anatomy of facial nerve, applied anatomy of facial nerve

1. Dr Safika Zaman
Post Graduate Trainee
Dept of ENT & Head Neck Surgery

2. Nerve of 2nd branchial arch
Facial nerve affects non verbal humanistic
expression.
Normal daily functions, such as eating and
drinking.
May disrupt the protective function of the eye.

3.  Facial nerve has the longest and complex course in its bony canal. The anatomical
variations make the nerve prone to injury during mastoid surgeries. Having a
thorough anatomical knowledge and its variations is must for the surgeons to
avoid injury to this vital structure and for the safe surgery.
 The reported rate of iatrogenic injury to the facial nerve in primary
tympanomastoidectomy surgeries was 0.6% to 3.7%. The risk is doubled in
revision surgeries to 4% to 10%. Kalaiarasi R, Kiran A Satya,
Vijayakumar C, et al. (August 02, 2018)
Anatomical Features of Intratemporal
Course of Facial Nerve and its
Variations. Cureus 10(8): e3085. DOI
10.7759/cureus.3085

4.  Facial nucleus is represented in the precentral
gyrus of cerebral cortex.
 Fibres run down through genu of Internal
Capsule.
 Nucleus:1. The motor nucleus of the facial
nerve.
2. The superior salivatory nucleus
3. The nucleus solitarius,
4. Spinal tract of 5th nerve

5.  Four major functions
 General somatic efferent :motor supply to facial muscles.
 General visceral efferent :parasympathetic secretomotor supply to submandibular and
sublingual salivary glands and the lacrimal gland.
 Special visceral afferent :taste sensation from anterior two-thirds of the tongue.
 General somatic afferent :cutaneous sensations from the pinna and the external
auditory meatus.

7.  1. Intracranial
 2. Intra-temporal
 3.Extra-temporal

8.  The facial nerve is smaller in diameter
than the vestibulocochlear nerve (l.8 mm
versus 3 mm).
 The facial nerve then crosses the
cerebellopontine angle (a distance of 15
to 17 mm) with the eighth cranial nerve.
 Nerve of Wrisberg (nervus intermedius).,

10. The length of the IAC portion of the nerve is
approximately 8 to10 mm

11.  The facial nerve enters the labyrinthine segment of its
fallopian canal through the meatal foramen.
 Meatal foramen is the narrowest portion of the entire
canal and measures approximately 0.68 mm in
diameter.
 The labyrinthine segment ( 4 mm in length) makes up
the first segment of the bony fallopian canal and is the
narrowest and shortest portion of the canal.
 A dense band encircles the nerve at the lateral end of
the IAC. This band contributes to the anatomic
"bottleneck“.

12.  The facial nerve takes a sharp (75 degree)
posterior turn at the first genu.
 The GG contains bipolar ganglion cells for
the sensory functions of the nervus
intermedius.
 The greater superficial petrosal nerve arises
from the GG and en1erges through the
hiatus of the fallopian canal (facial hiatus)
onto the floor of the middle fossa.

13. With Deep petrosal nerve,
forming the nerve of the
pterygoid canal - also called
the Vidian nerve.
The parasympathetic fibers
synapse at the
pterygopalatine ganglion
Vasomotor innervation to the
lacrimal, nasal, and palatine
glands.

14.  Courses posterio-inferiorly in its tympanic (horizontal)
segment.
 Measures 1 l mm in length.
 Portion of the tympanic segment becomes the cephalad
margin of the oval window niche.
 The nerve then takes a second turn (the second or external
genu).
 At 2nd genu, the facial nerve gives off a branch to the stapedius
muscle.

15.  Supplies the stapedius muscle.
 Contraction of the stapedius muscle
stiffens the middle ear ossicles and
tilts the stapes in the oval window of
the cochlea; this effectively decreases
the vibrational energy transmitted to
the cochlea.

16.  The facial nerve then proceeds vertically in
the mastoid cavity.
 which measures 13 mm in length.
 Approximately midway in its mastoid
segment, the facial nerve gives off the
chorda tympani nerve.

17.  posterior colliculus.
 The chorda tympani goes between
the malleus and incus and re-
emerges anterior to the middle ear
cavity.
 It then enters medially to the
temporomandibular joint through the
petrotympanic fissure.
 the chorda tympani joins the lingual
nerve, after exiting the petrotympanic
fissure,

18.  At stylomastoid foramen, it becomes
encircled by the fibrous tendon of
the digastric muscle, which becomes
part of the nerve sheath and firmly
attaches the nerve to surrounding
structures.

19.  The extratemporal portion of the
nerve divides into the
temporofacial and cervicofacial
trunks.

20.  Three branches of arteries have numerous
anastomoses and constitute the extrinsic vascular
system.
 Veins accompany the arteries in the fallopian canal.
 An intraneural vascular plexus (intrinsic system)
originates from the extrinsic system.
 This plexus can support segments of the nerve when
it is mobilized.

21.  The cog identifies the 1st genu.
 Cochleariform process is immediately inferior to
the nerve.
 The nerve lies above the oval window.
 LSC is posterosuperior

22.  Tragal pointer: Nerve is located about 1cm medial.
 Tympanomastoid suture: Nerve lies deep to the suture.
 The styloid process: lateral to the styloid process at skull
base.

23.  Congenital bony dehiscence:
Most frequent site is above the oval
window.
There may be more than one dehiscence.
Severe dysplasias of middle ear is associated
with aberrant course of the nerve.

24. The canaliculer segment may
enter petrous pyramid instead of
IAM.
Bifurcation of labyrinthine
segment.
FN crossing superiorly to LSC.
FN over oval window.
Hypoplasia of the nerve

27. Clinical anatomy of the chorda tympani:a
systematic reviewL J MCMANUS1, P J D
DAWES2, M D STRINGER1
1Department of Anatomy, Otago School of
Medical Sciences, and 2
Department of Otorhinolaryngology and
Head and Neck Surgery, Department of
Surgical Sciences, Dunedin School of
Medicine, University of Otago,
Dunedin, New Zealand

28. Topodiagnostic testing,eg, Taste and saliva testing,
Schirmer's tear test,
Stapedial reflex test,
Submandibuler salivery flow
test
These tests has been replaced by more objective and accurate
investigations.
Topodiagnostic tests evaluate different functions of the nerve
to determine the site of the abnormality or lesion.

30.  Upper motor vs Lower motor paralysis.

31.  CP Angle lesion:The close anatomical
relationship between the motor root of the
facial nerve,nervus intermedius and
vestibulocochlear nerve along theircisternal
and meatal portions explains the disturbances
in lacrimation, taste, salivary flow, hearing,
balance or facial motor control that may result
from lesions in either the CPA or IAM.

32.  Trauma: 80% of fructures
are longitudinal, from
blows to the temporal or
parietal areas, Fructure
line is usually anterior to
otic capsule, usually
facial is spared, usually
there is delayed onset
facial nv paralysis due to
edema.

33.  Hemifacial spasm: symptom complex of
unilateral facial nerve hyperactive
dysfunction, characterized by the onset of mild
and intermittent spasm of orbicularis oculi.
 Secondary hemifacial spasm may occur
secondary to nerve trauma.

34.  It is the only segment of the facial nerve
that lacks anastomosing arterial
cascades and so is vulnerable to embolic
phenomena, low-flow states and
vascular compression: it is most likely
to be affected by ischaemia in the event
of oedema following trauma or
inflammation

35.  The geniculate ganglion lies in a fossa covered
by a very thin layer of bone that separates it
from the floor of the MCF. Dehiscences here are
not uncommon: when present they render the
nerve vulnerable during middle fossa surgery

36. Thank
you