Isolated atraumatic third nerve palsy: clinical features and imaging techniques.

We have reviewed 34 consecutive patients imaged for an isolated third nerve palsy over a 2-year period. With pupil sparing the third nerve palsy was most often due to ischaemic microvascular disease. The commonest cause of a third nerve palsy with pupillary involvement was a posterior communicating artery aneurysm. Clinical features such as speed of onset, pain and completeness of palsy were not reliable in the diagnosis of either the nature or the location of the cause. Pupillary involvement was however often associated with a compressive lesion. Imaging along the whole course of the nerve is recommended for adequate evaluation.