Down and Out: Oculomotor nerve palsy

The lenses are usually seen on MRI and often on CT and can act as a clue to the diagnosis. This patient presented with an acute oculomotor nerve palsy on the right. In this case no cause for the palsy could be found.
An oculomotor nerve palsy results in weakness of the superior rectus, inferior rectus, medial rectus, inferior oblique, and levator palpebrae, leading to an eye that is “down and out”. 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 , ischaemic involvement of the nerve, basal meningeal processes, including infection, neoplastic infiltration, and inflammatory lesions (e.g. sarcoidosis)
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) ), cavernous sinus syndrome (e.g. Tolosa-Hunt syndrome).
Orbital portion: Intraorbital tumours (optic nerve glioma, optic nerve meningioma) and inflammatory orbital pseudotumor.
References
1. eMedicine.com
Credit: Dr Frank Gaillard
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