Facial Nerve Anatomy

1. Facial Nerve – Anatomy
The nerve of 2ND pharyngeal arch
Presenter: Adhishesh Kaul
Postgraduate Student – ENT
AIMS RC, Bengaluru
Moderator: Dr. Poornima S.
Associate Professor – ENT
AIMS RC Bengaluru

3. “Cranial nerves are the conduits by which the
brain receives information directly from, and
controls the functions of, structures that are
mainly but not exclusively in head and neck”

4. Arch Nerve Muscle Skeletal
Structure
Ligament
2nd Arch
(Hyoid
Arch)
Facial
Nerve
(VII
nerve)
Muscle of facial
expression
Stapes Stylohyoid
ligament
Stapedius Styloid
process
Stylohyoid Lesser
cornu of
hyoid
Posterior belly of
digastric
Upper part
of body of
Hyoid
Structures from 2nd Brachial Arch

6. Functional Components
SENSORY COMPONENT
• General Visceral Afferent
• Special Visceral Afferent
• General Somatic Afferent
MOTOR COMPONENT
• Special Visceral Efferent
• General Visceral Efferent

7. We have a Neural tube and Sulcus limitans
Sulcus limitans divides NT into
1. Alar Plate (Dorsal Part – represents dorsal horn
of spinal cord and is SENSORY in function)
2. Basal Plate (Ventral Part – represents ventral
horn of spinal cord and is MOTOR in function)

9. • CN nuclei developing in
– ALAR PLATE – SENSORY
– BASAL PLATE – MOTOR

10. • Neural Tube opens to accommodate – 4th
Ventricle
• Sensory Nuclei (afferent) – develop in Alar plate
• Motor Nuclei (efferent) – develop in Basal Plate

11. What is this SVE, GVE, GVA, etc?
• The neurons form cell columns, which are
divided by anatomists into functional
categories.
• Cell columns are divided into
– Motor vs Sensory
– General vs Special
– Somatic vs Visceral

13. Motor Nuclei
• nerves from General Somatic Efferent – supply
skeletal muscles
• nerves from General Visceral Efferent – supply
smooth muscles
• nerves from Special Visceral Efferent – supply
muscles from pharyngeal arches

14. Sensory Nuclei
• nerves from General Visceral Afferent:
for general sensation from viscera –
temperature, touch, pressure
• nerves from Special Visceral Afferent:
for special sensation from the viscera – taste
• nerves from General Somatic Afferent:
for general sensations from the skeletal muscles

15. So what all cell columns is facial nerve
involved with?

16. Functional Components
SENSORY COMPONENT
• General Visceral Afferent
• Special Visceral Afferent
• General Somatic Afferent
MOTOR COMPONENT
• Special Visceral Efferent
• General Visceral Efferent

18. Cranial Nerve Nuclei
“Cranial nerves which attach to brain stem are
associated with a number of cell groupings of
varying size referred to as cranial nerve nuclei”

19. Facial Nerve Nuclei
Fibres of facial nerve are connected to 4 nuclei
in lower Pons
• Motor Nucleus – deep reticular formation of lower pons
• Parasympathetic Nuclei – posterolateral to motor nucleus
– Superior Salivatory nucleus: afferent from hypothalamus and
NTS
– Lacrimal Nucleus: from hypothalamus for emotional,
sensory nuclei of CN V for reflex lacrimation
• Sensory Nucleus – is upper part of Nucleus of tractus
solitarius.

22. Motor Nucleus
• Site: deep in reticular formation of pons
anterior and cranial to nervus intermedius
lateral surface of brain stem, close to lower
border of pons
• Supply: Upper part of face: receives corticonuclear
fibres from both motor cortex
Lower part of face: receives corticonuclear
fibres only from opposite cortex

27. Intracranial
Intratemporal
Extracranial/ Extratemporal
Course
25mm in length
(atlas of facial nerve)
15mm (dhingra)
~33mm in length
XX mm in length
Segments
1. Meatal
2. Labyrinthine
3. Horizontal/
Tympanic
4. Vertical/
Mastoid
FACIAL
CANAL

29. Course
INTRACRANIAL EXTRACRANIAL
ENTERS TEMPORAL BONE
THROUGH IAM IN PETROUS
PART OF TEMPORAL BONE
(IN TEMPORAL BONE)
LEAVE: IAM
ENTERS: FACIAL CANAL
AFTER LEAVING CRANIUM AND
FACIAL CANAL THROUGH SMF
EVENTS IN FACIAL CANAL: (Z-SHAPE STR)
1. 2 ROOTS FUSE IN MEATUS
2. NERVE FORMS GENICULATE GANGLION
3. NERVE GIVES RISE TO ITS 3 BRANCHES

30. Course
INTRACRANIAL
FACIAL CANAL
IAM/ IAC
EXTRACRANIAL

31. Course of Facial Nerve
• Roots (at brain stem):
– Motor:
• supply muscles of face
– Sensory (nervus intermedius):
• perception of taste
• Parasympathetic fibres to lacrimal glands/ submandibular
gland/ sublingual gland
• Attached to lower part of Pons – medial to CN VIII

33. • Emerges from brainstem at junction of Pons and
Medulla (pontomedullary junction – 1.5mm
anterior to CN VIII)
• Till Internal Acoustic Meatus:
Lateral + Forward (rostolateral course) (with CN
VIII) through cerebellopontine cistern across
posterior cranial fossa in subarachnoid space TO
ENTER INTERNAL AUDITORY CANAL

35. • Emerges from brainstem
at junction of Pons and
Medulla (pontomedullary
junction – 1.5mm
anterior to CN VIII)
• Till Internal Acoustic
Meatus:
Lateral + Forward (rostolateral
course) (with CN VIII) through
cerebellopontine cistern across
posterior cranial fossa in
subarachnoid space TO ENTER
INTERNAL AUDITORY CANAL

36. • Relation to artery:
– Anterior Inferior Cerebellar Artery, may lie
Anterior or posterior
or loop around
or pass between the nerves
• IN CP ANGLE SURGERIES, THIS ARTERY MUST
BE PRESERVED
• AICA supplies: Labyrinthine artery

38. CP angle cistern
CP angle cistern is triangular CSF filled cistern
between anterior surface of cerebellum and
lateral surface of pons
Related structures
– AICA
– CN VII, CN CN VIII
– Foramen luschka

39. Intratemporal Course
• Segments
– Meatal
– Labyrinthine – from meatal foramen to geni. gang.
– Tympanic
– Mastoid

41. Course in IAC/ Meatal Segment
(IAC: location: anterior to superior SCC)
In IAC location of CN VII: Ant Sup Quad
Enters Fallopian canal/Facial Canal at fundus
of IAC
(at entrance of fallopian canal (meatal foramen), FN is
narrowest 0.61mm)

43. Meatal Segment
• FN enters Temporal bone through IAM on
posteromedial surface of petrous ridge
• Motor and sensory roots join at fundus/ base
of IAM
• It is located on the ant sup quad of IAM above
falciform crest, anterior to bill bar
These are important landmark for facial nerve via
translabyrinthine, transcochlear and middle cranial
fossa approach
Bill Bar: divides superior quad of IAM into Ant and Post quad
(named after William Fouts House)

44. Course within Facial Canal
Facial Canal: runs across medial wall and down
posterior wall of tympanic cavity to Stylomastoid
foramen
3 Parts of Facial Nerve in Facial Canal
Course: Lateral and Forward
• 1st Part: directed laterally above vestibule
• 2nd Part: runs backward in relation to medial wall of
middle ear
• 3rd Part: directed vertically downward – behind the
promontory

46. • Enters Fallopian canal/Facial Canal at fundus
of IAC
• As the FN enters FC, FC has a bend that
contains geniculate ganglion
• Branches in temporal bone –(explained ahead)
can be divided into
– From geniculate ganglion
– Arise within facial canal

47. Labyrinthine Segment
• From fallopian canal/ facial canal
• Course:
– Anterior-lateral course between and superior to
cochlea and vestibule
– Turns back on geniculate ganglion
(Geniculate ganglion resides in distal part of labyrinthine
segment)
• Relation: Covered by superior part of petrous
bone
Runs over junction of cochlea and
vestibule

48. Tympanic Segment
• ~11mm long
• From: Geniculate ganglion (genu)
• Runs between lateral semicircular canal
superiorly and the stapes inferiorly
• Forms the superior margin of the fossa ovale
• Relation: Below FN – Promontory (basal turn of
cochlea) and Oval window (fenestra vestibuli)
Above FN – Ampullary end of SCC

50. Mastoid Segment
• ~13mm long
• From: Posterior end of Fenestra Vestibuli
• Course in Bony posterior wall of middle ear
• Direction: Downward and lateral
• Nerve exits at anterior margin of digastric
groove, behind root of styloid
• Relation: Posterior FN: Mastoid Antrum

51. Extracranial Course
• Exit: Stylomastoid foramen at 2.5cm – 4cm deep to
middle of anterior border of mastoid (9mm from post belly
of digastric and 11mm from bony EAC)
• Course:
– Crosses lateral side of base of styloid process
– Enters: Parotid at Posteromedial surface
– Runs forward and downward behind mandibular
ramus
– Crosses retromandibular vein and ECA
– Behind neck of mandible divides into 5 terminal
branches

53. Relation with Parotid Gland
• FN divides the gland into Suprafacial and
Subfacial parts
• Tracing
– Forward : expose trunk at SMF: 1cm FN before
entry into parotid: 1cm after it enters but before it
divides Temporofacial and Cervicofacial: use to
make plane of cleavage
– Traced backward from terminal branches

55. Branches of Facial Nerve
• Within Facial Canal
Greater petrosal nerve (from geniculate ganglion)
Nerve to stapedius (behind pyramidal eminence of post wall of
tympanic cavity) – at level of 2nd genu
Chorda tympani
• At Exit from Stylomastoid Foramen
 Posterior Auricular (supply occipetal belly of occipetofrontalis)
 Digastric
 Stylohyoid
• Terminal Branches
• Communicating branches with adjacent CN

56. Terminal Branches
• Temporal
• Zygomatic
• Buccal
• Mandibular (marginal mandibular)
• Cervical

58. Greater Petrosal Nerve
• Fibres for Pterygopalatine ganglion and taste fibre from
palate
• Branch of: Nervus Intermedius
• Receives a branch from: Tympanic Plexus
• Course:
– Passes anteriorly
– Transverses hiatus on ant surface of petrous part of
temporal bone
– Enters middle cranial fossa and runs forward on the groove
above lesser petrosal nerve
– Passes beneath trigeminal ganglion to reach foramen
lacerum
– Joined by deep petrosal nerve to become VIDIAN NERVE

59. Chorda Tympani
• Leaves FN 6mm above SMF
• Arises from middle of vertical segment
• Secretomotor fibre to submandibular and
sublingual gland
• Runs: anterosuperiorly in canal
enter tympanic cavity via posterior canaliculus
curves anteriorly in substance of Tym Membrane
crosses medial to upper part of handle of malleus
to ant wall
enters ant. Canaliculus
exits skull/tympanic cavity at petrotympanic fissure

62. Posterior Auricular Nerve
• Supplies: pinna,
occipital belly of occipitofrontalis
• Communicates with auricular branch of vagus

63. Distribution of Facial Nerve Branches

65. Blood Supply of Facial Nerve
• Anterior Inferior Cerebellar artery: supply CP angle
• Labyrinthine artery: br of A-I cerebellar art., supply IAC
• Superficial Petrosal artery: br of MMA, supply Geni. gangli.
• Stylomastoid artery: br of post. auricular art., supply mastoid
and tympanic

67. Variation and Anomaly of Facial Nerve
• Bony dehiscence: mc in tympanic segment over oval window>
region near geniculate ganglion> retrofacial mastoid
• Prolapse of nerve: dehiscent nerve may prolapse over stapes
and make stapes surgery/ ossicular reconstruct difficult
• Hump: posteriorly: vulnerable while exposing antrum
• Bifurcation and trifurcation: vertical part divides
• Bifurcation and enclosing the stapes: division proximal to
oval window with one part above and one part below, then
rejoining
• Between oval and round window: before oval window nerve
crosses middle ear passing between oval and round window

69. In cholesteatoma, facial nerve may
1. Lie under the bone
2. Be dehiscent (congenitally or acquired due to cholesteatoma)
3. Be protuberant
Hence great caution must be exercised in removing cholesteatoma from
extensively eroded facial nerve, esp when protuberant or inflame

71. Lesions of Facial Nerve
Upper Motor Neuron
• Lesion above the FN
nucleus in Pons
• Paralysis: Lower half of the
face as upper part is
supplied by both the
hemispheres.
Lower Motor Neuron
• Lesion at FN nucleus in Pons
or distal to it.
• Site: by topodiagnostic test
– Homolateral lacrimation
– Stapedial reflex
– Homolateral submandibular
salivation
– Taste from homolateral
anterior 2/3 tongue

72. UMN vs LMN Lesion

74. • Schimers Test: proximal to greater petrosal nerve
(geniculate ganglion)
• Stapedial relex: proximal to nerve to stapedius
(tympanic segment)
• Salivary flow test: proximal to chorda tympani nerve
(mastoid/ vertical segment)
• Taste Test: proximal to chorda tympani nerve (mastoid/
vertical segment)

76. Other Clinical Aspects
• Before mastoid development in child, FN lies
subcutaneously and is at a danger of being cut if
any postauricular incision is given too deep.
• 1st brachial arch anomalies are associated with
facial nerve, that they’re either superficial to it or
deep
• Radical neck dissection, mandibular branch of
facial nerve is to be identified and preserved.

77. Centrally localized lesions
• Preganglionic secretion fibers to the lacrimal gland: These branch off from
the nerve at the geniculate ganglion into the greater superficial petrosal
nerve. A lesion in the preganglionic or ganglionic segments leads to
unilateral impairment of lacrimal secretion. A Schirmer test for pathologic
values can be useful for detection.
• Preganglionic secretion fibers to the submandibular gland: These exit the
nerve together with the chorda tympani. Damage in the tympanic portion
causes reduced ipsilateral saliva production of the submandibular gland. A
sialometry test is used (cannulation and collection of whole saliva). A
pathologic sialogram, along with remarkable Schirmer values on the same
side, are a sign of damage in the tympanic portion of the nerve course. If
the Schirmer test is additionally positive, the lesion can be presumed to be
more centrally localized (usually in the labyrinthine portion).
• Motor fibers to the stapedius muscle: Damage occurring proximal to the
pyramidal process causes reflex dysfunction or increased reflex threshold
on the injured side.

78. References
1. Anatomy for plastic surgery of the face, head and neck
2. B D Chaurasia’s Human Anatomy, ed 8
3. Clinical Neuroanatomy, Richard S. Snell, ed 7
4. Cummings Otolaryngology Head and Neck Surgery, ed 6
5. Disease of ear, nose and throat and head and neck surgery, ed 6
6. Entokey
7. Gray’s Anatomy for Students, ed 3
8. Gray’s Clinical Neuroanatomy
9. Lee McGregor’s Synopsis of Surgical Anatomy, ed 12
10. Scott-Brown’s Otorhinolaryngology Head & Neck Surgery, ed 8
11. Snell’s Clinical Anatomy