The rhombencephalon (or hindbrain) is divided into
the myelencephalon (caudal), which becomes the
medulla oblongata, and the metencephalon (cranial),
which becomes the pons and cerebellum.
The facioacoustic (acousticofacial) primordium
appears during the third week of life
It is attached to the metencephalon just cranial to the
The facial part of the acousticofacial primordium
migrates cranial and ventral to end adjacent to the
epibranchial placode, which is located on the dorsal
and caudal aspect of the first branchial cleft
By the end of the fourth week of gestation the facial
nerve splits into 2 parts, caudal and rostral trunks.
The chorda tympani nerve exits rostrally and courses
ventrally to the first pharyngeal pouch to enter the
Shortly thereafter, the nerve approaches the
epibranchial placode, inducing the appearance of the
large dark nuclei of neuroblasts that represent the
future geniculate ganglion.
Mesenchymal concentrations that form the cephalic
muscles are seen in association with their nerves, while the
epibranchial placode disappears and the geniculate
ganglion is identifiable.
The greater superficial petrosal nerve (GSPN) is present.
The chorda tympani nerve enters the mandibular
arch and terminates just proximal to the submandibular
ganglion, near a branch of the trigeminal nerve that will
become the lingual nerve.
The posterior auricular nerve appears near the chorda
a discrete nervus intermedius develops, making this an
important temporal reference point for gestational
The GSPN courses to the lateral aspect of the developing
internal carotid artery (ICA), where it joins the deep
petrosal nerve and continues as the nerve of the pterygoid
canal. It terminates in a group of cells that will become the
At this point, the most distal branches of the facial nerve
are a loose network or interconnecting twigs
The nervus intermedius is now smaller than the
motor root and enters the brain stem between the
vestibulocochlear nerve and the motor root of the
The chorda tympani and lingual nerve unite proximal
to the submandibular gland.
The posterior auricular nerve now divides into cranial
and caudal branches.
Several branches are visible in the peripheral portion
of the seventh nerve. All of the peripheral branches lie
deep to the myoblastic laminae that will form the
At the end of the seventh week, the separations
between the terminal branches continue to increase
to the extent that all peripheral divisions can be
The parotid gland is beginning to develop from the
parotid bud at this stage.
The temporal, zygomatic, and upper buccal branches
are superficial to the parotid primordium, while the
lower buccal, mandibular, and cervical branches are
Multiple facial muscles appear at this time as well,
including the zygomaticus major and minor,
depressor anguli oris, buccinators, and frontalis.
A sulcus develops around the facial nerve that is the
beginning of the fallopian canal. The orbicularis oris,
levator anguli oris, and orbicularis oculi muscles appear.
Auricularis anterior, corrugator supercilii, occipital and
mandibular platysma, and levator labii superioris alaeque
nasi muscles appear. All the cranial nerves more closely
resemble their adult relationships.
week the facial nerve has branches extensively and
the majority of anastomosis have occurred .
At term the anatomy of the facial approximates that
of the adult with the exception of its superficial
location within a poorly formed mastoid.
The facial nerve (FN), like most of the cranial
nerves, is a mixed nerve containing motor,
sensory and parasympathetic fibers.
Nuclei of the facial nerve
Motor nucleus: in the Pons fibers from it will
surround the abducent nerve nucleus to form the
Nucleus solitarious: in the medulla oblongata and
receives the taste fibers
Superior salivatory nucleus: in the Pons and gives
rise to the parasympathetic fibers
Functional components of the FN
The facial nerve can be divided into four functional
components: two efferents and two afferents:
Motor fibers (efferent): The upper part of the facial
nucleus receives pyramidal fibers from both sides,
while the lower part receives pyramidal fibers only
from the contra lateral side.
Parasympathetic fibers (efferent).
Taste fibers (afferent).
Sensory fibers (afferent).
Functional components of the FNFunctional components of the FN
Course of the FN
The facial motor nucleus lies in the lower part of
pons, close to the abducent nerve nucleus.
The fibers of the facial nerve wind around the
abducent nerve nucleus and emerge from the
lower border of the pons.
Course of the FN
The course of the FN is divided into three portions:
1)Intracranial portion (23-24 mm long).
2)Intratemporal portion (28-30 mm): It is divided into:
a-meatal segment (8-11).
b-Labyrinthine segment (3-5 mm): Narrowest part.
c-Tympanic segment (8-11 mm).
d-Mastoid segment (10-14 mm).
Facial Nerve Anatomy – Intracranial
The portion of the nerve from the
brainstem to the internal auditory canal
Made up of two components
1. Motor root
2. Nervus intermedius – carries preganglionic
parasympathetic fibers and special afferent sensory fibers
- Both join at the CPA/IAC to form the common facial
Facial Nerve Anatomy – Intratemporal
• Meatal (8-10mm)
– Portion of the facial nerve traveling from
porus acusticus to the meatal foramen of
– Travels in the anterior superior portion
of the IAC (7-UP, 8-Down)
» Posterior superior – superior vestibular
» Posterior inferior – inferior vestibular
» Anterior inferior – cochlear nerve
– From fundus to the geniculate
– Runs in the narrowest portion of the
IAC (0.68mm in diameter)
– Greater superficial petrosal nerve
comes off at this point
The term labyrinthine segment is derived from the
location of this segment of the nerve immediately
posterior to the cochlea.
The nerve is posterolateral to the ampullated ends of
the horizontal and superior semicircular canals and
rests on the anterior part of the vestibule in this
The transtemporal course of the facial
nerve is shown. Note the vascular arcades
feeding the facial nerve throughout its
course in the bony fallopian canal.
Facial Nerve Anatomy – Intratemporal
• Tympanic (8-11mm)
– At the geniculate ganglion the nerve makes
40-80 degree turn to proceed posteriorly
across the tympanic cavity to the pyramidal
– Highest incidence of dehiscence here (40-
50% of population)
The tympanic segment extends from the geniculate ganglion to
the horizontal semicircular canal
The nerve passes behind the cochleariform process and the tensor
The cochleariform process is a useful landmark for finding the
facial nerve. The nerve lies against the medial wall of the cavum
tympani, above and posterior to the oval window.
The distal portion of the facial emerges from the
middle ear between the posterior wall of the external
auditory canal and the horizontal semicircular canal.
This is just distal to the pyramidal eminence, where
the facial nerve makes a second turn marking the
The most important landmarks for identifying the
facial nerve in the mastoid are the horizontal
semicircular canal, the fossa incudis, and the digastric
The second genu of the facial nerve runs inferolateral
to the lateral semicircular canal. This is a relatively
• Mastoid (10-14mm)
– The second genu marks the beginning of the
– The second genu is lateral and posterior to the
– The nerve continues vertically down the anterior
wall of the mastoid process to the stylomastoid
– Gives off branches to the stapedius muscle and
the chorda tympani
Facial Nerve Anatomy – Extratemporal
• Nerve exits stylomastoid foramen
– Postauricular nerve - external auricular and occipitofrontalis
– Branches to the posterior belly of the digastric and stylohyoid
• Enters parotid gland splitting it into a superficial and
• It enters the posteromedial surface of the parotid gland
superficial to ECA and retromandibular vein
• Pes Anserinus
– Branching point of the extratemporal segments in the parotid
– To Zanzibar By Motor Car
» Marginal mandibular
Facial Nerve Components
• Supplies muscles of facial expression
• Stylohyoid muscle
• Posterior belly of digastric
• Stapedius muscle
• Taste to anterior 2/3 of the tongue
• Sensation to part of the TM, the wall of the EAC, postauricular
skin, and concha
• Supplies secretory control to lacrimal gland and some of the
seromucinous glands of the nasal and oral cavities
• Chorda tympani carries parasympathetics to the
submandibular and sublingual glands
The geniculate ganglion
The geniculate ganglion is formed by the juncture of
the nervus intermedius and the facial nerve into a
Additional afferent fibers from the anterior two thirds
of the tongue are added to the GG from the chorda
Three nerves branch from the geniculate ganglion:
the greater superficial petrosal nerve, the lesser
petrosal nerve, and the external petrosal nerve.
The greater petrosal nerve
emerges from the upper portion of the ganglion and
carries secretomotor fibers to the lacrimal gland.
The greater petrosal nerve exits the petrous temporal
bone via the greater petrosal foramen to enter the
middle cranial fossa.
The nerve passes deep to the Gasserian ganglion (ie,
trigeminal ganglion) to the foramen lacerum, through
which it travels to the pterygoid canal.
The greater petrosal nerve
In the pterygoid canal, the greater petrosal nerve joins
the deep petrosal nerve (sympathatic nerve from
plexsus around ICA) to become the nerve of the
Axons from this nerve synapse in the pterygopalatine
ganglion; postganglionic parasympathetic fibers,
which are carried via branches of the maxillary (V2)
divisions of the trigeminal nerve (CN V), innervate the
lacrimal gland and mucus glands of the nasal and oral
The chorda tympani is the terminal branch of the
nervus intermedius. The chorda runs laterally in the
middle ear, between the incus and the handle of the
The nerve crosses the middle ear cavity and exits
through the petrotympanic fissure (ie, canal of
Huguier) to join the lingual nerve.
The chorda tympani nerve carries preganglionic
secretomotor fibers to the submaxillary and
The chorda also carries special sensory afferent fibers
(ie, taste fibers) from the anterior two thirds of the
tongue and fibers from the posterior wall of the
external auditory canal responsible for pain,
temperature, and touch sensations.
Nerve to stapedious
Posterior auricular nerve
Nerve to posterior belly of diagastric
Surgical anatomy of the FN
A) Identification of intratemporal part:
During middle ear and mastoid surgery: the short process of the incus
(fossa incudis), cochleariform process, horizontal and posterior canals,
pyramid, and digastric ridge mark the course of the FN.
The second genu hugs the inferior aspect of the lateral SCC. The pyramid
is a useful landmark for the second genu.
B) Identification of extratemporal part:
During parotid surgery, the main trunk of the nerve is identified by the
tragal pointer. The nerve is usually located 1 cm medial and inferior to
Another useful landmark is the tympanomastoid fissure, the nerve can be
identified 6-8 mm below the inferior drop off of the fissure.
A peripheral branch can be identified and followed proximally towards
the main trunk of the FN.
Hitselberger` sign involving decrease sensitivity in
the posterosuperior aspect of the concha
corresponding to sensory disturbance of the facial
suggests a space occupying lesion in IAC
findings that alert the physician to possible facial
abnormalities: ossicular anomalies, craniofacial
Why might a tumor of the middle ear cause
abnormal taste sensation???
A patient with hyperacusis and unusual taste,facial
weakness, hearing loss???
What may result from the relative small size of
Dropped lower lip with submandibular growth???
Hyperacusis is a very acute sense of hearing caused
by damage of stapedious
Blood supply to facial nerve – clinical
Courses between the epineurium and periosteum –
making the blood supply at risk when mobilizing at the
External carotid artery
Stylomastoid artery (branch of the postauricular artery
of external carotid artery)
Greater petrosal artery (branch of middle meningeal
Internal auditory artery (branch of the AICA)
Labyrinthe segment - lacks anastomosing arterial cascades
thereby making the area vulnerable to ischemia
Components of a Nerve
Surrounds each nerve fiber
Provides endoneural tube for regeneration
Much poorer prognosis if disrupted
Surrounds a group of nerve fibers
Provides tensile strength
Protects nerve from infection
Surrounds the entire nerve
Provides nutrition to nerve
Radiology facial nerve
let’s follow the facial nerve back out, from internal to external, on coronal CT
Radiology facial nerve axial
On axial CT images, an easy landmark to start with the styloid process.
From there, the course of the facial nerve can be traced from inferior to
superior, external to internal, as follows:
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