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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4399_Библиотеки_им_академика_М_И_Перельмана
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Figure 4–3. Temporal bones of newborn and adult, lateral view, with special emphasis on the lack of development of themas-
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toid process in the newborn and the differences in the tympanic ring. (From http://hearinghealthmatters.org/waynesworld
/2014/human-ear-canal/. With permission.)
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4. Temporal Bone Osteology 47
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CLINICAL CAVEAT: In young childhood, the subarcuate fossa is an important preformed pathway
between the middle ear and mastoid and the intracranial cavity, and may be instrumental in development of meningitis from acute otitis media (AOM)
in infants. Therefore, AOM in infants is managed
aggressively, in order to prevent this intracranial
complication.
Further laterally and downward, mid-distant between the IAM and the sigmoid sulcus, the vestibular aqueduct carrying the endolymphatic duct and sac
opens up on the posterior surface of the petrous bone.
This aperture is like a vertical slit overhung by a scale
of bone called the operculum. The operculum is thought
to protect the sac and the inner ear fluids from the pulsations of the brain.
iii. Inferior Surface
The inferior surface lies in a horizontal plane and is uneven and roughened for attachment of muscles. Near
the apex is a quadrilateral area for attachment of the levator palati muscle. The lateral edge of the bone dips,
and, coupled with the adjoining sphenoid edge, forms a
gutter where the cartilaginous Eustachian tube lodges.
Behind the quadrilateral area is the circular opening of
the carotid canal. Immediately behind is the wide opening of the jugular fossa, which contains the jugular bulb.
The jugular fossa area, along with the neighboring occipital bone, forms the jugular foramen. The lateral
portion of the foramen contains the sigmoid sinus. The
medial part is occupied by the inferior petrosal sinus,
the glossopharyngeal nerve (CN IX) and its superior
ganglion, the vagus nerve (CN X) and its jugular (Nodosal) ganglion, and the spinal accessory nerve (CN XI).
The mastoid canaliculus for the auricular branch of the
vagus nerve (Arnold’s nerve) opens into the fossa. Medial to the fossa and behind the carotid foramen is a
funnel-shaped expansion of the cochlear canaliculus, also
known as the cochlear aqueduct, containing the perilymphatic duct. On the edge between the carotid foramina and jugular fossa is a petrosal fossula for the glossopharyngeal ganglion. At the bottom of this fossula is an
opening for transmission of the tympanic branch of the
glossopharyngeal nerve (Jacobson’s nerve). Behind the
jugular fossa is the jugular process of the occipital bone
(Figure 4–2C).
CLINICAL CAVEAT: Vernet’s syndrome or jugular foramen syndrome is a constellation of cranial
nerve palsies of CN IX, X, and XI caused by compression from a jugular foramen lesion such as glomus jugulare tumor or a schwannoma. Paralysis
of muscles supplied by these cranial nerves should
raise suspicion for a jugular foramen lesion.
iv. The Margins or Borders of the Petrous Bone
The posterior surface is bordered above by the superior petrosal sulcus lodging the superior petrosal sinus, which is lodged in the attached margin of cranial
dura mater. Likewise, the inferior border of this sulcus
widens at the border of the jugular fossa, and as it lies
along the occipital bone it provides a sulcus for the inferior petrosal sinus.
The Tympanic Temporal Bone
The tympanic part of the temporal bone is a thin plate of
roughly quadrilateral form located anterior to the mastoid process. It is C-shaped and open superiorly. Medially it fuses with the petrous part at the petrotympanic
fissure. Laterally it has two surfaces: posterior and anterior. The posterior surface is concave and forms the
anterior wall, floor, and part of the posterior wall of the
bony external auditory meatus. The open roof of the C
is called the Notch of Rivinus and is completed by the
squamous bone. Medially on the posterior surface is
the tympanic sulcus for the tympanic membrane. The
anterior surface is quadrilateral and concave and forms
the posterior wall of the mandibular fossa. A portion of
the parotid gland contacts this area. This surface’s rough
lateral border gives attachment to the cartilaginous meatus. The inferior border of the tympanic bone is sharp
and splits to ensheath the styloid process.
The Styloid Process
Slender, pointed, about an inch long, the styloid process
projects downward from the inferior aspect of the temporal bone. The proximal part is called the tympanohyal
and is ensheathed by the tympanic bone. The distal part
is called the stylohyal and gives attachment to muscles
Temporal Bone Histology and Radiology Atlas48
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Figure 4–4. Cross-section of the right ear showing the origin of the styloid process from the tympanic ring. (From “Gray907” by
Henry Vandyke Carter. Henry Gray (1918), Anatomy of the Human Body, Bartleby.com, Gray’s Anatomy, Plate 907. Licensed under Public Domain via Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Gray907.png#/media/File:Gray907.png.)
and ligaments. The styloid process is covered laterally
by the parotid gland. The facial nerve crosses its base as
it proceeds toward the parotid gland. The external carotid artery crosses its tip, embedded in the gland. Medially the stylopharyngeus muscle separates it from the
internal jugular vein. The length of the styloid process is
quite variable, usually quoted as 2.5 to 3 cm, but ranging
up to 4 or more cm (Figure 4–4).
CLINICAL CAVEAT: Eagle syndrome is characterized by recurrent pain in the oropharynx and face
due to an elongated styloid process or calcified stylohyoid ligament. The average length of the styloid
process in symptomatic patients is 35 to 45 mm.1
Treatment can include surgical removal of the process, either intraorally or via a cervical approach.
4. Temporal Bone Osteology 49
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OSSIFICATION OF THE TEMPORAL BONE
The four components ossify independently. The squamosa is ossified in a sheet of condensed mesenchyme
from a single center appearing at the eight month of fetal
life. The petromastoid part ossifies from many centers—
as many as 14. The otic capsule is fully ossified by the
sixth month of gestation. The tympanic part is ossified
from one center, appearing at the third month. At birth
it is an incomplete ring, deficient above (see Figure 4–3).
The styloid process develops at the cranial end of cartilage of the second branchial arch from two centers.
REFERENCE
1. Balcioglu HA, Kilic C, Akyol M, Ozan H, Kokten G.
Length of the styloid process and anatomical implications
for Eagle’s syndrome. Folia Morphol (Warsz). Nov 2009;68:
265–270.
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CHAPTER 5
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The Facial Nerve
Hosakere K. Chandrasekhar and Sujana S. Chandrasekhar
A precise knowledge of the course and relationships
of the seventh cranial nerve (the facial nerve) is a prerequisite while embarking on temporal bone surgery.
Some surgeons hold the idea that surgery of the temporal bone is quite often a process of skeletonizing the
facial nerve, partially or fully.
OVERVIEW OF THE COURSE
OF THE FACIAL NERVE
The facial nerve is a mixed nerve, containing both motor
and visceral components.1 The motor facial nerve has its
nucleus in the lower pons. From the nucleus the nerve
runs dorsally in the pons to approach the floor of the
fourth ventricle. Here the fibers make the first genu (or
knee bend) on the surface of the abducens nucleus, creating the facial colliculus, and the nerve turns backward to
exit at the lower border of the pons, just above the olive
and passes laterally toward the cerebellopontine angle.
The sensory part of the nerve, also called nervus
intermedius, originates in the pons and medulla, and
leaves the brainstem to meet up with the motor facial
nerve in the cerebellopontine angle. The nerves then
pass laterally and enter the internal acoustic meatus.
In the internal auditory canal (IAC), the sensory
fibers of the facial nerve stay close to the motor fibers,
being located between them and the cochlear nerve
in the anterior portion of the canal. Laterally, the two
portions of the facial nerve pierce the anterosuperior
quadrant of the fundus of the IAC. As the facial nerve
leaves the IAC laterally in the narrow labyrinthine
segment, it makes a sharp bend anteriorly and at this
point the nervus intermedius enlarges into the geniculate ganglion, and has fused with the motor nerve.
The combined facial nerve turns posteriorly and
travels along the medial wall of the middle ear in the
fallopian canal, superior to the promontory and the
oval window. Laterally, just below the bulge of the lateral semicircular canal, the nerve makes its second surgical bend to travel inferiorly, deep to the aditus ad
antrum, passing down the stylomastoid canal. Having
shed all the hitchhiking nervus intermedius fibers, it
emerges from the stylomastoid foramen a purely motor
nerve and divides as the pes anserinus to subsequently
innervate the facial and cervical musculature of expression (Figure 5–1).
2
NERVUS INTERMEDIUS
The nervus intermedius is a visceral nerve whose functions are both secretomotor and sensory in nature. The
secretomotor nucleus is the superior salivatory nucleus which is located in the depth of the pons, and its
fibers are destined to reach the submandibular gland.
The fibers leave at the lower border of the pons and,
together with the sensory fibers destined to reach the
tractus solitarus in the medulla, join to form the nervus intermedius and enter the porus acousticus to lie
between the motor facial nerve and the cochlear nerve.
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Figure 5–1. Course and contributions and branches of the facial nerve. (Reprinted from Figure 788, Henry Gray, Anatomy of
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the Human Body, 1918.)
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5. The Facial Nerve 53
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After exiting the IAC medially, the nervus intermedius
and motor facial nerves fuse at the geniculate ganglion
to form a single facial nerve.
Branches are given off by the nervus intermedius
as described next.
1. Greater Petrosal Nerve
The greater petrosal nerve contains entirely secretomotor fibers for the palate and above. The nerve leaves the
geniculate ganglion and travels forward from the hiatus
facialis. It then passes beneath the trigeminal ganglion,
reaching the foramen lacerum. Here it is joined by the
deep petrosal nerve that has been given off from the
sympathetic plexus around the internal carotid artery.
It is now called the vidian nerve and it passes through
the pterygoid canal and enters the sphenopalatine ganglion at the back of the lateral wall of the nose. After
relaying in the ganglion, it innervates five territories:
the nasal septum, the lateral nasal wall, the hard palate, the soft palate, and the nasopharynx. Lacrimatory
post-ganglionic fibers join the zygomatic branch of the
maxillary nerve to reach the lacrimal gland.
CLINICAL CAVEAT: Site-of-lesion testing in facial
paresis includes testing of ipsilateral eye tear production, known as Schirmer’s tear test. Reduction
in lacrimation indicates injury to the facial nerve
proximal to the geniculate ganglion. Gustatory rhinorrhea is much less commonly reported and more
difficult to measure, but can also occur with a proximal facial nerve injury.
2. Lesser Petrosal Nerve
The lesser petrosal nerve is formed by the tympanic
branches given off to join the tympanic plexus. Through
the plexus the lesser petrosal nerve gathers the tympanic branch of the glossopharyngeal nerve (also called
Jacobson’s nerve) to reach the otic ganglion. The otic
ganglion is attached to the mandibular nerve (cranial
nerve V3) as it emerges from the foramen ovale. From
the otic ganglion, secretomotor fibers reach the parotid
gland. The secretomotor nucleus in the brainstem is the
inferior salivatory nucleus from whence fibers pass into
Jacobson’s nerve.
3. Sensory Fibers
Some sensory fibers that have survived from the embryonic stage via the tympanic plexus also supply the
skin of the posterosuperior external auditory meatus,
having pierced the tympanic membrane. Some fibers
also supply the mucosa of the supratonsillar fossa contiguously. The nucleus for all these fibers, however, is
the tractus solitarus in the medulla. Presence of blisters
in the auricle and external auditory canal in RamseyHunt syndrome (herpes zoster oticus) is explained by
viral geniculate ganglionitis.
CLINICAL CAVEAT: A subset of patients with vestibular schwanomma (acoustic neuroma) may present with decreased sensation in the posterosuperior
quadrant of the external auditory meatus or canal.
This is called Hitselberger’s sign,3 and is primarily
of historical interest at this time.
4. Chorda Tympani Nerve
The chorda tympani nerve supplies secretomotor innervation to glands in the floor of the mouth and the
ipsilateral anterior tongue. It leaves the seventh cranial
nerve above the stylomastoid foramen and, passing
through the middle ear from the iter (tunnel) chordae
posterior, flying between the long processes of the incus and malleus, enters the iter chordae anterior, emerging at the petrotympanic fissure. It then passes by the
spine of the sphenoid to join the lingual nerve, which
is a branch of the mandibular nerve (V3). It carries
taste fibers to the anterior tongue as well as secretomotor fibers to the submandibular ganglion to supply
the submandibular gland. The nucleus for this in the
brainstem is the superior salivary nucleus.
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CLINICAL CAVEAT: Site-of-lesion testing in facial
nerve weakness includes checking for ipsilateral
taste sensation on the anterior tongue. Injury to the
facial nerve beyond the geniculate ganglion in the
temporal bone will result in normal tearing but impaired gustatory function.
CLINICAL CAVEAT: The relationship of the chorda
tympani nerve to the long processes of the malleus
and incus are very important in chronic ear surgery.
The nerve is always medial to the malleus and lateral to the incus, and can thus serve as a reliable
guide to the surgeon, particularly in an inflamed
middle ear space. Therefore, it should be preserved
as long as possible during surgery.
rior auricular muscles. The more anterior branches
supply the frontalis, the orbicularis oculi, and corrugator supercilii muscles. Branches join the supraorbital and lacrimal branches of the ophthalmic nerve
(V1 division of the trigeminal nerve). The temporal
branch of the facial nerve acts as the efferent limb of
the corneal reflex.
2. The zygomatic branch has upper and lower division
and reaches the orbicularis oculi musculature. A few
twigs reach the upper and lower eyelids as well.
3. The buccal branch supplies the buccinator muscle
and upper lip fibers of the orbicularis oris muscule.
4. The mandibular branch supplies the muscles of the
lower lip. This nerve emerges from the lower border
of the parotid gland and passes into the neck below
the mandible. It crosses the inferior border of the
mandible to reach the face at the anterior border of
the masseter muscle. At this point it lies on the facial
artery and the anterior facial vein. A small lymph
gland lies over this spot.
5. The cervical branch travels inferiorly to supply the
platysma muscle.
MOTOR FACIAL NERVE
In the vertical (also called descending or mastoid) segment of its intratemporal course, the motor facial nerve
gives off a branch to the stapedius muscle.
As the nerve leaves the stylomastoid foramen it
gives off a communicating branch to the auricular branch
of the vagus nerve (10th cranial nerve) and proceeds to
give off three more branches. One goes to the occipital
belly of the occipitofrontalis muscle; the other two innervate the posterior belly of the digastric and stylohyoid muscles. The nerve then approaches the posteromedial surface of the parotid gland. Just before entering
the gland it divides into upper and lower branches.
The upper is the temporozygomatic branch; the lower
is the cervicofacial branch. Within the substance of
the gland, each branch divides and rejoins to divide
again and finally emerges from the parotid gland in
five main groups of branches. The plexiform arrangement, called the pes anserinus, lies in the gland superficial to the retromandibular vein and the external carotid
artery.
There are five named branches of the facial nerve.
1. The temporal branch crosses the zygomatic arch to the
temporal region, supplying the anterior and supe-
CLINICAL CAVEAT: Site-of-lesion testing in fa cial
nerve weakness includes measurement of stapedius muscle function, as measured by acoustic reflex testing (ART). The acoustic reflex is an eighth
and seventh cranial nerve arc and can be measured
ipsi- and contralaterally. Absence of the ipsilateral
ART in a patient with facial weakness but intact
lacrimation implies injury to the facial nerve distal
to the geniculate ganglion. Presence of the ipsilateral ART in such a patient but ipsilateral gustatory
dysfunction implies that the injury is at the vertical
segment of the facial nerve, distal to the stapedius
nerve branch.
IMAGING OF THE FACIAL NERVE
Imaging plays an important role in the evaluation of
facial nerve disorders.4 The facial nerve has a complex
anatomical course, and dysfunction can be due to
Figure 5–2. Normal facial nerve canal on axial temporal bone CT scan. The facial nerve is anterior in the IAC (black arrow).
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The narrowest portion of the facial nerve canal is the 3 mm long labyrinthine segment (red arrow). The geniculate ganglion is
identied by the yellow arrow. The horizontal (or tympanic) segment of the facial nerve is indicated by the green arrow. Note
the malleus and incus in the epitympanum lateral to the Fallopian canal. (CT image reprinted with permission from Gupta S,
Mends F, Hagiwara M, Fatterpekar G, and Roehm PC, Imaging the facial nerve: A contemporary review, Radiology Research and
Practice, 2013; Article ID 248039.)
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