256

6  Ocular Motor Nerve Palsies in Children

As the fascicular oculomotor fibers exit from the nucleus,

In a study of 30 children with isolated oculomotor palsy,

they are separated in both a mediolateral and a rostrocaudal

fashion.305 Fascicular fibers designed for the superior rectus

Miller368 found the differential diagnosis to include congeni-

and inferior oblique muscles lie in the lateral fascicle, while

tal palsy (43%), trauma (20%), infection and inflammation

those corresponding to the inferior rectus, medial rectus, and

(13%), tumor (10%), aneurysm (7%), and ophthalmoplegic

pupil are segregated medially, with pupillary fibers taking

migraine (7%). Other series reflect a similar distribu-

the most rostral course.478 Consequently, brainstem lesions

tion,222,271,399 although a series by Ing et al243 included a higher

involving the lateral oculomotor fascicle produce a monocular

percentage with traumatic cases.

elevation deficit and ptosis,236 while those involving the medial

fascicle produce an inferior divisional oculomotor palsy.305

The inferior oblique fascicles are situated most laterally,

Clinical Anatomy

while pupillary fibers are situated most medially.95

The presence of coexistent neurological signs may enable

the examiner to specifically localize the site of a fascicular

Nucleus

oculomotor injury. A midbrain lesion in the region of the

brachium conjunctivum may produce an oculomotor palsy and

The oculomotor nerves arise from nuclei in the tectum of the

cerebellar ataxia (Nothnagel syndrome). A dorsal fascicular

midbrain just anterior to the cerebral aqueduct. The nucleus

lesion involving the red nucleus may produce oculomotor

has a midline opthalmologic paired portion and lateral paired

palsy combined with contralateral hemidyskinesia (Benedikt

portions. The currently accepted anatomic scheme was

syndrome). A ventral fascicular lesion involving the oculo-

described by Warwick587 in rhesus monkeys and is supported

motor nerve may also damage the cerebral peduncle, produc-

by neuroimaging correlations in humans.83 The paired supe-

ing contralateral hemiplegia (Weber syndrome).369 As it exits

rior rectus subnuclei are unique in providing innervation to

the midbrain in the interpeduncular cistern, the oculomotor

the contralateral superior rectus muscles. The cells that sup-

nerve passes between the posterior cerebral and superior cer-

ply the levator palpebrae superioris muscle of both eyes lie in

ebellar arteries. An extra-axial lesion in this location can

a single midline structure located dorsally in the caudal por-

compress, infarct, inflame, or infiltrate the adjacent cerebral

tion of the nucleus. Medial rectus neurons are distributed in

peduncle and produce a Weber syndrome,117,369 while an

multiple areas in the nucleus, making an isolated nuclear

intra-axial lesion is usually necessary to produce a Benedikt

medial rectus palsy unlikely.135 However, isolated paresis of

syndrome.

convergence (with normal adduction) has been attributed to

The nerve then traverses the subarachnoid space in a long

selective involvement of a subgroup of neurons within the

course between the midbrain and the posterior aspect of the

medial rectus subnucleus.555 Pupillary involvement in nuclear

cavernous sinus. Here, it is vulnerable to compression by an

third nerve palsy indicates dorsal, rostral damage that is usu-

internal carotid-posterior communicating artery aneurysm

ally bilateral and is generally associated with additional

and to injury from basilar skull fracture or contiguous arach-

infranuclear or supranuclear vertical gaze palsies.369

noiditis. The oculomotor nerve passes medial to and slightly

Nuclear third nerve palsies are rare. A nuclear lesion is

inferior to the ridge of the free edge of the tentorium. The

certain in the presence of (1) a unilateral third nerve palsy

tentorial edge may form a deep groove in the oculomotor

with contralateral superior rectus palsy and bilateral ptosis or

nerve, indicating the susceptibility of the nerve to pressure

(2) a bilateral third nerve palsy with normal levator func-

with transtentorial herniation at this site. In the subarachnoid

tion.135 A nuclear lesion is possible if there is complete bilat-

space, the pupilloconstrictor fibers are located superficially

eral third nerve palsy, bilateral ptosis, or a selective deficit of

in the superior portion of the nerve.