Neck

Skin

• Relaxed skin tension lines generally have a gentle slope posterior to anterior

Fascia

• Many of the so-called fascial layers in the neck are over-defined and don't amount to much more than a slight thickening of connective tissue, which does not have much surgical importance

Deep cervical fascia

• • Superficial (investing) layer - comparable to deep fascia underlying subcutaneous fat in limbs etc. Surrounds neck like a collar. Splits around SCM and trapezius, with anterior and posterior layers adherent to them. Attached to skull between hyoid and occiput. Splits to form a capsule for the parotid - forming parotid fascia superficially; deep layer attaches to tympanic plate; forms the stylo-mandibular tunnel, through which tumours from parotid can spread. Lower attachment is to pectoral girdle.
  • Pre-tracheal fascia - deep to straps, but splits to enclose thyroid gland. Fuses laterally with the front of carotid sheath. Essentially provides a slipper surface so the trachea can glide up and down.
  • Pre-vertebral fascia- a firm tough membrane that lies in front of the prevertebral muscles. Covers the floor of posterior triangle, but accessory nerve is superficial to it. Cervical plexus and trunks of brachial plexus lie deep to it. Becomes prolonged as axillary sheath.
  • Carotid sheath - not really a fascia, just a feltwork of areolar tissue surrounding the carotids, IJV and vagus.

Tissue spaces

• Pre-vertebral space - enclosed within pre-vertebral fascia, no entry without breaching fascia.
• Retro-pharyngeal space - immediately in front of pre-vertebral fascia, extending from base of skull to diaphragm, continuous with posterior mediastinum. Can become involved in infections spreading from the pharynx, and infection can then spread behind the carotid sheath into the posterior triangle. Between the pre-vertebral fascia posteriorly and the bucco-pharyngeal fascia (on the outer surface of the pharynx) anteriorly.
• Para-pharyngeal space - lateral continuation of retropharyngeal space. Bounded laterally by pterygoid muscles and parotid sheath. Continuous anteriorly in the upper neck with the submandibular space.
• Sub-mandibular space - Infection here produces Ludwig's angina.
  • Roof: investing layer of deep cervical fascia
  • Floor: floor of mouth
  • Inferior: hyoid
  • Superior: mandible

Bones/cartilage

• Thyroid cartilage - 'shield' is top
• Cricoid cartilage - 'ring' (because it resembles a signet ring) is the second cartilage

Muscles

Platysma

• • Broad sheet of muscle fibres
  • Extends from midline downwards beyond clavicle, superiorly up to mandible where it blends with facial muscles, and as far posteriorly as about EJV
  • Supplied by cervical branch of facial nerve

Digastric

• • Anterior belly arises from the back of mandible, in a fossa near the midline
  • Intermediate tendon held by a fibrous sling to the hyoid
  • Posterior belly passes backwards and upwards to insert on the medial side of mastoid process (deep and anterior to SCM)
    • Crosses internal and external carotid arteries, the hypoglossal nerve, IJV, the transverse process of the atlas, and the accessory nerve
  • Supplied by a branch from the facial nerve

Sternocleidomastoid

• • Arises from the front of manubrium and superior surface of medial clavicle, and ascends obliquely backwards to insert into the outer surface of the mastoid process and the anterior part of the superior nuchal line
  • EJV courses across it from below the earlobe to about the midpoint of the clavicle, from where it plunges deep
  • Cutaneous nerves of neck are closely related (see below)
  • Nerve supply from accessory nerve from the muscle's deep surface, about 5cm below mastoid process
  • Main function is level rotation of the head

Scalenes

• • Descend from transverse process of first six or seven cervical vertebrae to insert in the first two ribs
  • Subclavian artery and brachial plexus found between middle and anterior scalenes
  • Lateral border of anterior scalene is about the same as lateral border of SCM
  • Supplied by branches of the cervical nerve roots
  • Thyrocervical trunk of subclavian artery typically arises alongside the medial border of the scalenus anterior muscle
  • Phrenic nerve crosses anterior scalene from lateral to medial

Infrahyoid strap muscles - function of swallowing, depressing larynx; depressing hyoid. Nerve supply via ansa cervicales, often dual innervation above level of lower border of thyroid cartilage and also at level of suprasternal notch - so divide midway between lower border of thyroid cartilage and suprasternal notch.

• • Sternohyoid
    • Originates from back of manubrium; ascends to body of hyoid
  • Omohyoid
    • Inserts immediately lateral sternohyoid on hyoid bone; passes downwards to an intermediate tendon behind SCM (held in position by a condensation of cervical fascia attaching it to clavicle); then passes obliquely to upper border of scapula, near scapula notch
  • Sternothyroid
    • Arises from back of manubrium inferior to origin of sternohyoid; passes upwards; inserts on thyroid cartilage
  • Thyrohyoid
    • Direct extension of sternothyroid
    • Arises from line of insertion of sternothyroid; inserts to body and greater cornu of hyoid

Structures

Submandibular gland

• • Paired salivary glands located behind and below the ramus of the mandible
  • Embryology - ectodermal origin
  • Two lobes
    • Large superficial lobe - between mandible, mylohyoid and the surrounding fascia
    • Smaller deep lobe - between mylohyoid and hyoglossus
  • Relations
    • Lies in submandibular triangle - between anterior and posterior bellies of the digastric, and the inferior border of the mandible. Floor hyoglossus/mylohyoid. Roof platysma.
    • Lateral surface
      • Mandible
      • Deeply grooved by the facial artery which hooks under the mandible to reach the face, running between mandible and gland
    • Superficial/inferior surface
      • Skin, platysma, investing fascia
      • Crossed by the facial vein and cervical branch of facial nerve
      • Can also be crossed by marginal mandibular branch, if that is running very low
    • Medial surface
      • Lies against mylohyoid
      • Towards the back it overlaps the hyoglossus, lingual nerve, submandibular ganglion, hypoglossal nerve and deep lingual vein
  • Has a secretomotor ganglion nearby - submandibular ganglion. Hangs from lingual nerve above deep part of submandibular gland.
  • Submandibular duct runs forwards between mylohyoid and hyoglossus muscles, and then between the sublingual gland and the genioglossus muscle before opening at the sublingual papilla, close to midline in anterior floor of mouth
    • Lingual nerve (branch of CN V3) passes around the duct, also running between hyoglossus and mylohyoid, can be injured during duct ligation
  • Hypoglossal nerve is below the gland, but usually quite separate, seen lying on hyoglossus
  • Blood supply - branches of facial and lingual arteries, drainage to facial vein
  • There are often submandibular lymph nodes nearby too, which drain to jugulodigastric lymph nodes
  • Innervation
    • Superior salivary nucleus
    • Facial nerve
    • Chorda tympani
    • Lingual nerve
    • Submandibular ganglion (hangs from lingual nerve above the deep part of the gland)

Trachea

• • Begins at lower border of the cricoid cartilage and descends in neck in front of oesophagus
  • Tracheostomy through rings 2-6 or 7 - avoid going too high because it can cause dysphagia, and maybe stenosis later
  • Main blood supply through inferior thyroid arteries
  • Nerve supply from vagus and RLN

Arteries

Common carotid artery

• • Origin
    • Right - brachiocephalic trunk bifurcates into common carotid and subclavian
    • Left - arises from the arch of the aorta
  • Course
    • Posterior to sternoclavicular joint
    • Lies within the medial part of the carotid sheath, with IJV lateral to it and vagus nerve deep between the two vessels
    • Lateral to the larynx and trachea
    • Sympathetic trunk is behind the artery and outside the sheath
  • Branches
    • None
    • Bifurcates into internal and external carotids near the great horn of the hyoid bone (C4). A good marker is the tendon joining the two bellies of omohyoid. Deep to the anterior margin of SCM. The facial vein also usually crosses the bifurcation.
  • Surgical exposure
    • See 'carotid endarterectomy'

External carotid artery

• • Course
    • Initially medial to ICA, then slopes upward in front of ICA
    • Passes deep to posterior belly of digastric and stylohyoid
    • Pierces parotid fascia to enter the gland, where it divides into two terminal branches
  • Branches ('some anatomists like f***ing over poor medical students')  - from caudal to cranial:
    • One from deep/medial
      • Ascending pharyngeal
    • Three from the front
      • Superior thyroid
      • Lingual
      • Facial
    • Two from behind
      • Occipital - look for hypoglossal nerve at this level
      • Posterior auricular
    • Terminal branches
      • Maxillary
      • Superficial temporal

Internal carotid artery

• • Course
    • At its commencement shows a slight bulge (carotid sinus)
    • Lateral to ECA at origin
    • Slopes up posteriorly to occupy a deeper level
    • Continues upwards within the carotid sheath
    • Beside the pharynx to the carotid canal in the base of skull
  • Branches
    • No branches in the neck (cervical segment C1)
    • Branches from the petrous (C2 - ophthalmic artery), cavernous (C4), and ophthalmic (C6) segments
    • Terminates as the middle and anterior cerebral arteries

Subclavian artery

• • Asymmetric paired arteries that supply blood to the posterior cervical circulation, cerebellum, posterior neck, upper limbs and the chest wall
  • Origin
    • Right: terminal branch of the brachiocephalic artery
    • Left: third branch of the aortic arch
  • Course
    • Exits the thorax via the superior thoracic aperture between the anterior and middle scalene muscles
    • Then passes between the first rib and clavicle to continue as the axillary artery
  • Parts
    • The vessel can be split into three parts depending on the position in relation to scalenus anterior
    • First part (origin to medial border scalenus anterior)
      • Vertebral artery, coursing cranially, arising from posterior/superior aspect
        • Ascends behind CCA for 3cm before entering the foramen of the transverse process of C7
        • Stellate ganglion tends to lie behind it
      • Internal thoracic artery, coursing caudally, from inferior surface
        • See separate topic under 'thoracic cavity'
      • Thyrocervical trunk, which divides into four branches, from superior surface, opposite internal thoracic origin
        • Inferior thyroid
        • Suprascapular
        • Transverse cervical
        • Ascending cervical
    • Second part (posterior to scalenus anterior, as much as 2cm above clavicle)
      • Costocervical trunk, which courses cranially before bifurcating into superior intercostal and deep cervical
    • Third part (from the lateral border of scalenus anterior to lateral border of first rib)
      • Dorsal scapular artery, which courses posteriorly to join the scapular anastomosis
  • Branches
    • VIT C, D
    • Very Indignant Tired Individuals Sip Tasty Almond Coffee Served Double Daily (including branches)
  • Variants
    • Aberrant right subclavian - arteria lusoria

Veins

• IJV and EVJ sandwich SCM, and the two veins communicate distally through the retromandibular veins

EJV

• • Mostly lies deep to platysma
  • Commences at lower border of parotid, with union of posterior division of retromandibular vein and posterior auricular vein
  • Penetrates deep fascia and joins subclavian vein just above the midpoint of the clavicle
  • Tributaries:
    • Anterior jugular
    • Transverse cervical
    • Suprascapular
    • Posterior external jugular vein

IJV

• • Formed by the union of inferior petrosal and sigmoid dural venous sinuses, in or just distal to the jugular foramen
  • Descends in carotid sheath with ICA, then more distally in between the two heads of SCM
  • Unites with the subclavian vein to form the brachiocephalic vein
  • Tributaries
    • Pharyngeal veins
    • Common facial vein - usually enters IJV at the level of the carotid bifurcation
    • Lingual vein
    • Superior thyroid vein
    • Middle thyroid vein

Nerves

Glossopharyngeal nerve (CN IX)

• • Leaves skull through jugular foramen
  • Superior to hypoglossal
  • Passes between IJV and ICA
  • Curves forward, lying upon stylopharyngeus and middle pharyngeal constrictor
  • Deep to hyoglossus

Hypoglossal nerve (CN XII)

• • Motor nerve to all the muscles of the tongue, except palatoglossus
  • Emerges from hypoglossal canal, and crosses behind IVJ but in front of ECA/ICA, 1-2cm above the carotid bifurcation (gives off hitching C1 fibres to ansa cervicales)
  • Curves forward at the level of the angle of the mandible
  • Emerges from behind posterior belly of digastric and over occipital branch of ECA
  • Crosses over the loop of the lingual artery
  • Passes up in between hyoglossus and mylohyoid, inferior to deep part of submandibular gland
  • Continues forward deep to floor of mouth and reaches tip of tongue

Ansa cervicales - the nerve loop supplying the strap muscles, with parts from both C1 (hypoglossal) and C2-C3 (cervical plexus).

• • Carries fibres from C1 which curve off from the hypoglossal nerve as it passes
  • C2-3 fibres come down on the lateral surface of IJV before curving forwards to join the upper root
  • The union between upper and lower fibres occurs at the point where omohyoid crosses carotid.
  • Passes down along medial side of CCA

Cervical plexus

• • Superior root of ansa cervicales (C1)
  • Branches to SCM (C2 and C3)
  • Branches to trapezius (C3 and C4)
  • Inferior root of ansa cervicales (C2 and C3)
  • Phrenic nerve
  • Cervical cutaneous nerves - arise from C2-C4 spinal nerves. Emerge from posterior surface of SCM. Note 'Erb's point' where these nerves emerge from SCM is the target for a regional block.
    • Lesser occipital nerve (C2) passes upwards and backwards along the posterior border of SCM and supplies skin from auricle back to occipit
    • Great auricular nerve (C2, 3) passes upwards immediately behind EJV to supply skin of the auricle and pre-auricular region, lying deep to platysma. Anterior division supplies skin over parotid and ear lobe, and posterior division supplies retro-auricular skin.
    • Transverse cervical nerve (C2, 3) passes horizontally across SCM to supply skin of anterior neck
    • Supraclavicular nerve (C3, 4) passes downwards and divides into branches which pass over the clavicle supplying the more lateral reaches of the neck

Lymphatic drainage

• Horizontal ring: submental, submaxillary, parotid, retro-auricular and occipital nodes
• Vertical:
  • Main lymphatic drainage is arranged along the IJV as a vertical chain, especially posteriorly and lateral to the vein
  • Superficial vertical drainage along superficial cervical (EJV) and anterior cervical (anterior jugular veins)

Lymph node levels

• 1: Hyoid inferiorly, mandible superiorly, and laterally a line from posterior submandibular gland to anterior SCM
• 2-3-4 along SCM:
  • 2: Superiorly mandible/skull base, laterally posterior SCM, inferiorly hyoid, medially a line between posterior submandibular gland and anterior SCM
  • 3: A square - superiorly level of hyoid, inferiorly level of cricoid cartilage, medially carotid, laterally posterior SCM
  • 4: Superiorly level of cricoid cartilage, inferiorly clavicle, medially anterior SCM/carotid, laterally posterior SCM
• 5: Laterally trapezius, medially posterior SCM, inferiorly clavicle
• 6: Superiorly hyoid, laterally carotid, inferiorly sternal notch
• 7: Pre-tracheal and paratracheal superior mediastinal lymph nodes down to level of innominate artery

Triangles

Anterior triangle

• • Between anterior border of SCM, mandible, midline
  • Roof - investing layer of deep cervical fascia
  • Floor - pre-vertebral fascia
  • Can be divided further into carotid, digastric, muscular and submental triangles
  • Contents
    • Arteries
      • Carotid sheath/branches of ECA
    • Veins
      • IJV, EJV and tributaries
    • Nerves
      • Vagus
      • Hypoglossal
      • Ansa cervicales
      • Nerve to mylohyoid
    • Glands
      • Thyroid and parathyroid
      • Trachea
      • Hyoid bone
      • Nodes
      • Oesophagus

Posterior triangle

• • Between posterior border of SCM, middle third of clavicle, anterior border of trapezius
  • Roof - investing layer of deep cervical fascia
  • Floor - pre-vertebral fascia
    • Splenius capitis
    • Levator scapulae
    • Scalenus medius
  • Contents
    • Occipital artery (at apex)
    • Lymph nodes of the posterior triangle
    • Accessory nerve (CN XI - see above)
    • Cutaneous branches of cervical plexus
    • Inferior belly of omohyoid
    • Transverse cervical and supra-scapular vessels
    • Third part of subclavian artery
    • EJV

Zones - see separate topic under 'trauma'

• Zone 1 - root of neck to cricoid cartilage
• Zone 2 - upper part of zone 1 to the angle of the mandible
• Zone 3 - angle of mandible to skull base