====== Non-pupil-sparing oculomotor palsy ======

The rule of the [[pupil]] in [[third nerve palsy]]:

Elucidated in [[1958]] by Rucker. In effect, the rule states, “[[Third nerve palsy]] due to extrinsic compression of the [[nerve]] will be associated with impaired [[pupillary constriction]].” However, it is often overlooked that in 3% the pupil is spared
((Trobe JD. Third nerve palsy and the pupil. Footnotes to the rule. Arch Ophthalmol. 1988; 106:601–602)).
===== Etiology =====

Most cases are due to extrinsic compression of the [[3rd nerve]]. Etiologies include:

1. tumor: the most common tumors affecting the 3rd nerve:

a) [[chordoma]]s

b) [[clival meningioma]]s

2. vascular: the most common vascular lesions:

a) [[Posterior communicating artery aneurysm]]-(pupil sparing with aneurysmal oculomotor palsy occurs
in < 1%). 

★ Development of a new 3rd nerve palsy ipsilateral to a p-comm aneurysm may be a sign of expansion with the possibility of imminent rupture and is traditionally considered an indication for urgent treatment

b) [[Basilar bifurcation aneurysm]] or aneurysms of the [[distal basilar artery]] ([[basilar tip]])

c) carotid-cavernous fistula: look for pulsatile proptosis

3. uncal herniation

4. cavernous sinus lesions: usually cause additional cranial nerve findings (V1, V2, IV, VI); see
[[Cavernous sinus syndrome]]. Classically the third nerve palsy, e.g. from enlarging cavernous aneurysm, will not produce a dilated pupil because the sympathetic which dilate the pupil are also paralyzed