Cranial Nerves

Imaging Anatomy and Frequent Pathologies

Sven Haller, Frederik Barkhof, Robin Smithuis, andBernhard Schuknecht

ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Part 1: General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Perineural Spread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

This publication is endorsed by: European Society ofNeuroradiology (www.esnr.org).

S. Haller (*)CIRD – Centre d’Imagerie Rive Droite, Geneva,Switzerland

Department of Surgical Sciences, Radiology, UppsalaUniversity, Uppsala, Sweden

Faculty of Medicine, University of Geneva, Geneva,Switzerlande-mail: sven.haller@me.com

F. BarkhofDepartment of Radiology & Nuclear Medicine,VU University Medical Centre, Amsterdam, Netherlands

UCL Institutes of Neurology & Healthcare Engineering,London, UKe-mail: f.barkhof@vumc.nl; f.barkhof@ucl.ac.uk

R. SmithuisDepartment of Radiology, Alrijne Hospital, Leiderdorp,Netherlandse-mail: rsmithui@xs4all.nl

B. SchuknechtDiagnostic, Vascular and Interventional Neuroradiology,Medical Radiological Institute, Zurich, Switzerlande-mail: image-solution@ggaweb.ch

© Springer Nature Switzerland AG 2019F. Barkhof et al. (eds.), Clinical Neuroradiology,https://doi.org/10.1007/978-3-319-61423-6_84-1

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Cavernous Sinus Pathologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Imaging Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Part 2: Specific Imaging of Cranial Nerve Pathology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8CN I: Olfactory Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8CN II: Optic Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Cranial Nerves for Eye Movements (CN III, IV, VI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12CN V: Trigeminal Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15CN VII: Facial Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18CNVIII: Vestibulocochlear Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20CN IX: Glossopharyngeal Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Cranial nerves of the jugular foramen IX, X and XI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24CN X: Vagal Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25CN XI: Accessory Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Selected Pathologies of CN IX to XI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Hypoglossal Nerve XII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

AbstractCranial nerves (CN) provide efferent (motor,autonomic) and afferent (sensory and auto-nomic) innervation to the head, face, andneck. Isolated CN palsies come with a typicaldifferential diagnosis (e.g., vestibularschwannoma in hearing loss), based on theCN and the segment involved (central, cister-nal, foraminal, peripheral). Multiple cranialnerves palsies reflect the impact of pathologyin certain anatomical regions such as the cav-ernous sinus or systemic disorders such assarcoid.

The first part of this chapter discussesrecommended radiological techniques for theimaging of cranial nerve with a focus on thesegment involved. The second part reviews theessential anatomy and clinical neuroradiologyapproach for each CN to depict themost frequentpathologies, including neoplasm (perineuraltumor spread,meningioma, schwannoma), infec-tious/inflammatory diseases, vascular diseasesincluding neurovascular compression, andtrauma.

KeywordsImaging · CT · MRI · Cranial nerves

AbbreviationsAICA Anterior inferior cerebellar artery

CISS Constructive interference in steadystate

CN Cranial nerveCPA Cerebello-pontine angleDWI Diffusion-weighted imagingFat-sat Fat-saturationFIESTA Fast imaging employing steady-

state acquisitionGad GadoliniumICA Internal carotid arteryIJV Internal jugular veinINO Internuclear ophthalmoplegiaMR Magnetic resonanceMRA Magnetic resonance angiographyMS Multiple sclerosisNVCS Neurovascular compression

syndromePCA Posterior cerebral arteryPICA Posterior inferior cerebellar arteryREZ Root entry zoneSCA Superior cerebellar arterySPACE Sampling perfection with applica-

tion optimized contrastTHRIVE T1-weighted high-resolution iso-

tropic volume examinationTOF Time of flight (angiography)TSE Turbo spin echoTZ Transition zoneVIBE Volumetric interpolated breath-

hold examination

2 S. Haller et al.

Introduction

Cranial nerves (CNs) provide efferent (motor,autonomic) and afferent (sensory and autonomic)innervation to the head, face, and neck. The olfac-tory nerve (CN I) and the optic nerve (CN II) areexceptions, in that they are extensions of the tel-encephalon and therefore not cranial nerves in thestrict sense.

The relevant segments include supranuclearpathways (e.g., cortex of secondary relay station),the nucleus and medullary segments(in brainstem), cisternal segments, skull-baseforaminal passage, and to the extraforaminaltrajectories of the viscerocranium and the neck.

The cranial nerves III to XII connect to nucleilocated within the midbrain (III, IV), pons (e.g.,VI–VIII) to the medulla oblongata, or even theupper cervical cord (X–XI) as shown in Fig. 1.Cranial nerves III, IV, VI, XI, and XII are purely

efferent and deliver motor fibers to the orbit, theneck, and tongue. Cranial nerves V, VII, IX, and Xhave a mixed composition of efferent and afferentfibers harboring both motor and sensory supply. Inthe brainstem, nuclei providing efferent neuronsare located medially and ventral to their afferent –dorsolateral – counterparts.

Cranial nerve dysfunction may arise from acompromise of any segment between the nuclearorigin to its end organ. A supranuclear injury is ingeneral clinically indistinguishable from a nuclearlesion. The exception is the facial nerve thatreceives dual – ipsi- and contralateral – supply toits dorsal portion for the motor neurons of theupper face. These muscles are not affected by acentral palsy while the lower face (ventralnucleus) receives contralateral supply only andinvolvement thus leading to paresis.

The CNs exit the skull through a series ofopenings in the skull base, including the

Fig. 1 Schematic coronal drawing showing the trajectory of the cranial nerves

Cranial Nerves 3

cribriform plate (CN I), optic canal (CN II), supe-rior orbital fissure (CN III, IV, V1, and VI), andseveral foramina in the middle and posterior fossa(Fig. 2).

Part 1: General Considerations

In many cases, there is involvement of only onecranial nerve. Based on the CN involved, the typeof onset, and additional (systemic) clues, there is atypical differential diagnosis (Table 1). Purelynuclear lesions (e.g., due to brainstem ischemia)are rare and the cisternal segments are frequentlyinvolved.

There are a number of conditions with simul-taneous involvement of multiple cranial nerves,including larger brainstem lesions. Extra-medullary sites involved and the affected CNsare listed in Table 2, with an example of petrousapex infection in Fig. 3.

Common types of pathology with multiple cra-nial nerve pathology in Table 3, with an example ofrelapsing inflammatory polyneuropathy in Fig. 4.

Fig. 2 Superior view of the cranial nerves and corresponding foramina

Table 1 Common causes of isolated cranial nerveinvolvement

DiseaseCommonlyinvolved

Infrequentlyinvolved

Meningioma I, II, VII, VIII IV, IX–XII

Schwannoma VII, VIII V, IX–XII

Perineural tumorspread

V, VII III, IV, VI,IX

Infectious/inflammatory

I, II, III, V, VII,cavernous sinus

Neurovascularcompression

V, VII IX

Trauma I, II, VII, VIII, XII VI

Aneurysm III (PcomA) VI

Vascularischemic lesion

II, III, V, VI, VII

4 S. Haller et al.

Perineural Spread

Extracranial tumors may spread along the cranialnerves intracranially. The facial nerve serves as animportant conduit for perineural extension ofmalignancy into the skull base. Other common

pathways are the first, second, and third branchesof the trigeminal nerve and less frequently thehypoglossal nerve. Rarely, alternate routes areused by anastomoses related to CN IX–VII(Jacobson’s nerve) and X–VII (Arnold’s nerve)via the tympanic plexus. High-resolution 3Dgradient-echo volume sequences withGad-enhancement and fat-sat increase the conspi-cuity of MR to identify perineural spread anddelineate the extension.

The cavernous sinus (Fig. 5) is an importantstructure in the central skull base.

This parasellar structure is formed by duralfolds containing the carotid artery embedded in avenous plexus that also contains CN III, IV, V1,V2 from rostral to caudal and CN VI in a moremedial position (Fig. 5).

Table 2 Multiple cranial nerve involvement by extra-medullary location

Location Cranial nerve involvement

Cavernoussinuous

III, IV, V1, V2, VI

Internalauditory canal

VII, VIII

Gradenigosyndrome

Petrous apicitis; VI nerve palsy inDorello’s canal; V1 V2 pain due toextension of inflammation intoMeckel cave

Craniocervicaljunction

IX–XII

Fig. 3 A 67-year-old man with Gradenigo syndrome dueto osteomyelitis of the petrous apex presenting with peri-orbital pain and fever. On examination, he was found tohave otorrhea and diplopia due to involvement of 5th and6th cranial nerve, reflective of involvement of Meckel’s

cave and the clivus and cavernous sinus. Due to the exten-sion into the jugular foramen, he also presenting withinvolvement of multiple lower cranial nerves (IX–XI) –referred to as Vernet syndrome

Table 3 Multiple cranial nerve involvement by type of pathology

Disease Mechanism CN commonly involved

Stroke Ischemia or hemorrhage inbrainstem nuclei

III, VI, VII

Neurofibromatosis 1 NF-1 gene on chromosome 17 Unilateral or bilateral optic nerve glioma

Neurofibromatosis 2 NF2 gene on chromosome 22 Multiple schwannomas of all CNs,meningiomas (and ependymomas)Note: Bilateral CN VIII (vestibular)schwannomas are diagnostic of NF2

Inflammation, e.g., sarcoid Granulomatous spread in basalleptomeninges

III–VIII but also lower CNs

Miller-Fisher syndrome(CN variant of Guillain-Barré)

Anti-GQ1b neuronal antibodies(postinfectious)

III–VI and others

Neoplasm Foraminal compression orperineural tumor spread

V2, V3, VII, IX–XII

Cranial Nerves 5

The cavernous sinus has rich connections withthe ophthalmic veins, superior and inferior petro-sal veins, the subcranial pterygoid venous plexus(via emissary veins), and superficial middle cere-bral veins, draining the lateral hemispheres.

Cavernous Sinus Pathologies

Various types of pathology can affect the cavern-ous sinus and cause multiple cranial nerve palsies.Sinus thrombosis, carotid-cavernous fistula, andTolosa-Hunt syndrome (inflammatory painful

Fig. 4 An 8-year-old girl presenting with relapsinginflammatory polyneuritis. Several episodes of cranialnerve palsy occurred over the course of years involvingoculomotor, trigeminal, and facial nerves, each time

responding will to short courses of steroid. MRI showsextensive enhancement of oculomotor and trigeminalnerves over their entire length

Fig. 5 Schematic drawing of the cavernous sinus (left)and coronal reconstruction of 3DT2-Gad illustrating therostral to caudal organization of CN III, IV, V1, V2 and the

more medially located CN VI and internal carotid artery(ICA)

6 S. Haller et al.

ophthalmoplegia) will have associated findings ofpain/swelling/headache, while carotid aneurysmsand tumor invasion (Fig. 6) tend to be painless.

Imaging Recommendations

GeneralIn general, MRI is the preferred imaging modalityto depict medullary, cisternal, and (extra)forami-nal involvement; CT may reveal the foraminalinvolvement. The imaging strategy needs to betailored to the segments of the CN potentiallyaffected (nuclear, cisternal, foraminal, peripheral)considering the anatomical and clinical clues inTables 1, 2, and 3.

Nuclear LesionsTo assess a central (medullary) lesion causingcranial nerve palsy, the examination shouldinclude a sagittal and axial T2/FFLAIR andwhen of acute onset, a DWI sequence. While thenuclei themselves are usually not visible on MRI,the expected level of involvement should be scru-tinized (e.g., mesencephalon for CNs III and IV).

Cisternal PathologyHeavily T2-weighted gradient-echo sequencessuch as Constructive Interference in Steady State(CISS), Fast Imaging Employing Steady-StateAcquisition Cycled Phases (FIESTA-C), BalancedFast Field Echo (B-FFE), and Sampling Perfectionwith Application Optimized Contrast (SPACE)sequences enable short imaging times, highSNRs, and high contrast and isotropic spatial reso-lution. A maximum partition thickness of0.5–0.7 mm in CN I–VIII and of 0.8–1.0 mm for

CN IX–XII is preferred. A coronal imaging plane isfavored for CN I–IV and an axial orientation forCNs V–XII.

Due to the multiangular course of many cranialnerves, multiplanar isotropic reconstructions(MPRs) are essential for the precise assessmentof their extramedullary segments. MPR also pro-vides comprehensive information about the rela-tion of the nerves with the adjacent dural,vascular, and osseous structures.

The proximity of the cisternal and (inter)duralcourse of CNs III–XII to basal cerebral arteriesand veins implies addition of a time-of-flight(TOF) MR angiography (MRA) in case an aneu-rysm or a neurovascular conflict may be advanta-geous. Noncontrast (TOF) MRA is preferred forthe CN III, IV, VI in order to avoid enhancementof the cavernous sinus. For V–XII, a contrast-enhanced TOF MR-angiography may improvevisibility of smaller arterial vessels and detectionof a potential venous contact.

Foraminal and Extraforaminal SegmentsThe peripheral segments of the CNs are bestassessed using submillimetric 3DT1 fat-satsequence (0.5–0.8 mm) including gadoliniumadministration. Advantages of this sequence aremotion robustness and high spatial resolution fromthe skull base to the end organs. Lesions that arisewithin or adjacent to the skull base may addition-ally be investigated by high-resolution CT(0.5–0.8 mm). Bone window settings allow exam-ination of a cranial nerve within or adjacent to theskull base. This may be due to tumors, degenera-tive, developmental, or vascular lesions. The extentof any calcified portion of a lesion such as in

Fig. 6 A 68-year-old woman with CN III (oculomotor)compression due to non-Hodgkin lymphoma presentingwith double vision since 2 weeks and on examination

was found to have oculomotor paresis. MRI revealed alymphoma deposit in the superior part of left cavernoussinus which harbors the oculomotor nerve

Cranial Nerves 7

meningiomas, chordomas, and chondrosarcomasmay carry additional information.

CT and MR images acquired with high spatialresolution enable image fusion to unite informa-tion provided by bone window CT and 3D T2gradient echo data sets or by 3D T1 Gad informa-tion. Navigation data are mandatory for potentialsurgical or radio-surgical candidates with lesionslocalized at the skull base.

General imaging for CN

Imaging volume centered on CN of interest anterior,middle, or posterior skull base

Routine brain sequences (incl. DWI) to rule our central/nuclear involvement

3DT2 (CISS, THRIVE, CUBE) for cisternal segments

3DT1 fat-sat +/� Gad in case of suspected inflammationor neoplasm, especially cavernous sinus and skull base

In cases of trauma: CT (including temporal bone for CNVII/VIII pathology)

Specific imaging for CN

I +/� Cor T2 high res (512 matrix/3 mm slices)II DWI (focused/zoom), coronal T2 fat-sat orbit

through sella/chiasm

III, IV,VI

TOF and 3DT2 (CISS, THRIVE, CUBE) orT1-FS Gad for cavernous sinus

V 3DT2 (CISS, THRIVE, CUBE), TOF

VII,VIII

3DT2 (CISS, THRIVE, CUBE)+/� Non-EPI diffusion (in particular ifpossible cholesteatoma)

IX–XII 3DT2 (CISS, THRIVE, CUBE) +/� TOF

Part 2: Specific Imaging of CranialNerve Pathology

CN I: Olfactory Nerve

Clinicalpresentation

Most commoncauses

Less common butimportant

Anosmia Meningioma ofcribriform plate(olfactorygroove), anteriorskull base trauma

Viral/idiopathicParkinson andotherneurodegenerativediseases

Normal AnatomyThe olfactory fibers provide sensory afferent pro-jections of the brain via olfactory fila that arisefrom the olfactory epithelium of the nasal cavityand unite to 10–20 bundles on each side of thenose. These enter the anterior cranial fossa via thecribriform plate and synapse within the olfactorybulb which is an extension of the telencephalon.Each olfactory tract runs posteriorly and dividesrostral to the anterior perforated substance into themedial and lateral olfactory stria to reach theamygdala, primary olfactory or “piriform” cortex,the subcallosal, and the anterior perforated sub-stance itself.

Segments of CN I

Nasal Olfactory rim, superior turbinate

Cisternal Olfactory sulcus to anterior perforatesubstance

Central-medial

Subcallosal area surrounding theparaterminal gyrus

Central-lateral

Insula, hippocampus, amygdala, andentorhinal cortex

The cisternal segment is often involved andbest depicted using coronal T2-wieghted imageswith high in-plane resolution (Fig. 7).

Selected Olfactory Nerve Pathologies

Meningioma of Cribriform Plate/OlfactoryGrooveMeningioma of cribriform plate/olfactory grooverepresent about 12% of all basal meningiomas andmay present with olfactory impairment (Fig. 8).The differential diagnosis is esthesioneuro-blastoma, which in contrast to meningiomaextends into the nasal cavity.

Traumatic AnosmiaPost-traumatic lesions often affect the anteriorskull base, hence the region of the olfactory bulband tract. Up to 20% of patients suffering fromtraumatic brain injury (TBI) exhibit olfactory dys-function. However, due to the relatively low clin-ical impact of anosmia as compared to impairmentof other CN, post-traumatic changes in CN I and

8 S. Haller et al.

resulting post-traumatic anosmia tend to remainunrecognized.

Infection/Inflammation of CN IPatients commonly remain asymptomatic as anos-mia is not perceived as disturbing. This mayexplain why infectious or inflammatory changesof CN I are rare in comparison notably to inflam-mation of CN VII and CN V. In case of infection(Fig. 9), viral infections are most likely notablyherpes varicella, yet the inciting agent oftenremains undetermined.

Anosmia in Neurodegenerative Diseases,Notably Parkinson DiseaseAnosmia is a frequent early (or even preceding)finding in neurodegenerative diseases, notablyParkinson Disease. In Alzheimer’s disease, anos-mia may be an early finding as well. However, in

both the disorders, the functional loss is not asso-ciated with a structural imaging abnormality.

Nasal Cavity Pathology: IndirectHyposmiaPathology of nasal cavity including infection,polyposis, or other obstruction of the superiornasal cavity is one of the most frequent causes ofhyposmia or even anosmia. In general, CN I isnormal in those conditions.

CN II: Optic Nerve

Clinicalpresentation

Commoncauses

Less commonbut important

Uni-ocular visionloss/visual field loss(with or withoutpain)

OpticneuritisOpticpathway

Sellar/suprasellarlesions (e.g.,macroadenoma)

(continued)

Fig. 7 The olfactory fossa (yellow arrow) and olfactory sulcus (white arrow) serve as guideline to the olfactory cortex

Fig. 8 A 51-year-old women with grade 2 olfactory meningioma presenting with headache and on examination had mildolfactory impairment only

Cranial Nerves 9

Clinicalpresentation

Commoncauses

Less commonbut important

Note: Lesions ofchiasma causingbitemporal orbinasal vision loss

gliomaOptic nervesheathmeningeomaIschemia

IdiopathicintracranialhypertensionMitochondrialdisease (Leber)

AnatomyThe CN II can be viewed as a direct extension ofthe brain rather than a cranial nerve. It issurrounded by meninges and can be divided into

four segments (Fig. 10). At the chiasm, it mergeswith the contralateral CN II. The fibers of the nasalretinal hemisphere cross to the other side. As aconsequence, beyond the chiasm, the optic tractsconvey the homonymous visual information ofthe ipsilateral retinal hemisphere, i.e., the contra-lateral visual hemifield. The chiasm itself lies justanterior to the pituitary stalk. Through the optictract, most fibers then reach the lateral geniculatenucleus, and a smaller branch goes to the superiorcolliculus. From the lateral geniculate, fibersreach the primary visual cortex around thecalcarine sulcus via the ophthalmic radiation.The more anterior extension in the temporal lobeis called Meyer’s loop and lesions or resectionscause a supero-lateral field defect (pie-in-the-sky).

Segments of CN II

Intra-ocular Retinal nerve fibers exit the ocular globevia lamina cribrosa sclerae, length�1 mm

Intra-orbital Back of the olfactory globe to orbitalapex, length 20–30 mm; covered bythree meningeal layers, surrounded byCSF connecting to suprasellar cistern;central retinal artery (first branch ofophthalmic artery) and vein enter theoptic nerve around 10 mm posterior toglobe

Intra-canalicular

Bony optic canal, length 4–9 mm,ophthalmic artery inferior to CN II, Duraof CN II fuses with the orbital periost(periorbita)

Cisternalsegment

From optic canal to chiasm, covered bypia mater and surrounded by CSF, length�10 mm

Fig. 10 Normal anatomy of CN II. Composite 3DT2image of CN II illustrating intra-ocular, intra-orbital,intra-canalicular, and cisternal segments

Fig. 9 A 54-year-old man presenting with progressiveanosmia. Slight T2 hyperintense signal of olfactory bulb,and contrast enhancement, suggestive neuritis of CN1

(presumably due to herpes varicella). Coronal T2w (a),coronal reconstruction of 3DT1 without (b) and with(c) Gad

10 S. Haller et al.

Common Optic Nerve Pathologies

Optic NeuritisOptic neuritis or inflammation of CN II occursmost frequently in the context of multiple sclero-sis (MS), and frequently is the presenting symp-tom with subacute unilateral loss of vision andpainful eye movement in a relatively youngpatient (Fig. 11). Optic neuritis commonly in theposterior canalicular or cisternal portion is also akey finding in neuromyelitis optica spectrum dis-order (NMOSD, Fig. 12), due to autoantibody to

aquaporin 4 (AQP4) or myelin oligodendrocyte-associated glycoprotein (MOG).

From a radiological point of view, there are aseveral features that may contribute to the differ-entiation of optic neuritis in MS versus NMOSD.In MS, optic neuritis is more likely focal in oneoptic nerve segment. In NMOSD, optic neuritis ismore likely longitudinally extensive (as in thespinal cord) involving at least two optic nervesegments, more likely to be bilateral and toinvolve the optic chiasm (especially in AQP4-antibody positive NMOSD). In older subjectswith cardiovascular risk factors, ischemic optic

Fig. 11 Active optic neuritis in a 36-year-old woman with MS. Note the hyperintense signal of the intra-orbital segment ofthe left CN II on coronal T2 fat-sat (a) associated with contrast enhancement on coronal T1 Gad fat-sat (b)

Fig. 12 A 34-year-old woman presenting withneuromyelitis optica (NMO). Over a short period of time,she presenting with bilateral optic neuritis and paraplegiadue to transverse myelitis. Note hyperintensity of both optic

nerves on STIR (compared to normal white matter), with amore swollen aspect on the more recently affected right sideand extensive Gad-enhancement of the spinal cord

Cranial Nerves 11

neuropathy should be considered as alternativediagnosis (see chapter ▶ “NMOSD”).

Optic Pathway GliomaAlso referred to as optic glioma or optic nerveglioma, the term optic pathway glioma bestreflects the fact that optic glioma can extend intothe chiasm and optic tract. Optic pathway gliomasoccur most frequently in children and are associ-ated with neurofibromatosis type I (NF 1), whichoften presents bilaterally (Fig. 13).NFI-associated gliomas are less frequent, yetcommonly more aggressive in adults and tend tobe located more anteriorly, while sporadic opticpathway gliomas more commonly affect the chi-asm and retro-chiasmatic pathway. Visual dys-function is the most frequent clinicalpresentation. Extension of the tumor into thehypothalamus may result in polyuria/polydipsia,obesity, sexual precocity, and endocrinedysfunction.

Optic Nerve Sheath MeningiomaOptic nerve sheath meningioma is a benign tumorand represents approximately 10–30% of orbitaltumors. In most cases, an optic nerve sheathmeningioma is sporadic (with a female predomi-nance) and may extend intracranially. Althoughmost cases are sporadic, patients with neurofibro-matosis II (NF 2) are at an increased risk. Painlessand progressive visual loss is the most frequent

clinical symptom in up to 95% of cases. Notablyat later stages, proptosis may also occur (Fig. 14).

Optic Nerve Acute IschemiaOptic nerve ischemia is rare, and typically occursin patients with important vascular risk factors.The most vulnerable zone of the optic nerve is justposterior to the globe. However, due to the smallsize, motion, and susceptibility artifacts, standardbrain diffusion MRI is negative in most cases(Fig. 15), even when using focused or zoomeddiffusion techniques. Restricted diffusion as evi-dence for acute optic nerve ischemia can beestablished only in a minority of cases, and non-specific hyperintensity on FLAIR/T2 may be theonly finding.

Cranial Nerves for Eye Movements(CN III, IV, VI)

Clinicalpresentation Most common causes

Lesscommon butimportant

DoublevisionEyemovementdisorder

Aneurysm (Pcom);diabetic neuropathy;brain stem ischemia;inflammatory lesions;cavernous sinus lesion(aneurysm, Tolosa-hunt, cavernous sinusinvasion, perineuralspread)

Infection/inflammationTraumaIgG4 diseaseSkull basetumors

Fig. 13 A 22-year-old patient presenting with NF1 andbilateral optic pathway glioma. Note the enlargement ofCN II notably in the cisternal segment of CN II without

significant enhancement with enlargement of the chiasmand extension into the optic tracts. Note the typical lack ofenhancement (right)

12 S. Haller et al.

http://link.springer.com/search?facet-eisbn=978-3-319-61423-6&facet-content-type=ReferenceWorkEntry&query=``NMOSD��

Normal AnatomyThe oculomotor nerve CN III is a mixed nerveincluding motor and parasympathetic function(Fig. 16). The accessory oculomotor nucleus(Edinger–Westphal nucleus) is a rostral compo-nent that provides preganglionic parasympatheticinnervation of the pupil. CN III innervates four ofthe six eye muscles (superior rectus, medial rec-tus, inferior rectus, and inferior oblique muscles),as well as the levator palpebrae superior muscle.The trochlear nerve CN IV is a pure motor nerveinnervating the superior oblique muscle (Fig. 17).The abducens nerve CN VI is a pure motor nerveinnervating the lateral rectus muscle (Fig. 18). Themedial longitudinal fascicle connects the nuclei ofCN VI and CN III. Pathological processes

disrupting these fibers (e.g., MS lesions anteriorto the 4th ventricle) cause a so-called intranuclearophthalmoplegia (INO) with failure to adductwhen looking at the contralateral side.

CN III segments

Nucleus andmedullary

Two mesencephalic nuclei at the levelof the superior colliculus

Oculomotor nucleus: superior,medial, and inferior rectus, andinferior oblique muscles

Edinger–Westphal nucleus:parasympathetic fibers to the eye viathe ciliary ganglion; sphincterpupillae muscle (pupil constriction),and ciliary muscle (accommodation)Fibers travel anteriorly through thered nucleus

(continued)

Fig. 15 Optic nerve ischemia in an 82-year-old womanwith acute onset mono-ocular vision loss. Note restricteddiffusion (left), reduced ADC (middle), and beginning T2

FLAIR hyperintensity (right) in the proximal orbitalsegment

Fig. 14 A 56-year-old female patient presenting with optic nerve sheath meningioma. Circular enhancement around theleft optic nerve on coronal (left) and “tram track” sing on axial (right) 3DT1 fat-sat Gad-enhanced images

Cranial Nerves 13

CN III segments

CN III emerges into theinterpeduncular cistern

Cisternal Antero-lateral trajectory ininterpeduncular and prepontinecistern, between PCA (cranial) andSCA (caudal)

Cavernous Most cranially located nerve in thecavernous sinus

Orbital Passes through superior orbital fissureinto the orbit

(continued)

CN III segments

Superior branch: smaller, passesmedially over the optic nerve,supplies the superior rectus andlevator palpebrae superioris

Inferior branch: larger, supplies themedial rectus, inferior rectus, andinferior oblique muscles, andbranches to the lower part of theciliary ganglion

Fig. 16 Schematic drawing of the oculomotor nerve in themesencephalon and its peripheral course and compositeMR image (axial oblique, coronal oblique, and sagittaloblique reconstructions of 3DT2 post-Gad) illustrating

CN III including cisternal, cavernous, and orbital seg-ments. Note the typical anatomic location/course of CNIII between the PCA and the SCA

Fig. 17 The trochlear nerve is the only nerve that exitsfrom the posterior aspect of the brainstem and after cours-ing through the ambient cistern, runs closely along CN IIItoward the cavernous sinus and superior orbital fissure

cranial nerves. Right: 27-year-old woman with NF-2. Onsurveillance MRI, a neurinoma was found dorso-laterallyto the mesencephalon, which can only arise from the troch-lear nerve

14 S. Haller et al.

CN IV segments

Nucleus andmedullary

Small nucleus immediately below andposterior to motor nucleus of CN IIICourses posteriorly, crossingcontralaterally in the velum medullaresuperior, and then emerges posteriorlybelow the inferior colliculus

Cisternal Courses laterally and then anteriorlyin the ambient cistern immediatelyinferior to the tentorium (subtentorialsegment)

Cavernous Just inferior to CN III in cavernoussinus

Orbital Passes through the superior orbitalfissure into orbit to innervate thesuperior oblique muscle

CN VI segments

Nucleus andmedullary

Near floor of 4th ventricle. Theintramedullary segment passesanteriorly through the pons and exitsat the ponto-medullary junction intothe prepontine cistern. Nucleussurrounded by the geniculum (internalknee) of CN VII

Cisternal Oblique trajectory in antero-superiordirection, then enters into Dorello’scanal located in a dural fold behind theclivus

Cavernous Continues over the medial petrousapex into the cavernous sinusmedially to CN V1 and V2 and justinfero-laterally to the ICA

Orbital Passes through superior orbital fissureinto the orbit and innervates the lateralrectus muscle

Selected CN III, IV, and VI Pathologies

Focal Lesions of Brainstem NucleiFocal lesions of brainstem nuclei including vas-cular lesions (Fig. 19) or inflammatory lesions(notably in MS) may affect CNs III, IV, and VI.

NeoplasmSchwannomas rarely affect CN III, IV, and VI(Fig. PP). Primary tumors include brainstem gli-oma (especially in children). Secondary neo-plasms include perineurial tumor spread andlymphoma.

Neurovascular CompressionNeurovascular compression syndromes (NVCSs)most commonly affect CNVand VII, yet may alsoaffect CN III, VI (Fig. 20), VIII, IX, and X.

CN V: Trigeminal Nerve

Normal AnatomyThe trigeminal nerve CN V is the largest and oneof the most complex cranial nerves (Figs. 21 and22) with three branches, called ophthalmic nerve(V1), maxillary nerve (V2), and mandibular nerve(V3). It has a large sensory component for the skinof the face. It has a motor component for mastica-tion and a parasympathetic component includingtaste. CN V has three sensory and one motor

Fig. 18 Abducens nerve (CN VI). Schematic drawing(left) shows the facial geniculum around the CN VInucleus in the tegmentum of the pons. MR images showing

cisternal segment of CN VI including the entry intoDorello’s canal in axial (middle) and sagittal (right) planes

Cranial Nerves 15

Fig. 19 A 63-year-old manpresenting withhypertension with CN VInuclear infarct. Hedeveloped acute-onsetabducens nerve palsy. MRIrevealed extensivesupratentorial white matterlesions, an old cerebellarinfract, and a left pontinelesion with diffusionrestriction at the location ofthe abducens nucleus

Fig. 20 A 72-year-old man presenting with intermittentabducens paresis due to a neurovascular contact betweenthe AICA and the cisternal segment of CNVI. The AICA is

seen just above CN VI in sag/axial/coronal CISS images(from left to right)

Fig. 21 Left: Schematic drawing of the CN V with itsthree branches and related foramina. Right: Coronal T1-wimage after Gad administration going from dorsal (top-left)

to ventral (bottom right), showing Meckel’s cave, cavern-ous sinus, and exiting V3 and V2 branches through fora-men ovale and rotundum

16 S. Haller et al.

brainstem nucleus and peripherally interconnectswith cranial nerve VII.

CN V segments

Nuclear Three sensory (from spinal tomesencephalic) and one motornucleus

Intramedullary Runs obliquely to exit at the mid ponsanteriorly

Cisternal Somatotopic arrangement; V1 top, V2middle, V3 bottom

Meckel’s cave The CN V splits into the threesegments in the ganglion of Gasser.Note that V1 and V2 continues into thecavernous sinus, while V3 runsinferiorly without entering into thecavernous sinus

CN V divisions (Fig. 22)

V1 orophthalmic

Courses anteriorly in the lateral wall ofthe cavernous sinus inferior to CN IVwith meningeal, lacrimal, frontal, andnasociliary branches

V2 ormaxillary

Courses anteriorly in the lateral wall ofthe cavernous sinus below V1 withinfraorbital, inferior palpebral, nasal, andzygomatic branches

V3 ormandibular

Courses inferiorly through the foramenovale to enter the infratemporal fossawith masticatory, sensory buccal andauriculotemporal branches, lingualnerve, and inferior alveolar nerves

Selected Trigeminal Nerve PathologiesClinicalpresentation Common causes

Less common butimportant

HypesthesiaTrigeminusneuralgia

NVCS/trigeminalneuralgiaInfectious/inflammatoryCompression(meningioma)Schwannoma

Perineural tumorspread

Neurovascular Compression SyndromeNeurovascular compression syndrome (NVCS) iscaused in general by a direct contact of an arteryand a cranial nerve. Note that a neurovascularcontact is a frequent imaging finding, and notalways pathologic. The transition zone (TZ)between central and peripheral myelin of CN Vis the site of highest mechanical vulnerability;consequently most symptomatic NVCS occur inthe area of the TZ, which is in the region of theroot exit zone of CN V (Fig. 23). Deformation ofthe TZ by an adjacent artery and local atrophy arethe most specific imaging signs suggesting asymptomatic NVCS.

NeoplasmSchwannoma is a primary neoplasm affecting theCN V (Fig. 24). Secondary neoplasms includeperineural tumor spread.

Fig. 22 CNV segments of V1 ophthalmic division, V2 maxillary division, and V3mandibular division with their relatedforamina and distal branches

Cranial Nerves 17

CN VII: Facial Nerve

Clinicalpresentation

Most commoncauses

Less commonbut important

Hemifacial spasmCentral/peripheralfacial nerve palsy

Neoplasm(schwannoma)Inflammatory(Bell’s palsy)TraumaNeurovascularcompression

Perineuraltumor spreadParotid glandlesions

Normal AnatomyThe facial nerve CN VII is located superiorly andanteriorly in the internal acoustic canal (Fig. 25)and has three major functions: motor innervationof muscles for facial expression, posterior belly ofdigastric, stylohyoid, stapedius; sensory innerva-tion of the taste to anterior two-thirds of tongue;and parasympathetic innervation of submandibu-lar gland, sublingual gland, and lacrimal glands.CN VII is the only cranial nerve that may shownormal postcontrast enhancement only in thegeniculate ganglion segment.

CN VII segments

Nuclear Three brainstem nuclei: motor, visceral,sensory

Medullary Facial colliculus (due to the geniculumaround nucleus of CNVI) in the floor of4th ventricle

Cisternal Merges with nervus intermedius shortlyafter exiting

Meatal(canalicular)

Superior and anterior portion of internalauditory canal

Labyrinthine From internal auditory canal togeniculate ganglion

Tympanic From geniculate ganglion to pyramidaleminence

Mastoid From pyramidal eminence tostylomastoid foramen

Fig. 23 Neurovascular conflict between left CNVand leftAICA in a 48-year-old woman with left-sided trigeminalneuralgia. Note the neurovascular contact in the vulnerable

root entry zone of the proximal cisternal segment of CNV. In this case, the AICA is located between the CN V(lateral) and the pons (medial)

Fig. 24 A 54-year-old man presenting with trigeminalschwannoma. This diabetic patient presenting with sensorydisturbances relating to the 1st and 2nd branch of thetrigeminal nerve and abnormal corneal reflex. Note adumbbell-shaped lesion centered on Gasser’s ganglionextending into an enlarged Meckel’s cave

18 S. Haller et al.

Selected CN VII Pathologies

NeoplasmsPathologies affecting the facial nerve includeintrinsic neoplasms (facial nerve schwannoma).Extrinsic neoplasms are more common such asvestibulocochlear schwannoma, meningioma, orcavernous hemangioma causing compression ofthe facial nerve. Neoplasms arising from theparotid gland may show perineural spread intomastoid segment. Within the basal cisterns, carci-nomatous meningitis or rarely lymphoma mayaffect the nerve.

Schwannomas arise from sensory fibers of CNVII as solitary (geniculate ganglion > intrameatal> parotid) or skip lesions along the course of thefacial nerve. These neoplasms are rare and in theinternal auditory meatus need to be distinguishedfrom the much commoner vestibulocochlearschwannomas.

Hemangioma is an extra-neural vascular neo-plasm (malformation) arising from the capillaryplexus at the geniculate ganglion > tympanic >intra-meatal segment. Theymay be very small andcause VII palsy or hemifacial spasm; typical ismild enhancement for all types, with cancellousbone density in the ossifying variant (Fig. 26).

InflammationBell’s palsy (unilateral idiopathic facial paralysis)is probably mostly due to viral infections such asherpes simplex virus, herpes zoster, EBV, orCMV. Facial nerve involvement can be demon-strated using Gad T1 fat-sat images (Fig. 27). Incase of herpes zoster, additional cranial nervesinfection may be present such as the trigeminal(V) or vestibulo-cochlear nerve (VIII). Additionalinvolvement may be visible at the geniculate gan-glion, proximal tympanic segment, and – typicalfor herpes zoster – in further cranial nerves such asthe trigeminal nerve.

Fig. 25 Schematic drawing (left) and radiographic anat-omy (right) of the nerves in the internal acoustic canal. Therelationship of the facial, acoustic, and sup/inf vestibular

nerves is best shown in oblique/sagittal plane (right lowerpanel) with the facial nerve in antero-superior position

Fig. 26 T1 Gad (left), CT (right): ossifying hemangioma of facial nerve

Cranial Nerves 19

TraumaTemporal bone fractures occur as labyrinth cross-ing – transverse – fractures or labyrinth sparingfractures traditionally called “longitudinal” frac-tures. While transverse fractures constitute about10–30% of temporal bone fractures, complica-tions are common leading to sensorineural hear-ing loss in 50–100% and facial nerve palsy inabout 50%. Common observations on imagingare fracture lines crossing the cochlea onCT. Only MR enables identification of ahematolabyrinth and/or a hematoma along thetympanic segment of the facial nerve once a frac-ture line crosses the labyrinth and facial nervecanal.

Neurovascular Compression Syndrome(NVCS)Hemifacial spasm maybe caused byneurovascular compression of the facial nerve.The incidence of neurovascular compression syn-dromes is linked to the length of the root entryzone formed by the TZ between central – oligo-dendroglia – and the peripheral Schwann cellmyelination; a combination of a focal defect ofinsulation at the transition zone and compressionby a vessel are mandatory to identify aneurovascular conflict. High-resolution 3D T2gradient echo sequences preferentially combinedwith TOF MR-angiography need to focus ondelineation of a vascular compression in theexpected location of the transition zone (5–7 mmafter exiting the brainstem). Causative vessels arethe AICA in 50%, PICA in 21%, vertebral arteryin 3%, and a combination of the aforementioned

vessels in 25%. Fusion images of T2 gradientecho and MRA images provide enhanced visual-ization of the degree of vascular indentation at thetransition zone (Fig. 28).

CNVIII: Vestibulocochlear Nerve

Clinicalpresentation Most common causes

Lesscommon butimportant

Hearing loss(cochlearis)Tinnitus(cochlearis)Vertigo(vestibularis)

CongenitalNeoplasm(schwannoma/neurinoma,meningioma)TraumaNeurovascularcompression

HydropsMeniereTraumaInfection

AnatomyThe vestibulocochlear nerve receives afferent sen-sory input by two different bipolar neurons: thecochlear nerve and the vestibular nerve (Fig. 25).Cochlear cell bodies (spiral ganglion) are locatedalong the modiolus and axons constitute the audi-tory portion of eighth cranial nerve. Vestibular cellbodies (= ganglion of Scarpa) are composed of asuperior division (fibers form superior and lateralsemicircular canal, utriculus) and an inferior divi-sion (fibers from utriculus and posterior semicir-cular canal) which unite with the cochlear divisionwithin the internal auditory canal to form thevestibule-cochlear nerve. The transition zonebetween central (oligodendroglia) provided

Fig. 27 Gad-enhancement of geniculate and tympanic segments in Bell’s palsy

20 S. Haller et al.

myelination and Schwann cell myelin is locatedwithin the internal auditory canal.

CN VIII segments

Nuclear Near the pontomedullary junction,close to lateral recess of fourthventricle, connecting to ipsilateralflocculonodular lobe, the eyes via themedial longitudinal fasciculi, andspinal cord via vestibulospinal tracts

Cisternal Crosses the CPA to enter the brainstemat the ponto-medullary junction lateralto the facial and intermedius nerve

Meatal(canalicular)

Cochlear nerve: inferior and anterior.Superior vestibular nerve: superior andposterior. Inferior vestibular nerve:inferior and posterior (Fig. 25)

Selected CN VIII Pathologies

CongenitalMalformation of the inner ear encompasses aspectrum from absence to slight hypoplasia ofthe cochlea, vestibule, and semicircular canals.The vestibulo-cochlear nerve may be absent in anarrow internal auditory canal. Oblique sagittalreformatted thin section T2 gradient-echo images(Fig. 25) are best suited to depict the contents ofthe internal auditory meatus. In case of absence ofCN VIII, a single nerve – the facial nerve – is theonly structure in a narrow canal (Fig. 29). In lesssevere malformations, only divisions such as thecochlear portion maybe affected in an otherwisenormal vestibulo-cochlear nerve (Fig. 29).

Fig. 29 Cochlear and vestibular nerve aplasia with only CN VII visible in a narrow internal auditory meatus (left) andhypoplasia of the cochlear division of the vestibulo-cochlear nerve (right)

Fig. 28 (a–c) Fusion MPR of T2 and MRA in the coronal(left) and sagittal (mid) plane at the point of vascularconflict with the facial nerve origin. Volume rendering of

MRA (right) shows indentation of the right facial nervetransition zone by an elongated upward directed loop of theright vertebral artery

Cranial Nerves 21

NeoplasmsVestibulo-cochlear schwannomas are benignencapsulated neoplasms arising anywhere alongthe vestibulo-cochlear nerve beyond the glia –Schwann cell transition; the majority areintrameatal. When small, the nerve of originmaybe determined based on high-resolutionaxial and sagittal T2 gradient echo images; 90%of intrameatal neoplasms arise from the vestibularportion. A superior vestibular origin is likelywhen the neoplasm is above the falciform crestwith contact to the facial nerve, and there is pre-dominantly superior contrast location in the coro-nal plane. Inferior vestibular origin is likely in asmall neoplasm located below the falciform crestand inferior location on coronal images (Fig. 30).

Larger vestibulo-cochlear schwannomas(Fig. 31) tend to display variable extension intothe cerebello-pontine angle (CPA). Exclusively cis-ternal location is rare. Bilateral vestibulocochlearschwannomas are a strong indicator for Neurofi-bromatosis type 2.

Checklist for reporting of vestibularschwannoma include:

• The exact location of the neoplasm and size ofthe tumor

• Relation to facial nerve in case of cisternalneoplasm

• Extension toward the fundus of the internalauditory canal (lack of apical “CSF cap”)

• Inner ear involvement (decreased T2 peri-lymph signal or enhancement)

• Medial extension with contact or compressionof the brainstem

• Deformation of the 4th ventricle or ventricularenlargement

Intralabyrinthine schwannomas arise fromneural elements within the membranous labyrinthand in 80% are intracochlear, 15% areintravestibular while only a minority extendsfrom the fundus into either the cochlear of vestib-ular portion of the labyrinth.

Meningiomas are the second most commonneoplasms in the CPA comprising approximately10–15% of CPA tumors. Arising from arachnoidcaps cells, meningiomas may originate from the

Fig. 30 Left: Composite image of axial T2, coronal T1Gad enhanced, and sagittal oblique MPR: intrameatalschwannoma arising from the superior vestibular portionwith contact to the facial nerve sparing the cochlear nerveand inferior vestibular division on sagittal oblique images.

Right: Composite image of axial T2, coronal T1 Gad, andsagittal oblique MPR: intrameatal schwannoma arisingfrom the inferior vestibular portion with contact to thecochlear nerve and superior vestibular segment

22 S. Haller et al.

posterior wall of the petrous bone, the tentorium,or the dural circumference of the internal auditorycanal. Rarely, meningiomas arise purely withinthe internal auditory meatus or even the labyrinth.

Manifestations of CPA meningiomas includean eccentric origin to the internal auditory canal ora mushroom-like appearance with the meningi-oma crossing of the porus (Fig. 32).

Fig. 32 Thin section T2demonstrating the threemost common variants ofmeningiomas of thecerebellopontine angle.Top: eccentric from theposterior porus or dorsalpetrous bone surface;middle: mushroom-likecrossing of the porus;bottom: internal auditorymeatus meningioma

Fig. 31 Axial T2 (left) and T1 Gad (right): Classical intrameatal schwannoma with extension into the CPA but sparingthe fundus. Extension along the superior vestibular portion is visible on the axial T2 image

Cranial Nerves 23

Meningeomas may have a hemispherical appear-ance but with a broad dural attachment. Bluntangles toward the temporal bone surface are indic-ative of a meningioma rather than the acute anglethat is typical for vestibulo-cochlear schwannomas.Hyperostosis may be present at the dural attach-ment site. Meningiomas that arise eccentric dis-place the vestibulo-cochlear and facial nervetoward the neoplasm’s periphery. A rare variant isa meningioma which arises from the internal audi-tory canal dura and fills the meatus mimicking avestibulo-cochlear schwannoma. A distinguishingfeature is the complete loss of CSF space within theinternal auditory meatus in a neoplasm that onlyslightly exceeds the limits of the porus and thetendency for blunt angles outside the porus.

Carcinomatous MeningitisThis frequently affects both vestibulo-cochlearand facial nerves and presents bilaterally(Fig. 33). Additional cranial nerves such as thetrigeminal nerve, oculomotor, or caudal cranialnerves may be involved as well. On imaging,additional cerebral metastases andleptomeningeal contrast enhancement may be pre-sent. The differential diagnosis encompassesinfectious and granulomatous diseases.

CN IX: Glossopharyngeal Nerve

AnatomyThe glossopharyngeal nerve harbors efferentmotor (stylopharyngeus and middle constrictormuscle), autonomic efferent fibers (parotidglands), afferent fibers (taste posterior 1/3 oftongue), and somatosensory afferent components(pharynx, tonsil, soft palate, posterior 1/3 oftongue, external ear) (Fig. 34).

Cranial nerves of the jugular foramenIX, X and XI

Clinicalpresentation Most common causes

Lesscommonbutimportant

Commonly minorclinical symptomsonly, e.g.,glossopharyngealneuralgia for CNIX

Skull base neoplasms(Schwannoma/neurinoma,meningioma)Jugular foramenlesions (e.g.,paraganglioma,NVCS, schwannoma,neurinoma,meningioma)

TraumaExtra-cranialmasses

CN IX: branches

Tympanic branch (=Jacobson nerve)

Via tympanic canaliculusto middle ear tympanicplexus ! lesser petrosalnerve

(continued)

Fig. 33 CoronalGad-enhanced T1:carcinomatous meningitiswith bilateral lesions withinthe internal auditory canaland along the trigeminalnerve arising fromcarcinoma of the breast

24 S. Haller et al.

CN IX: branches

Pharyngeal nerve withvagal nerve andsympathetic plexus

Pharyngeal plexus onmiddle constrictor muscle

Stylopharyngeus branch Tonsillar + lingual branch

Imaging AnatomyCN IX: segments

Nucleus Inferior salivatory nucleus in therostral medulla, spinal trigeminalnucleus, and caudal solitariusnucleus

Cisternal The glossopharyngeal nerve arisesfrom the retro-olivary sulcus of themedulla oblongata with 3–4 rootletsthat unite to form theglossopharyngeal nerve within thecerebello-medullary cistern to enterthe vascular portion of the jugularforamen

Foraminal andextraforaminal

Between the internal jugular vein(IJV) and internal carotid artery(ICA) along stylopharyngeusmuscle to terminate deep to thestylohyoid ligament and posteriorborder of hyoglossus muscle

CN X: Vagal Nerve

The vagal nerve is closely related to theglossopharyngeal nerve both anatomically andfunctionally. It arises just caudal to theglossopharyngeal nerve from the retro-olivarysulcus of the dorsolateral medulla oblongata byabout 10 rootlets that combine to create the cister-nal segment of the vagal nerve. The vagal nerveincludes axons which are closely related to thecentral portion of CN IX.

CN X: segments

Nucleus Nucleus ambiguus in the medulla (motorcontrol pharynx and larynx), dorsalnucleus in the floor of the fourth ventricle(visceral efferent to thorax and abdomen),spinal trigeminal nucleus (sensory ear andtympanic membrane), nucleus solitarius(visceral afferents including forbaroreception and gustation)

Cisternal A series 8–10 rootlets traverses thecerebello-medullary cistern laterally tocross the jugular tubercle and enter thejugular foramen

Jugularforamen

CN X exits the skull through the parsnervosa of the jugular foramenanteromedial to the jugular vein in acommon dural sheath with CN XI

(continued)

Fig. 34 Left: Schematic drawing of the lower cranialnerves and the jugular foramen. Right: Axial T2 and cor-onal MPR demonstrate cisternal segment of

glossopharyngeal nerve arising from the medullaoblongata entering the jugular foramen below the level ofthe internal auditory canal

Cranial Nerves 25

CN X: segments

The inferior petrosal sinus is a landmarkthat courses infero-laterally between thedescending portion of theglossopharyngeal nerve anteriorly and thevagal and accessory nerves posteriorly

CN XI: Accessory Nerve

The accessory nerve arises from the upper cervicalsegments of the spinal cord with a spinal root andreceives variable contribution from the dorsolat-eral surface of the medulla oblongata (cranialroot). The spinal rootlets and cranial rootlets – ifexistent – unite before entering or within the jug-ular foramen.

CN XI: segments

Nucleus Arises from a column of ventral horn cellswithin the upper five segments of thecervical spinal cord, just caudal to thenucleus ambiguus

Cisternal Ascending spinal cisternal segment joinsCN X into vascular portion of jugularforamen. Due to the ascending course inits cisternal segment, the CN XI isdifficult to identify

Jugularforamen

CN XI leaves the jugular foramenbetween internal carotid artery and veinposterior to vagal nerve

Selected Pathologies of CN IX to XI

Neurovascular Conflict of CN IXNeurovascular conflict of CN IX manifests asglossopharyngeal neuralgia which is defined asparoxysmal episodes of pain that are localized tothe base of the tongue, the tonsil, or the externalear and angle of the jaw. The clinical diagnosis ismore difficult than for “typical” trigeminal neu-ralgia or hemifacial spasm, and imaging isrequired to rule out a neoplasm within the phar-ynx, a lesion or anatomic variant below the skullbase (e.g., Eagle syndrome with symptomatic pro-longation of the styloid process) or within theCPA or skull base. As in trigeminal neuralgiaand hemifacial spasm, asymptomatic contact of avessel with the glossopharyngeal nerves is com-mon. Deformation of the CN IX at the transitionzone (

the adventitia of the jugular bulb. Tumors arehighly vascular and harbor flow voids or displayintratumoral vessels (Fig. 36). Because of insidi-ous growth, erosion of the adjacent hypotympanicbone plate, and infiltration of the tympanic cavity,the infralabyrinthine petrous bone and extensionalong the carotid foramen is commonly observed.A time-resolved 4D MR-angiography may depictthe degree of vascularization and depict the col-lateral supply ipsilateral to the tumor location.

Due to its infiltrative nature of paragangliomas,the cranial nerves IX to XI are invariably involvedrendering tumor resection challenging. The pres-ence of preoperative lower cranial nerve deficits isdirectly proportional to the size of paraganglioma.Among the lower cranial nerves, theglossopharyngeal nerve is most commonlyaffected. Postoperative cranial nerve deficit

occurs in 50% of patients. Intracranial intraduralextension is an unfavorable sign, as is anteriorextension along the petrous segment of the inter-nal carotid artery toward the foramen lacerum.

Hypoglossal Nerve XII

Clinicalpresentation

Most commoncauses

Less commonbut important

Often only minorclinicalsymptoms, tongueatrophy/paralysis

Skull baseneoplasms(schwannoma/neurinoma,meningioma)Perineural tumorspreadCarotid arterydissection

Trauma/fracturesExtra-cranialmasses (e.g.,synovial cyst)

Fig. 36 Jugular foramenparaganglioma.Noncontrast TOFangiography (top) showsabnormal vessels within theenhancing tumor (middle)in the right jugular foramenwith extension (arrow) intothe tympanic cavity(bottom)

Cranial Nerves 27

AnatomyHypoglossal nucleus: general somatic efferentfibers supply the muscles of the tongue (extrinsicand intrinsic). The hypoglossal nerve originates inthe preolivary sulcus, between the olive and thepyramid by 10–15 rootlets which coalesce into2 roots and join in the hypoglossal canal (Fig. 37).

CN XII: segments

Nucleus Located in the paramedian floor, the 4thventricle along the majority of the dorsalmedulla (hypoglossal eminence),medially adjacent to the dorsal motornuclei of CN X

Cisternal 10–15 rootlets fuse to 2 roots within thepre-medullary cistern anterolaterally,between the vertebral artery and thePICA to reach the canalicular segment

(continued)

CN XII: segments

Canalicular Roots unite in the hypoglossal canal andconnect to ventral rootlets of 1st cervicalnerve

Extracranial Deep to the internal carotid arteryanterior to the vagal nerve

Selected PathologiesIn patients who present with CN XII palsy leadingto atrophy of the tongue muscles (Fig. 38), neu-roimaging studies are mandatory in order toexclude tumors, spontaneous or traumatic vascu-lar causes, or compression of the nerve in thepremedullary cistern at the level of the hypoglos-sal canal and below the skull base.

Fig. 37 Axial Gad-enhanced T1 renders the hypoglossal nerve visible within the vascular plexus of the hypoglossalcanal inferiorly and medial to the jugular foramen

Fig. 38 A 51-year-old man presenting with hemi-atrophyof tongue (fatty degeneration on the left) due to CN XIIcompression. This previously healthy man presenting with

difficulties with swallowing over 2 weeks. MRI revealed amass at the right lower skull base extending into the hypo-glossal canal (middle/right), most likely a chondrosarcoma

28 S. Haller et al.

MeningiomaMeningiomas arising from the foramen magnum,the jugular tubercle, or adjacent to the jugularforamen may affect the hypoglossal canal aswell. Lower cranial nerve palsy, however, isuncommon. The “en-plaque” variant (Fig. 39) ismore likely to cause lower cranial nerve palsy byinfiltration of the hypoglossal canal or jugularforamen as brainstem or cerebellar compressionis missing or occurs late in the course.

Perineural Tumor ExtensionNot to be mistaken for a schwannoma is peri-neural tumor extension. Though it rarely affectsthe hypoglossal nerve, direct extension is a com-mon pathway by a tumor that arises within thenasopharynx and via the fossa of Rosenmüller orhiatus Morgagni gets access to the post-styloid

parapharyngeal space. Squamous cell carcinoma,adenoid cystic carcinoma, and lymphoma are themost common neoplasms. Extension into thehypoglossal canal effaces the linear contour ofthe hypoglossal nerve (Fig. 40) that usually ren-ders the nerve visible within its intracanalicularcourse (“target sign”).

Internal Carotid Artery DissectionHypoglossal nerve palsy is an uncommon but welldescribed complication of internal carotid arterydissection (Fig. 41). As the hypoglossal nerveexits the hypoglossal canal, and passes betweenthe internal jugular vein and internal carotidartery, it is vulnerable to compression from ahigh internal carotid artery dissection.

Fig. 40 Nasopharynx carcinoma with infiltration towardthe carotid space and into the hypoglossal canal. Axial(left) and coronal (right) Gad-enhanced T1 at the level of

the hypoglossal canal depicts leading to loss of normalvisibility of the hypoglossal nerve within the enhancingplexus (normal “target sign” on the left)

Fig. 39 Patient with hypoglossal compression andEustachian tube dysfunction due to “en-plaque” meningi-oma at the level of the hypoglossal canal on the left with

dural thickening on axial gad-enhanced T1 (left) and oblit-eration of the hypoglossal canal, with causing scleroticbone changes of the lateral skull base on coronal CT (right)

Cranial Nerves 29

Suggested Reading

Casselman J, Mermuys K, Delanote J, Ghekiere J,Coenegrachts K. MRI of the cranial nerves – morethan meets the eye: technical considerations andadvanced anatomy. Neuroimaging Clin NAm. 2008;18(2):197–231.

Leblanc A. The cranial nerves. Anatomy, imaging,vascularisation. Vienna: Springer; 1995.

Naidich T. Cranial nerves: intra-axial and cisternal seg-ments. In: Duvernoy’s atlas of the human brain stemand cerebellum. Vienna: Springer; 2009.

Fig. 41 A 37-year-old female presenting with hypoglos-sal paresis and Horner syndrome due to carotid dissection.Axial T2 at the level of the hypoglossal canal (top-left) and

C1-level (lower-left) show narrowing of vessel lumen dueto hematoma lateral to hypoglossal canal. The mural hema-toma is better seen on fat-sat T1 coronal images (right)

30 S. Haller et al.

Cranial NervesIntroductionPart 1: General ConsiderationsPerineural SpreadCavernous Sinus PathologiesImaging RecommendationsGeneralNuclear LesionsCisternal PathologyForaminal and Extraforaminal Segments

Part 2: Specific Imaging of Cranial Nerve PathologyCN I: Olfactory NerveNormal AnatomySelected Olfactory Nerve PathologiesMeningioma of Cribriform Plate/Olfactory GrooveTraumatic AnosmiaInfection/Inflammation of CN I

Anosmia in Neurodegenerative Diseases, Notably Parkinson DiseaseNasal Cavity Pathology: Indirect Hyposmia

CN II: Optic NerveAnatomyCommon Optic Nerve PathologiesOptic NeuritisOptic Pathway GliomaOptic Nerve Sheath MeningiomaOptic Nerve Acute Ischemia

Cranial Nerves for Eye Movements (CN III, IV, VI)Normal AnatomySelected CN III, IV, and VI PathologiesFocal Lesions of Brainstem NucleiNeoplasmNeurovascular Compression

CN V: Trigeminal NerveNormal AnatomySelected Trigeminal Nerve PathologiesNeurovascular Compression SyndromeNeoplasm

CN VII: Facial NerveNormal AnatomySelected CN VII PathologiesNeoplasmsInflammationTraumaNeurovascular Compression Syndrome (NVCS)

CNVIII: Vestibulocochlear NerveAnatomySelected CN VIII PathologiesCongenitalNeoplasms

Carcinomatous Meningitis

CN IX: Glossopharyngeal NerveAnatomy

Cranial nerves of the jugular foramen IX, X and XIImaging Anatomy

CN X: Vagal NerveCN XI: Accessory NerveSelected Pathologies of CN IX to XINeurovascular Conflict of CN IXJugulotympanic Paraganglioma

Hypoglossal Nerve XIIAnatomySelected PathologiesMeningiomaPerineural Tumor ExtensionInternal Carotid Artery Dissection

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