Cerebral aneurysms are abnormal bubbles on the blood vessels (usually arteries) in and around the brain. Cerebral aneurysms are estimated to be present in about 5% of the general population, and 20% of aneurysm patients may actually harbor multiple aneurysms.
The image on the right shows a lateral view of a right internal carotid angiogram showing a posterior communicating artery aneurysm (arrow).
The diagnosis of a cerebral aneurysm is usually made after the aneurysm leaks or ruptures. A CT scan or MRI/MRA scan may show evidence of bleeding from an aneurysm or sometimes even show a portion of the aneurysm itself. While an MRA scan is often adequate to screen patients for an aneurysm, a cerebral angiogram is required to see the complete aneurysm and to plan the appropriate treatment.
The exact cause of a cerebral aneurysm is not known. However, it appears that smoking and hypertension (high blood pressure) may be risk factors for the development of aneurysms. We also know that aneurysms are more common in certain patients with genetic diseases such as polycystic kidney disease, fibromuscular dysplasia, connective tissue disorders, and coarctation of the aorta. In addition, aneurysms are associated with arteriovenous malformations and Moyamoya disease. For these reasons, many physicians recommend that patients with these disorders or with a family history of cerebral aneurysms undergo a noninvasive screening test (MRA).
The most common problem associated with cerebral aneurysms is rupture, which usually leads to a subarachnoid hemorrhage. Cerebral aneurysms are estimated to rupture at a rate of 1-2% per year. This rate is cumulative. However, certain types of aneurysms may have considerably lower or higher rupture rates. Aneurysms can also cause problems through mass effect, that is by compressing other important nearby structures.
Rupture of an aneurysm is the most feared aneurysm complication. While the initial bleeding may be fatal, the subarachnoid hemorrhage produced can also lead to other problems such as hydrocephalus and/or vasospasm. For this reason, the major focus of aneurysm treatment is to obliterate the aneurysm before it has a chance to burst. When this is not possible, occlusion of the aneurysm is usually performed as soon as possible after the initial hemorrhage in order to prevent recurrent bleeding.
Craniotomy and Microsurgical Aneurysm Clipping
The two major methods for aneurysm treatment are microsurgery and endovascular surgery. Microsurgery is a well-established method for treating brain aneurysms. Microsurgical treatment for aneurysms involves a surgical procedure called a craniotomy to open the skull and expose the aneurysm by slipping under and around the brain using delicate instruments and high-powered microscope magnification. Once the aneurysm has been located, a titanium clip is placed across the neck (base) of the aneurysm. The clip stops blood from entering the aneurysm, thereby preventing it from bleeding. Microsurgical techniques have been around for many years and are constantly advancing. Long-term follow-up of patients after microsurgical clipping is available and shows an excellent success rate in preventing rebleeding. However, in some patients with severe bleeding, other medical problems or aneurysms that are difficult to get to with surgery, the risks of surgical treatment may be quite high.
Endovascular Aneurysm Surgery
Endovascular surgery for aneurysms is a newer, less invasive technique for treating brain aneurysms. During endovascular surgery, a catheter is introduced into a patient's peripheral artery and navigated by means of an angiogram to the area within the head where the aneurysm is located. Once found, the aneurysm is then filled from the inside with tiny platinum coils. The coils react with the surrounding blood causing it to clot, thereby obliterating the aneurysm. Endovascular treatment can be particularly effective for some aneurysms that are difficult to reach with "open" microsurgery. In addition, the risks of treatment in older patients, patients with major medical problems, and patients with severe bleeding may be much less than the traditional surgery. The short-term results using endovascular treatment for cerebral aneurysms are excellent. However, its long-term effectiveness is uncertain, and some aneurysms may re-grow even after complete treatment. For this reason, patients require close follow-up with repeated angiograms or MRA studies. Occasionally, additional treatment may be necessary.
Depending on the size and location of the aneurysm as well as the health of the individual patient, some aneurysms may not need to be treated at all. Alternatively, some complex aneurysms may require a combination of both major treatment techniques or even other types of procedures.
Both the microsurgical and endovascular therapies have advantages and disadvantages. A treatment that is appropriate for one patient may not be appropriate for another. Here at Penn State Hershey Medical Center, we have had considerable experience and special training in evaluating patients for both microsurgical and endovascular aneurysm treatment. Patients are discussed by a team of physicians well versed in all aspects of aneurysm management, and a treatment plan is carefully individualized to each patient.