What’s the diagnosis?
- There are many different possible causes of new-onset ophthalmoplegia, or restricted ocular movement.
- One important potential neurovascular cause of an oculomotor nerve (cranial nerve 3) palsy is irritation of the oculomotor nerve at its cisternal segment by a posterior communicating (PCOMM) artery aneurysm.
- The precise pathophysiology of this “irritation” is poorly understood. Some argue it is related to direct aneurysmal mass effect on and mechanical compression of the oculomotor nerve. Others believe it is arterial pulsations of the aneurysm that irritate the neighboring oculomotor nerve.
- When a PCOMM artery aneurysm ruptures and causes subarachnoid hemorrhage, emergent treatment is necessary to secure the aneurysm and prevent recurrent hemorrhage. However, in the case of unruptured PCOMM artery aneurysms that cause new-onset ophthalmoplegia, it is felt that some change in the shape or behavior of the aneurysm must be occurring to cause these new symptoms. Aneurysms that are “changing” are believed to be higher risk for impending rupture.