Cerebral Aneurysm
This localized dilation of a cerebral artery results from a weakness in the arterial wall. Its most common form is the saccular (berry) aneurysm, a saclike outpouching in a cerebral artery. (See Comparing aneurysm types.) Cerebral aneurysms commonly rupture, causing subarachnoid hemorrhage. Sometimes bleeding also spills into the brain tissue and subsequently forms a clot. This may result in potentially fatal increased intracranial pressure (ICP) and brain tissue damage.
Most cerebral aneurysms occur at bifurcations of major arteries in the circle of Willis and its branches. An aneurysm can produce neurologic symptoms by exerting pressure on the surrounding structures such as the cranial nerves.
Comparing aneurysm types
Review the following to familiarize yourself with the various types of aneurysms.
Saccular (berry) aneurysm
Most common type
Secondary to congenital weakness of media
Usually occurs at major vessel bifurcations
Occurs at the circle of Willis
Has a neck or stem
Has a sac that may be partly filled with a blood clot.
Fusiform (spindle shaped) aneurysm
Occurs with atherosclerotic disease
Characterized by irregular vessel dilation
Develops on internal carotid or basilar arteries
Rarely ruptures
Produces brain and cranial nerve compression or cerebrospinal fluid obstruction.
Mycotic aneurysm
Rare
Associated with septic emboli that occur secondary to bacterial endocarditis
Develops when emboli lodge in the arterial lumen, causing arteritis; the arterial wall weakens and dilates.
Dissecting aneurysm
Caused by arteriosclerosis, head injury, syphilis, or trauma during angiography
Develops when blood is forced between layers of arterial walls, stripping intima from the underlying muscle layer.
Traumatic aneurysm
Develops in the carotid system
Associated with fractures and intimal damage
May thrombose spontaneously.
Giant aneurysm
Similiar to saccular, but larger—11/8″ (3 cm) or more in diameter
Behaves like a space-occupying lesion, producing cerebral tissue compression and cranial nerve damage.
Charcot-Bouchard aneurysm
Microscopic
Associated with hypertension
Involves basal ganglia or brain stem.
Cerebral aneurysms are much more common in adults than in children. Incidence is slightly higher in females than in males, especially females in their late 40s or early to middle 50s, but cerebral aneurysm may occur at any age. In about 20% of patients, multiple aneurysms occur.
The prognosis is usually guarded but depends on the patient’s age and neurologic condition, the presence of other diseases, and the extent and location of the aneurysm. About half of the patients who suffer subarachnoid hemorrhages die immediately. With new and better treatment, the prognosis is improving.
Causes
Cerebral aneurysm results from a congenital defect of the vessel wall, head trauma, hypertensive vascular disease, advanced age, infection, or atherosclerosis, which can weaken the vessel wall.
Complications
Potentially fatal complications after rupture of an aneurysm include subarachnoid hemorrhage and brain tissue infarction. Cerebral vasospasm, probably the most common cause of death after rupture, occurs in about 40% of all patients after subarachnoid hemorrhage occurs.
Other possible complications of a cerebral aneurysm include rebleeding, which usually occurs within the first 24 to 48 hours after rupture, 7 to 10 days after the initial rupture, or anytime within the first 6 months; meningeal irritation from blood in the subarachnoid space; and hydrocephalus, which can occur weeks or even months after rupture if blood obstructs the fourth ventricle.
Assessment
Most cerebral aneurysms produce no symptoms until rupture occurs.
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