trigeminal nerve abnormality

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AJR:176, January 2001 247

he trigeminal nerve has an exten-sive anatomic course. Comprehen-

sive knowledge of trigeminal

nerve anatomy facilitates understanding of the

relationship between the brainstem, skull base,

and facial area. In our article we attempt to so-

lidify this knowledge using examples of ab-

normalities. We will describe the anatomy

from the peripheral branches toward the brain-

stem in keeping with the direction of sensory

propagation and perineural spread of malig-nant and inflammatory disease.

Peripheral D ivisions of the Trigeminal

Nerve

The trigeminal nerve trifurcates into oph-

thalmic, maxillary, and mandibular nerves

distal to the trigeminal ganglion. The oph-

thalmic nerve passes forward in the lateral

wall of the cavernous sinus. It gains access

into the orbit via the superior orbital fissure(Fig. 1). The ophthalmic nerve then divides to

supply sensation to the eyeball, lachrymal

glands, conjunctiva, part of the nasal mucosa,

skin of the nose, eyelid, and forehead [1].

The maxillary nerve exits the skull base

through the foramen rotundum ossis sphe-

noidalis inferolateral to the cavernous sinus.

It then enters the pterygopalatine fossa

where it gives off several branches. Its main

Trigeminal Nerve Anatomy: Illustrated Using Examplesof Abnormalit ies

H. A. M. Kamel

1,2

and J. Toland

3

Received August 17, 1999; acc epted aft er revi sion M arch 2, 2000.

1

Department of Neuroradiology, The Royal Victoria Hospital, Grosvenor Rd., Belfast BT12 6BA, United Kingdom.

2

Present address: Radiology Depar tment, Hamad Medical Corporation, P. O. Box 3050, Doha, Qatar. Address c orrespondence t o H. A. M. Kamel.

3

Department of Neuroradiology, Beaumont Hospital, Dublin 9, Ireland.

AJR

2001;176:247251 0361803X/01/1761247 Ameri can Roentgen Ray Society

Pictorial Essay

T

Fig. 1. Diagram shows trigeminal nerve(TGN), trigeminal ganglion, and peripheraldivisions and their branches. From fora-men rotundum ossis sphenoidalis, maxil-lary nerve (thin underline) gains access topterygopalatine fossa and continues infloor of orbit as infraorbital nerve. Inferioralveolar and lingual nerves (thick underline)are branches of mandibular nerve.


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AJR:176, January 2001

Kamel and Toland

trunk continues anteriorly in the orbital floor

(Fig. 1) and emerges onto the face as the in-

fraorbital nerve to innervate the middle third

of the face and upper teeth [1].

The mandibular nerve runs laterally along

the skull base then exits the cranium by de-

scending through the foramen ovale into the

masticator space. The motor root of the trigemi-

nal nerve bypasses the trigeminal ganglion and

reunites with the mandibular nerve in the fora-

men ovale basis cranii (Fig. 2). As the mandibu-

lar nerve enters the masticator space, it divides

into several sensory branches to supply sensa-

tion to the lower third of the face and the

tongue, floor of the mouth, and the jaw (Fig. 1).

The motor root of the mandibular nerve inner-

vates the four muscles of mastication: the mylo-

hyoid, the anterior belly of digastric, the tensor

muscle of the tympanic membranes, and ten-

sor muscle of valum palatinum [2]. Infection

and neoplasia most commonly involve the pe-

ripheral divisions of the trigeminal nerve. Direct

spread from local tumors (Figs. 3 and 4) or me-

tastases from distant malignancies are the most

common causes of malignant involvement [1].

Trigeminal Ganglion and Preganglionic

Trigeminal Nerve

The trigeminal ganglion is contained

within the Meckels cavity posterolateral to

the cavernous sinus on either side of the sphe-

noid bone. The Meckels cavity is a cere-

brospinal fluidcontaining arachnoidal pouch

protruding from the posterior cranial fossa.

Medial to the ganglion in Meckels cavity isthe internal carotid artery in the posterior por-

tion of the cavernous sinus. Inferior is the

motor root of the trigeminal nerve (Fig. 2)

and the apex of the petrous temporal with the

internal carotid artery in its bony canal [1].

The Meckels cavity can be involved either

by extrinsic or intrinsic disease. Extrinsic le-

Fig. 2. Sagittal diagram shows three peripheral divisions of trigeminal nerve entering convexity and root bundlesleaving concavity of sic kle-shaped trigeminal ganglion. Motor root (solid arrowhead) bypasses ganglion and re-

unites with mandibular nerve in foramen ovale basis crani i. Open arrow head indicates descending spinal trigeminaltrac t. Diagram also shows motor and sensory trigeminal nuclei (underline) in brainstem and cervica l cord. A, B, andC track nuclear origin of fi bers cont ributing to opthalmic; D and E, the maxillary; and F, H, and I, mandibular divisionsof trigeminal nerve.

Fig. 3. 72-year-old man with nasopharyn-

geal carcinoma. Coronal contrast-enhancedT1-weighted spin-echo MR image with fatsuppression shows enhancement and thick-ening of mandibular nerve extending intotrigeminal ganglion (arrow). Note wideningof foramen ovale basis cranii and enhancingsoft-tissue mass causing destruction of rightside of sphenoid bone.

Fig. 4. 55-year-old man with squamous cell carci-noma of skin.A, Axial T2-weighted spin-echo MR image showsthickening of skin and subcutaneous tissue of rightcheek and band of intermediate signal intensity ex-tending along course of infraorbital nerve (arrow).High signal is noted in thickened mucosa of both max-illary sinuses.B, Coronal T1-weighted spin-echo M R image after IVcontrast injection shows spread of irregular enhanc-ing mass (arrow) along infraorbital nerve. Note nor-mal mucosal enhancement in both maxillary sinuses.

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Trigeminal Nerve Anatomy


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sions, usually bony metastasis, chordoma, or

chondrosarcoma, destroy adjacent bone as

they extend toward the Meckels cavity. Intrin-

sic lesions simply expand the Meckels cavity

(Fig. 5). When the tumor is large enough, the

pressure exerted by it leads to erosion of the

surrounding bone. Tumors may also extend

away from the Meckels cavity with enlarge-ment of the foramen ovale basis cranii, fora-

men rotundum ossis sphenoidalis, or the

superior orbital fissure. Intrinsic lesions in-

clude primary tumors of the Meckels cavity as

well as secondary neoplasms from perineural

spread of local tumors, leptomeningeal, or he-

Fig. 5. 15-year-old girl w ith known diagnosis of leu-kemia.A, Expansion and reduction of normal high signal i n-tensity in Meckels cavity (arrows) on T2-weightedspin-echo MR image. Note signal void from internalcarotid artery medial to Meckel's cave.B, Coronal T1-weighted spin-echo M R image after IVcontrast injection shows bilateral Meckels cavity en-hancement (arrows), particularly of left side, as resultof leukemic deposits.

BA

Fig. 6. 29-year-old woman withpituitary adenoma. Spread oflarge enhancing pituitarymass through cavernous sinus toinvolve trigeminal ganglion inMeckels cavity on T1-weighted c ontrast-enhancedcoronal spin-echo MR image.Left-sided Meckels cavity

(arrow) is normal. Signal void as-sociated with flowing blood dif-ferentiates carotid artery withinenhancing pituitary adenoma.

Fig. 7. 48-year-old man w ith pial ar teriovenous mal-formation.A, Tangle of di lated blood vessels (arrow) at root entry

zone of right trigeminal nerve on T2-weighted spin-echo M R image.B, Late arterial phase of vertebral angiogram showsarteriovenous malformation supplied by dilated pon-tine artery (small arrow). Note also early shunting intodilated draining vein (large arrow).

BA

Fig. 8. 56-year-old woman with pet-rous apex meningioma. Homogenousenhancing mass involving root entryzone and Meckels cavity. Mass formsobtuse angle with dura on axial con-trast-enhanced T1-weighted spin-echoMR image. Arrow indicates normalright-sided Meckels cavity and duraltail on posterior surface of clivus.

98

Fig. 9. 57-year-old man with trigemi-nal schwannoma. Dumbbell-shapedhigh-signal-intensity mass extendingbetween middle and posterior cranialfossa, along course of trigeminal nerve,on axial T2-weighted spin-echo MR im-age. Trigeminal schwannomas havesmooth margins and appear iso- to hy-perintense to brain on T2-weighted M Rimaging. Larger tumors may show het-erogeneous signal intensity.


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Kamel and Toland

matogenous metastasis. Primary tumors of the

Meckels cavity include trigeminal schwan-

noma, meningioma, and epidermoid cyst [1].

Pituitary fossa and cavernous sinus lesions

(Fig. 6) may extend to the Meckels cavity or

involve the cavernous portion of the trigemi-

nal nerve divisions. As many as one third of

patients with intracavernous carotid aneu-

rysms have trigeminal nerve manifestations

[1, 2]. Metastatic disease is the second most

common lesion to present as a cavernous si-

nus mass with trigeminal neuropathy [1].

The root entry zone is the cisternal part of

the trigeminal nerve just as it enters the pons

(Fig. 2). Lesions affecting the root entry zone

include vascular compression, primary and

secondary neoplasms, and infection. Vascular

contact with the root entry zone is thought to

represent the most common cause of idio-

pathic trigeminal neuralgia. Other conditions

leading to vascular compression include an-

eurysms, arteriovenous malformations (Fig.

7), dural arteriovenous fistulas, and verte-

brobasilar ectasia. Primary tumors involving

the prepontine cistern include meningioma

(Fig. 8), trigeminal schwannoma (Fig. 9), epi-

dermoid cyst (Fig. 10), vestibular schwan-

noma, and lipoma [1]. Secondary neoplasms

affecting the root entry zone include perineu-

ral spread of tumors from head and neck

malignancy, hematogenous metastasis, and

leptomeningeal spread of tumors [3] (Fig.

11). Benign inflammatory or infectious con-

ditions such as sarcoidosis (Fig. 12), viral en-

cephalitis, herpes neuritis [4], and Lyme

disease can also affect the root entry zone [1].

Brainstem

The trigeminal nerve has three sensory and

one motor nuclei. The sensory nuclei are the

principal, mesencephalic, and spinal sensory

(Fig. 2). The spinal trigeminal tract emerges

from the sensory root in the pons and extends

downward into the upper cervical cord. Fi-

bers of this tract end in the spinal trigeminal

nucleus, which merges rostrally with the

principal sensory nucleus. Cervical exten-

sion of the spinal tract explains why some pa-

tients with upper cervical disk herniation

present with trigeminal sensory neuropathy

[5]. The motor nucleus of the trigeminal

nerve forms an oval column of cell anterome-

dial to the motor root and the principal sen-

sory nucleus in the pons (Fig. 12). The

principal sensory nucleus lies lateral to the

entering trigeminal root. The mesencephalic

trigeminal nucleus forms a slender cell col-

umn near the lateral margin of the central

gray matter anterior to the upper fourth ven-

tricle and aqueduct. Afferent fibers of the

mesencephalic nucleus convey propriocep-

tion from teeth, hard palate, and tempero-

mandibular joint. Cells of the mesencephalic

nucleus form the sickle-shaped mesencepha-

lic tract, which descends to the level of the

motor nucleus and conveys impulses that

control mastication and the force of a bite.

Eventually all tracts from the principle sensory

and spinal trigeminal nuclei project to the

posteromedial nucleus of the thalamus, from

which they track through the most posterior as-

Fig. 10. 53-year-old man with histologic diagnosis ofepidermoid cyst. (Courtesy of M cKinstry CS, Belfast,United Kingdom)A, T2-weighted spin-echo MR image shows spread ofslow-gr owing smooth mass of high signal intensity fromcerebellopontine cistern to prepontine cistern acrossroot entry zone of trigeminal nerve. Note septa and focalareas of high signal intensity within mass. Associatedbrainstem compression is causing hydrocephalus.B,T1-weighted spin-echo MR image shows cauli-flow er-shaped contours and nonhomogeneous low tointermediate signal intensity within mass.

BA

Fig. 11. 8-year-old boy with leptomeningeal metastasis from cerebellar medullo-blastoma. Contrast-enhanced T1-weighted spin-echo MR image shows bilateralsymmetric enhancement and thickening of root entry zone of both M eckels cavitys.In addition, nodular enhancement and thickening are seen on undersurface of bothtemporal lobes, superior surfac e of cerebellum, anterior surfac e of pons, and liningof lateral ventricles. (Courtesy of McKinstry CS, Belfast, United Kingdom)

Fig. 12. 28-year-old man w ith diagnosis of neurosarcoidosis. Coronal T1-weightedspin-echo MR image shows bilateral asymmetric thickening and enhancement oftrigeminal (solid straightarrow) and occulomotor (curved arrow) nerves and hypo-thalamus (open straight arrow). Lateral ventric les are dilated.


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Trigeminal Nerve Anatomy


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pect of the posterior limb of the internal capsule

and project to the postcentral gyrus [1].

Multiple sclerosis (Fig. 13), glioma, and in-

farction (Fig. 14) are the most common brain-

stem and upper cervical cord lesions resulting in

fifth cranial nerve symptom. Less common le-

sions include metastasis, cavernous heman-

giomas [6], hemorrhage, and arteriovenous

malformation [1]. Rarely, rhombencephalitis

may develop as a result of retrograde extension

of herpes simplex virus type 1 from the trigemi-

nal ganglion into the brainstem [4] (Fig. 15).In conclusion, a variety of conditions may

involve the different segments of the trigemi-

nal nerve. Knowledge of its anatomic course

allows an understanding of disorders involv-

ing the brainstem and adjacent skull base.

Acknowledgment

We thank C. S. McKinstry, Belfast, United

Kingdom, for his assistance in revising this paper

and for providing Figures 10 and 11 of this article.

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1995

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3. Donnet A, Moullin G, Tubiana N, Gras R, Robert

JL. Lymphomatous meningitis: neuroradio-

logical appearances. Neuroradiology

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411412

4. Tien RD, Dillon WP. Herpes trigeminal neuritis

and rhombencephalitis on Gd-DTPA-enhanced

MR imaging. AJNR

1990

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5. Barakos JA, DAmour PA, Dillon WP, Newton

TH. Trigeminal sensory neuropathy caused by

cervical disc herniation. AJNR

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;95:97101

Fig. 13. 45-year-old man with diagnosis ofmultiple sclerosis. Oblong plaque of high signalintensity (arrow) involving right trigeminal sen-sory nucleus on T2-weighted spin-echo MR im-age. Note small area of high signal intensityadjacent to fourth ventricle and high signal in-

tensity in white matter of temporal lobes.

Fig. 14. 42-year-old woman with lateral medullarysyndrome caused by spontaneous vertebral arterydissection. Localized high signal intensity caused byarea of infarction on right side of medulla oblongata(arrow) on T2-weighted spin-echo MR image. Noteabsence of flow void in right vertebral arter y.

Fig. 15. 33-year-old w oman with herpes zoster. Axial con-trast-enhanced T1-weighted spin-echo MR image showsenhancement along pontine course of trigeminal nerve andlow signal intensity at site of main trigeminal sensory nu-cleus (arrow).

trigeminal nerve abnormality

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