The most common form of cerebral aneurysm is called a berry aneurysm, because its shape resembles a small berry. They develop at branching points of cerebral arteries where the arterial wall tends to be thin. The aneurysm wall can thin out and leak, especially at its dome. An aneurysm may never leak, but once it does, the risk of subsequent hemorrhage increases.
Patients with leaking cerebral aneurysms typically present with the sudden onset of severe headache, often followed by nausea, vomiting, and varying degrees of altered consciousness or neurological deficit. These symptoms are caused by sudden leakage of arterial blood from the aneurysm. The degree of leakage varies from mild to severe. After the initial hemorrhage, there is risk of recurrent hemorrhage – particularly in the first 24 hours.
The treatment goal is to stabilize the patient medically then take the steps necessary to exclude the aneurysm from the cerebrovascular circulation. There are several techniques to accomplish this including a direct surgical intervention or endovascular obliteration of the aneurysm. There may be delayed complications as a result of the hemorrhagic event, which must be managed medically while treating the aneurysm itself.
Arteriovenous malformations consist of an abnormal network of arteries and veins that are usually present from birth and may enlarge over a period of years. These lesions may also produce hemorrhage, although the risk of death from a single hemorrhage is not as high as it is with cerebral aneurysms. Malformations may also cause progressive neurological deficit and seizures.
Arteriovenous malformations may be surgically excised, treated by endovascular techniques, or by a combination of endovascular and surgical management.
Arteriovenous fistulae are lesions consisting of an abnormal communication between an artery and a vein, usually around the base of the skull where the arteries and veins are in close proximity. These lesions can be present from birth or can be acquired as a result of head trauma. They can often be managed by endovascular techniques.
Hemorrhage is the medical term for bleeding. The rupture of one of the brain’s blood vessels can cause bleeding into the subarachnoid space; beneath the arachnoid membrane, on top of the pia mater; and into brain tissue. The bleeding usually stops, at least temporarily, when a clot forms over the ruptured area.
The most frequent cause of spontaneous subarachnoid hemorrhage (not due to injury) is the rupture of a small aneurysm, or bulging sac, on one of the blood vessels that supplies the brain. It is usually impossible to determine why the aneurysm forms and bursts, but the condition is common in adults and may be associated with aging, diabetes, pregnancy, hypertension (high blood pressure), heredity, or trauma.
Cerebral aneurysms are usually of three types: saccular with a narrow “neck” (called “berry” aneurysms because of their shape and their tendency to occur in clusters); saccular with a broad base; and fusiform, in which a short section of the artery bulges all the way around. Each shape determines the degree of difficulty a surgeon faces in attempting to treat the problem.
An aneurysm ruptures spontaneously, even during sleep, and therefore is not related to the strain of hard work, sexual intercourse, or other physical activity.
Although it is not always possible to discover the exact source of bleeding, other causes of spontaneous subarachnoid hemorrhage include: arteriovenous malformations, small angiomas, certain types of infections, and bleeding disorders.
A ruptured cerebral aneurysm at first causes severe headache, which can be followed by nausea, vomiting, double vision or sensitivity to light, neck pain or stiffness, weakness, memory loss, paralysis, coma, or death. How severe the symptoms are and how long they last will depend on the amount and location of the bleeding. Blood in and around the brain can cause pressure, swelling, and brain irritation, which can lead to drowsiness, confusion, weakness or paralysis, memory loss, speech problems, behavior changes, or coma (complete loss of consciousness).
The blood vessels around the aneurysm are irritated by the blood from the hemorrhage and will at times go into a state of spasm, tightening and narrowing. This vasospasm (“vaso” meaning vessel) can occur any time after the rupture until the hemorrhaged blood has been absorbed by the body, and it can increase any or all symptoms. It is the body’s own attempt to prevent a second hemorrhage by restricting the flow of blood through the vessels around the aneurysm. Vasospasm thus reduces pressure on the delicate aneurysm but unfortunately also reduces the normal blood supply to parts of the brain.
Ongoing research is being done to discover a medicine that will control vasospasm; as yet, none has proven effective.
Other complications from subarachnoid hemorrhage, such as hydrocephalus, hematoma (blood clot), and brain swelling, involve the brain; but other body systems can also be affected because of the severe nature of the illness. Pulmonary embolus, heart abnormalities, and bleeding from an ulcer may cause further complications.
Several tests are used to confirm the diagnosis of ruptured cerebral aneurysm. Some are explained in the latter portion of this section.
Because cerebrospinal fluid flows within the subarachnoid space, a sample of CSF taken during a spinal tap at the base of the spine will show blood from the hemorrhage. A CT scan will show blood inside the skull and indicate how much bleeding has occurred.
To find the source of the hemorrhage, an angiogram is performed, which may have to be repeated to try to pinpoint the aneurysm’s exact location.
Because the aneurysm can rupture again, a quiet, restful atmosphere is important. The patient usually is placed in the Intensive Care Unit (ICU), a highly specialized area providing close observation with specialized nursing care. Complete bedrest without physical strain is essential while the patient’s condition stabilizes, usually in preparation for surgery.
Medications will be given when necessary to reduce pain, control blood pressure, relieve stress, and maintain fluid balance.
If necessary, a respirator may be used to help the patient breathe and to control intracranial pressure. Most often, however, oxygen is merely administered to the patient through nasal prongs or a mask.
Various monitoring devices may be used to assess the patient’s condition during recuperation. Among the most common are: an EKG (heart) monitor, an ICP monitoring device, a Swan-Ganz catheter to assess the patient’s fluid balance, and an arterial line to continuously measure blood pressure and aid in drawing frequent blood samples for laboratory study.
Intravenous (I.V.) fluids may be given until liquids and food can be taken adequately by mouth. The amount of fluid given will be closely monitored until the dangers of brain swelling (edema) and vasospasm lessen.