Download Cranial nerves

“Unravelling a Bundle of Nerves”
ASNR 2016 Electronic Educational Exhibit
Saunders D, Adams B, Craven IJ, Warren DJ, Macmullen-Price J,
Currie S
Department of Neuroradiology, Leeds Teaching Hospitals Trust, Leeds UK
eEdE#: eEdE-174
Disclosures
• We, the named have authors have no
disclosures of conflicts of interest
Oh the nerves, the nerves; the mystery of this
machine called Man!
Charles Dickens - The Chimes (1844)
Objectives
• This educational resource is designed to use pathology to help better
understand the anatomy of the cranial nerves as seen on cross-sectional
imaging
• Each nerve is described in relation to its course, any special considerations
when evaluating individual nerves and some select pathological cases that
can be diagnosed radiologically (primarily on MRI)
• The user has the option of working through each nerve in turn or
alternatively, if time is short focusing on specific nerves by utilising the
hyperlinks on the following slide. There are also multiple hyperlinks within
the presentation to allow the user to view additional information, images
and illustrations
• The eventual aim is to adapt this resource to be used in both an
undergraduate and postgraduate setting to complement established
anatomical and pathological teaching models
Contents
• CN I – Olfactory
• Pathology
• Pathology
• CN II – Optic
• CN VIII –Vestibulocochlear
• Pathology
• Pathology
• CN III – Oculomotor
• Pathology
• CN IX – Glossopharyngeal
• Pathology
• CN IV – Trochlear
• Pathology
• CN X – Vagus
• Pathology
• CN V – Trigeminal
• Pathology
• CN XI – Spinal Accessory
• Pathology
• CN VI – Abducens
• Pathology
• CN VII – Facial
• CN XII - Hypoglossal
•
Pathology
Appendix of images, diagrams and
further information
Olfactory Nerve (I) Course
• Origin: olfactory bulb – cribiform plate
• Course and pathway:
– Primary neurosensory cells in the roof of both nasal cavities
– Efferent axons pass through the cribiform plate to synapse with the
olfactory bulb
– Pass posteriorly deep within the olfactory grooves inferior to the gyri
recti
– Enter the inferior frontal regions via medial and lateral olfactory striae
– Medial striae – subcallosal medial frontal lobe
– Lateral striae – Inferomedial temporal lobes
• Tertiary pathways:
– Orbitofrontal cortex
– Hypothalamus (via septum pellucidum)
– Limbic system
CONTENTS
Olfactory Nerve (I) Notes
– Olfactory nerves are white matter tracts not
surrounded by schwann cells (unlike most other
CNs)
– The limbic responses to olfaction are derived
through connections to the hypothalamus,
habenular nucleus, reticular formation, and
cranial nerves controlling salivation, nausea and
GI motility.
CONTENTS
Olfactory Nerve (I) Pathology
• Presentation: Anosmia, Parosmia, Phantosmia
• Most commonly caused by damage at the olfactory
bulb level
– Trauma
– Upper respiratory tract infection
– Nasopharyngeal neoplasm
• Central causes described include:
– Temporal lobe epilepsy (Usually transient)
– Parkinson’s disease
CONTENTS
I – Olfactory groove meningioma
46F presenting with altered sense of smell.
Triplanar MRI demonstrates the typical well circumscribed and homogenously increased T1/T2
signal intensity lesion within the olfactory groove causing elevation of the gyri recti and
compression of CN I
CONTENTS
I – Olfactory groove meningioma
This case of a different patient with a larger olfactory groove meningioma demonstrates
the typical well defined and homogenously enhancing CT appearances of a meningioma
CONTENTS
I - Neuroblastoma
32F with nasal discharge and altered sense of smell.
In contrast to the previous well defined benign meningioma which was seen to displace
structures, this case of neuroblastoma appears much more aggressive with invasion and
destruction of the cribiform plate
CONTENTS
I - Schwannoma
53M – headache and altered sense of smell.
These images demonstrate a more in-homogenous but still well defined
lesion, demonstrating intense enhancement. This was a rare case of
schwannoma affecting the olfactory nerve – remember the olfactory
nerves are white matter tracts and are not associated with Schwann cells!
CONTENTS
Optic Nerve (II) Course
• The optic pathway consists of nerves, chiasm, tracts and
radiations
• The optic nerve has 4 main segments
– Retinal: Leaves globe through lamina cribrosa sclerae
– Orbital/Retrobulbar: Surrounded by dural sheath, visible through
fat filled orbit
– Canalicular: Within the optic canal beneath the ophthalmic artery
– Cisternal: Suprasellar cistern leading to optic chiasm
• The optic nerve terminates at the chiasm. Bilateral nerves meet,
decussate and form optic tracts
• The optic tracts pass around the cerebral peduncles and enter
the lateral geniculate body (LGB) of thalamus
• From LGB the optic radiations loop around the occipital horns of
the lateral ventricles to enter the visual cortex of the occipital
lobe
CONTENTS
Optic Nerve (II) Notes
• Optic nerves are white matter tracts with no
surrounding Schwann cells
• The canalicular portion of the nerve is frequently
overlooked and should be a review area in cases
of visual disturbance
• Important relations of the suprasellar segment:
– Anterior cerebral artery
– Infundibulum
– Mamillary bodies (posteriorly)
CONTENTS
Optic Nerve (II) Pathology
•
•
•
•
•
Enlargement of an optic nerve has a large differential
The commonest ‘tumours’ are meningioma and glioma
– NF1 – increased incidence of glioma
– NF2 – increased incidence of meningioma
The nerve is covered with dura therefore hydrocephalus and raised ICP can
manifest as swelling of the optic nerve (and papilloedema)
Other causes of nerve enlargement include, but are not limited to:
– Optic neuritis
– Orbital pseudotumour
– Direct extension of retinoblastoma
– Lymphoma and leukaemia
– Metastases
– Sarcoidosis and other granulomatous diseases.
The chiasm can also be compressed by pituitary tumours and the optic
radiations can be compromised by infarction, masses and demyelination
CONTENTS
II – Optic glioma
8M – Known history of Neurofibromatosis 1 and new onset eye pain with decreased visual
acuity in the left.
Imaging demonstrates gross fusiform enlargement of the left optic nerve in comparison to the
right with marked peripheral enhancement typical of an optic glioma which show significantly
increased prevalence in patients with NF1.
CONTENTS
II – optic chiasm glioma
7F: Gliomas can also be very large at presentation as is the case in this young patient who had
bilateral visual symptoms and was demonstrated as having a very extensive, avidly enhancing
glioma centred on the optic chiasm and extending posteriorly to involve the proximal optic
radiations.
On axial, post-contrast imaging the basic outline of the chiasm is still vaguely apparent owing to
the initially fusiform type enlargement
CONTENTS
II - meningioma
61F: Meningiomas can occur anywhere where there is meninges as
in this case of one affecting the Planum Sphenoidale. Even on precontrast T1 imaging the proximity to the right optic nerve within the
optic canal (small arrows) is evident.
Imaging characteristics are again typical of meningioma with
prominent but homogenous enhancement.
CONTENTS
Oculomotor Nerve (III) Course
• The oculomotor nuclei lie:
– Deep to superior colliculus
– Ventral to cerebral aquaduct
– Inferior to pineal gland
• Course:
• Root entry zone in interpeduncular cistern
• Travels in pre-pontine cistern between superior cerebellar and
posterior cerebral arteries
• Most superior nerve along the lateral wall of the cavernous sinus
• Enters orbit through the superior orbital fissure
• Splits into superior and inferior divisions lateral to the optic nerve
• A smaller parasympathetic branch accompanies the motor branch
to control pupillary constriction and accommodation
CONTENTS
Oculomotor Nerve (III) Notes
• In most cases, to easily identify CN III look:
– For the root entry within the interpeduncular cistern
– Between the superior cerebellar and posterior cerebral
arteries in the coronal plane
• The Oculomotor nerve innervates all the extra-occular
muscles except the superior oblique and lateral rectus:
Denervation therefore results in the resting eye position being
down and out
CONTENTS
Oculomotor Nerve (III) Pathology
• The commonest cause of a CN III palsy is secondary to focal
ischaemia/infarction affecting the nucleus and is seen more commonly in
the presence of diabetes
• Note: When secondary to ischaemia the pupillary reflex is usually spared
but when secondary to compression pupillary reflex tends to be involved
• CN III can be compressed anywhere along it’s path:
– Interpeduncular: PCOM aneurysm; basal meningeal (usually > 1 CN
affected) infection, inflammation (Sarcoidosis) and neoplastic
infiltration.
– Cavernous: Pituitary macroadenoma, meningioma, trigeminal
schwannoma; Diffuse inflammation (Tolosa-Hunt)
– Orbital: Usually have other orbital signs
CONTENTS
III - Infarct
50F patient with diabetes presented with an acute onset of diplopia. Clinical examination
demonstrated reduced eye movements with the globe fixed in downward, lateral gaze.
MRI demonstrated increased signal on B1000 sequences with corresponding low signal on
ADC map in keeping with acute diffusion restriction within the left oculomotor nucleus
consistent with acute infarction.
CONTENTS
III – PCOM aneurysm
In cases of isolated CN III palsies, especially if
the onset is sudden and painful, rapid
expansion of a Berry aneurysm (most
commonly PCOM) should be excluded as was
the case in this 68yo female with a large right
PCOM aneurysm
CONTENTS
Trochlear Nerve (IV) Course
• Originates from the posterior (dorsal) midbrain
• Curves forwards to pass over the superior cerebellar
peduncle
• Runs alongside CN III between superior cerebellar and
posterior cerebral arteries
• Pierces dura to enter cisterna basalis between the
free and attached borders of the tentorium
• Courses immediately inferiorly to CN III within the
lateral wall of the cavernous sinus
• Enters the orbit through the superior orbital fissure to
supply the superior oblique extra-occular muscle
CONTENTS
Trochlear Nerve (IV) Notes
• Named trochlear after the pulley system (fibrous trochlea) that
the superior oblique muscle passes through
• The trochlear nerve is the only cranial nerve with a root entry
zone on the dorsum of the brainstem (midbrain)
– The cisternal segment is therefore generally most readily
identifiable postero-laterally
• CN IV has the longest intracranial course of the cranial nerves
• Is the smallest cranial nerve in terms of number of axons
• Innervates the contralateral superior oblique muscle (fibres cross
in the midbrain before exiting)
• For a variable part of its course the trochlear nerve lies between
dural layers making it difficult to identify on cross sectional
imaging
CONTENTS
Trochlear Nerve (IV) Pathology
• Isolated CN IV pathology is rare and the commonest cause is trauma
– Congenital defects/absence can also cause these symptoms but seen
very infrequently
• Other causes include (normally not isolated IV palsies):
– Any cause of stretching: hydrocephalus, oedema, haemorrhage
(Abducens normally the 1st nerve affected)
– Infections (herpes)
– Demyelination
– Cavernous sinus disease
– Tumours
– Infarction
CONTENTS
IV - Epidermoid
55F presenting with left sided diplopia on vertical gaze.
MRI demonstrates typical imaging appearances for an epidermoid
lying within the right ambient cistern and compressing the trochlear
nerve.
A cystic-looking lesion on T1 and T2 but devoid of attenuation on
FLAIR. No enhancement but diffusion restriction.
CONTENTS
Trigeminal Nerve (V) Course
•
•
•
•
Course
Large sensory root runs medial to smaller motor root
Originates from the mid-pons laterally
Travels through the prepontine cistern to enter Meckel’s cave
through the porus trigeminus
• It adopts a ‘mesh like’ form within Meckel’s cave
• Anteriorly, within Meckel’s cave it forms the Trigeminal
(Gasserian) ganglion before dividing into 3 divisions:
– V1 – Ophthalmic nerve moves medially and exits through the
superior orbital fissure
– V2 – Maxillary nerve moves medially and exits through the
Foramen Rotundum
– V3 Mandibular (+motor branches) travel inferiorly to exit
through the Foramen Ovale
CONTENTS
Trigeminal Nerve (V) Notes
• CN V is the largest cranial nerve
– Due to its size and anterior course it is normally easily
visualised on MRI
• Meckel’s cave is a CSF filled ‘pouch’ in the middle
cranial fossa that should be readily identifiable on fluid
sensitive sequences
CONTENTS
Trigeminal Nerve (V) Pathology
• CN V is the largest cranial nerve and has multiple nuclei and a
large number of sensory, motor and parasympathetic divisions.
• The range of pathology is vast but can be grossly divided into:
– Trauma: particularly of the skull base exit foramina
– Infection: Post-viral, direct spread from the face through the
cavernous sinus
– Inflammation and demyelination
– Vascular: Aneurysmal or aberrant artery (SCA) causing
compression; infarction of the trigeminal nuclei
– Neoplasia: Infiltration or compression within the skull base
foramina or elsewhere along it’s course
CONTENTS
V - Metastasis
66F with previous history of endometrial carcinoma presented
with right trigeminal nerve symptoms affecting all branches.
MRI demonstrated an irregular, ring enhancing lesion with
associated vasogenic oedema centred over the trigeminal
nucleus consistent with an intracranial metastasis
CONTENTS
V - Lipoma
Young patient with left trigeminal nerve sensory symptoms due
to compression by a small lipoma at the left root entry zone
Axial CISS, T1 and T2, coronal CISS and FLAIR demonstrate the
small lesion to be hyper-intense across all sequences with
corresponding negative HU on CT consistent with fat
CONTENTS
V - Schwannoma
48F with sensory disturbance within the right face (mainly V2/3).
Axial T2, Sagittal FLAIR and Coronal T1 pre and post gadolinium MR images demonstrate a
very large right sided mass showing intense enhancement with some central cystic areas. It
causes marked expansion of the Foramen Ovale (best appreciated on sag) and Foramen
Rotundum.
CONTENTS
V – Perineural spread of neoplasia
68M with a known right adenoid cystic carcinoma and
right trigeminal signs.
T2 fat saturated and contrast enhanced T1 images
demonstrate marked peri-neural thickening and
enhancement of the right trigeminal nerve
CONTENTS
Abducens Nerve (VI) Course
• Nuclei – anterior to the fourth ventricle
• Travels anteriorly through the pons to enter the prepontine cistern at the pontomedullary junction
• Crosses the prepontine cistern and then travels
vertically up the posterior aspect of the clivus through
Dorello’s canal (a fibrous sheath)
• Passes over the medial petrous apex
• Travels through the medial cavernous sinus
• Enters the orbit through the superior orbital fissure
• Innervates the lateral rectus muscle of the eye
CONTENTS
Abducens Nerve (VI) Notes
• In isolated CN VI palsy important review areas
include:
– The petrous apex
– The clivus (CN VI travels over almost its entire length)
• The cisternal portion of CN VI and the anterior
inferior cerebellar artery can appear similar –
they are easily distinguishable as they travel in
orthogonal directions with CN VI running
laterally from posterior - anterior
CONTENTS
Abducens Nerve (VI) Pathology
• CN VI has the longest sub-arachnoid course and is therefore prone
to stretching injuries at its entry to Dorello’s canal due to any cause
of raised ICP
• Other causes are similar to those of all the CNs:
– Abnormal subarachnoid space: haemorrhage, infection, tumour
– Infection/inflammation: post viral, diabetes
– Demyelination
– Trauma
– Pontine neoplasia
CONTENTS
VI - Abducens nucleus
demyelination
45M Presented with left sided diplopia on a
background of several previous transient
neurological symptoms for which an underlying
demyelination was suspected.
T2 and FLAIR images demonstrated a small focus
of signal hyper-intensity within the left abducens
nucleus consistent with demyelination
CONTENTS
VI - Chordoma
17M presenting with bilateral 6th nerve palsies, the right more pronounced than
the left
Axial T2 and sagittal T1 images demonstrate an aggressive, destructive lesion
within the clivus at the level of Dorello’s canal bilaterally with consequent neural
compromise
CONTENTS
Facial Nerve (VII) Course
•
The facial nerve has both sensory and motor components. It primarily supplies the facial
and auricular muscles, gives parasympathetic supply to some of the salivary glands and
supplies taste to the anterior two thirds of the tongue
•
During its course, the facial nerve traverses the posterior cranial fossa, internal acoustic
meatus, facial canal, stylomastoid foramen of the temporal bone, and parotid gland.
•
After traversing the internal acoustic meatus, the nerve proceeds a short distance
anteriorly within the temporal bone and then turns abruptly posteriorly to course along
the medial wall of the tympanic cavity. The sharp bend is the geniculum of the facial
nerve.
•
While traversing the temporal bone within the facial canal, the nerve gives rise to the
greater petrosal nerve, nerve to the stapedius and chorda tympani.
•
Then, after running the longest intraosseous course of any cranial nerve, it emerges from
the cranium via the stylomastoid foramen; gives off the posterior auricular branch and
enters the parotid gland, forming the parotid plexus, which gives rise to the following five
terminal motor branches: temporal, zygomatic, buccal, marginal mandibular, and
cervical.
•
•
•
For a diagrammatic representation of CN VII’s course click here
For more information on the function of this nerve click here
For more information on the nuclei that form this nerve please click here
CONTENTS
Facial Nerve (VII) Pathology
Pathologies that affect the facial nerve include facial schwannoma, congenital absence,
compression by vascular loops, inflammation and Moebius syndrome.
This 32 year old female presented with right hemifacial spasm.
Axial T2 and TOF sequences through the level of the IAM’s demonstrate prominent
arteries closely associated with the intracanalicular VII and VIII cranial nerves bilaterally.
The branches extend through the porus acousticus into the internal auditory meatus
and appear to be the anterior inferior cerebellar arteries on the angiographic images.
CONTENTS
Vestibulocochlear Nerve (VIII) Course
•
The vestibulocochlear nerve (CN VIII) emerges from the junction of the pons and
medulla and enters the internal acoustic meatus. Here it separates into the
vestibular and cochlear nerves.
•
The vestibular nerve is concerned with equilibrium. It is composed of the central
processes of bipolar neurons in the vestibular ganglion; the peripheral processes
of the neurons extend to the maculae of the utricle and saccule (sensitive linear
acceleration relative to the position of the head) and to the ampullae of the
semicircular ducts (sensitive to rotational acceleration).
•
The cochlear nerve is concerned with hearing. It is composed of the central
processes of bipolar neurons in the spiral ganglion; the peripheral processes of the
neurons extend to the spiral organ.
•
•
For a schematic of the course and MRI images of the normal nerve click here
For more information on the function and nuclei of this nerve click here
CONTENTS
Vestibulocochlear Nerve (VIII) Pathology
•
•
The most common pathology to affect the vestibulocochlear nerve is a vestibular
schwannoma (a.k.a. acoustic neuroma). This schwannoma arises from the inferior vestibular
nerve in the vast majority of cases.
It presents with unilateral sensorineural hearing loss, on the right side in the case shown
below. On imaging, it appears as a slightly T1 hypointense, T2 hyperintense soft tissue lesion
arising from the internal acoustic canal (IAC) and extending into the cerebellopontine angle.
It demonstrates avid enhancement with contrast. A meningioma is a consideration in the
differential but this will have a wide dural base and doesn’t tend to cause erosion and
widening of the IAC, which is considered highly specific for an acoustic neuroma.
CONTENTS
Vestibulocochlear Nerve (VIII)
Pathology
•
This patient presented with bilateral sensorineural hearing loss. Indistinct additional soft
tissue is seen on the axial T2-weighted imaging, which demonstrates avid enhancement postcontrast. The patient was found to have metastatic melanoma and the imaging appearances
below are thought to be metastatic leptomeningeal disease.
CONTENTS
Glossopharyngeal Nerve (CN IX) Course
• The glossopharyngeal nerve emerges from the lateral aspect of the
medulla and passes anterolaterally to leave the cranium through the
anterior aspect of the jugular foramen.
• CN IX follows the stylopharyngeus, the only muscle the nerve supplies,
and passes between the superior and the middle constrictor muscles of
the pharynx to reach the oropharynx and tongue. It contributes sensory
fibres to the pharyngeal plexus of nerves.
• CN IX is afferent from the tongue and pharynx and efferent to the
stylopharyngeus and parotid gland.
•
•
For a schematic of the nerve course and MRI of the normal appearances click here
For more information on the function and nuclei of this nerve click here
CONTENTS
Glossopharyngeal Nerve (CN IX) Pathology
Pathologies involving the glossopharyngeal nerve include glomus tumours
and glossopharyngeal neuralgia. This case is that of a clival chordoma, which
extends into the jugular foramen and has caused a left CNIX palsy. Classically,
they have very high T2 signal and intermediate T1 signal with heterogenous
enhancement in a honeycomb pattern. They can also cause blooming on
gradient echo due to their propensity to bleed.
CONTENTS
Glossopharyngeal Nerve (CN IX) Pathology
12 year old male with a mature
teratoma.
Presented with multiple left lower
cranial nerve palsies – left VII, IX, X
especially .
Axial T2 and coronal STIR images
demonstrate a large mixed
solid/cystic tumour centred on the
left cerebellopontine angle cistern.
•The white arrow shows left internal
auditory canal filled with tumour.
The blue arrows show tumour
extension through the left jugular
foramen and the bottom right axial
T2 image shows tumour extension
into the left carotid and
parapharyngeal spaces.
CONTENTS
Vagus Nerve (X) Course
•
The vagus nerve (CN X) has the longest course and most extensive distribution of all
the cranial nerves, most of which is external to the head. The term vagus is derived
from the Latin word vagari meaning “wandering”.
•
It arises by a series of rootlets from the lateral aspect of the medulla that merge and
leave the cranium through the jugular foramen positioned between CN IX and CN XI.
What was formerly called the cranial root of the accessory nerve is actually a part of
the vagus nerve. It has a superior ganglion in the jugular foramen that is mainly
concerned with the general sensory component of the nerve. Inferior to the foramen is
an inferior ganglion (ganglion nodose) concerned with the visceral sensory
components of the nerve.
•
In the region of the superior ganglion are connections to CN IX and the superior
cervical (sympathetic) ganglion. CN X continues inferiorly in the carotid sheath to the
root of the neck, supplying branches to the palate and pharynx.
•
The course of CN X in the thorax differs on the two sides, a consequence of rotation
of the midgut during development. CN X supplies branches to the heart, bronchi, and
lungs. The vagi join the oesophageal plexus surrounding the oesophagus, which is
formed by branches of the vagi and sympathetic trunks. This plexus follows the
oesophagus through the diaphragm into the abdomen, where the anterior and
posterior vagal trunks break up into branches that innervate the oesophagus,
stomach, and intestinal tract as far as the left colic flexure.
•
•
For a diagram of the course of CN X click here
For more information on the function and nuclei of this nerve click here
CONTENTS
Vagus Nerve (X) Pathology
Pathology affecting the vagus nerve includes schwannomas, neurofibromas, traumatic
injuries and direct infiltration by skull base lesions. The example below is of a glomus
jugulotympanicum paraganglioma. The patient presented with hoarseness due to vocal
cord palsy and tinnitus. The imaging demonstrates a high T2, low T1 signal lesion
involving both the middle ear and jugular foramen with intense enhancement following
contrast.
A “Salt and pepper appearance” is the classical MRI characteristics
CONTENTS
Vagus Nerve (X) Pathology
•
This 35 year old female presented with multiple lower cranial nerve palsies on the left.
Imaging demonstrates bilateral paragangliomas. The patient was found to have a succinate
dehydrogenase complex subunit D (SDHD) gene mutation, which predisposes to
paragangliomas.
CONTENTS
Spinal Accessory Nerve (XI) Course
•
Spinal portion
– arises from the upper spinal cord, specifically the C1-C5/C6 nerve roots. These fibres coalesce
to form the spinal part of the accessory nerve, which then runs superiorly to enter the cranial
cavity via the foramen magnum. The nerve traverses the posterior cranial fossa to reach the
jugular foramen. It briefly meets the cranial portion of the accessory nerve, before exiting the
skull (along with the glossopharyngeal and vagus nerves). Outside the cranium, the spinal part
descends along the internal carotid artery to reach the sternocleidomastoid muscle, which it
innervates. It then moves across the posterior triangle of the neck to supply motor fibres to
the trapezius.
•
Cranial portion
– arises from the lateral aspect of the medulla oblongata. It leaves the cranium via the jugular
foramen, where it briefly contacts the spinal part of the accessory nerve. Immediately after
leaving the skull, the nerve combines with the vagus nerve (CN X) at the ganglion nodose. The
fibres from the cranial part are then distributed through the vagus nerve. For this reason, the
cranial part of the accessory nerve is considered as part of the vagus nerve.
–
–
For a diagram of the normal course click here
For more information on the function and nuclei of this nerve click here
CONTENTS
Spinal Accessory Nerve (XI) Pathology
• The most common spinal accessory nerve
pathologies are similar to those for XI and X with
much of the pathology being centered on the jugular
foramen e.g. glomus jugulare tumours.
CONTENTS
Hypoglossal Nerve (XII) Course
•
The hypoglossal nerve (CN XII) arises as a purely motor nerve by several rootlets from the
medulla and leaves the cranium through the hypoglossal canal.
•
After exiting the cranial cavity, it is joined by branches of the cervical plexus conveying general
somatic motor fibres from C1 and C2 spinal nerves and general somatic sensory fibres from the
spinal ganglion of C2. These spinal nerve fibres “hitch a ride” with CN XII to reach the hyoid
muscles, with some of the sensory fibres passing retrogradely along it to reach the dura mater
of the posterior cranial fossa.
•
CN XII passes inferiorly, medial to the angle of the mandible and then curves anteriorly to enter
the tongue.
•
It ends in many branches that supply all the extrinsic muscles of the tongue, except the
palatoglossus (which is actually a palatine muscle).
•
•
For more information on the function and nuclei of this nerve click here
For a diagram of the nerve course and MRI image of a normal nerve click here
CONTENTS
Hypoglossal Nerve (XII) Pathology
•
Hypoglossal nerve pathologies include hypoglossal schwannoma and Collet-Sicard syndrome
(secondary to a glomus jugulare tumour). Below is a rare case of a left hypoglossal nerve
palsy. The CISS sequence demonstrates the left XII nerve as it exits the medulla and the post
contrast sequences show an enhancing structure compressing the nerve in the hypoglossal
canal. CE-MRA confirms this to be a left internal carotid artery aneurysm.
CONTENTS
Hypoglossal Nerve (XII) Pathology
•
Another case referred for MRI due to a left-sided tongue palsy reveals a well-defined lesion
arising from the cisternal segment of nerve root that is isointense on T1 and hyperintense on
T2 (not shown), with avid homogenous enhancement post contrast. These appearances are
in keeping with a hypoglossal schwannoma
•
Schwannomas are slow-growing lesions. Surgery is the treatment of choice. As schwannomas
do not infiltrate the parent nerve, they can usually be separated from it. Recurrence is
unusual, even after complete resection. They almost never undergo malignant change
CONTENTS
Appendix
• Further detail on selected cranial nerves
• Images
CONTENTS
Facial Nerve (VII) Functions
•Sensory
– Special afferent - Fibres carried by the chorda tympani join the lingual nerve to convey taste
sensation from the anterior two thirds of the tongue and soft palate.
– General somatic afferent - Some fibres arising from facial nerve supply a small area of the skin
of the concha of the auricle, close to external acoustic meatus.
•Motor
– Branchial motor - As the nerve of the 2nd pharyngeal arch, the facial nerve supplies striated
muscles derived from its mesoderm, mainly the muscles of facial expression and auricular
muscles. It also supplies the posterior bellies of the digastric, stylohyoid, and stapedius
muscles.
– Parasympathetic - The facial nerve provides presynaptic parasympathetic fibres to the
pterygopalatine ganglion for innervation of the lacrimal glands and to the submandibular
ganglion for innervation of the sublingual and submandibular salivary glands. The
pterygopalatine ganglion is associated with the maxillary nerve (CN V2), which distributes its
postsynaptic fibres, whereas the submandibular ganglion is associated with the mandibular
nerve (CN V3). Parasympathetic fibres synapse in these ganglia, whereas sympathetic and
other fibres pass through them.
•Proprioception to innervated musculature
BACK
KEY
CONTENTS
Facial Nerve (VII) Nuclei
Nuclei:
– Motor nucleus of the facial nerve - a branchiomotor nucleus in
the ventrolateral part of the pons.
– Spinal nucleus of the trigeminal nerve - (pain, touch, and
thermal) from around the external ear end here.
– Tractus solitarius – neurons associated with the sensation of
taste terminate here.
• The facial nerve (CN VII) emerges from the junction of the pons
and medulla as two divisions, the motor root and the
intermediate nerve.
• The larger motor root innervates the muscles of facial expression,
and the smaller intermediate nerve (L. nervus intermedius) carries
taste, parasympathetic, and somatic sensory fibres.
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KEY
CONTENTS
Vestibulocochlear Nerve (VIII) Function and Nuclei
• Function:
Special afferent - special sensations of hearing and
equilibrium.
• Nuclei: Four vestibular nuclei are located at the
junction of the pons and medulla in the lateral part
of the floor of the 4th ventricle; two cochlear nuclei
are in the medulla.
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KEY
CONTENTS
Glossopharyngeal Nerve (CN IX) Function and Nuclei
•
Sensory
– Special afferent - Taste fibres are conveyed from the posterior third of the tongue to the
sensory ganglia.
– General visceral afferent
• The carotid sinus nerve to the carotid sinus, a baroreceptor sensitive to changes in
blood pressure, and the carotid body, a chemoreceptor sensitive to blood gas
(oxygen and carbon dioxide levels).
• The pharyngeal, tonsillar, and lingual nerves to the mucosa of the oropharynx and
isthmus of the fauces, including palatine tonsil, soft palate, and posterior third of
the tongue. In addition to general sensation (touch, pain, temperature), tactile
stimuli determined to be unusual or unpleasant here may evoke the gag reflex or
even vomiting.
•
Motor
– Branchial motor - Motor fibres pass to one muscle, the stylopharyngeus, derived from
the 3rd pharyngeal arch.
– Parasympathetic - Following a circuitous route initially involving the tympanic nerve,
presynaptic parasympathetic fibres are provided to the otic ganglion for innervation of
the parotid gland. The otic ganglion is associated with the mandibular nerve (CN V3),
branches of which convey the postsynaptic parasympathetic fibres to the parotid gland.
– Nuclei: Four nuclei in the medulla send or receive fibres via CN IX: two motor and two
sensory. Three of these nuclei are shared with CN X.
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KEY
CONTENTS
Vagus Nerve (X) Function and Nuclei
Functions:
•
Sensory
– General visceral afferent and General somatic afferent
• Sensory from the inferior pharynx, larynx, and thoracic and abdominal
organs
– Special afferent - Sense of taste from the root of the tongue and taste buds on
the epiglottis. Branches of the internal laryngeal nerve (a branch of CN X) supply
a small area, mostly general but some special sensation; most general and
special sensation to the root is supplied by CN IX.
•
Motor
– Branchial motor - Motor to the soft palate; pharynx; intrinsic laryngeal muscles
(phonation); and a nominal extrinsic tongue muscle, the palatoglossus, which is
actually a palatine muscle based on its derivation and innervation.
– Parasympathetic to thoracic and abdominal viscera.
– Proprioception to innervated musculature
–
BACK
Nuclei: Four nuclei of CN X in the medulla send or receive fibres via CN IX; two
motor and two sensory. Three of these nuclei are shared with CN IX.
KEY
CONTENTS
Spinal Accessory Nerve (XI) Function and Nuclei
• Functions:
– Branchial motor to the striated sternocleidomastoid and trapezius
muscles.
• Nuclei: The spinal accessory nerve arises from the nucleus of the
accessory nerve, a column of anterior horn motor neurons in the superior
five or six cervical segments of the spinal cord .
BACK
KEY
CONTENTS
Hypoglossal Nerve (XII) Function and Branches
Functions:
• General somatic efferent to the intrinsic and extrinsic muscles of the tongue
(styloglossus, hyoglossus, and genioglossus).
Branches:
– A meningeal branch returns to the cranium through the hypoglossal canal and innervates
the dura mater on the floor and posterior wall of the posterior cranial fossa. The nerve
fibres conveyed are from the sensory spinal ganglion of spinal nerve C2 and are not
hypoglossal fibres.
– The superior root of the ansa cervicalis branches from CN XII to supply the infrahyoid
muscles (sternohyoid, sternothyroid, and omohyoid). This branch actually conveys only
fibres from the cervical plexus (the loop between the anterior rami of C1 and C2) that
joined the nerve outside the cranial cavity, not hypoglossal fibres. Some fibres continue
past the descending branch to reach the thyrohyoid muscle.
– Terminal lingual branches supply the styloglossus, hyoglossus, genioglossus, and intrinsic
muscles of the tongue.
BACK
KEY
CONTENTS
Key
Afferent
• Special afferent
• General somatic afferent
• General visceral afferent
Efferent
• Branchial motor
• Parasympathetic
• General somatic efferent
CONTENTS
Olfactory Bulb
Patrick J. Lynch, medical illustrator – 23/12/06
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Olfactory nerve course
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Optic pathway
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Optic nerve
•
Superior view of dissected robot showing the four anatomical parts of the optic nerve. Courtesy of Dr. John B. Selhorst.
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Bilateral CN III entering
cavernous sinuses
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Diagram of nuclei of cranial nerves (numbered). Image created by Patrick J.
Lynch, medical illustrator.
Back to CN IV
or CN VI
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These sagittal and axial CISS image shows nerves VII and VIII in the IAC
VII
Anterior
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Superior
Bill’s Bar
Sagittal section of IAC
VIII
Sup
Transverse Crest
VIII
Coch
VIII
Inf
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This is an axial CISS image showing the cisternal
segments of the IX and X as they enter the pars nervosa
of the jugular foramen. Contrast this appearance with the
next case of a chordoma involving the left jugular
foramen.
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