AJR 2001; 176:247-251
© American Roentgen Ray Society
Trigeminal Nerve Anatomy
Illustrated Using Examples of Abnormalities
H. A. M. Kamel1,2 and
J. Toland3
1
Department of Neuroradiology, The Royal Victoria Hospital, Grosvenor RD.,
Belfast BT12 6BA, United Kingdom.
2
Present address: Radiology Department, Hamad Medical Corporation, P.O. Box
3050, Doha, Qatar.
3
Department of Neuroradiology, Beaumont Hospital, Dublin 9, Ireland.
Received August 17, 1999;
accepted after revision March 2, 2000.
Address correspondence to H. A. M. Kamel.
Introduction
The trigeminal nerve has an extensive anatomic course. Comprehensive
knowledge of trigeminal nerve anatomy facilitates understanding of the
relationship between the brainstem, skull base, and facial area. In our
article we attempt to solidify this knowledge using examples of abnormalities.
We will describe the anatomy from the peripheral branches toward the brainstem
in keeping with the direction of sensory propagation and perineural spread of
malignant and inflammatory disease.
Peripheral Divisions of the Trigeminal Nerve
The trigeminal nerve trifurcates into ophthalmic, maxillary, and mandibular
nerves distal to the trigeminal ganglion. The ophthalmic 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].
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Fig. 1. —Diagram shows trigeminal nerve (TGN), trigeminal ganglion,
and peripheral divisions and their branches. From foramen rotundum ossis
sphenoidalis, maxillary nerve (thin underline) gains access to
pterygopalatine fossa and continues in floor of orbit as infraorbital nerve.
Inferior alveolar and lingual nerves (thick underline) are branches
of mandibular nerve.
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The maxillary nerve exits the skull base through the foramen rotundum ossis
sphenoidalis inferolateral to the cavernous sinus. It then enters the
pterygopalatine fossa where it gives off several branches. Its main trunk
continues anteriorly in the orbital floor
(Fig. 1) and emerges onto the
face as the infraorbital 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 descending through the foramen ovale into the masticator space. The
motor root of the trigeminal nerve bypasses the trigeminal ganglion and
reunites with the mandibular nerve in the foramen ovale basis cranii
(Fig. 2). As the mandibular
nerve enters the masticator space, it divides into several sensory branches to
supply sensation 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 innervates the four muscles of
mastication: the mylohyoid, the anterior belly of digastric, the tensor muscle
of the tympanic membranes, and tensor muscle of valum palatinum
[2]. Infection and neoplasia
most commonly involve the peripheral divisions of the trigeminal nerve. Direct
spread from local tumors (Figs.
3 and
4A,4B)
or metastases from distant malignancies are the most common causes of
malignant involvement [1].
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Fig. 2. —Sagittal diagram shows three peripheral divisions of
trigeminal nerve entering convexity and root bundles leaving concavity of
sickle-shaped trigeminal ganglion. Motor root (solid arrowhead)
bypasses ganglion and reunites with mandibular nerve in foramen ovale basis
cranii. Open arrowhead indicates descending spinal trigeminal tract. Diagram
also shows motor and sensory trigeminal nuclei (underline) in
brainstem and cervical cord. A, B, and C track nuclear origin of fibers
contributing to opthalmic; D and E, the maxillary; and F, H, and I, mandibular
divisions of trigeminal nerve.
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Fig. 3. —72-year-old man with nasopharyngeal carcinoma. Coronal
contrast-enhanced T1-weighted spin-echo MR image with fat suppression shows
enhancement and thickening of mandibular nerve extending into trigeminal
ganglion (arrow). Note widening of foramen ovale basis cranii and
enhancing soft-tissue mass causing destruction of right side of sphenoid
bone.
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Fig. 4A. —55-year-old man with squamous cell carcinoma of skin. Axial
T2-weighted spin-echo MR image shows thickening of skin and subcutaneous
tissue of right cheek and band of intermediate signal intensity extending
along course of infraorbital nerve (arrow). High signal is noted in
thickened mucosa of both maxillary sinuses.
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Fig. 4B. —55-year-old man with squamous cell carcinoma of skin. Coronal
T1-weighted spin-echo MR image after IV contrast injection shows spread of
irregular enhancing mass (arrow) along infraorbital nerve. Note
normal mucosal enhancement in both maxillary sinuses.
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Trigeminal Ganglion and Preganglionic Trigeminal Nerve
The trigeminal ganglion is contained within the Meckel's cavity
posterolateral to the cavernous sinus on either side of the sphenoid bone. The
Meckel's cavity is a cerebrospinal fluid-containing arachnoidal pouch
protruding from the posterior cranial fossa. Medial to the ganglion in
Meckel's cavity is the internal carotid artery in the posterior portion 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 Meckel's cavity can be involved either by extrinsic or intrinsic
disease. Extrinsic lesions, usually bony metastasis, chordoma, or
chondrosarcoma, destroy adjacent bone as they extend toward the Meckel's
cavity. Intrinsic lesions simply expand the Meckel's cavity (Fig.
5A,5B).
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 Meckel's cavity
with enlargement of the foramen ovale basis cranii, foramen rotundum ossis
sphenoidalis, or the superior orbital fissure. Intrinsic lesions include
primary tumors of the Meckel's cavity as well as secondary neoplasms from
perineural spread of local tumors, leptomeningeal, or hematogenous metastasis.
Primary tumors of the Meckel's cavity include trigeminal schwannoma,
meningioma, and epidermoid cyst
[1].
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Fig. 5A. —15-year-old girl with known diagnosis of leukemia. Expansion
and reduction of normal high signal intensity in Meckel's cavity
(arrows) on T2-weighted spin-echo MR image. Note signal void from
internal carotid artery medial to Meckel's cave.
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Fig. 5B. —15-year-old girl with known diagnosis of leukemia. Coronal
T1-weighted spin-echo MR image after IV contrast injection shows bilateral
Meckel's cavity enhancement (arrows), particularly of left side, as
result of leukemic deposits.
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Pituitary fossa and cavernous sinus lesions
(Fig. 6) may extend to the
Meckel's cavity or involve the cavernous portion of the trigeminal nerve
divisions. As many as one third of patients with intracavernous carotid
aneurysms have trigeminal nerve manifestations
[1,
2]. Metastatic disease is the
second most common lesion to present as a cavernous sinus mass with trigeminal
neuropathy [1].
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Fig. 6. —29-year-old woman with pituitary adenoma. Spread of large
enhancing pituitary mass through cavernous sinus to involve trigeminal
ganglion in Meckel's cavity on T1-weighted contrast-enhanced coronal spin-echo
MR image. Left-sided Meckel's cavity (arrow) is normal. Signal void
associated with flowing blood differentiates carotid artery within enhancing
pituitary adenoma.
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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 idiopathic trigeminal
neuralgia. Other conditions leading to vascular compression include aneurysms,
arteriovenous malformations (Fig.
7A,7B),
dural arteriovenous fistulas, and vertebrobasilar ectasia. Primary tumors
involving the prepontine cistern include meningioma
(Fig. 8), trigeminal
schwannoma (Fig. 9),
epidermoid cyst (Fig.
10A,10B),
vestibular schwannoma, and lipoma
[1]. Secondary neoplasms
affecting the root entry zone include perineural spread of tumors from head
and neck malignancy, hematogenous metastasis, and leptomeningeal spread of
tumors [3]
(Fig. 11). Benign inflammatory
or infectious conditions such as sarcoidosis
(Fig. 12), viral encephalitis,
herpes neuritis [4], and Lyme
disease can also affect the root entry zone
[1].
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Fig. 7B. —48-year-old man with pial arteriovenous malformation. Late
arterial phase of vertebral angiogram shows arteriovenous malformation
supplied by dilated pontine artery (small arrow). Note also early
shunting into dilated draining vein (large arrow).
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Fig. 8. —56-year-old woman with petrous apex meningioma. Homogenous
enhancing mass involving root entry zone and Meckel's cavity. Mass forms
obtuse angle with dura on axial contrast-enhanced T1-weighted spin-echo MR
image. Arrow indicates normal right-sided Meckel's cavity and dural tail on
posterior surface of clivus.
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Fig. 9. —57-year-old man with trigeminal schwannoma. Dumbbell-shaped
high-signal-intensity mass extending between middle and posterior cranial
fossa, along course of trigeminal nerve, on axial T2-weighted spin-echo MR
image. Trigeminal schwannomas have smooth margins and appear iso- to
hyperintense to brain on T2-weighted MR imaging. Larger tumors may show
heterogeneous signal intensity.
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Fig. 10A. —53-year-old man with histologic diagnosis of epidermoid cyst.
(Courtesy of McKinstry CS, Belfast, United Kingdom) T2-weighted spin-echo MR
image shows spread of slow-growing smooth mass of high signal intensity from
cerebellopontine cistern to prepontine cistern across root entry zone of
trigeminal nerve. Note septa and focal areas of high signal intensity within
mass. Associated brainstem compression is causing hydrocephalus.
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Fig. 10B. —53-year-old man with histologic diagnosis of epidermoid cyst.
(Courtesy of McKinstry CS, Belfast, United Kingdom) T1-weighted spin-echo MR
image shows cauliflower-shaped contours and nonhomogeneous low to intermediate
signal intensity within mass.
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Fig. 11. —8-year-old boy with leptomeningeal metastasis from cerebellar
medulloblastoma. Contrast-enhanced T1-weighted spin-echo MR image shows
bilateral symmetric enhancement and thickening of root entry zone of both
Meckel's cavitys. In addition, nodular enhancement and thickening are seen on
undersurface of both temporal lobes, superior surface of cerebellum, anterior
surface of pons, and lining of lateral ventricles. (Courtesy of McKinstry CS,
Belfast, United Kingdom)
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Fig. 12. —28-year-old man with diagnosis of neurosarcoidosis. Coronal
T1-weighted spin-echo MR image shows bilateral asymmetric thickening and
enhancement of trigeminal (solid straight arrow) and occulomotor
(curved arrow) nerves and hypothalamus (open straight
arrow). Lateral ventricles are dilated.
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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. Fibers of this tract end in the spinal trigeminal
nucleus, which merges rostrally with the principal sensory nucleus. Cervical
extension of the spinal tract explains why some patients with upper cervical
disk herniation present with trigeminal sensory neuropathy
[5]. The motor nucleus of the
trigeminal nerve forms an oval column of cell anteromedial to the motor root
and the principal sensory 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 column near the lateral
margin of the central gray matter anterior to the upper fourth ventricle and
aqueduct. Afferent fibers of the mesencephalic nucleus convey proprioception
from teeth, hard palate, and temperomandibular joint. Cells of the
mesencephalic nucleus form the sickle-shaped mesencephalic 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 aspect of the
posterior limb of the internal capsule and project to the postcentral gyrus
[1].
Multiple sclerosis (Fig.
13), glioma, and infarction
(Fig. 14) are the most common
brainstem and upper cervical cord lesions resulting in fifth cranial nerve
symptom. Less common lesions include metastasis, cavernous hemangiomas
[6], hemorrhage, and
arteriovenous malformation [1].
Rarely, rhombencephalitis may develop as a result of retrograde extension of
herpes simplex virus type 1 from the trigeminal ganglion into the brainstem
[4]
(Fig. 15).
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Fig. 13. —45-year-old man with diagnosis of multiple sclerosis. Oblong
plaque of high signal intensity (arrow) involving right trigeminal
sensory nucleus on T2-weighted spin-echo MR image. Note small area of high
signal intensity adjacent to fourth ventricle and high signal intensity in
white matter of temporal lobes.
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Fig. 14. —42-year-old woman with lateral medullary syndrome caused by
spontaneous vertebral artery dissection. Localized high signal intensity
caused by area of infarction on right side of medulla oblongata
(arrow) on T2-weighted spin-echo MR image. Note absence of flow void
in right vertebral artery.
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Fig. 15. —33-year-old woman with herpes zoster. Axial contrast-enhanced
T1-weighted spin-echo MR image shows enhancement along pontine course of
trigeminal nerve and low signal intensity at site of main trigeminal sensory
nucleus (arrow).
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In conclusion, a variety of conditions may involve the different segments
of the trigeminal nerve. Knowledge of its anatomic course allows an
understanding of disorders involving the brainstem and adjacent skull
base.
Acknowledgments
We thank C. S. McKinstry, Belfast, United Kingdom, for his assistance in
revising this paper and for providing Figures
10A,10B
and 11 of this article.
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Introduction
Peripheral Divisions of the...
