Anatomy of Organization of the Neck in a Nutshell

Intro:

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• Platysma: wrinkles skin, for facial expression

• • Tightly bound to skin
  • easily removed in dissection

• Sternocleidomastoid: divides region of the lateral neck:

• • posterior triangle of the neck
    • has muscle in the foor:

1. 1. 1. 1. Semispinalis capitis
         2. Splenius capitis
         3. Levator scapulae
         4. Scalene – has prominent white structure in it = root of Brachial plexus

• Anterior triangle of the neck
• Each triangle has relevance surgically, clinically, and for lab.
• These are the Cervical Triangles

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Neck organization: 3 compartments

• Vertebral compartment
  • Cervical vertebrae
  • Postural muscles: for the head and neck (levator scapulae, scalene, splenius capitus etc.)
  • Largely posterior in the neck
• Visceral compartment
  • Largely anterior
  • Glands: parathyroid, thyroid, remnant of thymus (largely fat in adult)
  • Portions of the repiratory and GI tract

1. 1. • Pharynx
      • Larynx
      • Esophagus

• Vascular compartments (one on each side)
  • Major blood vessels to head, neck, brain
  • Vagus nerve

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Thyroid cartilage and cricoid cartilage

• Laryngeal cartilages.
• These are continuous with trachea.
• Key features:

• • C3-4
    • Superior border of thyroid cartilage
    • Carotid bifurcation: common carotid artery as it ascends into the neck divides into

1. 1. 1. 1. Internal branch
         2. External branch

• C5-6
  • Lower limit of pharynx and larynx
  • Superior limit of trachea and esophagus
  • Indentation between cricoid cartilage  and 1^st tracheal ring

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Lateral view of the neck:

• Posterior triangle: superior to clavicle, anterior to anterior border of trapezius
• Inferior belly of omohyoid muscle
  • Cuts across inferior aspect
  • Not significant in function, but does divide posterior triangle

1. 1. • Small inferior triangle
      • Large superior triangle

• Anterior triangle: anterior to sternocleidomastoid
  • Divided by various muscles into 4 sub triangles

1. 1. • Submandibular
      • Carotid

• • • Submental

• • • Muscular

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Cross section of the neck:

• Visceral compartment:
  • Mostly anterior
  • Pretracheal fascia surrounds / defines it
• Vascular compartment:
  • One on either side, has carotid artery and internal jugular venous system, also vagus nerve.
  • Carotid sheath is fascia around it
• Vertebral compartment:
  • Fills most of the posterior half of the neck
  • Prevertebral fascia surrounds it

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Fascia:

• Superficial fascia around the neck:
  • Continuous with campers / scarpas etc.
  • A thin layer of fatty tissue
• There is some fat around the neck, but it is highly variable
• Not as much fat around the platysma (i.e. anterior region).
• Investing fascia: encircles the entire neck
  • Splits to encompass large muscles
  • Along with individual compartment fascia layers, these are more membranous layers of fascia as opposed to the fatty superficial fascia.
  • These 4 layers are aponeurotic, but they aren’t aponeuroses.
  • These 4 layers are deep fascia. They allow columns of tissue to slide past each other.
  • Extends to the anterior midline. Deep this area, will find the strap muscles- which are invested in their own deep fascia (pretracheal fascia).

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Posterior triangle: detail

• Boundaries
  • Anterior: the posterior border of SCM
  • Posterior: anterior border of trapezius
  • Inferior: middle 1/3 of clavicle

1. 1. • Clavicle covers the subclavian vein

1. • Roof: Investing fascia

1. 1. • Contributed by surrounding muscles
      • Is a type of deep fascia

1. • Floor: formed by muscles covered in fascia

1. 1. • Splenius capitis
      • Levator scapulae

• • • scalenes

• Omohyoid muscle:
  • Inferior belly cuts across the inferior part of this triangle
  • Superior belly attaches hyoid bone
  • Divides into:

• • • Occipital triangle
      1. Accessory nerve (CN XI) is most important structure here
         1. Comes right off with investing fascia in lab
         2. Has role in elevating / rotating shoulder
         3. Innervates the trapezius muscle
         4. Divides posterior triangle:
            1. Superior to nerve is a “safe zone”
            2. Inferior to nerve is a “danger zone”
               1. Contains many key structures
               2. More dangerous to have penetrating wound here
  • Supraclavicular nerves:

• • • • • Cutaneous sensory nerves
        • Very small
  • Brachial plexus trunks
  • Transverse cervical artery
  • External jugular vein
  • Superficial cervical lymph nodes
    • Subclavian triangle
      1. Inferior, much smaller
      2. 3^rd part of subclavian artery is most important
      3. External jugular vein portion
      4. Subclavian vein (sometimes) which is posterior to the clavicle and is thus not really in the subclavian triangle
      5. Suprascapular artery:
         1. supplies supraspinatus / infraspinatus
         2. supraclavicular lymph nodes

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Anterior triangle: Details

• Boundaries:
  • Anterior: anterior midline of neck
  • Posterior: SMC
  • Superior: mandible
  • Boundaries can vary
• Key structures:
  • Omohyoid muscle

1. 1. • Attaches hyoid bone superiorly
      • Attaches scapula inferiorly (“omo” means shoulder)
      • Superior belly helps divide anterior triangle

1. • Digastric muscle:

• • • Attaches mandible and a temporal bone
    • Also attached to hyoid bone

• • • Creates a “sling”

• • • Superior to this muscle: submandibular triangle
    • Between the 2 digastric bellies, have the submental triangle

• • 4 subtriangles:
    • Submandibular (AKA digastric): one on each side

1. 1. 1. 1. Superior border is the inferior border of mandible

1. 1. • Submental

1. 1. 1. 1. Is an unpaired triangle (the only unpaired one)
         2. Situated between the 2 digastric bellies

1. 1. 1. 1. Under the tip of the chin

1. 1. • Carotid

1. 1. 1. 1. Bilateral
         2. Situated laterally to muscular triangles

1. 1. • Muscular:

1. 1. 1. 1. Bilateral (one on each side)
         2. Situated anteriorly in the neck

• Contents of anterior triangle:
  • Submental triangle:

1. 1. • Has submental lymph nodes
      • Referred to as the nodal triangle

• • • Floor has: mylohyoid muscles

• • • Has some small veins

1. • Submandibular triangle:

• • • Largely glandular contents
      1. Submandibular gland: largest salivary gland
    • Have submandibular lymph nodes

• • • Mylohyoid nerve

• • • Hypoglossal nerve (CN XII)
    • Facial artery and vein
      1. Artery gives a pulse

1. • Carotid triangle: Very vascular

• • • Vessels:
      1. Common carotid artery
      2. External carotid artery
      3. Internal jugular vein
    • Nerves:
      1. Vagus
      2. Hypoglossal
      3. Accessory
      4. Cervical plexus

• • • Cartilages
      1. Larynx
      2. Pharynx

1. 1. • Thyroid and parathyroid glands

1. • Muscular triangle:

1. 1. • Has muscles and glands
      • Infrahyoid muscles

• • • Thyroid and parathyroid glands

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Cross section: Fascia detail

• Superficial fascia
  • Much the same as that found elsewhere in the body
  • Encompasses / encircles the entire neck
  • Very tightly applied posteriorly to musculature
• Deep fascia:
  • 4 subdivisions of deep fascia

• • • Investing
      1. Splits to surround the sternocleidomastoid muscle
      2. Splits posteriorly to surround the trapezius
      3. Attaches posteriorly to the ligamentum nuchae (nuchal ligament) and not to spinous processes.
      4. There is a gap between SCM and trapezius muscle
         1. Is the roof of the posterior triangle
         2. Investing fascia fills in the gap between these two muscles
  • Pretrachial
    • Surrounds the visceral compartment (contains pharynx, larynx, esophagus, thyroid glands etc.)
      1. Visceral portion: Buccopharyngeal fascia
         1. Posterior portion of the pretracheal fascia.
         2. Does not “surround” anything due to it being on one edge
         3. Is on the posterior edge of pharynx / esophagus
         4. Is the visceral component which surrounds non-muscular contents

• • Muscular portion:
    • Surrounds 4 muscles medial/anterior to SCM
    • Are situated just deep to anterior midline just deep to the superficial fascia
  • Retropharyngeal space:
    • Behind the pharynx, deep to buccopharyngeal fascia
    • Anterior to prevertebral fascia
    • Is a potential space and is clinically important for the spread of infection

• • Prevertebral
    • Surround the vertebral compartment (which contains cervical vertebrae and postural muscles)
    • Surrounds the muscles that surround the individual spinous processes etc.
    • Will run along with investing fascia posteriorly
    • Is beneath trapezius
    • Does not bind nuchal ligament, it comes around in a full investing circle

• • Carotid sheath:
    • At the lateral aspects of the retropharyngeal space
    • Is a long tube with 3 structures
      1. Internal jugular vein
      2. Common / internal carotid artery
      3. Cranial nerve X (Vagus)

• • Important contents

• • • Accessory nerve
      1. Just deep to sternocleidomastoid muscle (in its deep surface)
      2. Mostly in posterior triangle
    • Cervical sympathetic chain
      • Is on the anterior aspect of the prevertebral fascia
      • Adheres firmly to the fascia

• • • Phrenic nerve (C3-5)
      • Sits right on the anterior scalene muscle
      • Is covered by prevertebral fascia as oppose to sympathetics which are on top of the prevertebral fascia

1. 1. • Brachial plexus roots

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Saggital section of the neck:

• Investing fascia:
  • Comes all the way up to the midline anteriorly and covers the “strap muscles”
  • Posteriorly- extends past cervical vertebrae as deep fascia of other regions
  • Attaches inferiorly to manubrium of sternum
  • Attaches occipital bone superiorly
• Prevertebral fascia:
  • Deep to investing fascia
  • Superiorly appears to blend with nuchal ligament
  • Posteriorly, it is right on top of the spinous processes and thus blends with supraspinous ligament as move into thoracic region.
  • Anterior aspect of vertebral column: it goes inferiorly to fuse at T3 with the anterior longitudinal ligament.
  • Attaches superiorly to C1 and the anterior nuchal ligament and the occipital bone posteriorly
• Pretracheal fascia:
  • Open posterior aspect of pharynx / esophagus- referred to as buccopharyngeal fascia (subdivision of pretracheal fascia)
  • As it descends into thorax, it will blend with the fibrous pericardium.
  • Buccopharyngeal Ascends all the way up to attach occipital bone
• Clinical: spread of infection
  • Between investing fascia and pretracheal fascia
  • Have nameless space serving as root of infection into thorax anterior to pericardium
  • Between prevertebral fascia and buccopharyngeal fascia is another root of infection to superior / posterior mediastinum. This is the retropharyngeal space

1. 1. • Leads to dysphagia (difficulty swallowing)
      • Dysarthria (difficulty speaking)

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Muscles of the neck

• Infrahyoid muscles: aka Strap Muscles (4)
  • Omohyoid muscle (superficial)

1. 1. • Inferior / superior bellies are connected by the intermediate tendon.
      • Tendon held in place by deep fascia which acts as a sling to hold it down- fascia attaches to the clavical

1. • Sternohyoid (superficial)
   • Sternothyroid muscle (deep)

1. 1. • Attaches to manubrium of sternum inferiorly
      • Superiorly attaches thyroid cartilage
      • Is the inferior portion of a segmented column of muscle made up by the two deep muscles.

1. • Thyrohyoid muscle (deep)

1. 1. • Extends from thyroid cartilage to hyoid bone
      • Is superior portion of segmented column of muscle

1. • These muscles are tethered inferiorly, thus hyoid bone will move downward upon contraction = depress the hyoid

1. 1. • Move mandible and shape the oral cavity

1. • Hyoid: a U shaped bone

1. 1. • Very delicate, tucked up to base of mouth
      • Found at level C3

• • Thyroid cartilage: extends from C4-C5
  • Cricoid cartilage: at level C6
  • Larynx at C4-6
• Prevertebral and lateral vertebral cervical muscles
  • Longus colli:
  • Levator scapula
  • Scalene muscles (anterior / middle / posterior)

1. 1. • Anterior and middle scalenes: attach inferiorly to rib 1
      • Between anterior and middle scalenes: brachial plexus is emerging into posterior triangle.

• • • Posterior scalene muscle: goes to rib 2

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