Berry aneurysm at the junction between the posterior communicating artery and the internal carotid artery is an important cause of oculomotor nerve palsy.
The oculomotor nerve runs through the lateral wall of the cavernous sinus superiorly. It enters the cavernous sinus just above the petroclinoid ligament and inferior to the interclinoid ligament. Masses invading the cavernous sinus from within the sella are most likely to cause third cranial nerve dysfunction prior to involvement of the other cranial nerves in the cavernous sinus. This is probably because of the oculomotor nerve's close proximity to the unyielding interclinoid ligament above and the petroclinoid ligament below.
The axons for most of the muscles are uncrossed from the nucleus to the eye, but there are 2 exceptions: (1) Axons for the levator palpebrae come from both sides of the central caudal subnucleus via crossed and uncrossed pathways. (2) Those for the superior rectus muscle come from the superior rectus subnucleus on the contralateral side.
The pupillomotor and ciliary muscle neurons derive from the Edinger-Westphal subnucleus, which is in the midline in the most rostral and anterior part of the oculomotor nerve nucleus. These autonomic pathways are all ipsilateral or uncrossed.
From emedicine.
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