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Findings: An injection of the right internal carotid artery demonstrates filling of the right middle cerebral artery and right anterior cerebral artery. A 3 to 4 mm saccular aneurysm is identified along the cavernous carotid within the C-3 segment.
Diagnosis: 3 to 4 mm aneurysm of the C-3 segment of the right internal carotid artery.
Discussion: Intracranial saccular aneurysms are true aneurysms demonstrating weakness of all vessel wall layers. The aneurysmal sac itself is usually composed of only intima and adventitia with the media ending at the junction of the aneurysm neck. While the true incidence of intracranial aneurysms is unknown, 1% of patients undergoing four vessel cerebral angiography for indications other than subarachnoid hemorrhage were reported to have an aneurysm. 90% of saccular aneurysms arise from the circle of Willis or the bifurcation of the middle cerebral artery. 30 to 35% of saccular aneurysms arise off the anterior communicating artery. Additionally, 30 to 35% arise from the internal carotid artery at the posterior communicating artery origin. 20% of these intracranial aneurysms arise from the bifurcation of the middle cerebral artery.
15 to 20% of individuals with intracranial aneurysms have more than one. A strong female predominance is noted with intracranial aneurysm with a female to male ratio of 11 to 1. Multiple aneurysms are associated with fibromuscular dysplasia and polycystic kidney disease.
Typically, intracranial aneurysms become symptomatic between the ages of 40 and 60 years. The most common presenting symptom of an intracranial aneurysm is a subarachnoid hemorrhage. 80 to 90% of nontraumatic subarachnoid hemorrhage is caused by rupture of an intracranial aneurysm. Other presenting symptoms for an intracranial aneurysm include cranial nerve deficit, headache, seizure and infarction. For example, third nerve palsy may be secondary to a posterior communicating artery aneurysm.
The clinical outcome for patients with intracranial aneurysms is dismal with up to one third of patients dying. Many survivors are left with neurologic deficits. The bleeding rate for aneurysms is highest among those that have already bled. If untreated, at least one half of all aneurysms that have previously bled will rebleed within the next six months. Among aneurysms that have not previously ruptured, the incidence of bleeding is 1 to 2% per year. In aneurysms that have not previously bled, large size is the best indicator of an aneurysm's chance of bleeding.
References:
Atkinson, Sundt, Houser, et al: Angiographic Frequency of Anterior Circulation
Intracranial Aneurysms. Journal of Neurosurgery. 1989;70:551-555.
Osborn A. Diagnostic Neuroradiology, Mosby-Year Book, Inc; St. Louis, 1994: 248-281.
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