can spread to thoracic cavity anterior to mediastinum
• If infection occurs posterior to the prevertebral layer


  Pus may perforate the prevertebral layer and enter the retropharyngeal space, causing a bulge in the pharynx that leads to difficulty swallowing and speaking
• If infection occurs in the head

  May spread posterior to oesophagus to posterior mediastinum or anterior to the trachea to the anterior mediastinum
• If infection occurs in the retropharyngeal space

  May spread to the superior mediastinum
• Muscles of the anterior cervical region (extrinsic muscles of the larynx)

  • Suprahyoid muscles: Mylohyoid, Geniohyoid, Stylohyoid, Digastric
  • Infrahyoid muscles: Sternohyoid, Omohyoid, Sternothyroid, Thyrohyoid

  
• Mylohyoid


  • Originates from the mylohyoid line of the mandible, inserts into the mylohyoid raphe and body of the hyoid
  • Innervated by the nerve to mylohyoid from CN V3
  • Elevates the hyoid, floor of the mouth, and tongue
• Geniohyoid


  • Originates from the inferior mental spine of the mandible, inserts into the body of the hyoid
  • Innervated by C1 via CN XII
  • Pulls the hyoid anterosuperiorly, shortens the floor of the mouth and widens the pharynx

  
• Stylohyoid


  • Originates from the styloid process of the temporal bone, innervated by the stylohyoid nerve from CN VII
  • Elevates and retracts the hyoid, elongating the floor of the mouth

  
• Digastric

  • Anterior belly originates from the digastric fossa of the mandible, posterior belly originates from the mastoid notch of the temporal bone
  • Intermediate tendon inserts into the body and greater horn of the hyoid
  • Anterior belly innervated by the nerve to mylohyoid from CN V3, posterior belly innervated by the digastric branch of CN VII
  • Depresses the mandible against resistance, elevates and steadies the hyoid during swallowing and speaking
• Sternohyoid

  • Originates from the manubrium of the sternum and medial end of the clavicle, inserts into the body of the hyoid
  • Innervated by C1-C3 via a branch of the ansa cervicalis
  • Depresses the hyoid after elevation during swallowing
• Omohyoid


  • Originates from the superior border of the scapula near the suprascapular notch, inserts into the inferior border of the hyoid
  • Depresses, retracts and steadies the hyoid
• Sternothyroid


  • Originates from the posterior surface of the manubrium, inserts into the oblique line of the thyroid cartilage
  • Innervated by C2-C3 via a branch of the ansa cervicalis
  • Depresses the hyoid and larynx
• Thyrohyoid


  • Originates from the oblique line of the thyroid cartilage, inserts into the inferior border of the body and greater horn of the hyoid
  • Innervated by C1 via CN XII
  • Depresses the hyoid and elevates the larynx
• Anterior Triangles of the Neck


  • Submental Triangle
  • Submandibular Triangle
  • Muscular Triangle
  • Carotid Triangle
• Submental Triangle


  Lateral boundaries: Anterior bellies of digastric muscle

  Inferior boundary: Hyoid bone

  Apex: Mandible

  Floor: Mylohyoid muscle

  Contents: Anterior jugular veins, submental lymph nodes

  
• Submandibular Triangle


  Superior boundary: Ramus of mandible

  Inferior anterior and posterior boundaries: Anterior and posterior bellies of digastric muscle

  Floor: Mylohyoid, hyoglossus, and middle constrictor muscle of the pharynx

  Roof: Investing fascia

  Contents: Submandibular gland, submandibular lymph nodes, hypoglossal nerve (CN XII), nerve to mylohyoid, parts of facial artery and vein

  
• Muscular Triangle


  Superior boundary: Superior belly of omohyoid

  Inferior boundary: Anterior border of sternocleidomastoid

  Medial boundary: Midline

  Floor: Pretracheal fascia

  Contents: Infrahyoid muscles, thyroid and parathyroid glands, recurrent laryngeal nerve

  
• Carotid Triangle


  Superior boundary: Posterior belly of digastric muscle

  Inferior boundary: Superior belly of omohyoid

  Lateral boundary: Anterior border of sternocleidomastoid

  Floor: Thyrohyoid, middle and inferior constrictor muscles of the pharynx

  Contents: Common carotid artery, internal and external carotid arteries, carotid sinus and carotid body, internal jugular vein, glossopharyngeal nerve, vagus nerve, spinal accessory nerve, hypoglossal nerve, superior root of ansa cervicalis, branches of cervical plexus, thyroid gland, larynx and pharynx, deep cervical lymph nodes

  
• Boundaries of the posterior triangle of the neck

  • Anterior: Posterior border of sternocleidomastoid

  Posterior: Anterior border of trapezius

  Inferior: Middle ⅓ of the clavicle

  Apex: At superior attachments of sternocleidomastoid and trapezius

  Roof: Investing fascia

  Floor: Prevertebral fascia and muscles (splenius capitis, levator scapulae, middle/posterior/anterior scalene)

  
• Divisions of the posterior triangle


  • Occipital triangle

  Omoclavicular triangle
• Occipital Triangle


  Superficial contents: Cutaneous branches of cervical plexus (C1-4), external jugular vein, superficial branch of transverse cervical artery, superficial cervical lymph nodes

  Deep contents: Spinal accessory nerve (CN XI), phrenic nerve, trunks and roots of brachial plexus, occipital artery, thyrocervical trunk (1st part of subclavian artery)