Atlas of pathophysiology, 2 Edition
Part II - Disorders
In an intracranial, or cerebral, aneurysm, a weakness in the wall of a cerebral artery causes localized dilation. Cerebral aneurysms usually arise at an arterial junction in the circle of Willis, the circular anastomosis connecting the major cerebral arteries at the base of the brain. Many cerebral aneurysms rupture and cause subarachnoid hemorrhage.
Incidence is slightly higher in women than in men, especially those in their late 40s or early to mid-50s, but a cerebral aneurysm may occur at any age in either sex.
· Congenital defect
· Degenerative process such as atherosclerosis
Prolonged hemodynamic stress and local arterial degeneration at vessel bifurcations are believed to be a major contributing factor to the development and ultimate rupture of cerebral aneurysms. Bleeding spreads rapidly into the subarachnoid space and commonly into the intraventricular spaces and brain tissue, producing localized changes in the cerebral cortex and focal irritation of the cranial nerves and arteries. Increased intracranial pressure occurs, causing disruption of cerebral autoregulation and alterations in cerebral blood flow. Expanding intracranial hematomas may act as space-occupying lesions compressing or displacing brain tissue. Blockage of the ventricular system or decreased cerebrospinal fluid (CSF) absorption can result in hydrocephalus. Cerebral artery vasospasm occurs in the surrounding arteries and can further compromise cerebral blood flow, leading to cerebral ischemia and cerebral infarction.
Rebleeding is a major complication and can occur anytime, but the risk is highest within 24 to 48 hours and then again 7 to 10 days after the initial hemorrhage. The risk of rebleeding is eliminated after cerebral aneurysm obliteration.
Signs and symptoms
Cerebral aneurysms are generally asymptomatic until they rupture. Signs and symptoms of subarachnoid hemorrhage include:
· change in level of consciousness
· sudden severe headache
· nuchal rigidity
· lower back pain
· nausea and vomiting
· positive Kernig's sign
· positive Brudzinski's sign
· cranial nerve deficits
· motor weakness.
Diagnostic test results
· Cerebral arteriogram shows the presence of a cerebral aneurysm.
· Head computed tomography scan reveals subarachnoid hemorrhage.
· Transcranial Doppler ultrasound study shows increased blood flow if vasospasm occurs.
· Examination of CSF confirms bleeding.
· Electrocardiogram changes reveal bradycardia, atrioventricular blocks, and premature ventricular contractions.
· Complete blood count shows elevated white blood cell count.
· Bed rest in a quiet, darkened room with minimal stimulation
· Surgical repair by clipping, ligation, or wrapping
· Endovascular coiling
· Triple H therapy (hypervolemia, hypertension, hemodilution)
· Calcium channel blockers such as nimodipine
· Avoidance of caffeine or other stimulants; avoidance of aspirin
· Codeine or another analgesic as needed