An aneurysm is similar to a bulge that forms at a weak spot in an inner tube. A bulge like this may exist for years, and the tire may never blow out, but sometimes a bulge will unexpectedly rupture and the tire will go flat. A cerebral aneurysm, or brain aneurysm, is an abnormal, permanent bulging or ballooning of the weakened wall in one of the arteries of the brain. Cerebral aneurysms can occur in any artery of the brain, but they usually occur in the conjunction of arteries that forms the circle of Willis. The circle of Willis, also called the cerebral arterial circle, is a circular junction of arteries at the base of the brain. Researchers estimate that three to six percent of adults in the United States have at least one cerebral aneurysm and it is common for a patient to have more than one aneurysm. Though cerebral aneurysms can rupture without warning, many aneurysms remain small and never rupture or cause any symptoms.
Doctors classify aneurysms as true or false and by their size and shape. Blood vessels are muscular tubes with three-layered walls. A true aneurysm is a bulge contained by all three layers, while a false aneurysm, or pseudoaneurysm, is often more likely to burst because it is not contained by all three layers. The size of an aneurysm is usually measured in centimeters as the diameter of the widest part. An aneurysm can be fusiform, enlarged in all directions, or sacular, a bulge at one point on the circumference of the vessel resembling a sack. Berry aneurysms are the most common type of brain aneurysm. A berry aneurysm is a type of sacular aneurysm in which the bulge forms a spherical shape attached to the vessel by a narrow, cylindrical neck.
When the walls of an artery weaken, they may be susceptible to forming a bulge. Certain diseases and conditions, aging, trauma, and infection may weaken arterial walls causing an aneurysm. Chronic high blood pressure, or hypertension, may cause or aggravate a brain aneurysm. Smoking and stimulant use can cause hypertension as well as cause or aggravate an aneurysm. Alcohol consumption, especially binge drinking, can cause aneurysm rupture and may cause aneurysms to form in the brain. When atherosclerosis hardens and weakens the arteries of the brain by coating them with plaques, a cerebral aneurysm may result. Chronic high cholesterol, or hyperlipidemia, may cause atherosclerosis or may cause aneurysms itself. Researchers have discovered a genetic trend for cerebral aneurysms. Therefore, patients may inherit a susceptibility to forming aneurysms. Additionally, many genetic disorders are associated with cerebral aneurysm formation. Polycystic kidney disease is a genetic disease that causes groups of cysts to form on the kidneys until they reduce and replace normal renal tissue; this disease has been associated with cerebral aneurysms. Ehlers-Danlos syndrome and Marfan syndrome are genetically inherited disorders that can cause the middle layer of an artery’s wall to weaken. Neurofibromatosis refers to several inherited developmental disorders causing many pedunculated, soft tumors called nerofibromas to form along with café-au-lait spots and problems in the bones, muscles, nervous system, and skin. Neurofibromatosis has been associated with cerebral aneurysm formation. A brain disease, infection, or trauma from a head injury can all cause aneurysms to form in the brain. Cerebral aneurysms are no longer thought to be congenital, or present at birth, instead, all cerebral aneurysms are now considered to be acquired over a lifetime of wear and tear acting upon congenital weaknesses in the arteries or from a previously mentioned disease or condition.
Most cerebral aneurysms remain small and never cause any symptoms, and many others remain asymptomatic until they rupture and bleed into the brain or the area around it. However, some aneurysms that have not ruptured cause symptoms because they exert pressure on or leak into an area of the head or brain. An aneurysm that has not ruptured may cause the following symptoms depending on its size, location, and growth rate: double vision, loss of vision, headaches, eye pain, neck pain, loss of feeling in the face, dilated pupil in one eye, loss of motion range in one eye, changes in speech, severe headaches, and a droopy eyelid. Some patients will experience a severe headache or headaches a few days or weeks prior to aneurysm rupture. The cause of this “sentinel headache” is somewhat unknown, but it is believed to be caused by leakage from the aneurysm that is about to burst. Most people, however, do not know they have an aneurysm until the sudden onset of symptoms as the aneurysm ruptures. This rupture is a medical emergency. A common symptom of brain aneurysm rupture is a sudden, severe headache different from a patient’s customary headache. The rupture may also cause neck stiffness, nausea, vomiting, irritability, back pain, leg pain, seizures, vision problems, and sensitivity to light. After the initial symptom(s), the patient may suffer an alteration in mental status as benign as confusion or as extreme as a coma. In about one fourth of people, a ruptured aneurysm causes seizure.
Cerebral aneurysms can rupture suddenly and without warning. Ruptured aneurysms are fatal for about one half of those afflicted. One fourth die within one day of the rupture, and another one fourth die within three months. Of the survivors, half will have a permanent disability. A ruptured aneurysm can bleed into the space surrounding the brain or the brain itself. Subarachnoid hemorrhage, bleeding into the space between the brain and the skull, is a more common result of aneurysm rupture than intracerebral hemorrhage, bleeding into the brain itself. Subarachnoid hemorrhage can cause death, brain damage, or stroke. An intracerebral hemorrhage from a ruptured blood vessel in the brain can cause swelling or the blood may collect in a mass (a hematoma). Swelling and hematoma can both rapidly destroy brain tissue. Cerebral aneurysms can cause increased intracranial pressure that can push the brain downward where the pressure may interfere with brainstem function or cut off blood supply to the brain. After an aneurysm ruptures, it may seal itself with a clot which may hold the wall of the aneurysm for as much as seven to ten days. Fibrinolysis will begin to degrade the clot after about seven days, and the aneurysm may start bleeding again, at which point, the symptoms and hemorrhage will start over. When an aneurysm ruptures or after an aneurysm has ruptured, vasospasm (narrowing) may occur in other blood vessels of the brain where it can cause ischemia (lack of blood supply) or problems with brain function. Acute hydrocephalus may occur as cerebrospinal fluid collects in the brain case because of blockage by blood or adhesions.
Cerebral aneurysms can occur in anyone, but they are most common in certain groups. Patients who are between the ages of 35 and 60, whose lifestyle involves strenuous activities that cause a sudden increase in blood pressure, who have a family history of cerebral aneurysms or a personal history of cerebral aneurysms or hypertension, or who have polycystic kidney disease or coarctation of the aorta are at risk for developing a cerebral aneurysm, as well as females, African-Americans, and nicotine or stimulant drug abusers.
Aneurysms that do not or have not yet ruptured often produce no symptoms, so they are sometimes difficult to detect, and tests performed for an unrelated condition may reveal a cerebral aneurysm. An aneurysm may be suspected after a neurological and physical exam because of the symptoms it causes if it enlarges and compresses or bleeds in the brain or organs of the head. Some tests that doctors may use to find or confirm a suspected aneurysm as well as plan for treatment include the following: carotid angiogram, computed tomography angiogram (CTA) scan, magnetic resonance imaging (MRI) or magnetic resonance angiogram (MRA), and cerebral angiogram. A computed tomography (CT) scan performed in conjunction with a lumbar puncture can identify bleeding in the brain or cerebrospinal fluid (CSF) from a ruptured cerebral aneurysm and an electroencephalogram (EEG) may help determine the cause of seizures.
The “right” treatment option for an aneurysm that has not yet ruptured varies from patient to patient because the risks involved in surgery or non-invasive repair must be weighed against the risk that the aneurysm will rupture. Some factors used in determining treatment of the aneurysm include the patient’s age, history, and health and the size, growth rate, location, type, and symptoms of the aneurysm. A small aneurysm (less than 10mm) usually will not rupture, but a large aneurysm that causes symptoms has a higher risk of rupturing, especially if the patient has a history of ruptured aneurysm. The two procedures that doctors use to treat ruptured and unruptured aneurysms are surgical clipping and coil embolization. In addition to these two procedures, a surgeon may repair an aneurysm by cutting it out and stitching the blood vessel back to itself or inserting a blood vessel harvested from another part of the body. All of these procedures involve certain risks including stroke, damage to blood vessels, and aneurysm rupture or reformation. A doctor may want to control a patient’s blood pressure or encourage a patient with a cerebral aneurysm to avoid strenuous activities, cigarettes, and alcohol abuse.
Surgical clipping is an invasive surgery during which a surgeon uses general anesthesia and cuts open an area of the skull to place a small metal clip at the base of a berry aneurysm to seclude it from blood circulation and guard it against blood pressure, thus preventing it from growing or rupturing. For an aneurysm that has already ruptured, the goal of this procedure is to stop the bleeding. This surgery may not be advisable or possible depending on the patient’s health and the location and size of the aneurysm.
Coil embolization, also called microcoil thrombosis, is a noninvasive, catheter-based procedure during which a doctor inserts a thin tube (catheter) into the arterial system through the groin and guides it up to the aneurysm. The doctor then uses the tube to place tiny metallic coils into the aneurysm to make the blood clot, relieve the pressure on the aneurysm, and prevent it from growing or rupturing. This procedure is thought to involve less risk of complications than surgical clipping, but it is a relatively new procedure and may be less effective in preventing later rupture. Patients undergoing this procedure typically have shorter hospital stays and recovery times than those of patients undergoing surgical clipping. Balloon embolization is a similar procedure in which the doctor uses tiny balloons to prevent blood flow to the aneurysm
When a cerebral aneurysm ruptures, it is a medical emergency requiring immediate attention. The doctors or surgeons may decide to operate on the aneurysm using the same procedures that are often used on unruptured aneurysms, but first, they will often want to stabilize the patient in intensive care to maintain vital functions, control bleeding, prevent brain cell death by lack of oxygen, and lower the pressure in the brain. The doctors will also be concerned with preventing vasospasm in other arteries of the brain. The risk of vasospasm usually begins three days after the initial aneurysm rupture. Vasospasm occurs when some of the arteries carrying blood to the brain become constricted and starve the brain cells of oxygen. Lowering a patient’s blood pressure may help stop the bleeding, while high blood pressure may prevent vasospasm. A doctor may prescribe anticonvulsant medications because they can assist in preventing seizures. Sometimes, when an aneurysm has ruptured, fluid that has built up in the brain can be drained with a surgically inserted ventriculoperitoneal shunt. Researchers are currently working on new drugs and procedures that may help treat ruptured and unruptured aneurysms as well as prevent vasospasms and other complications.
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.