ETIOLOGY, CLINICAL FEATURES AND MANAGEMENT

OF OCULOMOTOR NERVE PALSY

Dr. BHIMALA HASIKAM.S.OPHTHALMOLOGY ( 2nd YR)

14-5-13

Overview Ocular motor nerve palsies may be partial or complete,

congenital or acquired, isolated or accompanied by signs of more extensive neurological involvement.

They can result from lesions located anywhere from the ocular motor nerve nuclei, along the fascicular course within the brainstem, in the subarachnoid space, in the cavernous sinus, to the termination of the nerves in the extra-ocular muscles within the orbit.

The diagnosis and management of ocular motor nerve dysfunction varies according to the age of the patient, characteristics of the ocular motor nerve palsies, and presence of associated symptoms and signs.

Recent advances in noninvasive neuroimaging facilitate earlier diagnosis and appropriate management.

For a patient with a complaint referable to cranial nerve dysfunction, the problem must be approached in an orderly, logical, and, above all, anatomic manner.

ANATOMY The oculomotor nerve (third cranial

nerve) supplies motor innervation for the superior rectus, medial rectus, inferior rectus, inferior oblique, and levator palpebrae superioris muscles and also parasympathetic input to the pupillary constrictor and ciliary muscles.

Cell bodies reside in the midbrain in a nuclear mass straddling the vertical midline.

Each target muscle has a subnucleus devoted exclusively to its function (the medial rectus has three subnuclei).

Most rostral and dorsal are the visceral nuclei (Edinger–Westphal nuclei and adjacent structures) that supply parasympathetic innervation to the pupillary sphincters and ciliary muscles via the ciliary ganglia.

Caudal and dorsal, the ‘caudal central nucleus’ is a single midline structure that innervates the levator palpebrae superioris muscles, subserving upper lid elevation.

The cell bodies in the superior rectus subnuclei send their axons directly across the midline to join the contralateral oculomotor fascicles.

The other subnuclei project ipsilaterally to their individual extraocular muscles.

Schematic arrangement of third cranial nerve fascicular fibers in a mediolateral and rostrocaudal plane. IO, inferior oblique muscle; IR, inferior rectus muscle; LP, levator palpebrae; MR, medial rectus muscle (subnuclei a, b, and c); P, pupil; SR, superiorrectus muscle; CCN, central caudal nucleus.

The oculomotor fascicles refer to the portion of the nerve that travels through the brain stem parenchyma to exit ventrally.

The fascicles pass through the substance of the red nuclei and the medial cerebral peduncles.

On leaving the brain stem, the nerve enters the subarachnoid space and courses forward and laterally between the posterior cerebral artery above and the superior cerebellar artery below to run briefly alongside the posterior communicating artery.

At this level, the pupillary fibers are located dorsally and peripherally.

Lateral view of the subarachnoid and intracavernous portions of the oculomotor nerve (III) and its vascular supply. DMB, dorsal meningeal branches; MHT, meningohypophyseal trunk; ICA, internal carotid artery; IHB, inferior hypophyseal branches; RB, recurrent collateral branches of the ophthalmic artery; IV, trochlear nerve; V1, ophthalmic division of the trigeminal nerve; OC, optic chiasm; PG, pituitary gland.

The nerve then pierces the dura and enters the cavernous sinus.

Within the anterior aspect of the cavernous sinus, the third nerve divides so that two divisions of the oculomotor nerve pass through the superior orbital fissure and enter the orbit.

The superior division contains axons destined for the levator palpebrae superioris and superior rectus muscles.

The inferior division carries the motor fibers to the medial rectus, inferior rectus, and inferior oblique muscles, as well as the preganglionic parasympathetic fibers to the ciliary ganglion.

A coronal section of the right cavernous sinus viewed anteriorly.

Orbital apex, superior and inferior orbital fissure. Note that the trochlear nerve lies outside the muscle cone. n., nerve; a., artery; v., vein; MR, medial rectus; IR, inferior rectus; LR, lateral rectus; SR, superior rectus; L, levator; SO, superior oblique.

ETIOLOGY OF THIRD CRANIAL NERVE PALSY

Any focally destructive lesion along the course of the third cranial nerve can cause oculomotor nerve palsy or dysfunction. Some of the most frequent causes include the following:

Nuclear Portion

Infarction Hemorrhage Neoplasm Abscess

Fascicular Midbrain Portion

Infarction Hemorrhage Neoplasm Abscess

Fascicular Subarachnoid Portion

Aneurysm Infectious meningitis - Bacterial,

fungal/parasitic, viral Meningeal infiltrative Carcinomatous/lymphomatous/leukemic

infiltration, granulomatous inflammation (sarcoidosis, lymphomatoid granulomatosis, Wegener granulomatosis)

Ophthalmoplegic migraine

Fascicular Cavernous Sinus Portion

Tumor - Pituitary adenoma, meningioma, craniopharyngioma, metastatic carcinoma

Pituitary apoplexy (infarction within existing pituitary adenoma)

Vascular Giant intracavernous aneurysm Carotid artery-cavernous sinus fistula Carotid dural branch-cavernous sinus fistula Cavernous sinus thrombosis Ischemia from microvascular disease in vasa

nervosa Inflammatory - Tolosa-Hunt syndrome (idiopathic or

granulomatous inflammation)

Fascicular Orbital Portion

Inflammatory - Orbital inflammatory pseudotumor, orbital myositis

Endocrine (thyroid orbitopathy) Tumor (eg, hemangioma,

lymphangioma, meningioma)

Childhood Causes of Third Nerve (Oculomotor) Palsy

1. Trauma2. Neoplasm3. Undetermined4. Ophthalmoplegic migraine5. Postoperative cause6. Meningitis/encephalitis7. Subdural hematoma8. Viral or post-upper respiratory tract infection9. Varicella-zoster virus10. Aneurysm11. Orbital cellulitis12. Sinus disease13. Mesencephalic cyst14. Cyclic oculomotor nerve palsy15. Poison

COMMON CAUSES OF NUCLEAR AND FASICULAR THIRD CRANIAL NERVE

PALSIES

CHILDRENCongenital

- with neurological abnormalities

- with aberrant rennervation- with cyclic oculomotor

spasm

Vascular ( AV malformations )

Primary tumour

Metastatic tumour

YOUNG ADULTS

Demyelinating

Vascular (hemorrhage or

infarction)

Tumor

OLDER ADULTS

Vascular (infarction)

Tumour

CLINICAL FEATURES OF OCULOMOTOR NERVE

PALSY

SYMPTOMS OF OCULOMOTOR NERVE

PALSY The classic presenting symptom of a patient with an abnormality in 3rd nerve function are

1. Usually masked by drooping of the lid2. Blurred monocular vision at near range (rarely)3. Complains of enlarged pupil or difficulty in focussing

with involvement of accommodation4. Horizontal and/or vertical binocular diplopia, may be

recognized only when the ptotic eyelid is elevated5. Limitation of ocular movements6. Associated symptoms : - headache, localized pain in the orbit, peri orbital region- Visual involvement- Facial or body numbness or weakness- Hearing loss, tinnitus and loss of taste

SIGNS OF OCULOMOTOR NERVE PALSY

1. Ptosis - paralysis of LPS muscle.2. Deviation – out, down and intorted –

unopposed action of LR and SO.3. Ocular movements : Adduction – MR Elevation – SR and IO Depression – IR Extorsion – IR and IO4. Pupil is fixed and dilated – paralysis of

sphincter pupillae muscle.5. Accommodation is completely lost – paralysis

of ciliary muscle.

6. Head posture – if the pupillary area is uncovered, head takes a posture consistent with the directions of actions of the paralysed muscles, i.e., head is turned on the opposite side, tilted towards the same side and chin is slightly raised.

DIFFERENTIAL DIAGNOSIS OF ISOLATED THIRD NERVE

PALSY1. Vasculopathic infarction2. Vasculitic infarction3. Compressive lesion4. Trauma5. Meningeal inflammation6. Ophthalmoplegic migraine or demyelination7. Myasthenia gravis8. Early signs of thyroid disease9. Generalised myopathic conditions10.Congenital blepharoptosis11.Type II Duane’s syndrome

The differential diagnosis of isolated third nerve palsy is not so lengthy because of the many structures innervated by the third nerve and the characteristic findings.

Nonetheless, if no pain or pupil involvement exists, myasthenia gravis must be considered.

Restrictive ophthalmopathy may mimic parts of a third nerve paresis, but does not involve the pupil, more often presents with lid retraction than ptosis if thyroid ophthalmopathy is the cause, and often has other orbital findings.

A supranuclear lesion may involve ptosis and an elevation deficit, but usually has other associated deficits that involve midbrain and diencephalic structures.

TECHNIQUES OF EXAMINATION

The patient with a suspected ocular motor nerve palsy must be observed for obvious ocular deviation, ptosis, palpebral fissure asymmetry, lagophthalmos, facial asymmetry, head tilt, proptosis, conjunctival injection, or chemosis.

During visual assessment, binocularity of the diplopia is verified by monocular occlusion.

Associated abnormalities of visual acuity, color vision, or visual fields may be important localizing features.

If there is ptosis, one must look for lid fatigue or lid twitch, because these might indicate myasthenia gravis.

The pupils should be assessed for relative size and reactivity.

Special attention must be given to testing corneal sensation, although several situations, including chronic contact lens wear, aging, previous cataract surgery, and concurrent use of topical medications, may make interpretation problematic.

Symmetry of the sensory function of the three divisions of the trigeminal nerve should be tested with light touch and pinprick.

Sometimes, subtle asymmetry in sensory function can be revealed by testing the perception of cold (the flat side of a piece of metal such as the handle of a reflex hammer or the end of a tuning fork is usually sufficient).

First-, seventh-, and eighth-nerve function should always be tested.

Olfactory pathways can be screened by using coffee or other substances that have easily identified odors.

Facial nerve function is assessed by having the patient smile, puff out the cheeks, forcibly close the eyes, and wrinkle the forehead.

Simple tests of hearing include the ticking of a watch, finger rubbing, and whispering common two-syllable words.

Ocular motility should be assessed monocularly (ductions) and binocularly (versions and vergence) with tests of saccadic and pursuit movements.

The extent of movement is ascertained for each of the nine diagnostic positions of gaze as defined by the primary actions of the 12 extraocular muscles

The nature and extent of the deviations of the eyes in relation to each other may be assessed subjectively with the red glass or Maddox rod and confirmed objectively by the alternate-cover test.

The latter test with prisms can provide quantifiable measurements that help to localize the underacting muscles and allow careful follow-up.

The principal actions of theextraocular muscles. SR, superior rectus; IO,

inferior oblique; LR, lateral rectus; MR, medialrectus; IR, inferior rectus; SO, superior oblique.

For a patient with a complaint referable to cranial nerve dysfunction, the problem must be approached in an orderly, logical, and, above all, anatomic manner.

Localization of the lesion helps to determine the differential diagnosis and subsequent management.

ABNORMALITIES IN THIRD-NERVE

FUNCTION Third-nerve palsies may be partial or

complete, congenital or acquired, isolated, or accompanied by signs of more extensive neurologic involvement.

They can result from lesions anywhere along the anatomic pathway from the nucleus to the muscle.

CONGENITAL Oculomotor nerve palsies present at birth are

presumed secondary to maldevelopment, intrauterine injury, or birth trauma.

Although relatively rare compared with acquired lesions, they constitute nearly half of the third-nerve palsies documented in children.

Typically, they are unilateral and isolated, although bilaterality and accompanying neurologic signs are reported occasionally.

Some degree of ptosis and ophthalmoplegia is the rule.

The pupil is usually involved (either miotic, because of presumed aberrant regeneration, or dilated), but pupillary sparing has been noted in some cases.

The location of the lesion probably varies among cases.

The significant occurrence of aberrant regeneration suggests that some of the lesions are along the peripheral course of the nerve, but modern neuroimaging has demonstrated more central loci.

Except in cases of obvious birth trauma in which some recovery is expected, most congenital oculomotor nerve palsies are permanent.

Congenital partial third-nerve palsy. Motility photographs (a) show poor elevation of the right eye in both adduction and abduction. MRI (b) revealed a lesion in the right midbrain oculomotor nerve fascicles most consistent with an old hemorrhage

ACQUIRED THIRD-NERVE LESIONS

NUCLEAR THIRD NERVE PALSY Lesions involving the oculomotor nucleus have a

particular constellation of clinical signs reflecting the unique anatomy.

Although a unilateral, stereotactically placed experimental lesion could conceivably result in bilateral ptosis, contralateral superior rectus dysfunction, and abnormalities of the remaining muscles ipsilaterally, the clinical picture is more likely that of a complete ipsilateral oculomotor nerve palsy with additional contralateral ptosis and superior rectus dysfunction.

If the nuclear lesion is rostral, pupillary involvement is likely and lid function may be spared.

Conversely, with caudal lesions, bilateral ptosis may be a prominent or even an isolated finding.

The most common cause of lesions of the oculomotor nucleus is infarction, usually a result of thrombotic occlusion of small perforating vessels off the basilar artery or embolic or thrombotic occlusive disease of larger vessels (‘top of the basilar’ syndrome).

Other causes to consider include small intraparenchymal hemorrhage resulting from presumed vascular malformations, metastatic neoplasms, and abscesses.

Bilateral oculomotor nucleus lesions. A 78-year-oldman had sudden onset of lethargy, left hemiparesis, bilateral ptosis, and ophthalmoplegia. Examination was notable for bilateral complete ptosis and no ocular motility except normal abduction of both eyes. MRI revealed bilateral infarction of the midbrain and thalami, involving the region of the third-nerve nuclei.

FASCICULAR THIRD NERVE PALSY

Classically, the feature differentiating fascicular from peripheral nerve lesions has been the accompanying neurologic signs reflecting the fascicles’ location within the parenchyma of the brain stem.

Several syndromes have been recognized, although the original descriptions and what are now included may differ :

Third-nerve palsy and ipsilateral cerebellar ataxia may result from involvement of the fascicles and the brachium conjunctivum (commonly called Nothnagel’s syndrome);

Oculomotor palsy and contralateral tremor may reflect a lesion in the region of the red nucleus (commonly called Benedikt’s syndrome;

and third-nerve dysfunction plus contralateral hemiparesis implicates involvement of the ipsilateral cerebral peduncle (commonly called Weber’s syndrome, but the eponym may actually have been originally applied to a variant of the dorsal midbrain syndrome).

Cross-section of the midbrain at the level of theoculomotor nerves depicting the location of lesions

responsible forWeber’s syndrome (1) and Benedikt’s syndrome

(2).

Infarction causing Weber’s syndrome. The patient was a 70-year-old woman with sudden onset of a right oculomotor nerve palsy and left

hemiparesis. MRI (a) axial view; (b) coronal view; revealed a hyperintense T2 lesion (arrows) in the right midbrain involving the oculomotor nerve

fascicles and the cerebral peduncle.

With the advent of more sensitive neuroimaging tests such as magnetic resonance imaging (MRI), isolated and even pupil sparing oculomotor nerve dysfunction has been shown to result occasionally from fascicular lesions.

MRI has also demonstrated that a lesion of the fascicles can cause isolated dysfunction of either the superior or inferior division of the third nerve.

This suggests that functional organization of the oculomotor nerve into divisions may occur before the anatomic separation seen grossly within the anterior cavernous sinus.

The causes of fascicular oculomotor nerve lesions are nearly identical to those of lesions of the nuclear complex, with vascular causes heading the list, followed by infiltrative and inflammatory causes.

Because the fascicles are white matter tracts, the diagnosis of multiple sclerosis must also be considered

Epidermoid cyst involving the right midbrain and optic tract. The patient, a 34-year-old woman, had severe deficits, including a right third-nerve palsy, a left hemiparesis, and a left homonymous hemianopia.

LESIONS IN SUBARACHNOID SPACE

Third-nerve involvement in the subarachnoid space is more often presumed clinically than demonstrated pathologically or with sophisticated neuroimaging.

The subarachnoid space is the most likely site of injury in cases of isolated oculomotor palsies.

Involvement may be partial or complete, although most commonly there is progression to total involvement over time.

Because of the dorsal and peripheral location of the pupillary fibers, a dilated pupil may be the first sign of a compressive lesion in the subarachnoid space.

A common cause of an isolated oculomotor nerve palsy with pupillary involvement in adults is an intracranial aneurysm, typically situated at the junction of the posterior communicating and internal carotid arteries.

CTA demonstrating an aneurysm of the posterior communicating artery (peoA)

Posterior communicating artery aneurysm causing a third-nerve palsy. The patient was an otherwise quite

healthy 85- year-old woman who presented with headache, diplopia, and ptosis and was found to have a right pupil-involved oculomotor nerve palsy. MRI with and without

gadolinium was normal but magnetic resonance angiography (a) revealed a posterior communicating

artery aneurysm (arrow), which was confirmed by cerebral angiography (b).

Almost without exception, there is pain (although sometimes modest) and eventually other evidence of oculomotor nerve involvement.

Other locations of aneurysmal dilatation that have been shown to cause third-nerve palsies include the top of the basilar artery and the junction of the basilar and superior cerebellar arteries.

Diabetic ‘microvascular’ oculomotor palsies are also commonly painful and can have pupil involvement in 10–38% of cases, although usually the degree of aniosocoria is 1 mm or less.

Other causes of oculomotor nerve dysfunction in the subarachnoid space include compressive or infiltrating neoplasms or inflammatory lesions, meningitis (infectious, inflammatory, or neoplastic), compression by large dolichoectatic vessels or cerebral structures shifted by expanding supratentorial lesions or edema, and trauma.

With the advent of more sensitive neuroimaging, many cases of idiopathic third nerve palsy, either permanent or recurrent, and so-called ‘ophthalmoplegic migraine’, have been revealed to be the result of intrinsic lesions of the oculomotor nerve, likely benign schwannomas, cavernomas, inflammation and hematomas.

The trauma necessary for third-nerve damage is typically severe enough to have caused skull fractures and loss of consciousness.

Beware the oculomotor palsy apparent after minor trauma, because it may reflect an underlying mass lesion or aneurysm.

Third-nerve dysfunction may be a component of a generalized polyneuropathy or the Fisher variant of the Guillain–Barré syndrome.

LESIONS IN CAVERNOUS SINUS There are no specific distinguishing features of

third-nerve involvement in the cavernous sinus.

Although bifurcation of the nerve into its two divisions typically occurs in the anterior cavernous sinus, there is evidence that a functional bifurcation occurs more proximally along the course of the oculomotor nerve, probably within the brain stem, making localization of a divisional paresis problematic.

To identify clinically a cavernous sinus location of an oculomotor nerve palsy, one must note the company it keeps.

Dysfunction of the trochlear and abducens nerves, the first or second division of the trigeminal nerve, the oculosympathetics, and the venous drainage of the eye and orbit may be apparent.

Pain may be a prominent feature.

The pupil may be small or midsized and poorly reactive because of concurrent oculosympathetic involvement.

Causes include neoplasms (pituitary tumors, craniopharyngioma, meningioma , nasopharyngeal carcinoma, schwannoma, metastatic lesions), inflammations (Tolosa–Hunt, sarcoid), aneurysmal compression, ischemia, cavernous sinus thrombosis, and arteriovenous fistulas.

Cavernous sinus meningioma causing a partial third-nerve palsy. The patient was a 42 year-old woman who had left ptosis and both horizontal and vertical diplopia for 3 weeks. Examination revealed a partial left third-nerve palsy. MRI (a) axial; (b) coronal; showed a uniformly enhancing mass of the left cavernous sinus, encasing the left intracavernous carotid artery (arrow), consistent with a meningioma, which was confirmed by biopsy.

LESIONS IN ORBIT Orbital lesions may cause third-nerve

palsies that respect the anatomic bifurcation of the nerve or that reflect individual muscle involvement.

Commonly associated clinical features include proptosis and visual loss.

Causes include trauma, neoplasms, mucoceles, vascular malformations, and inflammation.

Most studies reviewing the causes of oculomotor nerve palsies do not distinguish isolated from nonisolated palsies, nor do they list causes by location.

A large number of cases are recorded as of ‘undetermined’ cause and a still larger proportion, those of presumed ischemic origin, remain of uncertain location.

Newer, more sensitive neuroimaging modalities, such as MRI, are localizing more of these lesions and even providing clues about pathogenesis, but most third-nerve palsies remain poorly characterized.

Ischemic lesions causing oculomotor nerve palsies were believed to occur most frequently along the nerve’s subarachnoid or intracavernous course, although fascicular involvement was later demonstrated in some cases.

Conditions frequently associated with third-nerve dysfunction include diabetes mellitus and hypertension, and, more rarely hypertension, giant cell arteritis, carotid occlusion and dissection, systemic lupus erythematosus, and syphilis.

The site of third nerve involvement in ‘viral’ syndromes remains unknown.

The phenomenon of ‘pupillary sparing’ bears special mention.

True pupillary sparing implies that each of the extraocular muscles innervated by the oculomotor nerve is involved to some extent, but the pupil remains of normal size and reactivity.

Oculomotor nerve palsies without dysfunction of all of the muscles innervated by the third nerve that also do not involve the pupil are not ‘pupillary sparing’.

The distinction becomes important in

management.

The cause of most isolated pupil-sparing third-nerve palsies is believed to be microvascular ischemia, frequently associated with diabetes mellitus or other vascular risk factors.

The explanation for this may be anatomic in that the peripherally located pupillary fibers may receive more collateral blood than the main nerve trunk.

Microvascular third-nerve palsies may be quite painful but usually resolve after 2–4 months.

Rarely, isolated pupilsparing oculomotor nerve palsies may be secondary to compressive lesions, although the majority of these cases have incomplete palsies.

SPECIAL SYNDROMES

Cyclical Oculomotor Paresis This is an uncommon but dramatic condition typically

seen in patients with congenital third-nerve palsies.

The classic scenario is that of baseline paresis alternating with episodes lasting seconds of miosis, increased accommodation, elevation of the ptotic upper lid, and adduction of the eye.

In some cases, the spasms can be brought on by voluntary efforts in the direction of paretic muscles.

The cause is unknown, but most authors speculate some element of aberrant regeneration after nerve or nuclear damage, similar to proposed mechanisms of ocular neuromytonia

Aberrant Regeneration Although this phenomenon has been demonstrated

or suspected in virtually every peripheral nerve that has had partial damage, the oculomotor nerve is particularly interesting in this regard because of its many branches and target structures.

Signs include elevation of the upper lid with attempted downgaze (pseudo-Graefe’s sign), upgaze, or adduction; segmental constriction of the pupil with movement in the direction of action of muscles innervated by the third nerve; retraction of the globe with attempted vertical gaze (presumably secondary to co-contraction of the superior and inferior rectus muscles); and adduction of the eye with attempted up- or downgaze.

Rarely, when both oculomotor and abducens nerves are damaged, aberrant regeneration may be of the abducens fibers into the oculomotor nerve pathways.

Oculomotor synkinesis is generally believed to reflect the misdirection of regenerating fibers after partial damage to the peripheral portion of the nerve.

However, other theories involving more central mechanisms have been proposed.

A pseudo-Graefe sign is shown in a patient

with a right cavernous sinus aneurysm and

aberrant regeneration of branches of the

third nerve. On attempted downgaze

(bottom), theright lid elevates.

Oculomotor nerve synkinesis is most commonly seen 2–3 months after injury to the nerve by trauma or compression resulting from aneurysms or tumors. Ischemic lesions (i.e., secondary to diabetes) rarely if ever result in aberrant regeneration, and the presence of synkinesis requires a careful search for a nonischemic cause.

Slowly growing mass lesions are likely to be responsible for the phenomenon of ‘primary’ oculomotor nerve synkinesis, in which a recognizable paretic phase does not precede development of the aberrant movements.

Neuromyotonia Episodic involuntary contractions of the muscles

innervated by the oculomotor nerve have been described in patients with and without baseline ocular motility abnormalities.

The contractions are brief and myotonic and can sometimes be brought on by looking in the direction of action of the involved muscle.

Most of these patients have a history of radiation therapy to either the parenchymal or the peripheral course of the ocular motor nerves.

Neuromyotonia of the fourth and sixth cranial nerves has also been reported.

Neuromyotonia may respond to membrane-stabilizing agents, such as carbamazepine.

MANAGEMENT

An evaluation of the patient with a third-nerve palsy depends on the associated symptoms and signs, the pattern of oculomotor nerve involvement, and the age of the patient.

Evaluation of Third-Nerve Dysfunction

If the patient has findings localizable to the nerve’s nuclear or fascicular course within the brain stem, MRI or at least high-resolution computed tomography(CT) is indicated .

Accompanying meningeal signs (e.g., global headache, stiff neck, and depressed level of consciousness) or other cranial nerve involvement, especially if bilateral, should prompt cerebrospinal fluid examination.

Localization to the cavernous sinus warrants neuroimaging, preferably MRI with gadolinium.

High-resolution CT with thin coronal and axial views, after the administration of a contrast agent, or MRI with fat suppression techniques without and with gadolinium, is indicated if an orbital locus is suspected.

Hemorrhage into a midbraincavernous hemangioma. A 30-year-old man had sudden onset of diplopia, incoordination, and poor tandem gait and was noted to have a partial oculomotor nerve palsy in the right eye involving primarily the inferior rectus. MRI (a) axial; (b) sagittal; revealed a hemorrhage in the right midbrain.

The approach to the patient with an isolated third-nerve palsy differs among clinicians, and some of the issues remain controversial.

The sudden onset of a painful third-nerve palsy with associated meningeal signs demands an emergent neurologic evaluation, regardless of the patient’s age or the extent of third-nerve involvement, including those that spare pupillary function.

The work-up should include CT without contrast (looking for blood in the subarachnoid space), followed by CT with intravenous contrast or, preferably, MRI with gadolinium (looking for an intracranial aneurysm or alternative cause of oculomotor nerve palsy).

If no cause for the third nerve palsy is found, one must proceed in this setting to vascular imaging.

CT alone misses many cerebral aneurysms, and MRI is more sensitive than CT but is still not adequate to rule out the presence of a clinically significant aneurysm.

Magnetic resonance angiography (MRA) provides a more sensitive noninvasive means of screening for intracranial aneurysms With the appropriate techniques, especially in combination with conventional MRI, aneurysms of a size sufficient to cause third nerve compression and to be at risk of rupture will be detected more than 98% of the time.

However, small aneurysms can rupture, and the consequences of missing even 1.5% of intracranial aneurysms are potentially grave.

Computed tomographic angiography (CTA), if performed and interpreted by a skilled neuroradiologist, will detect most aneurysms large enough to cause third nerve palsies, and the combination of well-performed and wellinterpreted MRA and CTA may be sufficient to replace catheter angiography in the investigation of cerebral aneurysms.

Although most aneurysms are seen by angiography of the ipsilateral carotid circulation, the basilar circulation must also be studied to exclude a more posterior location.

The contralateral carotid circulation should also be evaluated, because ~20% of patients have more than one aneurysm.

All patients younger than 50 years who present with an isolated third-nerve palsy of any extent should also have a complete neurologic evaluation, including a cerebral angiogram if CT or MRI does not reveal the etiology.

There is some controversy about the application of this rule to children younger than 10 years, in whom aneurysms are extremely rare.

Patients older than 50 years who present with an isolated, pupil-sparing, but otherwise complete third-nerve palsy, even in the presence of pain, can usually be assumed to have an ischemic neuropathy.

Minimal work-up for the known diabetic patient would consist of a measurement of systemic blood pressure, serum glucose, erythrocyte sedimentation rate and C-reactive protein.

If there is no history of diabetes, a glucose tolerance test or a serum hemoglobin A1c level should be obtained.

These patients must be observed closely for the next week for evidence of pupillary involvement.

Some authors argue that even these patients

require some form of initial neuroimaging, preferably MRI.

The patient older than 50 years with an isolated complete oculomotor nerve palsy with some pupillary involvement or a partial third-nerve palsy presents the most difficult management dilemma.

All of these patients should have at least the minimal blood work-up outlined earlier and a neuroimage obtained, preferably MRI of the brain without and with gadolinium.

The majority of these patients will need vascular imaging, MRA or CTA or both.

Whether to pursue catheter angiography will depend on the level of suspicion for an aneurysm and the quality of the noninvasive vascular imaging and the skill and experience of its interpreter.

The majority of ischemic third-nerve palsies resolve within 3 months.

Compressive or traumatic oculomotor nerve palsies

may take longer to improve, and incomplete recovery with or without synkinesis is more likely.

Despite rare reports of continued improvement in third-nerve palsies years after onset, once the deficit has stabilized (usually within 6 months after injury), further recovery is unlikely.

The chronic oculomotor palsy, especially in younger age groups, requires serial neuroimaging over the years, especially as the sensitivity of the techniques improves.

Diabetic third-nerve palsy . The patient was a 62-year-old man with insulindependen diabetes mellitus and new-onse diplopia and complete left ptosis. Examinatio 2 weeks after symptom onset (a) showe resolution of the ptosis, but nearly complet deficits of adduction, elevation and depressio of the left eye, and equal and reactive pupils.

Six weeks later (b) his motility had become completely normal.

Microvascular third-nerve palsies, especially in diabetics, may be exquisitely painful during the acute phase. Intense pain may require analgesics for 1–2 weeks.

Various surgical procedures have been used to provide binocular fusion in at least primary position after third-nerve palsy and to correct vision-limiting or cosmetically annoying upper lid ptosis.

However, complete oculomotor nerve palsies rarely allow a completely satisfactory surgical result.

The Scott procedure (transposition of the insertion of the superior oblique tendon to a point anterior and medial to the insertion of the superior rectus muscle without trochleotomy) combined with large recessions of the lateral rectus muscle and, occasionally, recession-resection procedures of horizontal rectus muscles of noninvolved eyes can result in a satisfactory cosmetic outcome and alignment in primary position in some cases.

The role of botulinum toxin injection in the management of acute or chronic third-nerve paresis has not been adequately investigated.

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