Aneurysm, cerebral
LIFE-THREATENING DISORDERWith cerebral aneurysm, localized dilation of a cerebral artery results from a weakness in the arterial wall. Its most common form is the berry aneurysm, a saclike outpouching in a cerebral artery. Cerebral aneurysms usually arise at an arterial junction in the circle of Willis, the circular anastomosis forming the major cerebral arteries at the base of the brain. Cerebral aneurysms usually rupture, causing subarachnoid hemorrhage.
The prognosis is guarded. About half of all patients who suffer a subarachnoid hemorrhage die immediately; of those who survive untreated, 40% die from the effects of hemorrhage and another 20% die later from recurring hemorrhage. With new and better treatment, the prognosis is improving.
Causes
Cerebral aneurysms may result from a congenital defect, a degenerative process, or a combination of both. For example, hypertension and atherosclerosis may disrupt blood flow and exert pressure against a congenitally weak arterial wall, stretching it like an overblown balloon and making it likely to rupture. Such a rupture is followed by subarachnoid hemorrhage, in which blood spills into the space normally occupied by cerebrospinal fluid (CSF). Sometimes, blood also spills into brain tissue and subsequently forms a clot. This may result in potentially fatal increased intracranial pressure (ICP) and brain tissue damage.
These aneurysms are slightly more common in women than in men, especially those in their late 40s or early to middle 50s, but a cerebral aneurysm may occur at any age, in women and men.
Signs and symptoms
Occasionally, rupture of a cerebral aneurysm causes premonitory symptoms that last several days, such as headache, nuchal rigidity, stiff back and legs, and intermittent nausea. Usually, however, the rupture occurs abruptly and without warning, causing a sudden severe headache, nausea, vomiting and, depending on the severity and location of bleeding, altered level of consciousness (LOC), including a deep coma.
Bleeding causes meningeal irritation, resulting in nuchal rigidity, back and leg pain, fever, restlessness, irritability, occasional seizures, and blurred vision. Bleeding into the brain tissues causes hemiparesis, hemisensory defects, dysphagia, and visual defects. If the aneurysm is near the internal carotid artery, it compresses the oculomotor nerve and causes diplopia, ptosis, dilated pupil, and inability to rotate the eye.
Degrees of severity
The severity of symptoms varies from patient to patient, depending on the site and amount of bleeding. Patients with ruptured cerebral aneurysms are grouped as follows:
Grade I: minimal bleeding. The patient is alert with no neurologic deficit; he may have a slight headache and nuchal rigidity.
Grade II: mild bleeding. The patient is alert, with a mild to severe headache, nuchal rigidity and, possibly, third-nerve palsy.
Grade III: moderate bleeding. The patient is confused or drowsy, with nuchal rigidity and, possibly, a mild focal deficit.
Grade IV: severe bleeding. The patient is stuporous, with nuchal rigidity and, possibly, mild to severe hemiparesis.
Grade V: moribund (commonly fatal). If the rupture is nonfatal, the patient is decerebrate or in a deep coma.
Life-threatening factors
Generally, a cerebral aneurysm poses three major threats:
Death from increased ICP. Increased ICP may push the brain downward, impair brain stem function, and cut off blood supply to the part of the brain that supports vital functions.
