1. CRANIAL NERVES
PART II
Appearance of Normal Cranial Nerves
(REVIEW)
sherlockradiology.com

2. Abbreviations
• Olfactory nerve: CN1
• Optic nerve: CN2
• Oculomotor nerve:
CN3
• Trochlear nerve: CN4
• Trigeminal nerve:
CN5
• Abducens nerve: CN6
• Facial nerve: CN7
• Vestibulocochlear
nerve: CN8
• Glossopharyngeal
nerve: CN9
• Vagus nerve: CN1O
• Accessory nerve:
CN11
• Hypoglossal nerve:
CN12

3. Overview
• Cranial nerve groupings based on area of
brainstem origin
- Diencephalon: CN2
- Mesencephalon (midbrain): CN3 and
CN4
- Pons: CN5, CN6, CN7, and CN8
- Medulla: CN9, CN1O, CN11 and CN12

4. Imaging Approaches
• CN1, 2, 3, 4 and 6: Include focused orbital sequences
• CNS: Include entire face to inferior mandible if V3
affected
• CN7: Include CPA, temporal bone and parotid space
• CN8: Include CPA-lAC and inner ear
• CN9-12: Include basal cistern, skull base,
nasopharyngeal carotid space
• CN10: Follow carotid space to aortopulmonic window on
left, cervicothoracic junction on right
• CN12: Remember to reach hyoid bone to include distal
loop as it rises into sublingual space

5. CN7
Facial Nerve

6. Overview
• Seventh cranial nerve
• Cranial nerve that carries motor nerves to muscles of
facial expression, parasympathetics to lacrimal,
submandibular and sublingual glands and taste from
anterior 2/3 of tongue
• Mixed nerve: Motor, parasympathetic and special
sensory (taste)
• Two roots: Motor & sensory (nervus intermedius) roots
- Nervus intermedius exits lateral brainstem between
motor root of facial and vestibulocochlear nerves, hence
its name
• Four segments: Intra-axial, cisternal, intratemporal
and extracranial (parotid)

10. Intra-Axial Segment
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•
Three nuclei (one motor, two sensory)
Motor nucleus of facial nerve
- Located in ventrolateral pontine tegmentum
- Efferent fibers loop dorsally around CN6 nucleus in floor of fourth
ventricle forming facial colliculus
- Fibers then course anterolaterally to exit lateral brainstem at
pontomedullary junction
• Superior salivatory nucleus
- Located lateral to CN7 motor nucleus in pons
- Efferent parasympathetic fibers exit brainstem posterior to CN7 as
nervus intermedius
• To submandibular, sublingual and lacrimal glands
• Solitarius tract nucleus
- Termination of taste sensation fibers from anterior 2/3 of tongue
- Cell bodies of these fibers in geniculate ganglion
- Fibers travel within nervus intermedius

11. Cisternal Segment
• Two roots in cisternal CN7
- Larger motor root anteriorly
- Smaller sensory nervus intermedius
posteriorly
• Emerge from lateral brainstem at root exit zone
in pontomedullary junction to enter
cerebellopontine angle (CPA) cistern
- CN8 exits brainstem posterior to CN7
• 2 roots join together & pass anterolaterally
through CPA cistern with CN8 to internal
auditory canal (lAC)

12. Intratemporal Segment
• CN7 further divided in T-bone into 4 segments:
lAC, labyrinthine, tympanic and mastoid
• lAC segment: Porus acusticus to lAC fundus;
anterosuperior position above crista falciformis
• Labyrinthine segment: Connects fundal CN7 to
geniculate ganglion (anterior genu)
• Tympanic segment: Connects anterior to
posterior genu, passing under lateral
semicircular canal
• Mastoid segment: Inferiorly directed from
posterior genu to stylomastoid foramen

13. Extracranial Segment
• CN7 exits skull base through stylomastoid
foramen to enter parotid space
• Parotid CN7 passes lateral to
retromandibular vein
• Ramifies within parotid, passes anteriorly
to innervate muscles of facial expression

14. CN7 Branches
• Greater superficial petrosal nerve
- Arises at geniculate ganglion, passes anteromedially,
exits temporal bone via facial hiatus
- Carries parasympathetic fibers to lacrimal gland
• Stapedius nerve
- Arises from high mastoid segment of CN7
- Provides motor innervation to stapedius muscle
• Chorda tympani nerve
- Arises from lower mastoid segment
- Courses across middle ear to exit anterior T-bone
- Carries taste fibers from anterior 2/3 tongue
• These fibers travel with lingual branch of mandibular
division of trigeminal nerve
• Terminal motor branches

15. Imaging Recommendations
• Bone CT best for intratemporal segment of
CN7
• MR for intra-axial, cisternal, lAC and
extracranial segments
• Do not image routine Bell palsy!
• Imaging "Sweet Spots“: Include brainstem,
CPA cistern, lAC, T-bone and parotid
when MR completed for CN7 palsy

16. Imaging Pitfalls
• Mild enhancement of labyrinthine
segment, geniculate ganglion and
proximal tympanic segments of CN7 can
be normal on post-contrast T1 MR
- Secondary to circum neural
arteriovenous plexus
• Always check parotid in peripheral CN?
paralysis

17. Clinical Issues
Facial nerve paralysis can be central or peripheral
• Central: Supranuclear injury resulting in paralysis of
contralateral muscles of facial expression with forehead
sparing
• Peripheral: Injury to CN7 from brainstem nucleus
peripherally, resulting in paralysis of all ipsilateral
muscles of facial expression
- If lesion proximal to geniculate ganglion, lacrimation,
sound dampening and taste affected
- If CN6 involved, check pons for lesion
- If CN8 involved, check CPA-lAC for lesion
- If lacrimation, sound dampening and taste are variably
affected, T-bone lesion possible
- If lacrimation, sound dampening and taste are spared,
extracranial CN7 implicated

36. CN8
Vestibulocochlear nerve

37. Overview
• Eighth cranial nerve
• Afferent sensory nerve of hearing &
balance
• Sensory nerve consisting of two parts
- Vestibular part: Balance
- Cochlear part: Hearing
• CN8 best described from peripheral to
central

41. Cochlear Nerve
• Arises from bipolar neurons located in spiral ganglion
within modiolus of cochlea
- Peripheral fibers pass to organ of Corti in cochlear
duct (scala media) within cochlea
- Central fibers coalesce and pass as auditory
component of CN8 (cochlear nerve) to brainstem
• Central fibers pass from modiolus through cochlear
aperture into internal auditory canal (lAC)
- Cochlear aperture defined as bony opening into
anteroinferior quadrant of fundus of lAC
- Maximum diameter of cochlear aperture - 2 mm
• Cochlear nerve passes from lAC fundus to porus
acusticus within anteroinferior quadrant of lAC

42. Cochlear Nerve
• Near porus acusticus cochlear nerve joins together with
superior & inferior vestibular nerves to form
vestibulocochlear nerve (CN8)
• CN8 crosses cerebellopontine angle (CPA) cistern
posterior to facial nerve
• CN8 enters lateral brainstem at pontomedullary junction
posterior to facial nerve
• Cochlear nerve fibers bifurcate, ending in dorsal &
ventral cochlear nuclei
• Dorsal & ventral cochlear nuclei
- Cochlear nuclei found on lateral surface of inferior
cerebellar peduncle (restiform body)

43. Vestibular Nerve
Arises from bipolar neurons located in vestibular (Scarpa) ganglion
located within vestibular nerve in fundal portion of lAC
• Vestibular ganglion not visible on imaging
• Peripheral fibers pass to sensory epithelium of utricle, saccule &
semicircular canals
- Traverse multiple foramina in cribriform plate in lateral wall of lAC
fundus
• Central fibers coalesce to form superior & inferior vestibular nerves
that pass medially to brainstem
Fundus of lAC
• Superior & inferior vestibular nerves are separated by falciform crest
(transverse crest)
• Superior vestibular nerve separated from facial nerve anteriorly by
vertical bony structure called Bill bar
- Bill bar not visible on imaging (CT or MR)

44. Vestibular Nerve
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•
•
•
•
•
Superior & inferior vestibular nerves pass medially from lAC fundus
to porus acusticus within posterosuperior & posteroinferior
quadrants of lAC
Near porus acusticus superior & inferior vestibular nerves join
together with cochlear nerve to form vestibulocochlear nerve (CN8)
Vestibulocochlear nerve crosses CPA cistern posterior to facial
nerve
Enters lateral brainstem at junction pons & medulla posterior to
facial nerve
Vestibular nerve fibers divide into ascending & descending
branches which mainly terminate in vestibular nuclear complex
Vestibular nuclear complex
- Four nuclei (lateral, superior, medial & inferior)
- Located beneath lateral recess along floor of fourth ventricle
(rhomboid fossa) in lower pons
- Complex connections exist between vestibular nuclei, cerebellum,
spinal cord (vestibulospinal tract) & nuclei controlling eye movement

45. Imaging Recommendations
Sensorineural hearing loss (SNHL)
• Intracochlear lesion suspected
- CT & MR both useful for imaging
- Congenital lesions of membranous labyrinth seen as
abnormalities of fluid spaces on MR or in bony labyrinth shape on
bone CT
- Bone CT better for otosclerosis, Paget disease, labyrinthine
ossificans or if trauma suspected
- Only MR will demonstrate labyrinthitis or intralabyrinthine tumor
• CN8 lesion suspected (CPA-lAC)
- MR imaging method of choice
- Thin-section, high-resolution T2 sequence in axial & coronal
planes may be used to screen patients with unilateral sensorineural
hearing loss
- Tl C+ MR remains gold standard

46. Imaging "Sweet Spots"
• Unilateral sensorineural hearing loss
- Focus on brainstem (inferior cerebellar
peduncle )-CPA-lAC-cochlea
- Central acoustic pathway (intra-axial pathways
above cochlear nuclei) rarely site of offending
lesion
• Cisternal & lAC segments of CNS routinely
visualized on high-resolution T2 MR
Imaging Pitfalls:
• Beware small lesions of lAC (≤ 2 mm)!
- Follow-up imaging recommended as may be
transient finding where surgery not needed

47. Clinical Importance
• Vestibular nerve dysfunction (dizziness,
vertigo, imbalance) alone usually has
negative MR
• 95% of lesions causing unilateral SNHL
found by MR, are vestibulocochlear
schwannoma

60. Cranial Nerves VII
and VIII: The Facial and
Vestibulocochlear Nerves
• The facial and vestibulocochlear nerves have similar
cisternal and canalicular courses.
• They both emerge from the lateral aspect of the lower
border of the pons and traverse the cerebellopontine
angle cistern at an oblique angle.
• There, they may be in close proximity to the anterior
inferior cerebellar artery. Next, the nerves cross the
porus acusticus (an opening between the
cerebellopontine angle cistern and the internal auditory
canal; also known as the internal acoustic meatus) and
traverse the length of the internal auditory canal.
• Radiologic images that precisely depict the relationship
of the nerves to masses in the cerebellopontine angle
can help in surgical planning.
RadioGraphics 2009; 29:1045–1055

61. Cranial Nerves VII
and VIII: The Facial and
Vestibulocochlear Nerves
•
•
•
•
•
•
•
•
Within the internal auditory canal, the vestibulocochlear nerve splits into
three parts (cochlear, superior vestibular, and inferior vestibular).
These three vestibulocochlear nerve branches, along with the facial nerve,
have a characteristic appearance on sagittal oblique SSFP cross-sectional
images.
Images in that plane are most frequently used for the detection of cochlear
nerve aplasia.
On any single axial SSFP image, only two of the four nerves within the
internal auditory canal typically are visible.
If one of the nerves is seen to enter the modiolus of the cochlea, then the
two visible nerves are the cochlear and inferior vestibular nerves.
If the central modiolus is not depicted on the image, the visible nerves are
the facial and superior vestibular nerves.
A filling defect within the membranous labyrinth on SSFP images may signal
a nerve abnormality in a branch of the facial or vestibulocochlear nerve.
RadioGraphics 2009; 29:1045–1055

62. Cranial Nerves VII
and VIII: The Facial and
Vestibulocochlear Nerves
• The facial nerve exits the internal auditory
canal and enters the facial canal via the
fallopian aqueduct on the anterior aspect
of the Bill bar.
• After a complex course within the petrous
bone, the facial nerve exits the skull base
through the stylomastoid foramen and
enters the substance of the parotid gland.
RadioGraphics 2009; 29:1045–1055

63. Axial 0.8-mm-thick SSFP MR image shows the parallel courses
of the facial (black arrowheads) and superior vestibular (white
arrowheads) nerves as they cross the cerebellopontine angle to
enter the internal auditory canal through the porus acusticus
(double arrow).
RadioGraphics 2009; 29:1045–1055

64. Cerebellopontine angle meningioma in a 52-year-old woman
with left sensorineural hearing loss. (a) Axial 0.8-mm-thick SSFP
MR image shows a tumor that fills the internal auditory canal
(arrow) and extends into the cerebellopontine angle cistern. The
relation of the tumor to the facial and vestibulocochlear nerves
is not clearly shown. (b) Coronal oblique 0.8-mm-thick SSFP MR
image shows direct involvement of the facial nerve (arrowhead),
a contraindication against surgical resection. The tumor was
treated instead with stereotactic radiosurgery.
RadioGraphics 2009; 29:1045–1055

65. Cochlear nerve aplasia in a 4-year-old girl with congenital hearing loss who was under consideration
for cochlear implantation. Sagittal oblique 1.0-mm-thick SSFP images, obtained in planes
perpendicular to the left (a) and right (b) internal auditory canals, show the main branches of the
facial and vestibulocochlear nerves in cross section. The anterior (A), posterior (P), superior (S), and
inferior (I) aspects of the canals are labeled for ease of orientation. In both a and b, the facial (white
arrow), superior vestibular (white arrowhead), and inferior vestibular (black arrowhead) nerves are
depicted; however, the cochlear nerve (black arrow in a) is absent in b, and that finding is a
contraindication against cochlear implantation for the right ear. Incomplete separation of the superior
and inferior vestibular nerves, also shown in b, is a normal variant.
RadioGraphics 2009; 29:1045–1055

66. CN9
Glossopharyngeal nerve

67. Overview
• Ninth cranial nerve
• Complex cranial nerve functions
- Taste & sensation to posterior 1/3 tongue
- Sensory nerve to middle ear & pharynx
- Parasympathetic to parotid gland
- Motor to stylopharyngeus muscle
- Viscerosensory to carotid body & sinus
• Mixed nerve (sensory, taste, motor,
parasympathetic)
• Four segments: Intra-axial, cisternal, skull
base & extracranial

73. Intra-Axial Segment
• Glossopharyngeal nuclei are in upper & middle
medulla
- Motor fibers to stylopharyngeus muscle
originate in nucleus ambiguus
- Sensory fibers from tympanic membrane, soft
palate, tongue base & pharynx terminate in
spinal nucleus CNS
- Taste fibers from posterior 1/3 tongue
terminate in solitary tract nucleus
- Parasympathetic fibers to parotid gland
originate in inferior salivatory nucleus

74. Cisternal Segment
• Exits lateral medulla in postolivary sulcus
just above vagus nerve
• Travel anterolaterally through basal cistern
together with vagus nerve & bulbar portion
of accessory nerve
• Passes through glossopharyngeal meatus
into pars nervosa portion of jugular
foramen

75. Skull Base Segment
• Passes through anterior pars nervosa
portion of jugular foramen
- Accompanied by inferior petrosal sinus
- Vagus (CN10) & spinal accessory
(CN11) nerves are posterior within pars
vascularis portion of jugular foramen
- Superior & inferior sensory ganglia of
CN9 are found within jugular foramen

76. Extracranial Segment
• Exits jugular foramen into anterior
nasopharyngeal carotid space
• Passes lateral to internal carotid artery &
stylopharyngeus muscle
• Terminates in posterior sublingual space
in floor of mouth (posterior 1/3 taste
function)

77. Extracranial Branches
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•
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Tympanic branch (Jacobsen nerve)
- Sensation from middle ear & parasympathetic to parotid gland
- Arises from inferior sensory ganglion within jugular foramen
- Passes through inferior tympanic canaliculus into middle ear
(Aberrant internal carotid artery enters middle ear via this canal)
- Forms tympanic plexus on cochlear promontory (Glomus bodies
associated with this nerve form glomus tympanicum paraganglioma)
Stylopharyngeus branch
- Motor to stylopharyngeus muscle
• Sinus nerve
- Supplies viscerosensory fibers to carotid sinus & carotid body
- Conducts impulses from mechanoreceptors of sinus &
chemoreceptors of carotid body to medulla
Pharyngeal branches
- Sensory to posterior oropharynx & soft palate
Lingual branch
- Sensory & taste to posterior 1/3 of tongue

78. Imaging Recommendations
• MR imaging method of choice
- Superior sensitivity to skull base, meningeal,
cisternal & brainstem pathology
- Sequences should include a combination of
T2, T1 without fat-saturation & contrastenhanced T1 with fat-saturation in axial &
coronal planes
• Bone CT used to supplement MR when complex
skull base pathology discovered

79. Imaging "Sweet Spots"
• Focused enhanced MR imaging extends from
pontomedullary junction above to hyoid bone below
• CN9 nuclei & intra-axial segment not directly visualized
- Position inferred by identifying upper medulla,
posterior to postolivary sulcus
- Cisternal segment is not always visualized on routine
MR imaging (High-resolution thin-section T2 sequences
usually demonstrate CN9, 10, 11 nerve complex passing
through basal cisterns; Bone CT with bone algorithm
clearly demonstrates bony anatomy of pars nervosa)
• Extracranial segment not visualized
• Imaging Pitfalls: Remember to image entire extracranial
course of CN9; do not just stop at skull base!

80. Clinical Importance
• Glossopharyngeal nerve dysfunction
usually associated with CN1O & CN11
neuropathy
- Isolated glossopharyngeal neuropathy
exceedingly rare

87. Cranial Nerve IX: The
Glossopharyngeal Nerve
• The glossopharyngeal nerve emerges from the
lateral medulla into the lateral
cerebellomedullary cistern, above the vagus
nerve and at the level of the facial nerve.
• In the lateral cerebellomedullary cistern, the
glossopharyngeal nerve is closely associated
with the flocculus of the cerebellum.
• The flocculus is a lobule of cerebellar tissue that
is directly adjacent to the glossopharyngeal
nerve, and it should not be mistaken for an
abnormality.
RadioGraphics 2009; 29:1045–1055

88. Cranial Nerve IX: The
Glossopharyngeal Nerve
• From the lateral cerebellomedullary
cistern, the nerve plunges into the jugular
fossa and exits the skull through the
jugular foramen.
• In the jugular foramen, the
glossopharyngeal nerve is anterior to the
vagus and accessory nerves and is
surrounded by its own dural sheath (the
glossopharyngeal canal).
RadioGraphics 2009; 29:1045–1055

89. Coronal oblique 0.8-mm-thick SSFP MR image through the
cerebellopontine angle shows the glossopharyngeal nerve
(arrow) just beneath the flocculus (f) of the cerebellum.
The two roots of the vagus nerve (arrowheads) are visible in the
same plane, and the superior and inferior vestibular nerves can
be seen above the flocculus.
RadioGraphics 2009; 29:1045–1055

90. CN10
Vagus nerve

91. Overview
• Tenth cranial nerve
• CN1O: Parasympathetic nerve supplying regions of head
and neck and thoracic and abdominal viscera
• Additional vagus nerve components
- Motor to soft palate (except tensor veli palatini
muscle), pharyngeal constrictor muscles, larynx and
palatoglossus muscle of tongue
- Visceral sensation from larynx, esophagus, trachea,
thoracic and abdominal viscera
- Sensory nerve to external tympanic membrane,
external auditory canal (EAC) and external ear
- Taste from epiglottis
• Mixed nerve (sensory, taste, motor, parasympathetic)
• Segments: Intra-axial, cisternal, skull base and
extracranial

97. Intra-Axial Segment
• Vagal nuclei are in upper and middle medulla
- Motor fibers originate in nucleus ambiguus
- Taste from epiglottis goes to solitary tract nucleus
- Sensory fibers from viscera terminate in dorsal vagal
nucleus (afferent component)
- Parasympathetic fibers project from dorsal vagal
nucleus (efferent component)
- Sensory from regional meninges and ear project to
spinal nucleus CN5
• Fibers to and from these nuclei exit lateral medulla in
postolivary sulcus inferior to CN9 and superior to bulbar
portion of CN 11

98. Cisternal Segment
• Exits lateral medulla in postolivary sulcus
between CN9 and bulbar portion of CN11
• Travel anterolaterally through basal cistern
together with CN9 and bulbar portion of
CN11

99. Skull Base Segment
• Passes through posterior pars vascularis
portion of jugular foramen (JF)
- Accompanied by CN11 and jugular bulb
- Superior vagal ganglion is found within
JF

100. Extracranial Segment
• Exits JF into nasopharyngeal carotid space
• Inferior vagal ganglion lies just below skull base
• Descends along posterolateral aspect of internal carotid
artery into thorax
- Passes anterior to aortic arch on left and subclavian
artery on right
• Forms plexus around esophagus and major blood
vessels to heart and lungs
• Gastric nerves emerge from esophageal plexus and
provide parasympathetic innervation to stomach
• Innervation to intestines and visceral organs follows
arterial blood supply to that organ

101. Extracranial Branches in Head & Neck
• Auricular branch (Arnold nerve)
- Sensation from external surface of tympanic
membrane, EAC and external ear
- Arises from superior vagal ganglion within JF
- Passes through mastoid canaliculus extending
from posterolateral JF to mastoid segment CN7
canal
- Enters EAC via tympanomastoid fissure
• Pharyngeal branches
- Pharyngeal plexus exits just below skull base
- Sensory to epiglottis, trachea and esophagus
- Motor to soft palate (except tensor veli palatini
muscle - CNV3) and pharyngeal constrictor
muscles

102. Extracranial Branches in Head & Neck
• Superior laryngeal nerve
- Motor to cricothyroid muscle
- Sensory to mucosa of supraglottis
• Recurrent laryngeal nerve
- On right recurs at cervicothoracic junction,
passes posteriorly around subclavian artery
- On left recurs in mediastinum by passing
posteriorly under aorta at aortopulmonary
window
- Nerves recur in tracheoesophageal grooves
(TEG)
- Motor to all laryngeal muscles except
cricothyroids
- Sensory to mucosa of infraglottis

103. Imaging Recommendations
Proximal vagal neuropathy
• Image from medulla to hyoid bone
• MR imaging method of choice
• - Superior sensitivity to skull base, meningeal, cisternal and
brainstem pathology
• - Sequences should include a combination of T2, T1 without fatsaturation and contrast-enhanced T1 with fat-saturation in axial and
coronal planes
• - Bone CT used to supplement MR when complex skull base
pathology is present
• - Distal vagal neuropathy
• Image from hyoid bone to mediastinum
• Must reach carina if left vagal neuropathy
• Key areas to evaluate are carotid space and TEG
• CECT imaging method of choice

104. Clinical Importance
• Vagal nerve dysfunction separated into proximal
and distal symptom complexes
• Proximal symptom complex
- Injury site: Between medulla and hyoid bone
- Multiple cranial nerves involved (CN9-12) with
oropharyngeal and laryngeal dysfunction
• Distal symptom complex
- Injury site: Below hyoid bone
- Isolated CNlO involvement with laryngeal
dysfunction only

111. Cranial Nerve X: The Vagus
Nerve
• The vagus nerve comprises two roots that emerge from
the side of the medulla, from a groove called the
posterolateral sulcus.
• Leaving the medulla, the nerve roots enter the lateral
cerebellomedullary cistern in a position inferior to the
glossopharyngeal nerve and run parallel to it through the
cistern.
• Because of their parallel course, it may be difficult to
distinguish between the glossopharyngeal and vagus
nerves on axial SSFP images; coronal or oblique coronal
views along the course of the nerves probably are best
for that purpose.
RadioGraphics 2009; 29:1045–1055

112. Cranial Nerve X: The Vagus
Nerve
• After obliquely traversing the lateral
cerebellomedullary cistern, the vagus nerve
enters the jugular fossa and exits the skull
through the jugular foramen, between the
glossopharyngeal and accessory nerves.
• In the neck, the vagus nerve lies within the
carotid sheath, behind and between the internal
jugular vein and common carotid artery.
RadioGraphics 2009; 29:1045–1055

113. Axial oblique 0.8-mm-thick SSFP MR image shows the vagus
nerve (arrow) where it crosses the lateral cerebellomedullary
cistern (LCM) and approaches the jugular foramen.
The vagus and glossopharyngeal nerves, which are difficult to
distinguish in this plane, are clearly distinguishable in the coronal
oblique plane (see Fig 17).
RadioGraphics 2009; 29:1045–1055

114. CN11
Accessory nerve

115. Overview
• Eleventh cranial nerve
• Pure motor cranial nerve supplying
sternocleidomastoid & trapezius muscles
• Motor cranial nerve only
• Four CN11 segments are defined
- Intra-axial, cisternal, skull base &
extracranial

119. Intra-Axial Segment
Two distinct nuclear origins
• Bulbar (cranial) motor fibers originate in lower nucleus
ambiguus
- Fibers course anterolaterally to exit lateral medulla in
postolivary sulcus inferior to CN9 & 10
• Spinal motor fibers originate from spinal nucleus of
accessory nerve
- Narrow column of cells along lateral aspect of anterior
horn from C1 to C5
- Nerve fibers emerge from lateral aspect of cervical
spinal cord between anterior & posterior roots
- Fibers combine forming a bundle that ascends
entering skull base via foramen magnum

120. Cisternal Segment
• Bulbar portion travels anterolaterally
through basal cistern together with CN9 &
10
• Bulbar & spinal portions join together
within lateral basal cistern

121. Skull Base Segment
• Passes through posterior pars vascularis
portion of jugular foramen
- Vagus nerve (CN1O) & jugular bulb are
also in pars vascularis
• Bulbar & spinal portions remain together in
jugular foramen

122. Extracranial Segment
• Combined CN11 exits jugular foramen into
nasopharyngeal carotid space
• Fibers from bulbar portion which arose within nucleus
ambiguus transfer to vagus nerve
- Travels via CN10 to supply muscles of pharynx &
larynx
• Larynx: except cricothyroid muscle via recurrent
laryngeal nerve
• Pharynx: superior constrictor & soft palate via
pharyngeal plexus
• Fibers from spinal portion remain in extracranial CN11
- Diverges posterolaterally from carotid space
- Descend along medial aspect of sternocleidomastoid
muscle
- Innervates sternomastoid muscle
- Continues across floor of posterior cervical space in
cervical neck
- Terminate in & innervate trapezius muscle

123. Imaging Recommendations
• MR imaging method of choice
- Superior sensitivity to skull base, meningeal,
cisternal & brainstem pathology
- Sequences should include a combination of
T2, T1 without fat-saturation & contrastenhanced TI with fat-saturation in axial & coronal
planes
• Bone CT used to supplement MR when complex
skull base pathology is present

124. Imaging "Sweet Spots"
• CN11 nuclei & intra-axial segment not directly visualized
• Cisternal segment is often not visualized on routine MR
imaging
- High-resolution thin-section T2 MR sequence usually
demonstrates CN9, 10, 11 nerve complex passing
through basal cisterns from post-olivary sulcus to pars
vascularis of jugular foramen
• Bone CT clearly demonstrates bony anatomy of pars
vascularis of jugular foramen
• Extracranial CN11 segment not directly visualized
- Location inferred from its constant position deep to
sternocleidomastoid muscle in floor of posterior cervical
space

125. Imaging Pitfalls
• Hypertrophic levator scapulae muscle
following serious CNll injury may mimic
tumor
• Don't mistake this enlarged muscle for
mass!

126. Clinical Importance
• CNll innervates sternocleidomastoid & trapezius muscles
Function-Dysfunction
• CN11 dysfunction: Isolated CN11 injury
- Most common cause is radical neck dissection
because spinal accessory nodal chain intimately
associated CN11
- Initial symptoms of spinal accessory neuropathy
(downward & lateral rotation of scapula; shoulder droop
resulting from loss of trapezius tone
- Long term findings in spinal accessory neuropathy
(within 6 months results in atrophy of ipsilateral
sternocleidomastoid & trapezius muscles;
(compensatory hypertrophy of ipsilateral levator
scapulae muscle occurs over months)
• CN11 dysfunction: Complex CN11 dysfunction
associated with CN9 & 10 neuropathy

130. Cranial Nerve XI:
The Accessory Nerve
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•
•
The accessory nerve is composed of multiple cranial and spinal
rootlets.
The cranial rootlets emerge into the lateral cerebellomedullary
cistern below the vagus nerve.
The spinal rootlets emerge from upper cervical segments of the
spinal cord.
After leaving the spinal cord, the spinal rootlets pass superiorly
through the foramen magnum into the cisterna magna (ie, the
posterior cerebellomedullary cistern), in a position posterior to the
vertebral artery, and join the cranial rootlets in the lateral
cerebellomedullary cistern.
The conjoined nerve fibers then leave the skull through the jugular
foramen, posterior to the glossopharyngeal and vagus nerves.
Segmental spinal nerve roots at the C1 and C2 levels are
distinguishable from accessory nerve rootlets at these levels
because the spinal nerve roots are larger and extend to the neural
foramina instead of continuing superiorly.
RadioGraphics 2009; 29:1045–1055

131. Axial 0.8 mm-thick SSFP MR image at the level of the
cervicomedullary junction (CMJ) shows the cranial rootlets
(arrowheads) of the accessory nerve.
RadioGraphics 2009; 29:1045–1055

132. Coronal oblique 0.8-mm-thick SSFP MR image shows the spinal
rootlets (arrows) of the accessory nerve arising from the upper
spinal cord to cross the foramen magnum and join the cranial
rootlets.
RadioGraphics 2009; 29:1045–1055

133. CN12
Hypoglossal nerve

134. Overview
• Twelfth cranial nerve
• CN12: motor cranial nerve controlling intrinsic &
extrinsic muscles of tongue
• Motor cranial nerve to intrinsic & extrinsic
muscles of tongue
- Only extrinsic muscle not innervated by CN12
is palatoglossus muscle (Vagus nerve
innervates palatoglossus muscle)
• Hypoglossal nerve anatomic segments: Intraaxial segment, Cisternal segment, Skull base
segment, Extracranial

138. Intra-Axial Segment
• Hypoglossal nucleus
- Located in medulla between dorsal vagal nucleus &
midline
- Long, thin nucleus that is about same length as the
ventrolateral olive
- Extends from level of hypoglossal eminence in floor of
fourth ventricle just inferior to stria medullares to
proximal medulla
- In axial section, hypoglossal nucleus is located in
dorsal medulla, medial to dorsal vagal nucleus
• Hypoglossal intra-axial axonal course
- Efferent fibers from hypoglossal nucleus extend
ventrally through medulla, lateral to medial lemniscus
- Efferent fibers exit between olivary nucleus & pyramid
at ventrolateral sulcus also called pre-olivary sulcus

139. Cisternal Segment
• Efferent fibers coalesce to form multiple
rootlets
• Rootlets fuse into hypoglossal nerve just
as it exits skull base through hypoglossal
canal
• Hypoglossal filaments may merge with
vagal fibers

140. Skull Base Segment
• Hypoglossal nerve exits the occipital bone
via hypoglossal canal
- Hypoglossal canal is located in inferior
occipital bone caudal to jugular foramen
- Variant anatomy of hypoglossal canal
(osseous septa may bisect hypoglossal
canal)

141. Extracranial Segment
•
Carotid space component of CN12
- Hypoglossal canal "empties" into medial nasopharyngeal carotid
space
• Hypoglossal nerve immediately gives off dural branches after exiting
hypoglossal canal
- Hypoglossal nerve descends in posterior aspect of carotid space,
closely apposed with vagus nerve
- Exits carotid space anteriorly between jugular vein & internal
carotid artery at inferior margin of posterior belly of digastric muscle
• Trans-spatial component of CN12
- After leaving carotid space, runs anteroinferiorly toward hyoid
bone, lateral to carotid bifurcation
- At level of occipital artery base, hypoglossal nerve turns anterior,
continuing as muscular branch below posterior belly of digastric
muscle
- Gives off superior root of ansa cervicalis from horizontal segment
CN12 to anastomose with lower root of ansa cervicalis

142. Extracranial Segment
• Distal branches of imaging importance
- Muscular branch travels on lateral margin of
hyoglossus muscle in posterior sublingual space
• Muscular branch innervates extrinsic
(styloglossus, hyoglossus, genioglossus) and
intrinsic tongue muscles
• Geniohyoid innervated by C1 spinal nerve
- Ansa cervicalis: Formed from superior and
inferior (C1-C3 spinal nerves) roots
• Innervates infrahyoid strap muscles
(sternothyroid, sternohyoid, omohyoid)

143. Imaging Recommendations
• MR is preferred imaging study
- Best delineates brainstem, cisterns,
skull base & suprahyoid neck
• CECT with bone algorithm of skull base is
excellent for skull base & suprahyoid neck

144. Imaging "Sweet Spots"
• Coverage of hypoglossal nerve requires CT or
MR to visualize following anatomic areas
- Brainstem, basal cistern & hypoglossal canal
- Nasopharyngeal carotid space
- Posterior belly digastric & carotid bifurcation
- Hyoid bone & sublingual space
• Imaging Pitfalls: Failure to image to level of
hyoid bone will result in missed diagnoses!

145. Clinical Importance
• Unilateral hypoglossal lesion causes tongue
protrusion to "side of the lesion"
• Acute hypoglossal injury
- Tongue fasciculates
- Tongue deviates to side of injury when
protruded
• Chronic hypoglossal injury
- Tongue atrophy seen as fatty infiltration &
volume loss on CT or MR
- Infrahyoid strap muscles also atrophy

155. Cranial Nerve XII:
The Hypoglossal Nerve
• The hypoglossal nerve arises from nuclei in front of the
fourth ventricle, within the medulla, and emerges as a
series of rootlets extending from the ventrolateral sulcus
of the medulla into the lateral cerebellomedullary cistern.
• The combined rootlets then cross the lateral
cerebellomedullary cistern, where the nerve is
surrounded anteriorly by the vertebral artery and
posteriorly by the posterior inferior cerebellar artery.
• The hypoglossal nerve then exits the skull via the
hypoglossal canal, which runs obliquely in the axial
plane, at an angle of approximately 45° between the
coronal and sagittal planes.
• After exiting the skull, the hypoglossal nerve runs medial
to the glossopharyngeal, vagus, and accessory nerves
and deep to the digastric muscle, looping over the hyoid
bone to innervate a large part of the tongue.
RadioGraphics 2009; 29:1045–1055

156. Coronal oblique 0.8-mm-thick SSFP MR image shows multiple
hypoglossal nerve roots (arrows) converging toward the hypoglossal
foramen (arrowhead).
The nerve roots are immediately posterior to the vertebral artery (V).
RadioGraphics 2009; 29:1045–1055

157. Axial 0.8-mm-thick SSFP MR image shows the oblique course of
the hypoglossal nerve (black arrowhead) as it crosses the lateral
cerebellomedullary cistern toward the hypoglossal canal (white
arrowheads).
The vertebral arteries (white arrows) are anterior to the nerve,
and the posterior inferior cerebellar artery (black arrow) is
posterior to the nerve.
RadioGraphics 2009; 29:1045–1055

158. References
• Diagnostic and Surgical Imaging Anatomy.
Brain, Head & Neck, Spine / H. Ric
Harnsberger. [et al.] ; managing editor, Andre
Macdonald. n 1st ed. I:174-I:259.
• RadioGraphics 2009; 29:1045–1055 • Sujay
Sheth, BA • Barton F. Branstetter IV, MD •
Edward J. Escott, MD. Appearance of Normal
Cranial Nerves on Steady-State Free
Precession MR Images.