Oculomotor Nerve Cranial Nerve III

The third cranial nerve innervates the medial rectus, superior rectus, inferior rectus, and inferior oblique muscles, along with the pupillary sphincter and the levator palpebrae that elevates the upper eyelid.

The third nerve originates in a rostrocaudally elongated group of subnuclei clustered in the midbrain, just rostral to the level of the fourth cranial nerve nucleus. The architecture of this nuclear group has been the subject of intensive study over the years. The most widely accepted anatomical scheme is that of Warwick [2 and is represented in Figure 9-3 (Figure Not Available) . Warwick suspected that there is a subnucleus for each muscle and that these structures are in rostrocaudally elongated columns of cells. Axons from the more dorsally situated subnuclei pass through the middle and inferior columns of cells on their way to the point of exit from the ventral aspect of the midbrain near the cerebral peduncles. The nuclei for the inferior rectus, inferior

TABLE 9-1 -- CLINICOANATOMICAL CORRELATION OF DISORDERS OF CRANIAL NERVES III, IV, AND VI

Anatomical Structure

Ocular Findings

Etiologies

CRANIAL NERVE III

Nuclear

Bilateral ptosis and upgaze limitation; ipsilateral impairment of elevation, depression, adduction, and pupillary paralysis

Ischemia, central demyelinating disorders, neoplasm, inflammatory or infectious (abscess) lesions

Fascicular

Ipsilateral limitation of ocular elevation, depression, adduction; ptosis; pupillary paralysis

Ischemia, central demyelinating disorders, neoplasm, and inflammatory or infectious (abscess) lesions

Subarachnoid

Ipsilateral limitation of ocular elevation, depression, adduction; ptosis; pupillary paralysis

Meningeal neoplastic infectious, and inflammatory infiltrative disorders; aneurysm of the posterior communicating artery-internal carotid junction

Cavernous

Ipsilateral limitation of ocular elevation, depression, and adduction; ptosis; pupillary paralysis

Pituitary adenoma with lateral expansion, inflammatory (Tolosa-Hunt syndrome) and infection (aspergillosis), meningioma, giant carotid siphon aneurysm, pseudoaneurysm, carotid and dural branch to cavernous sinus fistulae, cavernous sinus thrombosis

Orbital

Ipsilateral limitation of ocular elevation, depression, and adduction; ptosis; pupillary paralysis

Orbital inflammatory pseudotumor, primary tumors (hemangioma, meningioma), metastatic tumors

CRANIAL NERVE IV

Nuclear

Failure of the ipsilateral eye to depress fully in adduction, excyclodeviation, ipsilateral hyperdeviation (greatest in adduction and depression)

Ischemia, central demyelinating disorders, neoplasm inflammatory or infectious (abscess) lesions

Fascicular

Failure of the ipsilateral eye to depress fully in adduction; excyclodeviation (torsion); ipsilateral hyperdeviation greatest in adduction and depression

Ischemia, central demyelinating disorders, neoplasm, inflammatory or infectious (abscess) lesions

Subarachnoid

Failure of the both eyes to depress fully in adduction; excyclodeviation (torsion); ipsilateral hyperdeviation greatest in adduction and depression and inflammatory or infectious (abscess) lesions

Head trauma (downward/backward displacement of the brain stem with impaction of both cranial nerves IV)

Ischemia, central demyelinating disorders, neoplasm, and inflammatory or infectious (abscess) lesions

Cavernous

Failure of the ipsilateral eye to depress fully in adduction; excyclodeviation (torsion); ipsilateral hyperdeviation greatest in adduction and depression

Pituitary adenoma with lateral expansion, inflammatory (Tolosa-Hunt syndrome) and infectious (aspergillosis) lesions, meningioma, giant carotid siphon aneurysm, pseudoaneurysm, carotid and dural branch to cavernous sinus fistulae, cavernous sinus thrombosis

Orbital

Failure of the ipsilateral eye to depress fully in adduction; excyclodeviation (torsion); ipsilateral hyperdeviation greatest in adduction and depression

Orbital inflammatory pseudotumor, primary tumors (hemangioma, meningioma), metastatic tumors (Iymphoma)

CRANIAL NERVE VI

Nuclear

Conjugate gaze palsy ipsilateral to the lesion, plus OEailure of ipsilateral eye to abduct fully and esotropia

Ischemia, central demyelinating disorders, neoplasm, inflammatory or infectious (abscess) lesions

Fascicular

Failure of ipsilateral eye to abduct; esotropia greatest in gaze toward the lesion side

Ischemia, central demyelinating disorders, neoplasm, inflammatory or infectious (abscess) lesions

Subarachnoid

Failure of ipsilateral eye to abduct; esotropia greatest in graze toward the affected side

Meningeal neoplastic, infectious, and inflammatory disorders; false-localizing cranial nerve VI palsy with elevated intracranial pressure

Cavernous

Failure of ipsilateral eye to abduct; esotropia greatest in gaze toward the lesion side

Pituitary adenoma with lateral expansion, inflammatory (Tolosa-Hunt syndrome) and infectious (aspergillosis) disorders, meningioma, giant carotid siphon aneurysm, pseudoaneurysm, carotid and dural branch to cavernous sinus fistulae, cavernous sinus thrombosis

Orbital

Failure of ipsilateral eye to abduct; esotropia greatest ingaze toward the affected side

Orbital inflammatory pseudotumor, primary tumors (hemangioma, meningioma), metastatic tumors (Iymphoma)

SUPRANUCLEAR CONTROL

Cortical

PPRF

Cerebellum

Vestibular system

Long latency, hypometric contralateral saccades, increased frequency square wave jerks; low-gain 'slow) ipsilateral smooth pursuit with catch-up (forward) saccades

Slow saccades, low-gain smooth pursuit with catch-up saccades, and conjugate gaze palsy all horizontal and ipsilateral

Gaze-evoked nystagmus with fast phases ipsilateral, macro-square wave jerks saccadic dysmetria, saccadic oscillations, macrosaccadic oscillations

Vestibular (constant velocity slow-phase) nystagmus in plane of affected semicircular canal for peripheral lesions, pure upbeat for central lesions

SUPRANUCLEAR CONTROL

Gaze-holding system

Failure of ipsilateral eye to adduct during versions (conjugate gaze) to the side opposite the lesion; dissociated sustained or transient nystagmus of the abducting eye with fast phases away from lesion side

Gaze-evoked nystagmus with fast phases ipsilateral

Degenerative diseases, benign and malignant primary and metastatic neoplasms, focal infectious or inflammatory lesions, ischemic and hemorrhagic stroke

Benign and malignant primary and metastatic neoplasms, focal infectious or inflammatory lesions, ischemic and hemorrhagic stroke involving dorsal medial pons

Cerebellar degenerative diseases, benign and malignant primary and metastatic neoplasms, focal infectious or inflammatory lesions, ischemic and hemorrhagic stroke

Cerebellar degenerative diseases (flocculus and nodulus), benign and malignant primary and metastatic neoplasms, focal infectious or inflammatory lesions, ischemic and hemorrhagic stroke

Multiple sclerosis, benign and malignant primary and metastatic neoplasms, focal infectious or inflammatory lesions, ischemic and hemorrhagic stroke

Cerebellar degenerative diseases (flocculus and nodulus), benign and malignant primary and metastatic neoplasms, focal infectious or inflammatory lesions, ischemic and hemorrhagic stroke

MLF, Medial longitudinal faseieulus, PPRF, pararr,edian pontine retieular formation oblique, and medial rectus muscles send axons only to the ipsilateral third cranial nerve. The caudal central subnucleus for the levator palpebrae is a midline structure and sends axons to both nerves. The Edinger-Westphal nucleus is also an unpaired midline nucleus situated rostral to the caudal central nucleus. Cells within this nucleus synapse in the ciliary ganglion in the inferior orbit. From this structure, postganglionic parasympathetic fibers innervate the pupillary sphincter muscle and the ciliary muscle that controls accommodation of the crystalline lens. Finally, the superior rectus subnucleus sends axons only to the contralateral third nerve trunk. These anatomical details lead to clinical rules by which one can determine whether a lesion is in the third nerve nucleus or in the fascicular portion, which is more distal. Fascicular cranial nerve III involvement by intramedullary lesions can also be distinguished from extramedullary lesions by concomitant involvement of either the red nucleus (Claude's syndrome), cerebral peduncle (Weber's syndrome), or both (Benedikt's syndrome) (see ChaptĀ§L22 ).

Within the subarachnoid space, the nerve trunk is fed by branches of the posterior cerebral artery, superior cerebellar artery, and branches of the meningohypophysial trunk. [3] In the cavernous sinus, cranial nerve III runs superior to cranial nerve IV in the deep layer of the lateral wall of the cavernous sinus ( .Fig. 9-4 ). Cranial nerve III enters the orbit inferior to the fourth cranial nerve. Within the common tendon sheath of the extraocular muscles, the annulus of Zinn, cranial nerve III then divides into the superior and inferior rami (.Fig 9.-5 ). The actual point of division varies among individuals and can occur within the cavernous sinus.

The superior ramus of cranial nerve III innervates the superior rectus and levator palpebrae muscles, while the inferior ramus innervates the medial and

TABLE 9-2 -- PRIMARY ACTIONS OF THE EXTRAOCULAR MUSCLES

Muscle

Action

Optimum Position

Medial rectus

Adduction

Lateral rectus

Abduction

Superior rectus

Elevation

In abduction

Inferior rectus

Depression

In abduction

Superior oblique

Depression

In adduction

Inferior oblique

Elevation

In adduction

inferior rectus muscles, inferior oblique muscle, and ciliary ganglion.

inferior rectus muscles, inferior oblique muscle, and ciliary ganglion.

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