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Cranial Nerve Palsies
Jonathan D. Trobe, MD
Professor of Ophthalmology and Neurology
Departments of Ophthalmology (Kellogg Eye Center) and Neurology
University of Michigan Medical System
Ann Arbor, Michigan, USA
Email: [email protected]
Telephone: 734 7639147
Fax: 734 2328181
Kellogg Eye Center
1000 Wall Street
Ann Arbor, Michigan 48105
Introduction
The ocular motor cranial nerves. The position and movement of the eyes is controlled by
three cranial nerves—oculomotor (cranial nerve III), trochlear (cranial nerve IV), and abducens
(cranial nerve VI). The most complicated of the three ocular motor nerves, the oculomotor
nerve controls adduction, supraduction, and infraduction via the medial, superior, inferior, and
inferior oblique muscles. It also controls pupil constriction via the iris sphincter muscle and
upper lid elevation via the levator palpebrae superioris muscle. The trochlear nerve controls
infraduction and intorsion via the superior oblique muscle. The abducens nerve controls
abduction via the lateral rectus muscle.
Clinical effects of ocular motor cranial nerve malfunction. When the oculomotor nerve
malfunctions, the patient develops some combination of adduction, supraduction, and
infraduction deficits, possibly together with ptosis and a dilated, poorly constricting pupil.
When the patient looks straight ahead, the affected eye will usually be deviated outward
(exotropia) and sometimes also upward (hypertropia) or downward (hypotropia).
When the trochlear nerve malfunctions, the patient develops a deficit in infraduction-inadduction. When the patient looks straight ahead, the affected eye will usually be deviated
upward (hypertropia) and extorted on its anterior-posterior axis (excyclodeviation).
When the abducens nerve malfunctions, the patient develops a deficit in abduction. When the
patient looks straight ahead, the affected eye will usually be deviated inward.
Accompanying these ductional deficits is a misalignment of the eyes in one or more gaze
positions. The misalignment is typically “incomitant,” that is, it varies in degree with gaze
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position. The misalignment will be greatest in the field of action of the palsied extraocular
muscles. For example, an oculomotor palsy typically causes exotropia in straight ahead gaze
that increases on contralateral gaze, as the weak medial rectus is activated. There will be an
increasing hypotropia on upgaze and an increasing hypertropia on downgaze, as the superior
and inferior rectus muscles become activated, respectfully. A trochlear palsy typically displays
a hypertropia on the affected side in straight ahead gaze that increases on contralateral and
downward gaze. An abducens palsy will cause an esotropia in straight ahead gaze that
increases on ipsilateral gaze.
Ocular motor cranial nerve lesions may be severe or mild. When the lesion is severe, the
ductional deficit will generally be marked and the diagnosis relatively easy. But when the
lesion is mild, the ductional deficit may be imperceptible, making diagnosis difficult. In such
cases, measurement of ocular alignment is critical to reaching a correct diagnosis. (1) Also
important in this setting is the assessment of the functions of the lid, pupils, and trigeminal
nerve, as well as an appreciation of ocular surface and orbital abnormalities (conjunctival
congestion, intraocular pressure, resistance to retropulsion of the eye, proptosis).
Conditions That Mimic Ocular Motor Cranial Nerve Malfunction. It is unwise to presume
that deficits in ocular movement and alignment are always due to ocular motor cranial nerve
palsies. Such deficits may also be caused by extraocular muscle disorders (inflammation,
trauma, neoplasms, dystrophies), failure of neuromuscular transmission (myasthenia gravis),
and disruption of input to the ocular motor cranial nerve nuclei in the brain stem (internuclear
ophthalmoplegia and skew deviation). (2) Distinguishing these conditions from ocular motor
palsies requires experience and skill. Reading this chapter ought to be a helpful starter!
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Diplopia. Ocular misalignment created by malfunction of the ocular motor nerves or its
mimickers usually evokes the symptom of diplopia, or seeing the same object in two different
locations. The fixating eye will focus the object of regard on its fovea, creating a clear image.
The deviating eye will focus the object of regard on an extrafoveal part of the retina. Lacking
the resolving power of the fovea, this extraretinal focus creates an unclear image that is
displaced from the clear image generated by the fixating eye according to the direction of
misalignment of the eyes. In some patients, ocular misalignment also creates the symptom of
“visual confusion”, in which the patient perceives two different but superimposed images. This
sensation results from the fact that the brain is recording images from the misaligned foveas of
the eyes. However, visual confusion is such a disturbing sensation that the brain usually
suppresses the image coming from the fovea of the deviating eye.
The diplopia caused by ocular misalignment is always binocular. That is, the diplopia
disappears when the vision of either eye is blocked (by closing the eye, applying an occluder).
Patients often report diplopia that is perceived when only one eye is viewing. This “monocular
diplopia,” in which the second (“ghost”) image overlaps the true image, is virtually always
caused by disordered optics within the eye—uncorrected refractive error, corneal surface
irregularity, iris hole, cataract, or displaced lens. The disordered optics can be confirmed by
introducing a pinhole in front of the symptomatic eye. Doing so should immediately eliminate
the ghost image. If not, the diplopia is either of psychogenic origin or the patient
miscommunicated the symptom.
Ocular misalignment without diplopia. Misalignment of the eyes does not always cause
diplopia. Patients with poor vision in one eye or both, and those with attentional or other
cognitive deficits may not appreciate diplopia. If the ocular misalignment is so minimal that it
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creates a narrow separation of images, patients may report the sensation as “blurred vision”
rather than double vision.
If the misalignment develops within the first decade of life, the second image is usually
promptly suppressed. Such suppression not only eliminates the sensation of diplopia, it
causes subnormal acuity in the eye whose image is being suppressed, a phenomenon called
“amblyopia.” Amblyopia is associated with neuronal drop-out in the lateral geniculate nucleus
and ocular dominance columns of the visual cortex served by the affected eye. Amblyopia
and its accompanying neurophysiologic effects develop only during the first decade of life
when visual pathways are capable of modification. It can be reversed by preventing the
unaffected eye from fixating and by forcing the affected eye to fixate, a task achieved by
patching the unaffected eye. The younger the patient, the more likely the amblyopia will be
reversed. Reversal of amblyopia has been documented up to age 12 years. (3)
Oculomotor palsy
Manifestations. (Figure 1) In its most extreme form, oculomotor palsy produces complete
ptosis, a fixed, dilated pupil, and total compromise of adduction, supraduction, and
infraduction. Incomplete palsies produce subtotal involvement of each of these components,
or sparing of one or more of them. Lesions usually lie within the extra-axial course of the
nerve, although brain stem lesions may sometimes be responsible.
Causes.(4-11) (Tables 1, 2) Oculomotor palsy is uncommon before age 40, except after
severe head trauma. It may rarely be present at birth. In youth, it may be acquired by
inflammation, but life-threatening lesions, including aneurysms and neoplasms, must be
scrupulously excluded even during this early phase of life. In middle and late adulthood, it
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results most often from ischemia of the subarachnoid or extradural portions of the nerve owing
to small vessel occlusive disease associated with diabetes mellitus, hypertension, and
arteriosclerosis. Less commonly, inflammation, neoplasm, and trauma may be causative
during this epoch.
The causes and evaluation of oculomotor palsy (and other ocular motor palsies, see below)
are determined by whether the palsy is “non-isolated” (one of several pertinent neurological
findings) or “isolated” (the only pertinent neurologic finding).
Non-isolated oculomotor palsy. Oculomotor palsy that is embedded among other pertinent
findings is usually caused by trauma, mass lesions, or meningeal inflammations and
neoplasms. For example, oculomotor palsy may be a sign of a cerebral hemispheric mass
lesion that has induced herniation of the temporal lobe uncus over the tentorium cerebelli,
compressing the oculomotor nerve against the rigid posterior clinoid process (“tentorial
herniation syndrome”). Injury to the peripherally-situated pupillomotor fibers (12) comes first,
so that a fixed, dilated pupil may be the initial sign. However, hemiparesis and reduced
consciousness soon follow. Oculomotor palsy that results from midbrain lesions (infarcts,
masses, demyelination) almost always causes tremor, ataxia, hemiparesis, or gaze palsies.
(2)
Cavernous sinus or superior orbital fissure lesions often cause other ocular motor palsies,
Horner syndrome, and trigeminal sensory dysfunction.
Orbital lesions rarely cause oculomotor palsy. Instead, the impaired ocular movements and
ptosis are caused by compression/infiltration of extraocular muscles and the levator palpebrae
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superioris. Orbital lesions can be clinically suspected because they cause conjunctival
congestion, elevated intraocular pressure, proptosis, or resistance to retropulsion of the eye.
Isolated oculomotor palsy. Such a palsy, in which there are no other pertinent neurologic
findings, has a different set of causes than does a non-isolated palsy. Oculomotor palsy noted
at birth (13) is often blamed on birth trauma. When there is no evidence of trauma, dysplasia
may be a better explanation. Aberrant regeneration (see below) is a common accompaniment,
indicating considerable structural damage. Amblyopia is a concern and can be difficult to treat
because of ptosis.
In childhood, acquired isolated oculomotor palsy is caused by head trauma, inflammation
(including infection), or neoplasm.(13) It must be investigated thoroughly. In children, recurrent
oculomotor palsy, previously labeled “ophthalmoplegic migraine,” is now understood to be an
idiopathic inflammatory mononeuropathy affecting the nerve root. MRI reliably shows
enhancement of its peduncular segment. (14)
In adulthood, extra-axial nerve ischemia accounts for at least 75% of cases. (2) Most patients
have a family or personal history of conditions associated with small caliber vasculopathy,
including diabetes, hypertension, cigarette smoking, and hyperlipidemia. (15, 16) The ischemia
typically spares the peripherally-situated iris sphincter fibers, (17-21) so that anisocoria rarely
exceeds 1mm.(21) Progression of the deficit up to 14 days after onset should not deter a
diagnosis of ischemia, as such progression has been amply documented.(22) Full recovery
occurs in nearly 100% of patients within three months.(23) If not, the ischemia occurred within
the brain stem (24-26), although in most such brain stem infarcts, other neurological
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manifestations are present (27) or ischemia was not the cause! The chance of recurrence of
an ischemic oculomotor (or abducens) palsy is 15%.(22)
The most important cause of isolated oculomotor palsy is cerebral berry aneurysm, usually
located at the junction of the carotid and posterior communicating arteries, and less commonly
at the apex of the basilar artery. (28-31) Patients are vulnerable over a wide age span,
extending from age 20 to 80 years! The palsy results more often from expansion than rupture
into the substance of the oculomotor nerve. It is therefore a “sentinel sign” of impending
rupture, which may be imminent and fatal in 50% of cases. Not all patients report severe
headache. Most cases will have an ipsilaterally dilated and weakly reactive pupil, but pupils
may be normal especially if the extraocular muscle palsy is incomplete, as is often the case.
(30, 31) Early diagnosis is essential, not only to preclude rupture and death, but because
treatment of an unruptured aneurysm is far more successful than treatment of a ruptured
aneurysm.
Other causes of isolated oculomotor palsy are cranial base meningeal or cavernous sinus
inflammations, neoplasms (especially pituitary adenomas), brain radiation, head trauma,
carotid cavernous fistulas, intracavernous aneurysms, and nerve sheath tumors. (2)
In the elderly, oculomotor palsy may rarely be a manifestation of giant cell (temporal)
arteritis.(32) The damage is actually more likely to be in the extraocular muscles than in the
nerve. Even so, consider this diagnosis even if constitutional symptoms are absent.
Sedimentation rate or C-reactive protein elevation prompts pre-emptive corticosteroid
treatment and temporal artery biopsy for definitive diagnosis.
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Lesions that produce disruption of the nerve cause its regenerating axons to sprout to the
wrong destinations. This phenomenon, known as “aberrant regeneration,” causes the upper lid
to elevate on adduction and sometimes on depression of the affected eye.(33, 34)
The significance of aberrant regeneration is that its cause is never ischemia, almost never
inflammation, and almost always compression by neoplasm, cyst, or aneurysm.
Mimickers. (Table 3) Imitators of oculomotor palsy are extraocular myopathy, myasthenia
gravis, trochlear nerve palsy, internuclear ophthalmoplegia, and skew deviation. Extraocular
myopathy is most commonly due to inflammation (Graves disease, idiopathic orbital
inflammation, connective tissue diseases). Signs of orbital congestion (proptosis, soft tissue
swelling, conjunctival hyperemia) will usually be present, although there are indolent forms
without such features. Myasthenia gravis may fortuitously affect only those muscles served by
the oculomotor nerve, but more commonly it also affects other extraocular muscles and
causes ptosis and weakness in forced lid closure, mouth closure, neck and shoulder
extension, and hip flexion. Difficulty breathing, chewing, and swallowing (“bulbar
manifestations”) may also be present. In trochlear nerve palsy (see below), the patient
typically reports seeing a torted image with one eye. In internuclear ophthalmoplegia, the eyes
are often aligned in straight ahead gaze, with exotropia developing on gaze to the side
contralateral to the palsy. Also, adduction of the affected eye is slow and often incomplete,
and abduction of the unaffected eye produces nystagmus. Often the patient achieves much
better adduction of the affected eye on convergence than on versions. In skew deviation,
vertical misalignment is present without horizontal or torsional misalignment; saccadic pursuit,
nystagmus, and limb or gait ataxia are frequent accompaniments.(35)
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Evaluation. (Flow Chart #1) Although the degree of pupil sparing has traditionally been used
to determine whether a compressive lesion such as aneurysm might be the cause of an
isolated oculomotor palsy, pupil signs are not adequate to make this distinction, (31)
particularly if the palsy is incomplete, as it usually is. Therefore, all patients who have isolated
(and nontraumatic) oculomotor palsy should undergo brain imaging, principally to exclude
aneurysm. CT angiography is more sensitive in detecting aneurysm, but is less sensitive in
detecting and defining non-vascular lesions. Also, it has the drawback of delivering radiation
and a dye load. But because it is so sensitive, widely available, and fast, it is the procedure of
choice for non-pregnant adults. Others should undergo MRI and MR angiography. (36, 37)
Because giant cell arteritis can give rise to manifestations that represent, or appear to
represent, an oculomotor palsy, this diagnosis should always be considered at outset.
If imaging studies are negative, giant cell arteritis is not a consideration, and the patient has
ample risk factors for arteriosclerosis, no further testing is necessary except as part of risk
factor abatement.
If arteriosclerotic risk factors are not evident, then further diagnostic
studies should be aimed at excluding inflammatory and neoplastic meningeal causes and
mimickers of oculomotor palsy. If the vascular imaging is inadequate or equivocal in excluding
aneurysm even after expert review, cerebral angiography may be necessary. (36, 37) A
critical intermediate step is having the non-invasive studies reviewed by an experienced
interventional neuroradiologist, as there is evidence that the studies may actually show the
aneurysm, but that it is overlooked by inexperienced interpreters. (38) If an aneurysm is
discovered as the cause of the oculomotor palsy, clipping may be allow improved recovery of
nerve function relative to coiling. (39)
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Among those who are initially suspected of having an ischemic oculomotor palsy, lack of
resolution within 3 months or progression after 3 weeks should prompt reinvestigation.
Non-isolated oculomotor palsies must undergo an evaluation contingent on the associated
findings.
Ophthalmic Treatment. Patients who have troublesome diplopia may sometimes be palliated
with press-on (Fresnel) prisms, spectacle occluders, or eye patches. If diplopia remains after
a period of at least six months, patients may be candidates for surgical realignment of the
eyes. Surgery involves weakening the lateral rectus muscle, strengthening the other rectus
muscles, and transposing the superior oblique to the insertion of the medial rectus muscle.
Unfortunately, these procedures rarely restore a useful field of single binocular vision. For
those who cannot be helped with eye muscle surgery, diplopia can be eliminated with an
opaque (black paint in pupil space) contact lens. (40)
Trochlear palsy
Manifestations. (Figure 2) The least common of the three ocular motor cranial nerve palsies,
trochlear palsy is also the most difficult to diagnose. Incomplete forms typically display full—or
apparently full--ductions. The distinctive feature is that damage to this muscle causes torsional
misalignment. The patient may not spontaneously report seeing a tilted image with one eye,
but this symptom can often be brought out on examination. The patient may affect a head tilt
to eliminate diplopia.
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The eyes will be vertically misaligned, the higher eye on the lesioned side (Figure 165.2). The
degree of misalignment will increase as gaze is directed away from the lesioned side and with
the head tilted toward the lesioned side. These phenomena are noted in the “three-step test.”
(1) Step one measures the hypertropia in straight-ahead gaze. Step two compares the
hypertropia in right and left gaze. Step three compares the hypertropia in right and left head
tilt. A right trochlear nerve palsy produces a “right-left-right” pattern of misalignment: right
hypertropia in straight-ahead gaze; greater hypertropia on left than right gaze; and greater
hypertropia on right than left head tilt. A left trochlear palsy produces a “left-right-left” pattern.
The examiner should also note whether the patient has pathologically high vertical fusional
reserves (4 prism-diopters or greater), and whether the vertical misalignment is greater in
upgaze than downgaze, indications of a long-standing (and possibly decompensated
congenital) lesion.
A final diagnostic step is the double Maddox Rod test for torsional misalignment. Maddox Rod
lenses are placed in the trial spectacle frames of both eyes with their axes aligned vertically.
As patients view a fixation light with both eyes, they will see two horizontal lines. They are
asked if the lines appear tilted with respect to each other. If so, they are instructed to adjust
the knob that controls the orientation of the Maddox Rod lens in the right spectacle frame so
as to make the two lines parallel. If the eyes are extorted with respect to each other, they will
move the Maddox Rod lens to a counterclockwise position. The torsional deviation is then read
in degrees from the trial frame. Excyclodeviation of more than 3 degrees is common in
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acquired trochlear nerve palsies. Greater than 10 degrees indicates a bilateral trochlear nerve
palsy.
Causes. (41-46) (Tables 1, 2) As with oculomotor palsy, the causes of trochlear palsy can be
divided into whether the palsy is non-isolated or isolated.
Non-isolated trochlear nerve palsies. Like non-isolated oculomotor nerve palsies, nonisolated trochlear nerve palsies are usually caused by traumatic, neoplastic, or inflammatory
lesions of the brainstem or cranial base. The most common lesion lies in the dorsal midbrain,
where brain stem or pineal region masses may cause damage. Some combination of vertical
gaze palsies, light:near dissociated pupils, upper lid retraction, and ataxia is likely to be
present.
Lesions of the cavernous sinus cause some combination of oculomotor, abducens, and
trigeminal dysfunction as well as Horner syndrome to the trochlear palsy. However, because
the trochlear nerve is the most resistant of the ocular motor nerves to any type of cavernous
sinus lesion, it is often spared.
Orbital lesions do not cause trochlear nerve palsy except surgery that peels the periorbita off
the medial orbital wall and trauma that fractures the trochlea.
Isolated trochlear nerve palsies. The three major causes of isolated trochlear nerve palsies
are closed head and surgical trauma, breakdown of a congenital weakness in the nerve, and
extra-axial ischemia. Nerve sheath tumors, extra-axial compression by tumor, and
inflammation are less common.
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Closed head injury is a very common cause. (47) The incisural course of the nerve makes it
particularly vulnerable to being impaled on the rigid tentorium as the brain is jostled. (48)
Neurosurgical manipulation in the tentorial region is another frequent traumatic cause. (40)
Breakdown of a congenital trochlear nerve palsy is common. Patients report that they could
originally eliminate diplopia by focusing their eyes, changing gaze position, or tilting the head.
For unexplained reasons, they eventually become unable to contain the tendency toward
misalignment and develop intermittent diplopia. Three examination features help identify the
palsy as congenital: the misalignment is worse in upgaze, fusional vergences are above
normal, and Double Maddox Rod testing fails to disclose the perception of a tilted image. MRI
may disclose a small superior oblique muscle.
Adult-onset trochlear nerve palsy may also be caused by extra-axial ischemia, although less
often than oculomotor and abducens palsies. Patients have ample arteriosclerotic risk factors.
The palsy disappears within three months.
Involvement of the peripheral segment of the nerve by inflammation, meningeal neoplasm, or
nerve sheath tumor is a rare but important cause of trochlear nerve palsy.(2)
Unlike oculomotor palsy, trochlear nerve palsy is not caused by berry aneurysm.
Mimickers. (Table 3) Four conditions imitate trochlear nerve palsy: 1) partial oculomotor nerve
palsy; 2) extraocular muscle disorder; 3) myasthenia gravis; and 4) skew deviation (see
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Differential diagnosis of oculomotor palsy, above). These conditions do not conform to the
three-step test and do not show excyclodeviation on double Maddox Rod testing. For
distinctive features of these mimickers, refer to the section on mimickers of oculomotor palsy.
Evaluation. Traumatic trochlear nerve palsies require no brain imaging or other diagnostic
studies unless the trauma is considered too trivial or remote to have been the cause.
Nontraumatic and non-isolated trochlear nerve palsies (Flow Chart #2) should be evaluated
according to the additional findings (see Oculomotor Palsy, above).
Patients with isolated trochlear nerve palsies who have features suggestive of a
decompensated congenital lesion do not need to undergo further evaluation. Nor do adults
who have enough arteriosclerotic risk factors to allow a presumptive diagnosis of ischemia as
the cause. They may be observed for recovery, which should occur within three months. All
others should undergo MRI, and if negative, lumbar puncture. Vascular imaging is
unnecessary because cerebral aneurysm is not a diagnostic consideration
Ophthalmic Treatment. Among patients who have troublesome diplopia from persistent
trochlear nerve palsies where the cause is known, eye muscle surgery is usually successful in
restoring single binocular vision over a wide gaze range.(40) Surgery consists either of
strengthening the superior oblique muscle or weakening its yoke muscle, the contralateral
inferior rectus muscle.
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Sixth cranial nerve palsy
Manifestations. (Figure 3) Abducens nerve palsy produces an esodeviation that is greatest on
gaze toward the affected side, with or without an abduction deficit. Underdiagnosis occurs
when there is no obvious abduction deficit. Overdiagnosis occurs when the examiner fails to
consider that an obvious abduction deficit may also be caused by a restrictive extraocular
(shortened) medial rectus muscle, spasm of convergence, or myasthenia gravis (see
Mimickers, below).
Causes.(2, 40, 49, 50) (Tables 1, 2) As with oculomotor and trochlear nerve palsies, the
causes of abducens palsy depend on whether the palsy is non-isolated or isolated.
Nonisolated abducens palsies. Mobius syndrome consists of esotropia with bilateral
horizontal gaze paresis, together with atrophic weakness of facial or tongue muscles and other
malformations. Multiple cranial nerve nuclear aplasias are found pathologically.(51)
Acquired non-isolated abducens palsies may also be caused by brainstem lesions that
damage the abducens fascicles.(2) Although brain stem fascicular lesions may rarely cause
an isolated abduction deficit,(52, 53) lesions in this region (inflammation, infarction, mass
lesions, Wernicke encephalopathy) typically also damage other pathways, including the medial
longitudinal fasciculus, cerebellar peduncles, trigeminal, facial, and acousticovestibular nerves,
or the corticospinal tracts. If the adjacent medial longitudinal fasciculus is affected, the patient
will develop a “one-and-one-half syndrome,” consisting of an ipsilateral gaze palsy and an
ipsilateral adduction deficit.(54) Involvement of the other structures causes ataxia, nystagmus,
facial palsy, or contralateral hemiparesis.
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Cavernous sinus lesions often damage the abducens nerve, but the proximity of other ocular
motor, trigeminal, and sympathetic nerves favors their involvement as well. However, the
abducens nerve differs from the other ocular motor and trigeminal nerves in lying within the
sinus rather than on its outer dural wall, so that internal sinus lesions such as aneurysms,
fistulas, and thrombosis are apt to affect it out of proportion to other nerves.
Orbital lesions rarely cause an abducens nerve palsy. Abduction deficits are more likely to
result from impaired function of the lateral rectus, which may be impeded by tumor, infiltrated,
or scarred.
Isolated palsies. Brainstem dysplasia accounts for most isolated congenital abducens
palsies. Often accompanied by other dysplastic manifestations, the most common variant is
Duane syndrome, in which neurons in the abducens nucleus whose axons are destined for the
lateral rectus muscle fail to develop.(55) The result is reduced or absent ipsilateral abduction,
often accompanied by palpebral fissure narrowing on attempted adduction. The fissure
narrowing is a consequence of retraction of the globe produced by co-firing of the medial and
lateral rectus muscles, the latter supplied by aberrant axons from the oculomotor nerve. The
lack of diplopia (because the misalignment is congenital) and narrowing of the lid fissure are
clues to the diagnosis.
Acquired isolated abducens palsies are unusual in children. Causes include inflammation and
neoplasm.
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In adults, most isolated abducens palsies are caused by extra-axial microvascular ischemia.(2)
Like oculomotor and trochlear nerve palsies, they should recover fully within three months.
Isolated abducens nerve palsies may also be caused by basal meningeal, clival, sphenoid,
and petrous inflammation and masses. Other considerations are increased (56) or decreased
intracranial pressure in spontaneous intracranial hypotension,(57) following lumbar
puncture,(58) spinal anesthesia,(59) or shunting (60) (“false-localizing abducens palsy”).
The abducens nerve is especially vulnerable to head trauma because it is anchored at the
petroclival junction, where it takes nearly a 90-degree turn to enter Dorello’s canal and the
cavernous sinus. Accordingly, concussive downward or backward displacement of the brain is
apt to shear the nerve as it goes through Dorello’s canal. Traumatic abducens palsy may be
associated with fractures and dislocations at the craniocervical junction. The presence of a
clival epidural hemorrhage on imaging should call attention to this possibility, which may
require stabilization to prevent spinal cord injury. (61)
As with oculomotor palsy, one should always consider giant cell arteritis as a cause of isolated
abducens palsy in the appropriate setting.
Intradural berry aneurysm is never the cause of an abducens palsy.
Mimickers. (Table 3) Abducens palsy may be mimicked by three conditions: 1) myasthenia
gravis; 2) extraocular muscle disorder; and 3) spasm of the near reflex.
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Although myasthenia gravis often produces ptosis and reduced eye movements in several
directions, it may present with an isolated abduction deficit in one eye. Inflammation,
contusion, entrapment, or scarring of the medial rectus muscle may also cause an isolated
abduction deficit. Diagnosis depends on clinical or imaging evidence of soft tissue
abnormalities in the orbit.
Spasm of the near reflex is a common and overlooked mimicker of abducens nerve palsy. It is
a psychogenic disturbance that consists of excessive convergence, which will interrupt lateral
gaze to produce a “quivering” movement of the eyes. The quivering results from intermittent
convergence movements that interrupt horizontal gaze. Pupil constriction and inappropriate
accommodation are accompaniments, but pupil constriction may be difficult to detect and
accommodation will not be measurable in older adults. (62) Abduction usually becomes full
when tested with the other eye occluded. This maneuver interrupts the visual cues that allow
the patient to maintain an artificial state of hyperconvergence. Patients who have spasm of the
near reflex have a somatoform disorder or are malingering.
Evaluation. Traumatic abducens palsy requires no brain imaging or other diagnostic studies
unless the trauma is considered too trivial or remote to have been the cause. Patients with
non-isolated abducens nerve palsies (Flow Chart #3) should undergo brain imaging guided by
the constellation of neurological findings.
If an isolated and non-traumatic abducens palsy in an adult has features of a Duane
syndrome, no diagnostic studies are necessary as the lesion is congenital. It no such features
are present, and the palsy can be attributed to an ischemic microvascular event, no diagnostic
studies are necessary unless the condition evolves or fails to resolve within three months.
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Otherwise, MRI with attention to the cranial base is the appropriate study, followed by lumbar
puncture as appropriate. Vascular imaging aimed at berry aneurysm is not necessary as such
lesions do not cause abducens nerve palsy. However, if the diagnosis of an unremitting
abducens palsy remains elusive, CTA or MRA, or even catheter angiography may be
necessary to detect a posterior-draining carotid-cavernous fistula.(63)
Ophthalmic Treatment. Among patients who have troublesome diplopia from persistent
abducens palsy where the cause is known, eye muscle surgery is often successful in restoring
single binocular vision in straight-ahead gaze. However, surgery provides a wide range of
single binocular vision only when some lateral rectus function is present preoperatively.(40)
When some abduction is present, the surgical options are weakening the medial rectus and
strengthening the lateral rectus muscles of the affected eye or resection of the lateral rectus
muscle in the affected eye and recession of the medial rectus in the unaffected eye. If no
abduction is present, the only option is transposing the vertical rectus muscles to the insertion
of the lateral rectus muscle, sometimes combined with chemodenervation of the medial rectus
muscle with intramuscular injection of botulinum toxin.(64)
Botulinum toxin denervation of the medial rectus has also been promoted as a means of
promptly but temporarily restoring normal alignment in patients with acute abducens nerve
palsy.(65, 66) However, it rarely provides a durable and wide zone of single binocular vision,
and it requires anesthesia and an ophthalmologist expert in injecting the toxin into the
extraocular muscle under electromyographic monitoring. A randomized prospective study
failed to show that it provided better outcome than observation alone.(67)
20
References
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26
TABLES
Table 1. Nontraumatic causes of isolated ocular motor nerve palsies in children*
Oculomotor palsy
Trochlear palsy
Abducens palsy
Idiopathic
Congenital
Duane syndrome
Inflammation/mass
Inflammation/mass
High ICP, Inflammation/mass
Miscellaneous**
Miscellaneous**
Pontine glioma
Miscellaneous**
*In order of estimated frequency.
**Brainstem demyelination; radiation injury, decreased intracranial pressure (abducens
only), berry aneurysm (oculomotor only).
______________________________________________________________
Table 2. Nontraumatic causes of isolated ocular motor nerve palsies in adults*
Oculomotor palsy
Trochlear palsy
Abducens palsy
Ischemia
Breakdown of
Ischemia
Berry aneurysm
Cranial base
inflammation/mass
Miscellaneous**
congenital lesion
Ischemia
Increased or decreased
intracranial pressure
Tentorial
Cranial base
inflammation/mass
Miscellaneous**
inflammation/mass
Miscellaneous**
*In order of estimated frequency
**Brainstem demyelination; giant cell arteritis, radiation injury, nerve sheath tumor, carotidcavernous fistula, cavernous sinus aneurysm, dental anesthesia, migraine, Wernicke
encephalopathy (abducens palsy).
27
Table 3. Mimickers of ocular motor nerve palsies
Oculomotor palsy
Trochlear palsy
Abducens palsy
Extraocular myopathy
Oculomotor palsy
Myasthenia gravis
Myasthenia gravis
Extraocular myopathy
Extraocular myopathy
Trochlear palsy
Myasthenia gravis
Spasm of near reflex
Internuclear ophthal-
Skew deviation
moplegia
Skew deviation
_______________________________________________________________
Figure Legends
Figure 1 Left oculomotor nerve palsy. Upper panel shows left upper lid ptosis. Lower panel
shows exodeviated left eye in primary gaze position with dilated left pupil (center), absent left
adduction (left), reduced left supraduction (top), reduced left infraduction (bottom), intact left
abduction (right).
28
Figure 2. Left trochlear nerve palsy. Upper panel shows slight left hypertropia in primary gaze
position (center), slight left hypertropia in right gaze (left) and normal alignment in left gaze
(right). Lower panel shows left hypertropia in left head tilt (right) and apparently normal
alignment on right head tilt (left).
Figure 3 Left abducens nerve palsy. Center panel shows inwardly deviated left eye
(esotropia); right panel shows that left eye does not abduct; left panel shows normal ductions
in both eyes.
29
Flow Chart #1. Evaluation of Isolated Non-traumatic Oculomotor Palsy. *Preferred for nonpregnant adults. **Clipping of aneurysm may provide relatively improved recovery of
oculomotor palsy (Reference 39).
30
Flow Chart #2. Evaluation of Isolated Non-traumatic Trochlear Palsy.
Flow Chart #3. Evaluation of Isolated Non-traumatic Abducens Palsy.
31