By Deepa Soni, MD
What is an aneurysm?
A cerebral or intracranial aneurysm is a dilation of an artery in the brain that results from a weakening of the inner muscular layer (the intima) of a blood vessel wall (detailed description of cerebral aneurysms). The vessel develops a "blister-like" dilation that can become thin and rupture without warning. The resultant bleeding into the space around the brain is called a subarachnoid hemorrhage (SAH). This kind of hemorrhage can lead to a stroke, coma, and/or death.
The exact mechanisms by which cerebral aneurysms develop are unknown. However, a number of factors are believed to contribute to the formation of cerebral aneurysms. These include: 1) hypertension (high blood pressure); 2) cigarette smoking; 3) congenital (genetic) predisposition; 4) injury or trauma to blood vessels; 5) complication from some types of blood infections.
Types of Aneurysms:
An unruptured aneurysm is one whose sac has not previously leaked. An aneurysm ruptures when a hole develops in the sac of the aneurysm. The hole can be small, in which case only a small amount of blood leaks, or large, leading to a major hemorrhage. Every year approximately 30,000 patients in the United States suffer from a ruptured cerebral aneurysm, and up to 6 percent of the population may have an unruptured cerebral aneurysm. The management of both ruptured and unruptured cerebral aneurysms poses a significant challenge for patients and their treating physicians.
Today there are three treatment options for people with the diagnosis of cerebral aneurysm: 1) medical (non-surgical) therapy; 2) surgical therapy or clipping; and 3) endovascular therapy or coiling.
How is an aneurysm surgically clipped? An aneurysm is clipped through a craniotomy, which is a surgical procedure in which the brain and the blood vessels are accessed through an opening in the skull. After the aneurysm is identified, it is carefully dissected (separated) from the surrounding brain tissue. A small metal clip (usually made from titanium) is then applied to the neck (base) of the aneurysm. Aneurysm clips come in all different shapes and sizes, and the choice of a particular clip is based on the size and location of an aneurysm. The clip has a spring mechanism which allows the two "jaws" of the clip to close around either side of the aneurysm, thus occluding (separating) the aneurysm from the parent (origin) blood vessel.
Endovascular Coiling: Endovascular techniques for treating aneurysms date back to the 1970s with the introduction of proximal balloon occlusion by Fjodor A. Serbinenko, MD. During the 1980s endovascular treatment of aneurysms with balloon angioplasty was associated with high procedural rate of rupture and complications. The development of Guglielmi detachable coils (GDCs) and their FDA approval in 1995, revolutionized endovascular treatment of cerebral aneurysms.
The common goal of both surgical clipping and endovascular coiling is obliteration (destruction) of the aneurysm. Efficacy (long-term success or effectiveness of the treatment) is measured by evidence of aneurysm obliteration (destruction), without evidence of recanalization (reformation of a blood channel through the blockage), nor evidence of recurrence (aneurysm regrowth) when assessed on follow-up radiographic imaging (MRA, CTA or conventional angiography).
How is an aneurysm endovascularly coiled? Guglielmi detachable coils, known as GDCs, are soft wire spirals made out of platinum. These coils are deployed (released) into an aneurysm via a catheter that is inserted into an artery in the groin and carefully advanced into the brain. Once the coils are released into the aneurysm, the blood flow pattern within the aneurysm is altered, and the slow or sluggish remaining blood flow leads to a thrombosis (clot) of the aneurysm. A thrombosed aneurysm is obliterated and, therefore, cannot rupture. Endovascular coiling is an attractive option for treating aneurysms because it is less invasive. The long-term durability of coiling, however, is still unknown and not all aneurysms are suitable for coiling. As experience with coiling grows, the indications and pitfalls continue to be refined.
Who performs the procedure? Surgical clipping of a cerebral aneurysm is always performed by a neurosurgeon, often one with expertise in cerebrovascular disease. Most cerebrovascular neurosurgeons have had 5-7 years of general neurosurgery training and an additional 1-2 years of special cerebrovascular training.
Endovascular coiling is done either by a neurosurgeon or by an interventional neuroradiologists. An interventional radiologist has undergone extensive training (3-5 years) in both radiology and interventional (invasive) procedures involving the brain and spinal cord. All neurosurgeons who perform endovascular coiling have undergone additional training in endovascular techniques in addition to full neurosurgery training (5-7 years of residency).
Safety and Common Complications.
Although the frequencies of certain complications vary according to the intervention, both clipping and coiling share the same complications. Rupture of the aneurysm is one of the most serious complications seen in either procedure. Exact frequencies of ruptures are not well documented, but reported rupture rates range from 2 percent to 3 percent for both coiling and clipping. Rupture can cause massive intracerebral hemorrhage (hemorrhagic stroke, or bleeding into the brain) and subsequent coma or death. Although rupture can have catastrophic consequences during either procedure, surgery probably provides a better opportunity to control hemorrhage because of direct access to the ruptured aneurysm and the supplying vessels.
Ischemic stroke (stroke secondary to a decreased blood oxygen) is another serious complication frequently encountered in both clipping and coiling. The pattern and distribution of strokes varies according to the aneurysm location and procedure type.
The actual length of the procedure, the associated risks, the projected recovery time, and the expected prognosis (outcome) depend on both the location of the aneurysm, the presence and severity of hemorrhage, and the patient's underlying medical condition. Therefore, each individual's case should be discussed with the treating neurosurgeon/physician.
Review of Current Literature
Comparing the safety, effectiveness, and long-term outcome of endovascular coiling to surgical clipping of cerebral aneurysms is a major research initiative in neurosurgery today. A randomized, controlled trial (what is a randomized control trial?) is needed to compare the safety and long-term outcome of surgical clipping to endovascular coiling for the treatment of cerebral aneurysms.
Results from the International Subarachnoid Aneurysm Trial (ISAT), a randomized control trial which compared surgical clipping to endovascular coiling in the treatment of ruptured aneurysms, were recently published in the Lancet (ISAT press release PDF 89KB). The results indicate that endovascular coiling is slightly less risky (6.9 percent) than surgical clipping. These results are informative, but they must be interpreted with caution (AANS/CNS position statement) because this study was the first of its kind, and the follow-up period for the patients was short (one year). The durability or long-term permanence of endovascular coiling has yet to be established. As far as the safety of clipping or coiling, the study showed no difference in the mortality (death) rate between clipping and coiling. Therefore, no definite conclusions can be made regarding the superiority of one treatment over the other. Additional study is needed.
How do I decide what procedure to have if I have a cerebral aneurysm?
The treatment of choice for an intracranial aneurysm, like all medical decisions, should be agreed upon by both the physician and the patient. In the case of either ruptured and unruptured intracranial aneurysms, the treating physician should discuss the risks and benefits of each available treatment option. The physician will usually make recommendations for one treatment over another, depending on the facts of each individual case.
Although unresolved controversies remain as to the best treatment option for an individual patient, both surgical clipping and endovascular coiling are considered to be viable treatment options in the management of cerebral aneurysms today.
; American Association of Neurological Surgeons /