Nerve compressed by aneurysm of posterior communicating aery is:

The main cause of compression of the oculomotor nerve is by an expanding aneurysm of the posterior communicating aery or the basilar aery. Progressively enlarging unruptured aneurysm most commonly involves the oculomotor nerve. Intracranial aneurysms: is due to progressive degenerative process affecting the vessel wall. Classification: They are based on Shape : saccular, fusiform or dissecting Size : non-giant or giant 4 2.5cm Location : anterior or posterior circulation Disease process: traumatic, non-traumatic, infectious Pathogenesis: The pathogenesis of intracranial aneurysms is a combination of degenerative changes in the elastica, and acquired defects and progressive thinning in the muscular layer leading to funnel shaped dilatation. Location: Eighty percent of intracranial aneurysms are located in the anterior circulation (circle of Willis). Twenty-five percent of these are located at the origin of the posterior communicating aery on the internal carotid aery. Clinical features: Most unruptured intracranial aneurysms are completely asymptomatic. Symptoms are usually due to rupture and resultant subarachnoid hemorrhage. Occasionally neurological symptoms may arise due to mass effect of the aneurysm. Oculomotor nerve palsy is a presenting feature in 20% of patients with posterior communicating aery aneurysms Visual field deficits (contralateral homonymous hemianopia) in relation to compression of the optic tract, Mental derangements if the aneurysm compresses the mammillary bodies Pituitary insufficiency if the aneurysm grows into the sella turcica Diagnosis: Aneurysms can be incidental, asymptomatic, or symptomatic. Incidental aneurysms are increasingly found on imaging at investigations for unrelated conditions. Ref: Harrison's, Principle of internal medicine, 17th Edition, Page 1727