Narrow Head and neck Flashcards
(152 cards)
1
Q
Vertebral arteries
A
• Forms part of the vertebrobasilar system
• The vertebral artery is typically divided into 4 segments:
o V1: origin to transverse foramen of C6
o V2: from the transverse foramen of C6 to the transverse foramen of C2
o V3: from C2 to the dura
o V4: from the dura to their confluence to form the basilar artery
Supply:
• Supply the posterior fossa and occipital lobes as well as provides segmental vertebral and spinal column blood supply
Origin:
• Arises from the subclavian artery
Terminates:
• Combines with the contralateral vertebral artery to form the basilar artery
2
Q
Vertebral arteries: course/relations
A
• V1:
o runs superoposteriorly between the longus colli and the scalenus anterior
o anteriorly: common carotid artery, vertebral vein, thoracic duct (left VA), lymphatic duct (right VA)
o posteriorly: sympathetic trunk, C7 transverse process, inferior cervical ganglion
o anteromedially: inferior thyroid artery, middle cervical ganglion
• V2:
o passes through transverse foramina of C6-C2 and is accompanied by vertebral veins and sympathetic nerves
• V3:
o emerges from the transverse process of C2 (axis)
o sweeps laterally to pass through the transverse foramen of C1 (atlas)
o passes around the posterior border of the lateral mass of C1 and below the inferior border of the posterior atlanto-occipital membrane
o passing superomedially it pierces the dura and arachnoid to continue as V4
• V4:
o ascends anterior to the roots of the hypoglossal nerve (CN XII), medulla and cerebellum
o joins its contralateral counterpart at the lower border of the pons to form the basilar artery
3
Q
Vertebral arteries: branches
A
- Numerous small muscular branches
- Numerous small spinal branches (supplies cord, dura, vertebral bodies)
- Posterior spinal artery
- Anterior spinal artery
- PICA
4
Q
Vertebral arteries: variant anatomy
A
• One side is dominant: may due to hypoplasia or absence
• Vertebral artery may terminate as PICA
• Complete or partial vertebral artery duplication
• Vertebral artery fenestration
• Variable origin
o aortic arch origin of left vertebral artery: incidence ~5% (range 3.1-8.3%)
o may be the second (not first branch) of the subclavian artery
o branch of the CCA or thyrocervical trunk
• Vertebral arteries may fail to unite to form the basilar artery (continues as two separate arteries)
• Variable level of entry into the cervical spine transverse foramina
5
Q
External carotid artery
A
Description:
• External carotid artery is a major artery of the head and neck
• Supplies neck, face and base of skull
Origin:
• Bifurcation of the common carotid (level of C4)
6
Q
External carotid artery: Course
A
- Begins at the level of the upper border of the thyroid cartilage (level of C4)
- Slightly curved course upwards and anteriorly before inclining backwards to the space behind the neck of the mandible
- Along its course, it rapidly diminishes in size and as it does so, gives of various branches
- As it enters the parotid gland, it gives rise to its terminal branches
- Lies deep to facial nerve and retromandibular vein within the parotid
7
Q
External carotid artery: Branches
A
• Some Anatomists Like Freaking Out Poor Medical Students o superior thyroid artery o ascending pharyngeal artery o lingual artery o facial artery o occipital artery o posterior auricular artery o maxillary artery (terminal branch) o superficial temporal artery (terminal branch)
8
Q
External carotid artery: Relations
A
• Anteriorly (ie. ECA is crossed by these structures)
o upper root of ansa cervicalis
o hypoglossal nerve (CN XII)
o posterior belly of digastric muscle
o stylohyoid muscle and ligament
o facial nerve (CN VII) (within the parotid gland)
• Passing between ECA and ICA
o pharyngeal branch of vagus nerve (CN X)
o glossopharyngeal nerve (CN IX)
o stylopharyngeus muscle
o styloglossus muscle
• Posteriorly (ie. ECA lies on these structures)
o pharyngeal wall
o superior laryngeal branch of vagus nerve (CN X)
o deep lobe of the parotid gland
9
Q
External carotid artery: variants
A
• Variations in level of bifurcation
• Variant branching pattern include
o linguofacial trunk (incidence ~20%): common origin lingual and facial arteries
o thyrolingual trunk (incidence ~2.5%): common origin superior thyroid and lingual arteries
o thyrolinguofacial trunk (incidence ~2.5%): common origin superior thyroid, lingual and facial arteries
o common occopito-auricular trunk (incidence ~12.5%): common origin occipital and posterior auricular arteries
10
Q
Ophthalmic artery
A
- Ophthalmic artery is a branch off the C6 segment of the internal carotid artery
- Arises medial to the anterior clinoid process after the ICA exits the cavernous sinus
- Passes into the orbit via the optic canal
- Supplies all the structures in the orbit as well as some structures in the nose, face and meninges
11
Q
Ophthalmic artery: branches
A
• Orbital group (ASSLIP) o lacrimal artery o supraorbital artery o posterior ethmoidal artery o anterior ethmoidal artery o internal palpebral artery o supratrochlear artery o dorsal nasal artery • Ocular group (CLAMS) o central retinal artery o long posterior ciliary arteries o short posterior ciliary arteries o anterior ciliary artery o muscular artery
12
Q
Ophthalmic artery: Variants
A
• Embryologically the orbit has dual supply, from the supraorbital branch (later becomes the MMA) and from the OA, so there can be variation
o communicating branch between the OA and MMA is present (usually passes through the superior orbital fissure)
o regression of OA and entire orbit is supplied by the MMA
• Variations in origin or branching patterns
o MMA can arise from the OA
o OA originates from the MMA
o cavernous origin of ophthalmic artery (less common)
13
Q
Nasal blood supply
A
• The arterial supply of the nasal cavity is rich and derives from both the internal and external carotid arteries (mnemonic: GASPS)
• Lateral nasal wall
o anterior and posterior ethmoidal arteries (branch of the opthalmic artery)
o sphenopalatine artery (branch of the maxillary artery)
o pharyngeal artery (branch of the ascending pharyngeal artery)
• Septum
o greater palatine artery (branch of the maxillary artery)
o sphenopalatine artery (branch of the maxillary artery )
o anterior and posterior ethmoid branches (branch of the opthalmic artery )
• Floor
o greater palatine artery (branch of the maxillary artery)
o superior labial arteries
• Rich arterial supply results in two anastomotic areas, which are common sites of epistaxis:
o Woodruff area: anastomosis of sphenopalatine and pharyngeal arteries just posterior to the inferior turbinate
o Kiesselbach plexus: anastomosis of the anterior ethmoid, greater palatine, sphenopalatine and superior labial arteries in the anteroinferior nasal septum
14
Q
Anterior scalene: Relations
A
• Anteriorly:
o phrenic nerve, vagus nerve
o ascending cervical artery, transverse cervical artery, suprascapular artery
o internal jugular vein, subclavian vein
o sternocleidomastoid muscle, omohyoid muscle
o clavicle
• Posteriorly:
o second portion of subclavian artery (which is divided in three parts by the muscle)
o spinal nerve roots that make up brachial plexus
• Medially:
o common carotid artery, first portion of subclavian artery, vertebral artery and vein
o stellate ganglion (sympathetic ganglion formed by the fusion of the inferior cervical ganglion and the first thoracic ganglion, located anterior to the transverse process of C7 - occurs in 80% people)
o thoracic duct (left) or right lymphatic duct (right)
• Laterally:
o brachial plexus
o third portion of subclavian artery
15
Q
Anterior scalene: neurovasculature
A
Nerve supply:
• Ventral rami of cervical nerves (C4, C5 and C6)
Blood supply:
• Ascending cervical artery (branch of inferior thyroid artery or thyrocervical trunk
16
Q
Anterior scalene: variants
A
Variants:
• Spinal nerve roots that make up the brachial plexus may pass through anterior scalene
• Subclavian artery may pass through or anterior to anterior scalene
• May be supplied by the phrenic nerve
17
Q
Anterior scalene: action
A
- Elevates first rib (inspiration)
* Adjunct in neck rotation/flexion
18
Q
Anterior scalene: action
A
- Elevates first rib (inspiration)
* Adjunct in neck rotation/flexion
19
Q
Cervical plexus
A
- Plexus of the ventral rami of C1 to C4 cervical segments
- Located laterally to the transverse processes and deep to the SCM
- Between prevertebral muscles medially and vertebral muscles laterally (scalenus, levator scapulae, splenius cervicis) from lateral side
- Anastomoses with the accessory nerve, hypoglossal nerve and sympathetic trunk
- Branches of the cervical plexus emerge from the posterior triangle
20
Q
Cervical plexus: branches
A
• Cutaneous (4 branches):
o great auricular nerve: innervates skin near outer ear and EAM (C2-3)
o transverse cervical nerve: innervates anterior region of neck (C2-3)
o lesser occipital: innervate the skin and the scalp posterosuperior to the auricle (C2-3)
o supraclavicular nerves: innervate region of supraspinatus, shoulder, and upper thoracic region (C3-4)
• Muscular
o ansa cervicalis (loop formed from C1-C3)
geniohyoid (C1), thyrohyoid (C1), sternothyroid, sternohyoid, omohyoid
o Joined by CN XII
o phrenic: innervates diaphragm and the pericardium (C3-C5)
o segmental branches: innervates anterior and middle scalenes (C1-C4)
• Two branches formed by roots of spinal nerves:
o preauricular nerve (posterior roots of C2–C3)
o postauricular nerve (posterior roots of C3–C4)
21
Q
Constrictor muscles of the pharynx
A
• Superior, middle, inferior constrictor muscles
• Constrictor muscles overlap each other and are arranged so that the superior one is innermost and the inferior one is outermost
• Primary action is to constrict pharynx to deliver food bolus to oesophagus
• Overlapping arrangement of the three constrictor muscles leaves 4 gaps in the pharyngeal musculature
o superior to the superior constrictor muscle
levator veli palatini muscle, torus tubarius, ascending palatine artery pass
o between superior and middle constrictor muscles
stylopharyngeus muscle, glossopharyngeal nerve (CN IX), stylohyoid ligament pass
o between the middle and inferior constrictor muscles
internal laryngeal nerve, superior laryngeal artery and vein pass
o inferior to the inferior constrictor muscles
recurrent laryngeal nerve, inferior laryngeal artery and vein pass into the larynx
22
Q
Constrictor muscles of the pharynx: origin and insertion
A
Origin:
• Superior constrictor - pterygoid hamulus, pterygomandibular raphe
• Middle constrictor - greater and lesser horns of hyoid bone
• Inferior constrictor - cricoid and thyroid cartilage
Insertion:
• Superior constrictor - pharyngeal raphe
• Middle constrictor - pharyngeal raphe
• Inferior constrictor - pharyngeal raphe
23
Q
Constrictor muscles of the pharynx: neurovasculature
A
Nerve supply:
• Pharyngeal plexus formed by the vagus (CN X) nerve
Blood supply:
• Ascending pharyngeal
• Tonsillar (branch of the facial artery)
• Greater Palatine and Pharyngeal (branches of maxillary artery)
• Lingual
• Superior and Inferior Laryngeal Arteries
Venous drainage:
• Pharyngeal plexus (formed on the middle constrictor) and draining into the IJV
Lymph drainage:
• Retropharyngeal lymph nodes to the upper or lower deep cervical nodes
24
Q
External jugular vein
A
• Drains the head, face and part of the pectoral region
Origin:
• Posterior auricular vein and posterior division of the retromandibular vein unite to form the EJV at the angle of the mandible
o anterior division of the retromandibular vein drains into the facial vein and subsequently the IJV
25
External jugular vein: course/relation
* Courses inferiorly in the subcutaneous anterolateral neck
* Deep to platysma but superficial to the SCM
* Pierces the deep cervical fascia posterior to the clavicular head of the SCM
* Drain into the subclavian vein
26
External jugular vein: tributaries
```
• PAST
o Posterior external jugular vein
o Anterior jugular vein
o Suprascapular vein
o Transverse cervical vein
```
27
Extraocular muscles
* Six muscles that control eye movement and one muscle that controls eyelid elevation
* Located in the conal space of the orbit
28
Extraocular muscles: origin and insertion
* Superior rectus - Annulus of Zinn and Eye (anterior superior surface)
* Superior oblique - Sup/med to Annulus of Zinn
* Medial rectus - Annulus of Zinn and Eye (anterior medical surface)
* Lateral rectus - Annulus of Zinn and Eye (anterior lateral surface)
* Inferior oblique - Maxilla and Eye (posterior inferior lateral surface)
* Inferior rectus - Annulus of Zinn and Eye (anterior inferior surface)
* Levator palpebrae superioris - Sphenoid bone and tarsal plate of upper eyelid
29
Extraocular muscles: action
* Superior rectus - Elevation
* Superior oblique - Intorsion + depression with eye adducted
* Medial rectus - Adduction
* Lateral rectus - Abduction
* Inferior oblique - Extorsion + elevation with eye adducted
* Inferior rectus - Depression
* Levator palpebrae superioris - Retracts and Elevates eyelid
30
Extraocular muscles: innnervation
* Superior rectus - Occulomotor nerve (superior branch)
* Superior oblique - Trochlear nerve
* Medial rectus - Occulomotor nerve (inferior branch)
* Lateral rectus - Abducens nerve
* Inferior oblique - Occulomotor nerve (inferior branch)
* Inferior rectus - Occulomotor nerve (inferior branch)
* Levator palpebrae superioris - Occulomotor nerve + sympathetics
31
Extraocular muscles: vasculature
Arterial supply:
• Primarily form opthalmic artery and branches
• Lacrimal artery (branch of opthalmic artery) supplies lateral rectus
• Inferior oblique and interior rectus receive branches of the infraorbital artery
Venous
- Sup opthalmic vein -> cavernous sinus
- Inf opthalmic vein -> pterygoid plexus -> Emmisary veins to cavernous sinus AND joint superficial temporal vein to become retromandoibular vein
32
Extraocular muscles: relations
- Discuss inside/out of common tendon
| - List extraconal/conal/globe/ Optic sheath spaces
33
Facial nerve
* Seventh cranial nerve
* Motor nerve to facial expression
* Also has taste and parasympathetic fibres
* Facial nerve nucleus in the pons
34
Facial nerve segments
o segments mnemonic: I Like Going To Makeup Parties
intracranial segment
labyrinthine segment (internal auditory canal to geniculate ganglion) - 3 branches
genu
tympanic segment (from geniculate ganglion to pyramidal eminence)
mastoid segment (from pyramidal eminence to stylomastoid foramen) - 3 branches
parotid / extracranial segment (from stylomastoid foramen to post parotid branches) - 5 branches
35
Facial Nerve - intracranial
o emerges from the lateral pontomedullary junction and courses anterolaterally through the pontine cistern to the internal auditory canal
36
Facial nerve - labrynthine
o in the canal the facial lies antero-superiorly
superior and inferior parts of the vestibular nerve take the posterior segments of the canal
cochlear nerve runs antero-inferiorly
Bill bar divides the superior compartment of the internal acoustic meatus into an anterior and posterior compartment
falciform crest divides IAM into superior and inferior parts
o enters the Fallopian canal, passing anterolaterally between and superior to the cochlea (anterior) and vestibule (posterior)
Fallopian canal = bony canal through which the facial nerve traverses the petrous temporal bone, from the internal acoustic meatus to the stylomastoid foramen
o then runs back posteriorly at the geniculate ganglion (where the nervus intermedius joins the facial nerve)
o three branches originate:
greater petrosal nerve: passes forward from the geniculate ganglion to the middle cranial fossa; unites with the deep petrosal nerve and passes to the pterygoid canal to become the nerve of the pterygoid canal (Vidian nerve)
lesser petrosal nerve
external petrosal nerve
37
Facial nerve - tympanic
o passes posteriorly from the geniculate ganglion between the lateral semicircular canal prominence and promontary
o immediately beneath the lateral semicircular canal in the medial wall of the middle ear cavity
o at the pyramidal eminence, the facial nerve turns inferiorly
38
Facial nerve - mastoid
o facial nerve descends within the mastoid, exits at the stylomastoid foramen
o branches
nerve to stapedius: arises around pyramidal eminence
chorda tympani: crosses medial to malleolar handle and joins lingual nerve (branch of CNV3) to supply the anterior 2/3 of the tongue
nerve from the auricular branch of the vagus nerve (CN X): pain fibers to the posterior part of the external acoustic meatus
39
Facial nerve - extracranial
```
o nerve exits the stylomastoid foramen
o gives off posterior auricular nerve
o passes between the posterior belly of the digastric muscle and the stylohyoid muscle and enters the parotid gland (also gives nerves off to these muscles)
o lying between the deep and superficial lobes of the gland the nerve divides into to main branches at the pes anserinus
o mnemonic: Two Zebras Bit My Cock off
temporal
zygomatic
buccal
mandibular (marginal)
cervical
```
40
Facial nerve - function
• Motor control to most of the muscles of facial expression
o also innervates the posterior belly of the digastric, the stylohyoid, and the stapedius muscle of the middle ear
• Taste sensations from the anterior two-thirds of the tongue via the chorda tympani
• Parasympathetic fibers to the submandibular gland and sublingual glands via chorda tympani
41
Facial nerve - arterial supply
• The facial nerve receives its arterial supply from three main sources:
o labyrinthine artery: a branch of the AICA
o superficial petrosal artery: a branch of the MMA which passes retrogradely along the greater superficial petrosal nerve
o stylomastoid artery: a branch of the occipital artery which pases retrogradely into the stylomastoid foramen
42
Facial nerve - variants
• Many branching patterns of extracranial facial nerve
43
Infratemporal Fossa: boundaries
* Medial: lateral pterygoid plate
* Lateral: ramus of the mandible
* Anterior: infratemporal surface of the maxillary sinus
* Posterior: articular tubercle of the temporal bone
* Floor: medial pterygoid muscle
* Roof: greater wing of sphenoid
44
Infratemporal Fossa: contents
```
• Muscles
o medial pterygoid
o lateral pterygoid
o temporalis
• Arteries
o maxillary artery
o MMA
o buccal
o inferior alveolar
o deep temporal
• Veins
o pterygoid venous plexus
o retromandibular vein
• Nerves
o mandibular nerve (V3)
o inferior alveolar nerve
o lingual nerve
o buccal nerve
o chorda tympani nerve
o otic ganglion
```
45
Internal jugular vein
• Major venous return from the brain, upper face and neck
Origin:
• Formed by the sigmoid sinus and the inferior petrosal sinus in or just distal to the jugular foramen
46
Internal jugular vein : course
* Formed by the union of inferior petrosal and sigmoid dural venous sinuses
* Descends in the carotid sheath with the internal carotid artery
* Vagus nerve (CN X) lies between the two
* Receiving tributaries (Mnemonic: Medical Schools Like Confident People)
* Descends into the thorax usually between the heads of the sternocleidomastoid muscle
* Unites with the subclavian vein to form the brachiocephalic vein just posterior to the sternoclavicular joint
47
Internal jugular vein: tributaries
* Middle thyroid vein
* Superior thyroid vein
* Lingual vein
* Common facial vein
* Pharyngeal veins
* Thoracic duct on the left side and the right lymphatic duct on the right side open into the angle of union of the internal jugular and subclavian veins
48
Internal jugular vein: relations
• Surrounded by accompanying jugular lymph nodes
• Relation to internal carotid artery
o C2 - posteriorly
o C3 - posterolaterally
o C4 - laterally
• Vagus nerve (CN X) always situated between the ICA and IJV
• Anteriorly (ie. is crossed by these structures)
o upper third - spinal root of accessory nerve (CN XI)
o middle third- lower root of ansa cervicalis
o lower third - SCM, tendon of omohyoid
• Posteriorly (from superior to inferior as the IJV descends in the neck)
o lateral mass of C1 (atlas)
o middle scalene muscle
o anterior scalene muscle
o pleura of lung apices
49
Larynx
• The larynx is the entrance to the airway
• It is situated between the root of the tongue and trachea
• Parts: epiglottis, supraglottis, glottis, subglottis
• Larynx houses the vocal cords which is essential for phonation
• Protects the trachea against food aspiration
• The cavity is divided into three parts by mucosal folds:
o false cords divide the upper (vestibule) and middle portion (ventricle) of the larynx
o true cords divides the middle (ventricle) from the subglottis
50
Larynx: relations
* Posterior: C3 to C6
* Anterior: strap muscles of the neck
* Lateral: carotid space (CCA, IJV, vagus)
51
Larynx - cartilages
* The framework of the larynx is formed by cartilage: three single and three paired
* Thyroid Cartilage: Largest cartilage of the larynx. It consists of two lamina, the anterior borders of which are fused. The vocal cords are attached to inner surface of the thyroid cartilage near its lower margin.
* Cricoid Cartilage: Smaller. And forms the lower and posterior parts of the wall of the larynx. It consists of two parts: a posterior quadrate lamina, and a narrow anterior arch.
* Epiglottis: Thin lamella of fibrocartilage projecting obliquely upward behind the root of the tongue. It is attached via the thyroepiglottic ligament to the thyroid cartilage and the hyoid bone by the hyoepiglottic ligament.
* Arytenoid Cartilages: Paired cartilages. Situated at the upper border of the lamina of the cricoid cartilage, at the back of the larynx. Each is pyramidal in shape. Mucosal folds pass from the epiglottis to the arytenoid cartilages (aryepiglottic folds).
* Two further paired cartilages lie within the aryepiglottic folds: the corniculate cartilages on top of the arytenoids and cuneiform cartilages immediately lateral in the free margin of the fold.
* Vestibular fold (false vocal cords) attach just superior to the true vocal cords (thyroid cartilage to the arytenoid cartilage)
52
Larynx: vasculature
Arterial supply:
• Above Vocal Cords - Superior Laryngeal Artery (Branch of Superior Thyroid)
• Below Vocal Cords - Inferior Laryngeal Artery (Branch of Inferior Thyroid)
Venous drainage:
• Above Vocal Cords - Superior Laryngeal Veins to the Superior Thyroid Veins
• Below Vocal Cords - Inferior Laryngeal Veins to the Inferior Thyroid Veins
Lymphatic drainage:
• Deep Cervical Nodes
53
Larynx: innervation
• Motor:
o Recurrent Laryngeal Nerve
o Except Cricothyroid muscle which is supplied by External Laryngeal Nerve (branch of the Superior Laryngeal)
• Sensory:
o Above Vocal Cords - Internal Laryngeal Nerve (branch of the Superior Laryngeal)
o Below Vocal Cords - Recurrent Laryngeal Nerve
54
Lymph node levels
Level I: Submental and submandibular nodes
Level Ia: Submental triangle
Level Ib: Submandibular triangle
Level II: Upper jugular nodes
Level III: Middle jugular nodes
Level IV: Lower jugular nodes
Level V: Posterior triangle group
Level Va: Superior posterior triangle group
Level Vb: Inferior posterior triangle group
Level VI: Anterior triangle group
Level VII: Upper mediastinal nodes
Anterior triangle borders:
Mandible, anterior margin of SCM, midline from chin to jugular notch on manubrium
Posterior triangle borders:
Anterior margin of trapezius, posterior margin of SCM, clavicle
55
Mandible
* The mandible forms the jaw
* It consists of two halves united at the symphysis menti
* Each half has a horizontal body and vertical ramus
56
Mandible: body
```
• External surface:
o midline ridge indicating the symphysis
o mental foramen: inferior to second premolar tooth, allows for the passage of the mental vessels and mental nerve
• Internal surface:
o mental spines: origin of geniohyoid
o fossas for the submental and submandibular salivary glands
o mylohyoid groove
• Superior (or alveolar) border
o attachment of buccinator muscle
• Inferior border
o groove for the facial artery
```
57
Mandible: Ramus
• External surface
o attachment to the masseter muscle
• Inner surface
o mandibular foramen: inferior alveolar vessels and nerve pass into the mandibular canal
mandibular canal runs obliquely downward in the ramus, and then horizontally forward in the body and communicates with alveoli via the incisive nerves through small openings
o lingula mandible: prominent, sharp ridge in front of the mandibular foramen, and attachment for the sphenomandibular ligament
• Lower border
o covered by the parotid gland
o angle of the mandible is at its junction of the posterior border and the body
o medial pterygoid inserts into the angle of the mandible
• Anterior border
o continuous with the oblique line
• Upper border
o consists of the coronoid process (anterior) and the condylar process (posterior), separated by the mandibular notch
58
Mandible: coronoid processes
* Separated from the condylar process by the mandibular notch
* Temporalis muscle insert into its medial and lateral surfaces
* Masseter muscle also inserts to its lateral surface
59
Mandible: condylar process
* Consists of two portions - condyle and neck
* Articulates with the articular disk of the TMJ, in the mandibular fossa of the temporal bone
* Lateral pterygoid muscle inserts into condylar neck
60
Mandible: arterial
* Facial artery (branch of external carotid artery)
* Lingual artery (branch of external carotid artery)
* Inferior alveolar artery (branch of maxillary artery)
61
Mandible : variants
* The mental foramen may be doubled or tripled
* The mylohyoid groove may be bridged over by a bony process and converted into a canal
* Anomalous teeth distributed throughout the mandible
62
Maxillary artery - mandibular part
Five branches, each of which enters a bony foramen:
deep auricular artery (enters squamotympanic fissure)
anterior tympanic artery (enters squamotympanic fissure)
middle meningeal artery (enters foramen spinosum)
accessory meningeal artery (enters foramen ovale)
inferior alveolar artery (enters mandibular foramen)
- branch is artery to mylohyoid
63
Maxillary artery - muscular part
Five branches although pterygoid branches are irregular in their number and origin:
```
anterior deep temporal branches
posterior deep temporal branches
pterygoid branches
masseteric artery
buccinator artery
```
64
Maxillary artery - pterygopalatine part
Six branches including the terminal branch:
posterior superior alveolar artery
infraorbital artery (enters inferior orbital fissure)
artery of the pterygoid canal
pharyngeal artery (enters palatovaginal canal)
greater (descending) palatine artery (enters greater palatine foramen)
sphenopalatine artery - terminal branch (enters sphenopalatine foramen)
65
Middle ear ossicles
• There are three ossicles (from lateral to medial):
o malleus
o incus
o stapes
• Mechanically amplify the vibrations of the tympanic membrane and transmit them to the cochlea
• Reside in the middle ear cavity and articulate with each other via tiny synovial joints
66
Middle ear ossicles: malleus
* Malleus has a head, neck, and three distinct processes (handle, anterior and lateral processes)
* Head is oval in shape, and articulates posteriorly with the incus
* Neck is the narrow contracted part just beneath the head
* Handle (manubrium) is connected by its lateral margin with the tympanic membrane
* Anterior process is directed towards the petrotympanic fissure
* Lateral process attaches to the upper part of the tympanic membrane
67
Middle ear ossicles: incus
• Articulating with the malleus laterally and the stapes medially
• Its parts include:
o body which articulates with the head of the malleus
o superior ligament of the incus attaches body to the roof of the middle ear cavity
o long crus down to the lentiform process (lenticular process) which articulates with the stapes
o short crus to which the posterior ligament of the incus is attached
68
Middle ear ossicles: stapes
• Smallest of the ossicles
• Has a base (foot piece / footplate) which seals the oval window and conducts vibrations to the cochlea
• Base is attached to the neck via an anterior and posterior arch (aka anterior and posterior crura)
• On top of the neck is a concave head which articulates with the lentiform nodule (lenticular process) of the incus
• The stapes has a number of attachments:
o incostapedial joint (a synovial joint)
o annular ligament around the oval window
o stapedeus (muscle attaches to the back of the neck)
69
Nasal cavity
• The nasal cavity is formed by:
o anteriorly: nasal aperture
o laterally: inferior, middle and superior nasal conchae or turbinates
o superiorly: cribiform plate of the ethmoid bone
o inferiorly: palatal processes of the maxilla and horizontal portion of the palatine bone
• In the midline, the nasal cavity is divided into right and left halves by a septum composed of fibrocartilage, the vomer and the perpindicular plate of the ethmoid bone
• Anteriorly it is continuous with the nose at the nasal aperture
• Posteriorly it is continuous with the nasopharynx
• Laterally, the three nasal conchae form three spaces:
o superior meatus
o middle meatus
o inferior meatus
70
Nasal cavity - relations
* Superior meatus communicates with the posterior ethmoidal air cells and sphenoid sinuses via the spheno-ethmoidal recess
* Middle meatus communicates with the frontal sinus via frontal recess, and the ethmoid and maxillary sinuses via the ostiomeatal complex
* Inferior meatus communicates with nasolacrimal duct
71
Nasal cavity - innervation
* CN V2: mucous membrane of the nasal septum
| * CN I: olfactory by the olfactory nerve
72
Nasal cavity - drainage
Venous drainage:
• Venous plexus drains into the sphenopalatine vein, facial vein, infraorbital veins, ophthalmic veins
• Note that posterior ethmoid veins anastomose with veins of the dura mater and orbit (making this a potential route of spread of infection)
Lymphatic drainage:
• Submandibular, retropharyngeal and deep cervical lymph nodes
73
Nasolacrimal apparatus
• The nasolacrimal drainage apparatus consists of:
o puncta (surrounded by lacrimal lake)
o lacrimal canaliculi
o lacrimal sac
o nasolacrimal duct
• Its function is to drain tears produced by the lacrimal gland, accessory lacrimal glands and Meibomian glands to the inferior nasal meatus of the nasal cavity
• Lacrimal apparatus = nasolacrimal apparatus plus the lacrimal gland and lacrimal duct
74
Lacrimal gland
* Serous gland
* Lies in lacrimal fossa (lateral roof of orbit - frontal bone)
* Nerve: Greater petrosal nerve
* Several ducts drain into lateral/superior fornix of conjunctiva
* Variation = accessory gland
75
Lacrimal canaliculi
o two canaliculi, superior and inferior on each side
o commence at the superior and inferior lacrimal puncta, which drain tears from the lacrimal lake that lies at the medial angle of the eye
o unite to form a common canaliculus and drains into the lacrimal sac posterior to the medial palpebral ligament and anterior to the orbicularis oculi muscle
76
Lacrimal sac
o lies in the lacrimal fossa on the inferomedial aspect of the orbit post to medial palpebral ligament
o has a superior fundus that tapers inferiorly to a slimmer body and continues as the nasolacrimal duct
o enclosed by the lacrimal fascia and the orbicularis oculi muscle
77
Nasolacrimal duct
o the inferior continuation of the lacrimal sac
o two parts to the nasolacrimal duct:
intraosseous part - lies within nasolacrimal canal of the maxilla
membranous part - runs in the nasal mucosa, terminates below the inferior nasal meatus as a slit-like opening where it is covered by a mucosal fold (valve of Hasler)
78
Nasopharynx
• The nasopharynx is the part of the pharynx between the posterior choanae and soft palate
• Communicates anteriorly with the nasal cavity and inferiorly with the oropharynx
• Laterally the eustachian tube opens into it with a cartilaginous end called torus tubarius
o tube that links the middle ear with the nasopharynx
o runs through petrous part of the temporal bone
• Posterior to these are the lateral pharyngeal recesses (fossa of Rosenmuller)
• Collection of lymphoid tissue on the roof of the posterior wall of the nasopharynx is called the pharyngeal tonsils / adenoids
• Tensor veli palatini and levator veli palatini raise the soft palate to prevent entry of food into the nasopharynx during swallowing
79
Nasopharynx: relations
* Roof: inferior surface of the sphenoid and clivus
* Lateral: parapharyngeal space
* Posterior: upper cervical vertebrae, longus colli, longus capitis
* Posterolateral: styloid muscles separate it from the carotid space
80
Nasopharynx: vasculature
Arterial supply:
• Ascending pharyngeal (branch of the ECA)
Venous drainage:
• Pharyngeal plexus to the IJV
Lymphatic drainage:
• Jugular chain (particularly jugulodigastric node)
81
Nasopharynx: innervation
Innervation:
• Pharyngeal plexus (CN IX & X)
• CN V3 innervates tensor veli palatini
82
Optic nerve
* The optic nerve is the second cranial nerve
* It is not surrounded by Schwann cells
* Transmits visual information from the retina to the brain
* At the optic chiasm, the nasal fibers of each optic nerve (fibers carrying light impulses from the nasal side of the retina) decussate while the temporal fibers don't
83
Optic nerve - Intraocular segment
o lies within the retina and emerges through the retinal opening
84
Optic nerve - Intraorbital segment
o located in the optic nerve-sheath complex
85
Optic nerve - Intracanilicular segment
o optic nerve courses through the optic canal with the ophthalmic artery below and to its lateral side
86
Optic nerve - Intracranial segment
o continues as the optic chiasma which rests upon the chiasmatic groove anterior to the tuberculum sellæ
o superior pituitary gland and cavernous sinus
o posterior to the AComA
o medial of the internal carotid arteries
o within the chiasm, the optic nerves undergo a partial decussation
o the optic tract passes backward and around the cerebral peduncle
o fibers terminate in the lateral geniculate body of the thalamus
o from the lateral geniculate body, fibers of the optic radiation pass to the visual cortex in the occipital lobe of the brain (divided into superior and inferior bundles), the pulvinar, and the superior colliculus
o superior bundle carries information from the superior retinal quadrant to the cuneus
o inferior bundle carries information from the inferior retinal quadrant to the lingual gyrus
87
Orbit
* The orbit is a feature of the face and contains the globe
* Has a roof, floor, medial and lateral wall - four sided pyramid with the apex posterior and the base forming the orbital margin
* Orbit open anterior, but bound by the orbital septum
* Communicates with the intracranial compartment via the optic canal and superior orbital fissure
88
Orbit: boundaries
• Made up of 7 bones
o Roof - pars orbitalis of the frontal bone, less wing of the sphenoid
o Floor - orbital surface of the maxilla, orbital process of the palatine bone, zygomatic bone
o Medial - greater and less wing of sphenoid, lamina papyracea of the ethmoid bone, orbital surface of maxillary bone, lacrimal bone
o Lateral - orbital process of the zygomatic bone, greater wing of sphenoid
89
Orbit: relations
* Superior: anterior cranial fossa, frontal sinus
* Medial: nasal cavity, ethmoid sinuses and sphenoid sinus
* Inferior: maxillary sinus
* Posterolateral: infratemporal fossa, middle cranial fossa
90
Orbit: contents
* Globe
* Extraocular Muscles
* Nerves: Optic, branches of Oculomotor, Trochlear, Branches of Opthalmic - V1 (Frontal, Lacrimal, Nasociliary), Abducens, Sympathetic Nerves
* Vessels: Opthalmic Artery, Superior and Inferior Opthalmic Veins
* Lacrimal Gland
* Orbital Fat
91
Orbit: vasculature
Blood Supply:
• Ophthlamic Artery
• Supraorbital Artery (branch of opthalmic artery)
• Infraorbital Artery (branch of maxillary artery)
Venous Drainage:
• The Superior and Inferior Ophthalmic Veins - to the Cavernous sinus and Pterygoid plexus
92
Orbit: innervation
* Optic Nerve supplies the globe
* Oculomotor Nerve: superior rectus, medial rectus, inferior rectus, inferior oblique, levator palpebrae superioris
* Trochlear Nerve: superior oblique muscle
* Ophthalmic Nerve (V1): function includes sensation to iris, lacrimal gland
* Abducens Nerve: lateral rectus muscle
93
Orbital spaces
• The globe is divided into compartments: globe, extraconal space, conal space, intraconal space, optic nerve-sheath complex
• Globe
o divided into anterior and posterior chambers by the lens
o parts: lens, iris, sclera, choroid, retina, vitreous humour
94
Orbital space: Extraconal space contents
o fat
o lacrimal gland and sac
o inferior opthalmic vein and portion of the superior ophthalmic vein
o extraconal branches of the opthalmic artery (eg. lacrimal artery) - initially intraconal then becomes extraconal
95
Orbital space: conal space
o extraocular muscles (LR, MR, SR, IR, SO, IO)
| o interconnecting fascia
96
Orbital space: intraconal space
o formed by the posterior half of the globe and the sides are formed by the extraocular muscles which pass posteriorly and converge on the tendinous ring at the orbital apex
o contents
orbital fat
intraconal branches of the ophthalmic artery
superior ophthalmic vein
cranial nerves III, IV, V1, VI
97
Orbital space: optic nerve-sheath complex
o optic nerve
o ophthalmic artery
o central retinal artery (branch of opthalmic artery) and vein
o surrounding sheath of meninges as an extension of the cerebral meninges
98
Ostiomeatal complex
• Channel that links the frontal sinus, anterior and middle ethmoid sinuses and the maxillary sinus to the middle meatus that allows air flow and mucociliary drainage
• The ostiometal complex is composed of five structures:
o maxillary ostium: drainage channel of the maxillary sinus
o infundibilum: common channel that drains the ostia of the maxillary and ethmoid sinuses to the hiatus semilunaris
o ethmoidal bulla: usually a single air cell that projects over the hiatus semilunaris
o uncinate process: hook-like process that arises from the posteromedial aspect of the nasolacrimal duct and forms the anterior boundary of the hiatus semilunaris
o hiatus semilunaris: final drainage passage, a region between the ethmoid bulla superiorly and free-edge of the uncinate process
frontonasal duct opens into the hiatus semilunaris
99
Ostiomeatal complex - variant anatomy
• Wide range of anatomical variants that affect the many structures that compose the ostiomeatal complex
o concha bullosa: aerated middle turbinate
o intralamellar cell: air cell within vertical portion of middle turbinate
o oversized ethmoid bulla (Agger nasi cells)
o Haller cells (infraorbital cells)
o uncinate process bullae
o deviation of uncinate process
o deviated nasal septum
o paradoxical middle turbinate: convexity of turbinate directed toward lateral nasal wall
o ethmoidal bulla may not be pneumatised, and be a bony prominence
100
Paranasal sinuses
• Four paired air-filled spaces, named after the facial bones in which they are located
• Exist to reduce the weight of the skull
• All drain directly or indirectly into a nasal cavity
Innervation:
• Supplied by branches of the opthalmic (CN V1) and maxillary nerves (CN V2)
101
Frontal sinus
o right and left frontal sinuses are separated by a bony septum
o drains into the middle meatus via the frontonasal duct which opens into the ostiomeatal complex
102
Ethmoid sinus
o ethmoidal sinus comprises numerous small cavities between the nose and orbit within the ethmoidal labyrinth
o anterior and posterior groups drain into the middle and superior meatuses
o lateral wall is the lamina papyracea
o Bulla ethmoidalis
103
Sphenoid sinus
o sinus is divided into right and left parts by a bony septum
o relations:
superior: pituitary, optic chiasma
lateral: cavernous sinus
o drains into the spheno-ethmoidal recess and then the superior meatus
104
Maxillary sinus
o pyramid-shaped paranasal sinus which drains into the middle meatus of the nose
o described as having a body and four processes: orbital, zygomatic, alveolar, palatine
o medial wall of the sinus is continued superiorly as the uncinate process
o maxillary ostium opens superiorly into the infundibulum
o region of the ostium, infundibulum and middle meatus is known as the ostiomeatal complex
105
Paranasal sinuses - variants
* Silent sinus syndrome
* Hypoplasia
* Haller cells: also known as infraorbital ethmoidal air cells or maxilloethmoidal cells, located on the medial floor of the orbit
* Sphenoethmoidal / Onodi air cell: ethmoid air cell that lies posterior to the sphenoid sinus
* Agger nasi air cells: most anterior ethmoid air cells
* Agenesis (rare; usually involves frontal sinus)
106
Parathyroid glands
* Endocrine glands located in the visceral space of the neck
* Produce parathyroid hormone which controls calcium homeostasis
* Normally two pairs of parathryoid glands, inferior and superior
* Variable location from carotid bifurcation to anterior mediastinum
* Usually in close relation to the thyroid gland, in the region of the tracheo-oesophageal groove, posterolateral to the thyroid lobes
* The parathyroid glands are usually extracapsular to the thyroid but sometimes they may lie intracapsular
107
Parathyroid glands: vasculature
```
Arterial supply:
• Superior thyroid artery
• Inferior thyroid artery
Venous drainage:
• Superior thyroid vein (to IJV)
• Middle thyroid vein (to IJV)
• Inferior thyroid vein (to brachiocephalic)
Lymphatics:
• Prelaryngeal lymph nodes
```
108
Parathyroid glands: innervation
* Middle cervical ganglion
| * Inferior cervical ganglion
109
Parathyroid glands: variants
* Supernumerary glands
* Absence of parathyroid glands (less than 4)
* Ectopic parathyroid gland: most commonly inferior to the inferior pole of the thyroid
* Parathyroid glands may be located anterior to the thyroid or be intracapsular
110
Parotid gland
* The parotids are the largest of the salivary glands
* Secretes saliva via the parotid duct into the oral cavity
* Wrapped around the mandibular ramus
* Anterior and inferior to the ear, located within the parotid space
* The facial nerve and it's branches pass through the parotid gland
* ECA forms its two terminal branches (maxillary and superficial temporal) within the parotid gland
* The retromandibular vein is formed within the parotid by confluence of superficial temporal and maxillary veins
* There is moderate fatty infiltration or fatty replacement of the parotid glands with age
* Consists of a deep and superficial part
* Stensen’s duct (~5cm long) begins in the superficial part and pierces the buccinator to drain into the oral cavity opposite the 2nd upper molar
111
Parotid gland: relations
* Superficial: great auricular nerve
* Anteromedial: mandibular ramus, masseter, medial pterygoid
* Posteromedial: mastoid process, SCM, digastric, styloid process (and stylohyoid, stylopharyngeus, and styloglossus), carotid sheath (ICA, IJV, deep cervical lymph nodes, vagus nerve)
* Medial: superior pharyngyeal constrictor
* Structures that pass through: facial nerve and its branches, ECA, superficial temporal artery, maxillary artery, retromandibular vein
112
Parotid gland: vasculature
Arterial supply:
• Transverse facial artery (branch of the superficial temporal artery)
• Small branches of the ECA
Venous drainage:
• Drainage via retromandibular vein into the external jugular vein
Lymph drainage:
• Preauricular and deep parotid lymph nodes, which drain to the superior deep cervical lymph nodes
113
Parotid gland: innervation
* Secretomotor are derived from CN IX (otic ganglion)
| * Sympathetic from the superior cervical ganglion
114
Parotid gland: variants
* Small accessory parotid glands are common (20%), and join the duct along its length
* Parotid gland may be displaced anteriorly, extend inferiorly
* Absent parotid
* There may be a double parotid duct
115
Pterygopalatine fossa
* Pterygopalatine fossa is a small triangular space at the junction of the orbital and pterygomaxillary fissures
* It is a neurovascular crossroad of the nasal cavity, masticator space, orbit, oral cavity and middle crania fossa
116
Pterygopalatine fossa- borders
* Medial: perpendicular plate palatine bone
* Lateral: narrowing to pterygomaxillary fissure
* Anterior: posterior wall of maxillary sinus
* Posterior: medial and lateral pterygoid plates, inferior aspect of lesser wing of sphenoid bone
* Roof: inferior orbital fissure, sphenoid bone
* Floor: narrowing to palatine canals
117
Pterygopalatine fossa - communications
* Medially: communicates with the nasal cavity via the sphenopalatine foramen (transmits: sphenopalatine artery, posterior superior nasal nerve)
* Laterally: communicates with the masticator space (infratemporal fossa) via the pterygomaxillary fissure
* Superiorly: communicates with the orbit via the inferior orbital fissure
* Postero-superiorly: communicates with the Meckel cave and cavernous sinus via the foramen rotundum
* Postero-inferiorly: communicates with the middle cranial fossa via the vidian canal (transmits the Vidian nerve)
* Inferiorly: communicates with the palate via the greater and lesser palatine canals
118
Pterygopalatine fossa - contents
* Pterygopalatine ganglion suspended by nerve roots from the maxillary nerve
* Maxillary artery (terminal portion)
* Maxillary division of trigeminal nerve (V2) - enters via foramen rotundum
* Nerve of the pterygoid canal (Vidian nerve)
119
Scalp layers
* Skin: contains sebaceous glands and hair follicles
*
Connective tissue: dense layer of fat and fibrous tissue, contains nerves and blood vessels
*
Galea Aponeurotica: tough fibrous band that extends over the cranium, runs from the frontalis muscle to the occipitalis muscle
*
Loose areolar connective tissue: allows superficial layers to shift in relation to the pericranium
*
Periosteum
120
Scalp innervation
* Zygomaticotemporal nerve
* Greater occipital nerve
* Lesser occipital nerve
* Auriculotemporal nerve
* Supratrochlear nerve
* Supraorbital nerve
121
Pharyngeal space - contents
* Fat
* CN V
* Maxillary artery
* Ascending pharyngeal artery
* Pterygoid venous plexus
122
parotid space - contents
* Parotid glands
* Intraparotid lymph nodes
* CN VII
* ECA
* Retromandibular vein
123
carotid space - contents
* CCA / ICA
* IJV
* CN IX, X, XI, XII
* Sympathetic nerves
* Deep cervical lymph node chain
124
Masticator space - contents
* Muscles of mastication
* Mandible
* Inferior alveolar nerve, artery and vein
* CN V3 (enters the masticator space via the foramen ovale)
125
Retropharyngeal space - contents
* Areolar fat
* Lymph nodes (lateral and medial retropharyngeal)
* Small vessels
126
Perivertebral space - contents
```
• Prevertebral portion
o cervical vertebral body and disc
o prevertebral muscles
o scalene muscles
o vertebral artery and vein
o phrenic nerve
o brachial plexus
• Paraspinal portion
o posterior elements of cervical vertebrae
o paraspinal muscles
```
127
Sternocleidomastoid
* Paired muscle in the superficial layers of the side of the neck
* One of the largest and most superficial cervical muscles
* Thick and narrow at its central part, but broader and thinner at either end
* Divides the neck region into anterior and posterior cervical triangles which helps define the location of structures
* SCM is within the investing fascia of the neck, along with the trapezius muscle, with which it shares its nerve supply (the accessory nerve)
128
Sternocleidomastoid - origin,insertion,action
Origin:
• Manubrium and medial portion of the clavicle
Insertion:
• Mastoid process of the temporal bone
Action:
• Unilaterally: cervical rotation to opposite side, cervical lateral flexion to same side
• Bilaterally: cervical flexion, raises the sternum and assists in forced inspiration
129
Sternocleidomastoid - innervation + vasculature
```
Innervation:
• Motor: accessory nerve
• Sensory: cervical plexus
Arterial supply:
• Occipital artery
• Superior thyroid artery
```
130
Sternocleidomastoid - relations
• Deep: internal jugular vein, common /internal /external carotid, vagus nerve, brachial plexus, omohyoid
131
Sternocleidomastoid - variants
• Variation in the extent of its origin from the clavicle (narrow or broad)
o if clavicular origin is broad, it is occasionally subdivided into several slips, separated by narrow intervals
o rarely, the adjoining margins of the sternocleidomastoid and trapezius are in contact (leaving no posterior triangle)
132
Suboccipital triangle -
* Suboccipital triangle is a region of the neck bounded by the three muscles of the suboccipital group of muscles
* Purpose of these muscles is to provide fine motor function in movements of the head
133
Suboccipital triangle - borders
* Superomedial: rectus capitis posterior major
* Superolateral: obliquus capitis superior
* Inferolateral: obliquus capitis inferior
* Roof: covered by a layer of dense fibro-fatty tissue, situated beneath the semispinalis capitis
* Floor: posterior atlanto-occipital membrane, posterior arch of the atlas
134
Suboccipital triangle - contents
* Third part of vertebral artery
* Dorsal ramus of nerve C1 (suboccipital nerve)
* Suboccipital venous plexus
135
Superior orbital fissure
* Superior orbital fissure is the communication between the cavernous sinus and the apex of the orbit
* It is straddled by the tendinous ring which is the common origin of the four rectus muscles (extraocular muscles)
* L: lacrimal nerve (branch of the CNV1)
* F: frontal nerve (branch of the CNV1 )
* T: trochlear nerve (CN IV)
* S: superior division of the oculomotor nerve (CN III)
* N: nasociliary nerve (a branch of the CNV1 )
* I: inferior division of the oculomotor nerve (CN III)
* A: abducens nerve (CN VI)
136
TMJ
• This is an atypical synovial joint (no hyaline cartilage) with both articulating surfaces surrounded by fibrocartilage
• The joint cavity is separated by a fibrocartilaginous disc
Articular Surfaces:
• Mandibular condyle
• Mandibular fossa of the squamous part of the temporal bone
137
TMJ - capsule
* Inferior attachment: neck of the mandible anteriorly with lower attachment posteriorly
* Superior attachment: articular eminence of the temporal bone anteriorly; the squamotympanic fissure posteriorly; and medially and laterally to the mandibular fossa margins
* The articular disc is attached to the capsule at the medial and lateral poles of the mandibular head
* The posterior aspect of the disc divides into two laminae: the superior attaches to the mandibular fossa and the inferior to the neck of the mandible
* Superior and inferior synovial compartments
138
TMJ - ligaments
* Defines limits of mandibular movement
* Temperomandibular ligament: thickened lateral portion of the capsule
* Stylomandibular ligament
* Sphenomandibular ligament
139
TMJ - Relations
* Anterior: masseteric nerve
* Medial: auriculotemporal nerve
* Posterior: external acoustic meatus
140
TMJ - neurovasculature
Nerve Supply:
• Branches of CN V3: auriculotemporal and masseteric nerve
Blood Supply:
• Branches of the superficial temporal
• Branches of the maxillary artery (masseteric and deep temporal)
Venous drainage:
• Superficial temporal and maxillary veins
• Pterygoid Plexus
141
Thyroid gland
* Thyroid gland is an endocrine organ in the neck
* Completely enveloped by the middle-layer of the deep cervical fascia and lies in the visceral space
* Thyroid lies anterior to the thyroid and cricoid cartilages of the larynx and the first three tracheal rings (extends from C5 to T1)
* H-shaped and is composed of two lobes, each with a superior and inferior pole, connected by an isthmus
* Thin fibrous capsule of connective tissue surrounds the thyroid gland
* Parathyroid glands lie posteromedially and are sometimes intracapsular
* During embryogenesis the gland migrates down from the foramen caecum at the posterior aspect of the tongue to its permanent location
142
Thyroid gland: relations
* Anterior: strap muscles
* Posterior: thyroid cartilage, cricoid cartilage, trachea
* Posteromedially: tracheo-oesophageal groove (containing lymph nodes, recurrent laryngeal nerve, parathyroid glands)
* Posterolaterally: carotid space (ICA, IJV, vagus nerve)
* Inferior: superior thoracic aperture
143
Thyroid gland: neurovasculature
Arterial supply:
• Superior thyroid artery (from external carotid artery)
• Inferior thyroid artery (from thyrocervical trunk)
o if the inferior thyroid artery arises from the subclavian artery it is referred to as an accessory inferior thyroid artery
Venous drainage:
• Superior thyroid vein (drains to internal jugular vein)
• Middle thyroid vein (drains to internal jugular vein)
• Inferior thyroid vein (drains to brachiocephalic vein)
Lymphatic drainage:
• Peri-thyroid to the prelaryngeal, pretracheal and paratracheal lymph nodes
Innervation:
• Sympathetic: superior, middle and inferior cervical ganglia
• Parasympathetic: superior laryngeal nerve, recurrent laryngeal nerve
Ligament:
• Suspensory ligament of the thyroid (Berry) to cricoid cartilage
144
Thyroid gland: Variants
• Lobar hemiagenesis
o failure of the embryologic development of a lobe of the thyroid gland
• Pyramidal lobe
o conical shape and extends from the upper part of the isthmus, up across the thyroid cartilage to the hyoid bone
• Thyroglossal duct cyst
o most common congenital neck cyst
o typically located in the midline and are the most common midline neck mass in young patients
o typically present during childhood and remain asymptomatic until they become infected
• Ectopic thyroid tissue
o during embryological development, the thyroid gland migrates down from the foramen caecum at the posterior aspect of the tongue, to its permanent location
o normal migration can be halted at any point, or can go 'off-target' with thyroid tissue coming to rest in unusual location within the neck
o most common location is near its embryological origin at the foramen caecum, resulting in a lingual thyroid
• Zuckerkandl's tubercle
o extension of the thyroid gland at the most posterior side of each lobe
o surgical significance due to close proximity to the recurrent laryngeal nerve and superior parathyroid gland
• May be supplied by a thyroidea ima artery
o which may replace the inferior thyroid artery (3%)
145
Thyroid ima Artery variants
• Thyroidea ima artery is an uncommon variant of the blood supply to the inferior aspect of the thyroid gland.
• Can arise from:
o brachiocephalic trunk (most common)
o right common carotid artery
o aortic arch
o internal thoracic artery
• Thyroidea ima artery ascends on the anterior surface of the trachea and supplies both the trachea and thyroid
• May terminate as a single trunk or as multiple bifurcations
• Often associated with absent inferior thyroid arteries
• When an anomalous artery arises from the subclavian artery, it is referred to as an accessory inferior thyroid artery (not thyroidea ima artery)
• Clinical significance of the thyroidea ima artery during head and neck surgery, particularly thyroidectomy, if unrecognised it can be a source of brisk and potentially difficult to control bleeding, as the cut vessel may retract behind the manubrium
146
Trigeminal Nerve
• 5th cranial nerve
• Primary role is relaying sensory information from the face and head, and provides motor control to the muscles of mastication
• Has multiple brainstem sensory nuclei are arranged in a column which spans from the midbrain through to the upper cervical cord
o mesencephalic nucleus: proprioceptive fibers for muscles of the face, orbit, mastication, and tongue
o main sensory nucleus: responsible for touch sensation for all three trigeminal divisions
o spinal nucleus: responsible for pain and temperature, also receives afferent fibers from the CNIX and CNX
• motor nucleus is located in the upper pons and innervates the muscles of mastication as well as mylohyoid and tensor palati
147
Trigeminal Nerve - course
* Trigeminal nerve exits at the mid pons anteriorly
* Courses through the prepontine cistern (cisternal portion)
* Enters Meckel's cave (cavernous portion) where its fibres form the trigeminal ganglion
* Divides into three main branches: opthalmic, maxillary, mandibular
148
Trigeminal Nerve - ophthalmic division
o travels through the cavernous sinus, inferior to the trochlear nerve
o enters the superior orbital fissure where it divides into the frontal, lacrimal, and nasociliary nerves
149
Trigeminal Nerve - maxillary division
o gives off middle meningeal nerve just after origin
o travels in the lateral wall of the cavernous sinus inferior to trochlear and opthalmic nerves
o passes through the foramen rotundum to exit skull and enter the pterygopalatine fossa
o zygomatic nerve branches off in the pterygopalatine fossa
o enters the orbit through the inferior orbital fissure
o then enters the infraorbital canal to become the infraorbital nerve
o other branches: anterior, posterior and middle superior alveolar nerves, greater and lesser palatine nerves
150
Trigeminal Nerve - mandibular division
o courses inferiorly through the foramen ovale to exit the skull
o a meningeal branch enters the foramen spinosum with the MMA
o divides into anterior and posterior division
o anterior division supplies muscles of mastication: masseteric, deep temporal, buccal and lateral pterygoid branches
o posterior division divides into auriculotemporal, lingual and inferior alveolar nerves
inferior alveolar nerve branches: mylohyoid, dental, incisive, mental
151
Tympanic membrane
he middle ear is a cavity housed in the petrous temporal bone
• Thin membrane that separates the external ear from the middle ear
• Acts to transmit sound waves from air in the external auditory canal to the ossicles of the middle ear
• Malleus is the first bone in the ossicular chain that eventually sees the sound wave transmitted to the oval window of the cochlea
• Scutum is a tiny spur of bone where the tympanic membrane is attached
• Three layers:
o cutaneum (skin)
o radiatum circulare (collagen fibres)
o mucosum (epithelium)
• Two distinct portions to the membrane:
o pars tensa: the tense portion of the membrane (larger portion)
o pars flaccida: the flaccid portion of the membrane
• Anatomically separated into four quadrants:
o anterosuperior
o anteroinferior
o posteroinferior
o posterosuperior
• Vessels and nerves (specifically chorda tympani nerve) pass through the superior portion of the membrane
152
Tympanic membrane - vasculature
Arterial supply:
• Deep auricular (branch of the maxillary artery)
• Anterior tympanic artery (branch of the maxillary artery)
• Stylomastoid artery (branch of the posterior auricular artery)
Venous drainage:
• Pterygoid plexus
• Superior petrosal sinus
Lymphatic drainage:
• Preauricular nodes
• Retropharyngeal nodes
• Superior deep cervical nodes
