GenSurg.nz

Head and neck anatomy

General Topography

  • T1 Thoracic Vertebra – Highest part of sloping Thoracic Inlet

  • Cervical column rises above gently convex forwards

  • Extensor muscles lie behind vertebrae

    • Supplied segmentally by Posterior Rami of Cervical Nerves emerging from Intervertebral Foramina

  • Flexor muscles (smaller amount)

    • Lies in front of the Vertebrae
    • Covered by Prevertebral Fascia
    • Lies behind the Pharynx
    • Supplied segmentally by Anterior Rami

  • C1 Vertebra level:

    • Hard Palate

  • C2 Vertebra level: Tip of Chin/Jaw

  • Between C2 and C3:

    • Lower border of the Mandible

  • C4 Vertebra level: Bifurcation of Common Carotid Artery

  • Pharynx extends from Base of Skull to level of Cricoid Cartilage (C6)

    • Then continues on as Oesophagus

  • C6 Vertebra level: Omohyoid crossing Common Carotid

  • Larynx and Trachea:

    • Anterior to lower Pharynx and upper Oesophagus
    • Hyoid Bone lies above Larynx at C3 Vertebra level
      • Connected to Mandible via Mylohyoid muscles (at the upper limit of anterior part of neck and form floor of mouth)

  • Carotid Sheath:

    • On each side of the Pharynx
    • Contains Common and Internal Carotid Arteries, Internal Jugular Vein with Cervical Sympathetic Trunk behind
    • External Carotid Artery lies outside the Sheath

  • Cranial nerves anatomy:

    • 9th, 10th, 11th and 12th Cranial Nerves descend into the neck
    • 9th and 12th pass forwards to Oropharynx and Tongue
    • 11th runs backwards to Sternocleidomastoid and Trapezius muscles
    • 10th continues down in Carotid Sheath

Fascia of the neck

Superficial cervical fascia

  • The contents of the superficial cervical fascia will vary depending upon location but include:
    • Platysma (and cervical branch of facial nerve that innervate the muscle)
    • Cutaneous nerves of the cervical plexus:
      • Lesser occipital
      • Great auricular
      • Transverse cervical (largest sensory contribution)
      • Supraclavicular
  • Deep to the superficial cervical fascia is the investing (or superficial) layer of deep cervical fascia

Superficial Structures

Platysma

  • Lies superficial to Investing Layer of Deep Cervical Fascia
  • Extends from fascia over upper parts of Pectoralis Major and Deltoid to lower border of Mandible
  • Some fibres extend into face blending with fascial expression muscles
  • Covers External and Anterior Jugular Veins
  • Separated below but converge above towards midline just beneath chin
  • Nerve Supply:
    • Cervical Branch of Facial Nerve
    • Afferent (proprioceptive) fibres run with Transverse Cervical Nerve
  • Action:
    • Involved in facial expression
    • May assist in mouth opening

Anterior Jugular Veins

  • Commence beneath chin from the confluence of the submental and submandibular veins
  • Side by side beneath Platysma
  • Reaches Suprasternal region
    • Pierce Deep Fascia and come to lie in Suprasternal Space (often connected by a short anastomotic vein - the jugular venous arch)
  • Angles laterally to pass deep to Sternocleidomastoid but superficial to Strap muscles
  • Opens into the External Jugular Vein near its termination

Deep Cervical Fascia

  • Four parts:
    1. Superficial (Investing) Layer
    2. Pretracheal Fascia
      • Posterior portion called the buccopharyngeal fascia - technically not part of the the pretracheal fascia but is continuous with it
    3. Prevertebral Fascia
      • Alar fascia is a delamination of the prevertebral fascia that swings forward to attach to the buccopharyngeal fascia approximately at the C7 vertebral level.
    4. Carotid Sheath

1. Investing Layer

  • Superficial investing fascia of the deep cervical fascia - confusing as there is also a superficial cervical fascia (above)
  • Surrounds neck like a collar
  • Splits around Sternocleidomastoid and Trapezius
    • NB: Investing layer does NOT enclose the infra-hyoid muscles
  • Posteriorly, blends with Ligamentum Nuchae (attached to spines of Cervical Vertebrae)
  • Anteriorly – attached to Hyoid bone
  • Above – attached to lower border of the Mandible
  • Also attached to:
    • Superior Nuchal Line
    • External Occipital Protuberance at Base of Skull
  • Encloses Parotid Gland between the Angle of the Mandible and the Tip of the Mastoid Process

2. Prevertebral Fascia

  • Lies in front of the Prevertebral muscles
  • Extends from Base of Skull downwards to blend with Anterior Longitudinal Ligament of T4 Vertebral Body in the Superior Mediastinum
  • Alar fascia is a delamination of the prevertebral fascia that swings forward to attach to the buccopharyngeal fascia approximately at the C7 vertebral level.

3. Pretracheal Fascia

  • Deep to Infrahyoid Strap muscles (Sternothyroid, Sternohyoid, Omohyoid)
  • Upward attachment limited by respective attachments of those muscles
    • I.e. Body of Hyoid Bone and Oblique Line of Thyroid Cartilage
  • Splits to enclose Thyroid Gland
  • Not adherent to Thyroid except:
    • At back of Isthmus – attached to 2nd, 3rd and 4th Tracheal Rings
  • Laterally – fuses with front of Carotid Sheath on deep surface of Sternocleidomastoid
  • Inferiorly – passes behind Brachiocephalic Veins to blend with Adventitia of Aortic Arch and Fibrous Pericardium
    • Thus, neck infections in front of the Pretracheal Fascia is directed into the anterior mediastinum
  • Part of Cervical Visceral Fascia surrounding Pharynx, Oesophagus, Larynx and Trachea
    • This is the buccopharyngeal fascia

4. Carotid Sheath

  • Feltwork of areolar tissue
  • Surrounds Common and Internal Carotid Arteries, Internal Jugular Vein, Vagus Nerve, and Deep Cervical Lymph Nodes
    • Common Carotid Artery is medial to the Internal Jugular Vein
      • Vagus Nerve deeply place between the two vessels

Strap Muscles

  • a.k.a. Infrahyoid Muscles
  • Consist of Sternohyoid, Omohyoid, Sternothyroid, Thyrohyoid
MuscleOriginInsertionActionsNerve Supply
Omohyoid (superior and inferior bellies connected by a tendon)Superior border of the scapulaBody of the hyoidDepresses the hyoidAnsa cervicalis
SternohyoidManubriumBody of the hyoidDepresses the hyoid
SternothyroidManubriumOblique line of the thyroid cartilageDepresses the larynx
ThyrohyoidOblique line of the thyroid cartilageGreater cornu (horn) of the hyoidDepresses the hyoidC1 (ventral ramus, which follows the hypoglossal n.)

Sternohyoid

  • Attachments:
    • Back of upper part of Manubrium and adjoining Sternoclavicular Joint and Clavicle
    • Lower border of Body of Hyoid
  • Lie edge-to-edge at Hyoid bone and diverge from each other below
  • Nerve supply:

Omohyoid

  • Attachments:
    • Lateral part of inferior border of Hyoid
    • Complex course as detailed below
    • Upper border of Scapula and Transverse Scapular Ligament
  • Course:
    • Lies edge-to-edge with Sternohyoid at its attachment
    • Diverges away from Sternohyoid as it descends
    • Passes deep to Sternocleidomastoid
    • Lie over Carotid Sheath
    • Muscle fibres replaced by flat tendon where it lies over the Internal Jugular Vein
    • Inferior Belly runs almost horizontally above the Clavicle
    • Intermediate Tendon and Supraclavicular portion of muscle bound down close to Clavicle by fascial sling derived from deep layer of the Investing Layer of the Deep Cervical Fascia
  • Nerve supply:
    • Superior Belly: Superior Root of the Ansa Cervicalis
    • Inferior Belly: Ansa Cervicalis

Thyrohyoid

  • Lies under cover of upper ends of Sternohyoid and Omohyoid
  • Attachments:
    • Greater Horn of Hyoid bone
    • Oblique Line of Thyroid Cartilage (alongside Sternothyroid)
  • Nerve supply:
    • Branch of Hypoglossal Nerve – but fibres are all ‘hitch-hiking’ from C1

Sternothyroid

  • Lies deep to Sternohyoid
  • Attachments:
    • Posterior surface of Manubrium (lower down than Sternohyoid) and adjacent 1st Costal Cartilage
    • Oblique Line of Thyroid Cartilage
  • Nerve supply:
    • Ansa Cervicalis – gives a branch to lower part of muscle

Actions of Infrahyoid Muscles

  • Depress Larynx
    • Sternothyroid acts directly on Thyroid Cartilage
    • Others act indirectly via Hyoid
    • Increases volume of resonating chambers during phonation and affects quality of voice
  • Oppose Larynx elevators
    • I.e. Mylohyoid, Palatopharyngeus, Stylopharyngeus, Salpingopharyngeus
    • Enables them to act progressively and gradually
  • Prevent ascent of Hyoid Bone when Digastric and Geniohyoid lower Mandible

Suprahyoid Muscles

MuscleOriginInsertionActionsNerve Supply
StylohyoidStyloid processBody of the hyoidElevates the hyoid
Retracts the hyoid		Facial n.
MylohyoidMylohyoid line of the mandibleMylohyoid of opposite side at the raphe
Body of the hyoid		Elevates the hyoid
Elevates the floor of the oral cavity		Trigeminal n. (mandibular division)
Digastric Muscle (posterior and anterior bellies connected by a tendon attached to the hyoid)Mastoid processDigastric fossa of the mandibleElevates hyoid
Helps depress and retract the mandible		Facial n. (posterior belly)
Trigeminal n. (anterior belly—mandibular division)
GeniohyoidInferior genial tubercleBody of the hyoidHelps move the hyoid and tongue anteriorlyC1 (ventral ramus, which follows the hypoglossal n.)

Digastric Muscle

  • Arises as the Posterior Belly from the Digastric Groove on medial surface of base of Mastoid Process
  • Tapers down to Intermediate Tendon held beneath a fibrous sling attached to junction of body and Greater Horn of Hyoid bone
  • Anterior Belly lies on inferior surface of Mylohyoid and connects to the Digastric Fossa on the inner surface of the mandible near the midline
  • Nerve Supply:
    • Posterior Belly – Facial Nerve (by a branch arising between the Stylomastoid Foramen and Parotid Gland)
    • Anterior Belly – Nerve to Mylohyoid
  • Action: Depress and retract the chin, and assist Lateral Pterygoid in opening mouth The posterior digastric is supplied by facial nerve and crosses (from posterior to anterior) the following:
  • Accessory nerve
  • Transverse process of the atlas
  • Internal jugular/internal carotid
  • Hypoglossal nerve
  • External carotid

Stylohyoid

  • Arises from back of Styloid Process
  • Lower end divides to embrace the Digastric Tendon
  • Inserted by 2 slips into the junction of the Greater Horn and Body of Hyoid
  • Nerve Supply: Facial nerve
  • Action: Retract and elevate Hyoid when swallowing

Mylohyoid

  • Forms diaphragm of floor of the mouth
  • Arises from Mylohyoid Line on inner aspect of Mandible
  • Posterior quarter of each side inserts onto body of Hyoid
  • Anterior three quarters interdigitate in a midline raphe extending from chin to Hyoid bone
  • Nerve Supply: Own nerve – Branch of the Inferior Alveolar Nerve (From Mandibular Division of Trigeminal Nerve) – Also supplies anterior belly of Digastric
  • Action: Contraction elevates the ‘gutter’ of the mouth causing tongue and hyoid bone elevation

Geniohyoid

  • Extends from Inferior Mental Spine (Genial Tubercle) of Mandible to body of Hyoid Bone
  • Nerve Supply: Branch from Hypoglossal Nerve (consisting of fibres from C1)
  • Action: Protract and elevate Hyoid Bone in swallowing or, if the Hyoid is fixed, to depress the Mandible

Triangles of the Neck

Posterior Triangle

  • Boundaries:
    • Posterior border of Sternocleidomastoid
    • Anterior border of Trapezius
    • Clavicle
  • Roof:
    • Investing Layer of the Deep Cervical Fascia
  • Floor:
    • Prevertebral Fascia lying on (from above downwards):
      • Splenius
      • Levator Scapulae
      • Scalenus Medius
    • Scalenus Anterior and the 1st digitation of Serratus Anterior may contribute to the floor
  • Apex lies high up at the back of the skull on the Superior Nuchal Line
  • Contents:
    • Nerves
      • [[Spinal Accessory Nerve
      • Cervical Plexus (Branches)
        • Lesser Occipital Nerve
        • Greater Auricular Nerve
        • Transverse Cervical Nerve
        • Supraclavicular Nerve
      • Deep to the Prevertebral fascia
    • Arteries
      • Subclavian Artery (3rd part)
      • Transverse Cervical
      • Suprascapular artery
      • Occipital Artery
    • Lymph Nodes
      • Lie between the roof and floor
      • 2-3 Occipital Nodes in the subcutaneous tissue at the apex
      • Several Supraclavicular Nodes above the clavicle (Really are outlying members of the lower group of Deep Cervical Nodes)
    • Muscles
      • Omohyoid Muscle (Inferior Belly)
      • Anterior, middle and posterior scalene
      • Levator scapulae
    • Vein
      • External Jugular Vein

Anterior Triangle

  • Boundaries:
  • Subdivided into Carotid Triangle, Digastric Triangle, Submental Triangle, and Muscular Triangle

Carotid Triangle

  • Boundaries:
    • Sternocleidomastoid
    • Posterior Belly of Digastric Muscle
    • Superior Belly of Omohyoid
  • Contents:
    • Artery
      • Bifurcation of Common Carotid Artery into internal and external
      • Branches of External Carotid Artery (except Posterior Auricular)
    • Veins
      • Internal jugular vein
      • Lingual Vein
      • Facial Vein
      • Superior Thyroid Veins
    • Nerves:
    • Lymph Nodes

Submandibular Triangle

  • Boundaries:
    • Mandible
    • Anterior and Posterior Bellies of Digastric
  • Contents:
    • Submandibular Gland
    • Submandibular Lymph Nodes
    • Facial artery and vein
    • Submental Vessels
    • Mylohyoid Vessels
    • Hypoglossal Nerve
    • Mylohyoid Nerve

Submental Triangle

  • Boundaries:
    • Anterior Bellies of Digastric
    • Body of Hyoid (Triangle crosses midline)
  • Contents:
    • Anterior Jugular Veins
    • Lymph Nodes

Muscular Triangle

  • Boundaries:
    • Sternocleidomastoid
    • Superior Belly of Omohyoid
    • Midline from Hyoid to Jugular Notch
  • Contents:
    • Parts of Larynx
    • Trachea
    • Pharynx
    • Oesophagus
    • Thyroid and Parathyroid Glands
      • Their Vessels
      • Their Nerves
    • Lymph Nodes

Surgical Lymph Node Levels of the Neck

  • Neck Lymph Nodes are divided into 7 levels

Level 1: Submental and Submandibular Nodes

  • Boundaries:
    • Level IA (Submental): (in the midline)
      • Lateral (bilaterally): Anterior Digastric muscles
      • Inferior: Hyoid
      • Superior: Mandible
    • Level IB (Submandibular):
      • Anterior: Anterior Digastric muscle
      • Posterior: Posterior Digastric muscle
      • Lateral: Posterior edge of Submandibular Glands
      • Superior: Mandible
  • Important Structures/Relationships:
    • Lingual Nerve
    • Hypoglossal Nerve
    • Submandibular Duct
    • Facial Artery
    • Facial Vein
      • Only structure found lateral to the Posterior Belly of Digastric
    • Marginal Mandibular Branch of Facial Nerve
      • Found in the fascia overlying the Submandibular Gland superficial to the Facial Artery and Vein
  • Sites Draining:
    • Floor of mouth
    • Anterior Tongue
    • Lower Lip
    • Submandibular Gland
    • Nasopharynx

Level 2: Upper Jugular Nodes

  • Boundaries:
    • Anterior:  Posterior edge of Submandibular Glands
    • Posterior: posterior border of the sternocleidomastoid muscle
    • Superior: skull base
    • Inferior: Level of the hyoid bone (clinical), carotid bifurcation (surgical)
    • Level II is divided by the accessory nerve into levels IIa (anteriorly) and IIB (posteriorly).
  • Important Structures
    • Spinal Accessory Nerve (CN XI)
      • Runs deep to Posterior Digastric and Occipital Artery
      • Runs superficial to IJV for majority of the time
      • Often gives small branch to Trapezius before entering SCM
  • Sites Draining:
    • Oropharynx
    • Nasopharynx
    • Nasal Cavity
    • Larynx
    • Parotid Gland

Level 3: Middle Jugular Nodes

  • Boundaries:
    • Lateral: Posterior border of SCM
    • Medial: Lateral border of Sternohyoid
    • Superior: Hyoid Bone
    • Inferior: Inferior border of Cricoid Cartilage
  • Important Structures:
    • Phrenic Nerve
      • Runs deep to the cervical rootlets and superficial to the Anterior Scalene muscle beneath the Deep layer of the Deep Cervical Fascia
  • Sites Draining:
    • Oral Cavity
    • Nasopharynx
    • Hypopharynx
    • Larynx

Level 4: Lower Jugular Nodes

  • Boundaries:
    • Lateral: Posterior border of SCM
    • Medial: Lateral border of Sternohyoid
    • Superior: Inferior border of Cricoid Cartilage
    • Inferior: Clavicle
  • Important Structures:
    • From superficial to deep, the structures encountered:
      • Omohyoid
      • Carotid Sheath
      • Thoracic Duct (more commonly seen in the left neck)
      • Transverse Cervical Artery
      • Phrenic Nerve
      • Anterior Scalene muscle
    • Lung Apices may also be present at inferior aspect of Level 4
  • Sites Draining:
    • Larynx
    • Hypopharynx
    • Thyroid
    • Cervical Oesophagus

Level 5: Posterior Triangle Nodes

  • Boundaries:
    • Lateral: Trapezius
    • Medial: Lateral border of SCM
    • Inferior: Clavicle
    • Horizontal line extended from inferior border of Cricoid divides this level into 5A (superior to Cricoid) and 5B (inferior to Cricoid)
  • Important Structures:
    • Phrenic Nerve
      • Embedded in fascia overlying Anterior Scalenes
      • Protected by staying superficial to this plane
    • Brachial Plexus
      • Courses on the floor of level 5B between Anterior and Middle Scalene
  • Sites Draining:
    • Nasopharynx
    • Oropharynx
    • Skin of Posterior Scalp and Neck
    • Virchow’s Node

Level 6: Central Compartment Nodes

  • Boundaries:
    • Lateral: lateral border of the sternohyoid muscle
    • Superior: Hyoid Bone
    • Inferior: Sternum
    • Divided into left and right by the Trachea
  • Important Structures:
    • Recurrent Laryngeal Nerve
    • Thyroid Gland
    • Parathyroid Glands
  • Sites Draining:
    • Thyroid
    • Subglottic Larynx
    • Cervical Trachea
    • Hypopharynx
    • Cervical Oesophagus

Level 7: Superior Mediastinal Nodes

  • Boundaries:
    • Superior: Inferior border of Suprasternal Notch
    • Inferior: Innominate Artery/Brachiocephalic Artery

Root of the Neck Anatomy

MuscleInsertionOriginInnervationAction
Posterior scalene2nd ribPosterior tubercles of transverse processes of C4-C6C5-C8Flexes neck laterally; elevates 2nd rib
Middle scalene1st ribPosterior tubercles of transverse processes of C2-C7C3-C7Flexes neck laterally; elevates 1st rib
Anterior scalene1st ribAnterior tubercles of transverse processes of C3-C6C5-C8Flexes neck laterally; elevates 1st rib
Overview
  • Root of Neck (a.k.a. Thoracic Outlet)
  • Bounded by T1 Vertebrae, 1st pair of Ribs and their Cartilage, and the Manubrium of the Sternum

Scalenus Anterior

  • Origin:
    • Anterior Tubercles of the four ‘typical’ Cervical Vertebrae (C3 – C6) by 4 slender tendons of origin which lie end to end with those of Longus Capitis
  • Muscle passes forwards, laterally and downwards to end in a narrow tendon
  • Insertion:
    • Scalene Tubercle and adjacent ridge on the inner border and upper surface of the 1st Rib
  • Nerve Supply:
    • Separate branches from the Anterior Rami of C4-C6 nerves
  • Actions:
    • Assists in Flexion and Rotation of the Neck
    • Helps to stabilize the 1st Rib
    • Shows some electromyographic activity even in quiet respiration

Anterior Relations

  • Phrenic Nerve
    • Passes vertically down across the obliquity of the muscle
    • Plastered on the muscle by the Prevertebral Fascia and a pad of fat lies in front of the Prevertebral Fascia
    • Nerve leaves the medial border of the muscle low down
    • Crosses anterior to the Subclavian Artery and its Internal Thoracic Artery Branch
    • Behind the Subclavian Vein
      • Occasionally, the Phrenic Nerve may pass in front of the Subclavian Vein or posterior to the Internal Thoracic Artery
    • Lies on the Suprapleural membrane
    • Passes medial to the Apex of the Lung
    • Crosses in front of the Vagus Nerve as it enters the Superior Mediastinum
  • Ascending Cervical Artery
  • Transverse Cervical Artery and Suprascapular Artery
    • Anterior to the Prevertebral Fascia
    • Lie between the Anterior Scalene and the Carotid Sheath (Internal Jugular Vein)
  • Subclavian Vein
    • Lies in a groove on the 1st Rib
      • Due to the slope, lies at a lower level than the insertion of Scalenus Anterior
    • Runs medially
    • Joins the Internal Jugular Vein at the medial border of Scalenus Anterior to form the Brachiocephalic Vein
      • Thoracic Ducton the left and the Right Lymphatic Duct on the right enters the angle of confluence of the 2 veins
    • Used for central venous lines:
      • Infraclavicular approach – from a point 2cm below the midpoint of the Clavicle along a line that passes behind the Clavicle towards the Jugular Notch of the Sternum
      • Needle pierces the Clavipectoral Fascia and enters the vein just behind the Fascia

Medial Relations

  • Medial edge of Scalenus Anterior makes a pyramidal shape with the lateral border of the lower part of Longus Colli
  • Prevertebral Fascia in front of these muscles attached to bone at their opposing margins
  • No fascial roof across the Pyramidal Space
  • Base of space: Subclavian Artery (1st Part) (lying on Suprapleural Membrane)
  • Apex: Carotid (Chassaignac’s) Tubercle on the Transverse Process of C6
  • Common Carotid Artery:
    • Medial to the Internal Jugular Vein:
    • Lies deep to Sternocleidomastoid immediately anterior to the Pyramidal Space
  • Inferior Cervical Sympathetic (or Stellate ganglion):
    • Posterior to the Common Carotid Artery (and Carotid Sheath)
    • Vertebral Artery and Vein anterior to the ganglion
  • Inferior Thyroid Artery
    • Arches medially in a bold curve whose upper convexity lies in front of the Apex of the Pyramidal Space (C6 Level)
    • Sympathetic Chain (usually the Middle Ganglion) in front of the Artery
  • Thoracic Duct (or Right Lymphatic Duct)
    • At a lower level and further anterior
    • Makes a similar convexity behind the Carotid Sheath
    • Arches over the Lung Apex and Subclavian Artery
    • Enters the confluence of the Subclavian Vein and Internal Jugular Vein
  • Vagus Nerve (slightly medial - can also be considered anterior)
    • Within the Carotid Sheath
    • Passes down anterior to the Subclavian Artery
    • Inclines posteriorly and run on the medial surface of the Apex of the Lung to enter the Superior Mediastinum
    • Internal Jugular Vein has Deep Cervical Lymph Nodes closely adjacent to it

Posterior Relations

  • Separated from the Scalenus Medius by:
    • Subclavian Artery
    • Anterior rami of the lower Cervical and 1st Thoracic Nerves, i.e. Roots of Brachial Plexus
  • Subclavian Artery(2nd Part)

Lateral Relations

  • Trunks of the Brachial Plexus:
    • Emerge from the lateral border of Anterior Scalene
  • Subclavian Artery (3rd Part) – see below
  • Both the above lie behind the Prevertebral Fascia on the floor of the Posterior Triangle

Subclavian Artery

  • See notes

Cervical Plexus

  • See notes

Graph View

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