11 Trigeminal Nerve
Athiya Agarwal
INTRODUCTION
The trigeminal nerve1,2 is the fifth cranial nerve and is both motor and sensory. On the sensory root there is a large ganglion called the trigeminal ganglion.
NUCLEUS
There are two portions to discuss regarding the nuclei: The first is the motor nucleus and the second is the sensory nucleus. The motor nucleus is in the upper pons. The sensory nucleus extends in continuity throughout the whole length of the brainstem and descends into the upper 2 or 3 segments of the spinal cord. The mesencephalic part is for propioception, the pontine part is for nice sensations, and the spinal or medullary nucleus is for nasty sensations.
EXIT FROM THE BRAIN
The trigeminal nerve exits from the brain at the level of the pons. Lateral to the fifth nerve is the middle cerebellar peduncle. The motor nerve emerges separately, slightly cranial and medial to its companion.
TRIGEMINAL CAVE
Together they pass below the tentorium cerebelli to the mouth of the trigeminal cave. This is a tubular prolongation of arachnoid. The sensory root expands into a large flat crescentic trigeminal ganglion. The motor root remains separate. The trigeminal ganglion lies in the trigeminal or Meckel’s cave. The anterior half of the ganglion gives off its three sensory divisions: (i) the ophthalmic division (V1), (ii) maxillary division (V2), and (iii) mandibular vision (V3). The motor
Trigeminal Nerve 141
root of the nerve has no connection with the ganglion but lies on its deep surface, crossing from the medial to the lateral side, to join the mandibular divisions of the trigeminal nerve (Fig. 11.1). The ophthalmic and maxillary divisions pass forwards in the lateral wall of the cavernous sinus . They are wholly sensory. The mandibular division passes straight down from the lower part of the ganglion to the foramen ovale. Here the motor root (Fig. 11.1) joins it.
OPHTHALMIC DIVISION
In the cavernous sinus, the ophthalmic division picks up sympathetic fibers from the cavernous plexus. These are for the dilator pupillae muscle. It divides just posterior to the superior orbital fissure into three branches, which pass through the superior orbital fissure to enter the orbit (Fig. 11.1).
Fig. 11.1: Ophthalmic division of the trigeminal nerve
1. Lacrimal nerve; 2. Frontal nerve: (A) Supraorbital N (B) Supratrochlear N; 3. Nasociliary nerve (A) Sensory root to the ciliary ganglion; (B) Long diliary nerve; (C) Posterior ethmoidal nerve; (D) Anterior ethmoidal nerve; (E) Infratrochlear nerve
142 Manual of Neuro-ophthalmology
Lacrimal Nerve
This is the smallest branch. It passes through the lateral portion of the superior orbital fissure lateral to the frontal and IV nerve and above the superior ophthalmic vein. In the orbit, it runs forwards just lateral to the upper border of the LR to reach the lacrimal gland. It also supplies the conjunctiva and skin of the lateral part of the upper lid.
Frontal Nerve
This is the largest of the three branches of the ophthalmic division. It arises in the cavernous sinus just behind the superior orbital fissure through which it enters the orbit. In the superior orbital fissure, it is between the lacrimal nerve and the IV cranial nerve. It runs above the LPS and divides into two branches—a large supraorbital and a small supratrochlear nerve.
Nasociliary Nerve
It is intermediate in size between the lacrimal and frontal nerve. It passes through the superior orbital fissure within the annulus tendon between the divisions of the third cranial nerve. In the orbit, it inclines medially with the ophthalmic artery above the optic nerve and below
the SR. Thus, the nasociliary nerve, ophthalmic artery and the superior ophthalmic vein lie between the optic nerve and the SR muscle. The branches of the nasociliary nerve are:
Sensory root of the ciliary ganglion This is given off just in front of the superior orbital fissure. It reaches the ciliary ganglion and does not synapse there. From the ciliary ganglion about 6 short ciliary nerves are given off which are sensory to the whole eyeball including the cornea but not the conjunctiva which is supplied by the lacrimal and supratrochlear nerves.
Long ciliary nerves They are two in number and come off the nasociliary nerve. They pierce the sclera and pass in the suprachoroidal space to supply the iris, ciliary muscle and cornea. They also carry sympathetic fibers to the dilator pupillae muscle.
Posterior ethmoidal nerve This passes through the posterior ethmoidal foramen.
Anterior ethmoidal nerve This passes through the anterior ethmoidal foramen. This nerve enters the anterior cranial fossa and reaches the tip
of the nose as the external nasal nerve. This is important as if a patient has herpes zoster and the tip of the nose is affected it means the nasociliary nerve is involved and that means the eye will definitely get involved. This is called
Hutchinson’s rule.
Trigeminal Nerve 143
Infratrochlear nerve This is the terminal branch of the nasociliary nerve.
MAXILLARY DIVISION
The maxillary division passes through the foramen rotundum and gives off three posterior superior alveolar nerves (Fig. 11.2), a middle superior alveolar nerve and an anterior superior alveolar nerve. Then, it passes through the infraorbital canal and emerges as the infraorbital nerve. A loop of nerve called the loop of Woodron connects the posterior and middle superior alveolar nerves. It also gives off a nerve to supply the lacrimal gland, which travels along the lacrimal nerve. It also gives off the zygomatotemporal and zygomatofacial nerves.
MANDIBULAR DIVISION
The mandibular division passes through the foramen ovale and gives off first the meningeal branch, which passes back into the skull through the foramen spinosum. It then divides into two divisions—the anterior and posterior division. Each in turn has some branches (Fig. 11.3). Thus, the branches of the mandibular division are:
•Meningeal branch
•Anterior division which in turn has:
1.Temporal branch
2.Masseteric branch
Fig. 11.2: Maxillary division of the trigeminal nerve
144 Manual of Neuro-ophthalmology
Fig. 11.3: Mandibular division of the trigeminal nerve
1.Meningeal branch; 2. Anterior division ; 3. Posterior division
3.Pterygoid branch
4.Buccal nerve.
•Posterior division which in turn has:
1.Auriculotemporal nerve
2.Nerve to medial pterygoid
3.Lingual nerve
4.Inferior alveolar nerve.
REFERENCES
1.Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee, India 2003.
2.Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
12 |
Facial Nerve and |
|
its Lesions |
||
|
||
|
Athiya Agarwal |
INTRODUCTION
The facial nerve1,2 is the seventh cranial nerve and it is both a motor as well as a sensory nerve.
NUCLEUS
The seventh cranial nerve has three nuclei:
The Main Motor Nucleus
This lies in the lower part of the pons. The part of the nucleus that supplies the muscles of the upper part of the face receives corticonuclear fibers from both cerebral hemispheres. The part of the nucleus that supplies the muscles of the lower part of the face receives corticonuclear fibers from the opposite cerebral hemisphere only.
Parasympathetic Nuclei
These include the superior salivatory and lacrimatory nuclei. The former supplies the submandibular and sublingual glands and the latter the lacrimal gland.
Sensory Nucleus
This is situated in the upper part of the medulla oblongata.
COURSE
The facial nerve exits from the brain (Fig. 7.3) at the level of the junction between the pons and the medulla. Medial to it lies the VIth nerve and lateral to it lies the VIIIth nerve. The nerve then passes through the internal auditory meatus (Fig. 12.1). At its exit from the brain a
146 Manual of Neuro-ophthalmology
cerebellopontine angle tumor can affect it. In such a case the nerves affected are the Vth, VIth, VIIth and VIIIth. The geniculate ganglion is located on the first bend of the facial nerve. This is a sensory ganglion.
A nerve starts from the geniculate ganglion called the greater superficial petrosal nerve. This joins another nerve called the deep petrosal nerve, which is a branch from the sympathetic plexus around the internal carotid artery. These two nerves join to become the Vidian nerve or the nerve of the pterygoid canal. This then passes through the Vidian canal or the Pterygoid canal and ends in the pterygopalatine ganglion. This ganglion is the largest parasympathetic peripheral ganglion. It serves as a relay station for secretomotor fibers to the lacrimal gland and to the mucous glands of the nose, palate and pharynx. From the pterygopalatine ganglion secretomotor fibers go to the lacrimal gland. These hitchhike on to V2 (maxillary division of the trigeminal nerve) and then onto the lacrimal nerve (branch of
Fig. 12.1: Course of the facial nerve
Facial Nerve and its Lesions 147
V1—ophthalmic division of the trigeminal nerve). Remember that the lacrimal gland’s tear production is due to the VIIth nerve and not due to the
Vth nerve.
From the geniculate ganglion the facial nerve curves downwards and gives off a nerve called the nerve to the stapedius. If this is cut the patient develops tinnitus. Then another nerve is given off called the chorda tympani nerve. This supplies taste for the anterior twothird of the tongue. The IXth (Glossopharyngeal nerve) nerve supplies the posterior one-third of the tongue. The VIIth nerve also supplies submandibular and sublingual glands.
The facial nerve then comes out through the stylomastoid foramen and gives of the posterior auricular nerve. It then goes to supply the muscles of the face by dividing into two branches—zygomatotemporal and cervicofacial. The former gives off the temporal and the zygomatic branches. The latter gives off the cervical and mandibular branches. The buccal nerve is between these two branches. Thus, these five nerves supply the muscles of the face and this distribution is like a claw of a tiger and hence is called pes anserinus. The zygomatic branch supplies the orbicularis oculi muscle.
LESIONS OF THE FACIAL NERVE
The lesions of the facial nerve are shown in Figure 12.2. They are as follows:
Supranuclear Lesion
If the lesion is supranuclear the lower half of the face is only involved and if it is a lower motor neuron lesion the whole half of the face is involved. This is because the upper half of the face has a bilateral innervation.
Cerebellopontine Angle Tumor
Just as the VIIth nerve comes out from the brain it can get affected by the cerebellopontine angle tumor. The patient has:
•Total ipsilateral facial weakness (VIIth nerve involvement)
•Decreased tearing (lacrimation involved)
•Hyperacusis (nerve to stapedius involved)
•Decreased taste from the anterior two-third of the tongue (chorda tympani nerve involved)
•Vth, VIth and VIIIth nerve involved with cerebellar dysfunctions.
148 Manual of Neuro-ophthalmology
Fig. 12.2: Lesions of the facial
1. Supranuclear lesion; 2. Cerebellopontine angle tumor; 3. Geniculate ganglionitis (Ramsay Hunt syndrome); 4. Isolate ipsilateral tear deficiency; 5. Lesion before nerve to stapedius; 6. Lesion after nerve to stapedius; 7. Lesion after chorda tympani nerve; 8. Bell’s palsy – isolated total ipsilateral facial palsy; 9. Isolated partial ipsilateral facial palsy
Geniculate Ganglionitis
Geniculate ganglionitis is known as the Ramsay-Hunt syndrome. The features are:
•Same findings as in cerebellopontine angle tumors except no associated neurological deficits
•May see zoster vesicles on tympanic membrane, external auditory canal or external ear.
Facial Nerve and its Lesions 149
Isolated Ipsilateral Tear Deficiency
Isolated ipsilateral tear deficiency occurs in nasopharyngeal carcinomas, which affect the Vidian nerve or the pterygopalatine ganglion.
Lesion before Nerve to Stapedius
Lacrimation is normal. The other findings are:
•Hyperacusis (nerve to stapedius involved)
•Decreased taste from the anterior two-third of the tongue (chorda tympani nerve involved)
•Total ipsilateral facial weakness (VIIth nerve involvement).
Lesion after Nerve to Stapedius
•Decreased taste from the anterior two-third of the tongue (chorda tympani nerve involved)
•Total ipsilateral facial weakness (VIIth nerve involvement).
Lesion after Chorda Tympani Nerve
Only total ipsilateral facial weakness (VIIth nerve involvement).
Bell’s Palsy
Only total ipsilateral facial weakness (VIIth nerve involvement).
Isolated Partial Ipsilateral Facial Palsy
In this only certain branches of the VIIth nerve are affected.
SUMMARY
Thus, if we understand the course of the facial nerve, we can diagnose the level of lesion in the facial nerve.
REFERENCES
1.Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee, India 2003.
2.Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
Congenital Optic
13 Nerve Anomalies
Priya Narang, Sameer Narang, Amar Agarwal
INTRODUCTION
Congenital optic nerve anomalies are quite a common entity and are often included in the differential diagnosis of various clinical disorders as they are often associated with visual field defects central nervous system (CNS) malformations and other ocular abnormalities. A thorough knowledge of the embryological development of the optic nerve entails a better understanding of the development of optic nerve anomalies.
The optic nerve develops from the optic stalk or optic pedicle. The closure of the fetal fissure converts the optic stalk into a rounded cord-like structure. Its cavity communicates on one side with the cavity of diencephalon and on the other side with the primary optic vesicle. The nerve fibers then grow from the ganglion cells towards the brain through the stalk. The optic nerve is then filled with glial tissue and fibrous septa. The sheaths of the optic nerve develop from the mesoderm. The medullation of the nerve fibers which begins from the brain and extends up to the lamina cribrosa is nearly complete at term. As stated above, any deviation from the normal development leads to congenital anomalies which are described here.
CAUSES
•Abnormal small optic disk
•Aplasia
•Abnormal shape of the optic disk
•Bergmister’s papillae
•Optic nerve head drusen (Fig. 13.1)
•Myelineated nerve fibers (Fig. 13.2)
•Optic disk coloboma
Congential Optic Nerve Anomalies 151
•Optic disk pit
•Morning glory syndrome
•Tilted disk.
APLASIA
Aplasia is a rare anomaly characterized clinically by a total blind eye with an afferent pupillary defect, an absent optic disk and an absent retinal vasculature.
HYPOPLASIA
The optic disk hypoplasia is a sporadic condition. The affected can be micro-ophthalmic or of normal size and usually exhibit a wide range of visual impairment from normal vision to severe visual loss with strabismus or nystagmus in bilateral cases. Visual acuity is determined primarily by the integrity of the papillomacular bundle. The visual fields show a localized defect. The disk is surrounded by a peripapillary halo, bordered by a dark pigment ring called as the double ring sign. Retinal vascular tortuosity is commonly seen. Histologically optic nerve hypoplasia is characterized by a subnormal number of optic nerve axons with normal mesodermal elements and glial supporting tissue.
Some of the optic nerve hypoplasia are segmental. A pathognomonic superior segmental hypoplasia with an inferior visual field defect occurs in some children of insulin dependent diabetic mothers. In cases of homonymous hemianopic hypoplasia, there is congenital cerebral hemiatrophy.
Patients with periventricular leukomalacia often have a unique form of optic nerve hypoplasia characterized by an abnormally large cup and a thin neuroretinal rim contained within a normal sized disk can be associated with intracranial and facial anomalies like septo-optic dysplasial De Morsiers syndrome, congenital hypopitutarism, hydrancephaly, arrhinencephaly, aniridia, homonymous optic hypoplasia associated with congenital hemispheric aplasia, cyclopia, enchelomeningocele and hypertelorism.
De Morsier’s syndrome refers to the constellation of small anterior visual pathways, absence of septum pellucidum, and agenesis or thinning of the corpus callosum. MRI is the optimal noninvasive neuroimaging modality for delineating congenital CNS malformations in patients with septo optic dysplasia. In bilateral optic nerve hypoplasia the coronal MRI shows diffuse thinning of the optic chiasma.
152 Manual of Neuro-ophthalmology
The detection of hypopitutarism is an essential component of the evaluation of children with optic nerve hypoplasia, because children with endocrinological deficiency are at risk for impaired growth, hypoglycemia, developmental delay, seizures and death. Parents should be asked about the history of protracted neonatal jaundice and previous episodes of hypoglycemia in the neonatal period.
Infants with optic nerve hypoplasia have superimposed delayed visual maturation. Therefore infants who initially appear to be blind may have improvement of their vision during the first several months of life.
Treatment
Superimposed ambylopia should be treated with a trial of occlusion therapy children with hypopitutarism should be treated with pituitary hormone replacement.
BERGMISTER’S PAPILLAE
The glial sheath of Bergmister envelops the posterior third of the hyaloid artery it begins to atrophy about the seventh month of gestation, even before the main vessel atrophies. The extent of the atrophy is below the surface of the disk. If the atrophy at the disk is less complete a tuft of glial tissue may be seen thorough out the life over the optic disk called the Bergmister’s papillae.
MYELINEATED NERVE FIBERS
Medullation or myelineation of the optic nerve begins in the fetal life from the lateral geniculate body towards the globe. Normally the myelination is completed shortly after birth at which time the myelin sheath reaches the posterior aspect of the lamina cribrosa. The medullated fibers may be seen starting from the disk and extending towards the periphery (Fig. 13.2). Fundus examination shows irregular feather-like patches which may or may not obscure the retinal blood vessels. Rarely, isolated peripheral patches of myelination may also occur.
Myelination of the nerve fibers results in visual field defects. Myopia, coloboma, polycoria, keratoconus, oxycephaly and
neurofibromatosis have been associated with myelineated nerve fibers.
OPTIC NERVE HEAD DRUSEN
Deposition of hyaline like calcified material within the substance of the optic nerve head.Optic nerve head drusen (Fig. 13.1) can be
Congential Optic Nerve Anomalies 153
inherited or can be associated with heredodegenerative conditions like retinitis pigmentosa or angioid streaks or can be following long standing papilledema, papillitis, vascular occlusions.
Clinically has an irregular, nodular, mulberry like appearance of the surface of the disk. The physiological cup can be absent but venous pulsation is present there can be abnormal tortous, anomalously branching vessels. Disk can be pallor sometimes but will have irregular margins. They vary greatly in size, shape and number, smaller ones often coalesce to form larger ones.
The differential diagnosis of optic disk drusen includes papilledema with which it is often confused. Fluorescein angiography helps to differentiate between both the conditions which closely simulate each other. Drusens’ exhibit the phenomenon of autofluorescence and may stain during the late stages of angiogram. They exhibit no leakage of fluorescein from the optic nerve head which is usually present in papilledema.
Patients with disk drusen usually remain asymptomatic although few cases have been reported to develop peripapillary and macular hemorrhage. Drusens may directly compress the nerve fibers within the disk and cause various visual field defects like enlargement of the blind spot, arcuate scotoma or peripheral field constriction. Central visual acuity is usually good.
COLOBOMA OF OPTIC DISK
A coloboma of the optic disk (Fig. 13.1) results from incomplete closure of the embryonic fissure. The fissure initially closes in the middle and then extends anteriorly and posteriorly until a small crescent at the posterior pole remains open. When the lips of the fissure fail to fuse, typical colobomas result. The coloboma of the optic nerve may occur alone or may be associated with coloboma of the iris, retina, choroid or ciliary body.
It usually occurs in two forms.
Optic Disk Coloboma in Association with Retinochoroidal Coloboma
This form of coloboma is more common and frequently occurs bilaterally. It is characterized by a large excavation which is usually situated inferiorly with the normal appearing disk tissue pushed superiorly. It is associated with superior visual field defects.
The retinochoroidal coloboma may involve the optic nerve completely or occasionally there is a patch of healthy tissue between
154 Manual of Neuro-ophthalmology
Fig. 13.1: Optic nerve head drusen
the retinochoroidal coloboma and the optic disk coloboma. Such colobomas are known as Bridge colobomas.
Coloboma of the Optic Nerve Entrance
These are isolated colobomas of the optic nerve wherein the disk shows an enlarged and excavated nerve head with an expanded scleral canal. It is usually unilateral and is associated with high myopia and amblyopia. The central area of the nerve shows persistent hyaloid remnants. The blood vessels which are believed to be cilioretinal in origin emerge like the spokes of a wheel in a radical fashion from the rim of the excavation. This is known as Morning glory syndrome (Fig. 13.2).
Fig. 13.2: Myelineated nerve fibers
Congential Optic Nerve Anomalies 155
Occasionally mild failure of closure of embryonic fissure leads to the development of inferior crescent which is situated at the lower edge of the disk. It closely resembles the myopic crescent and is found to occur more commonly in hypermetropic and astigmatic eyes.
MORNING GLORY SYNDROME
The morning glory anomaly is a congenital, funnel shaped excavation of the posterior fundus that incorporates the optic disk. The disk is markedly enlarged, orange or pink in color and typically situated within a funnel shaped excavation. Surrounding the excavation is a variably elevated annular zone of altered retinal pigmentation. A white tuft of glial tissue overlies the recessed central portion of the lesion. The blood vessels appear increased in number and arise from the periphery of the disk. They run an abnormally straight course over the peripapillary retina and tend to branch at acute angles. It is often difficult to distinguish arterioles from venules. The macula may be incorporated into the excavation called as macular capture. Computed tomography shows a funnel shaped enlargement of the distal optic nerve at its junction with the globe.
Visual acuity anges from 20/200 and finger counting. Morning glory syndrome is more common in females and rare in blacks.
Serous retinal detachment is the most noted complication of this anomaly 26 to 38 percent of the eyes with morning glory result in retinal detachment.
Associated with basal encephalocele with midfacial anomalies (hypertelorism, cleft lip, cleft palate, depressed nasal bridge, midline upper lid notch).
MRI is indicated in patients with mid facial anomalies and neurological deficits because these patients are at high risk for an associated basal encephalocele.
Treatment
superimposed ambylopia should be treated with a trial of occlusion therapy. Patients with basal encephalocele should be evaluated for surgical repair.
TILTED DISK
Tilted disk is caused by an oblique insertion of the optic nerve into the globe. The upper temporal portion of the disk often lies anterior to the lower margin. The vertical axis of the disk is directed obliquely
156 Manual of Neuro-ophthalmology
which gives it an oval appearance. This condition may be associated with visual field defects which involve the upper temporal quadrant because of the ectasia of inferonasal portion of the fundus. The visual fields in the congenital tilted disk does not respect the vertical meridian and it usually crosses the vertical meridian. Can be associated with the situs inversus of the blood vessels.
Tilted disk is often found to be associated with degenerative high myopia wherein scleral ectasia or staphyloma involve the posterior pole temporal to the disk. This results in an oblique exit of the optic nerve.
OPTIC DISK PIT
Optic disk pit is usually seen as a small excavation along the temporal border of the disk covering nearly one-third of the surface of the disk. It is usually round or oval in shape and appears darker than the surrounding disk tissue probably because of the inability to illuminate these small deep excavations. It is usually unilateral and the disk may appear larger as compared to the fellow eye.
In 15 percent of the cases it can be bilateral. A cilioretinal artery is found in 59 percent of the eyes with optic disk pit.
Approximately 45 percent of the eyes with congenital optic disk pit develop serous macular elevations.
The macula demonstrates the following progression of events.An inner layer retinoschisis cavity initially forms in direct communication with the optic pit an outer layer macular hole develops beneath the boundaries of the retinoschisis cavity.
An outer layer retinal detachment develops around the macular hole. This outer layer detachment ophthalmoscopically can be mistaken for an pigment epithelial detachment, but it does not hyperflouresce on FFA.
The outer layer detachment eventually enlarges and obliterates the retinoschisis cavity. At this stage, it becomes clinically indistinguishable from a primary serous macular detachment.
BIBLIOGRAPHY
1.Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
2.David J Apple, Maurice F. RABB (3rd ed) Ocular Pathology Mosby.
3.Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee, India 2003.