Aneurysms and subarachnoid hemorrhage

Intracranial aneurysms are acquired arterial out-pouchings that are most commonly located at the branching points of the major arteries coursing through the subarachnoid space at the base of the brain (Fig. 1).(19, 47, 52, 62) The prevalence of intracranial aneurysms ranges from 1% to 6% among adults in large autopsy series, and the annual rupture rate is approximately 0.5% to 2%.(1, 19, 47, 52) Aneurysms are multiple (usually two or three) in 20% to 30% of patients.(1, 19, 52) Subarachnoid hemorrhage from rupture of an intracranial aneurysm is a devastating event associated with high morbidity and mortality. Approximately 12% of patients die before receiving medical attention, 40% of hospitalized patients die within 1 month after the event, and more than one third of those who survive have major neurologic deficits.(1, 19, 52) Most intracranial aneurysms (90%) remain asymptomatic until they rupture and cause a subarachnoid hemorrhage, with only 10% presenting prior to rupture, usually with symptoms of mass effect. Such aneurysms are often large and are usually defined as "giant" when larger than 25 mm.(1, 19, 52) The most common symptom of aneurysmal mass effect is headache. Associated signs depend on the location of the aneurysm and are frequently neuro-ophthalmologic.(1, 2, 26, 47) Unruptured intracranial aneurysms causing mass effect have a high risk of subsequent rupture, with an estimated frequency of 6% per year.(1, 2, 19, 47, 52) The interval between warning signs, including those related to mass effect, and aneurysmal rupture varies from 1 day to 4 months (median, 14 days).(1, 2, 19, 52) Early diagnosis is therefore paramount to prevent a devastating subarachnoid hemorrhage. Most unruptured intracranial aneurysms that produce neuro-ophthalmologic signs arise from the junction of the internal carotid and posterior communicating arteries (Figs. 1, 2 and 3). These aneurysms typically compress the third nerve in the subarachnoid space. Compression of cranial nerves within the cavernous sinus is less common, resulting in single or multiple and often painful ocular motor nerve pareses. Unruptured aneurysms of the proximal and distal segments of the intracranial portion of the internal carotid artery can compress the anterior visual pathways and cause visual loss. Ocular symptoms and signs may be the presenting manifestations of intracranial aneurysms, allowing prompt recognition of an aneurysm prier to rupture. (2, 35, 40, 47) Moreover, visual complications are a not infrequent source of morbidity in those patients surviving acute intracranial bleeding.