Oculomotor nerve palsies, or third nerve palsies, result in weakness of the muscles supplied by the oculomotor nerve, namely the superior rectus, inferior rectus, medial rectus, inferior oblique, and levator palpebrae superioris muscles.

Terminology

If the pupil is normal-sized and reactive to light, it is called a pupil-sparing third nerve palsy; conversely if the pupil is enlarged and non-reactive, it is called a non-pupil sparing third nerve palsy.

Clinical presentation

Classically, patients present with diplopia and physical exam findings ipsilateral to the oculomotor nerve (CN III) lesion:

• "down and out" ocular positioning

  • abduction, slight depression, and intorsion (due to paralysis of adduction, elevation, and depression)

• complete ptosis

  • due to neuropathy affecting levator palpebrae superioris

• +/- enlarged unreactive pupil

  • if present, suggests compression of CN III, because the parasympathetic pupillary fibres are located peripherally in the nerve and are more likely affected by external compression

Pathology

Aetiology

It has numerous possible aetiologies which can be divided according to which portion of the nerve is affected:

• dorsal midbrain (nuclear lesions): usually due to small regions of infarction; often no other neurological symptoms

• ventral midbrain (fascicular): Benedikt syndrome and Weber syndrome

• interpeduncular (subarachnoid)

  • posterior communicating artery aneurysm

    • rapidly enlarging with or without SAH is the most common cause, and usually involves only the oculomotor nerve

    • ischaemic involvement of the nerve will usually be pupil sparing whereas aneurysmal compression usually involves the pupil

  • basal meningeal processes including infection, neoplastic infiltration, and inflammatory lesions (e.g. sarcoidosis) often involve additional cranial nerves

  • neurovascular compression without aneurysm ³

• cavernous sinus portion

  • neoplasms, most commonly pituitary macroadenomas extending into the sinus, meningiomas of the sella or sinus and any other sinus mass (e.g. trigeminal schwannomas) can compress the nerve against the interclinoid ligaments

  • when the process is more diffuse, such as in cavernous sinus syndrome, other cranial nerves are also involved (e.g. Tolosa-Hunt syndrome)

• orbital portion

  • usually there is associated proptosis or other focal orbital signs

  • conditions include intraorbital tumours (optic nerve glioma, optic nerve meningioma) and inflammatory orbital pseudotumour

Treatment and prognosis

In post-traumatic oculomotor nerve palsy, gaze movement training and steroid injections may be helpful ².

See also

• trochlear nerve palsy

• abducens nerve palsy