Decisions regarding how best to treat an aneurysm patient are always specific to that particular patient and must be made on an individual case by case basis in consultation with the treating physicians. It is important to consult with and obtain the advice of both a neurosurgeon and an interventional/neuroradiologist regarding choice of treatment. The advice of a neurologist can often be helpful as well. In some cases, as with a very small aneurysm, the risks inherent in treatment outweigh the risk of rupture, and careful monitoring is the best option. In such a case a change in the size or shape of the aneurysm may warrant treatment at a later date. For very complex aneurysms arterial bypass has been used.

In the U.S. surgical clipping, used since the 1960’s, has been the "gold standard" or default and the most common treatment. Coiling was first introduced in 1990. In Europe coiling has become more common than clipping, being used in approximately 75% of cases, whereas in the U.S. it is used in approximately 25% of cases. Since coiling has a shorter history of use, any potential long-term effects would not yet be confirmed. Studies have pointed to lower mortality and morbidity (neurological deficit) rates with coiling which is a less invasive procedure.

Angiogram: Note the aneurysm clip and the residual aneurysm under the clip. - Click image for a larger view.
Courtesy of Dr. Kieran Murphy, Johns Hopkins University, Department of Radiology

Angiogram: Coils were placed endovascularily in the residual aneurysm, and it was excluded from the circulation. This operation illustrates that many situations can require both the coiling and clipping procedures. - Click image for a larger view.
Courtesy of Dr. Kieran Murphy, Johns Hopkins University, Department of Radiology

According to the American Heart Association Statement and other sources, factors that influence the outcome of clipping and coiling treatments include:

Age - The older the patient, the more favorable less invasive procedures like coiling become as older patients suffer more post-surgery complications/damage.
Presence or absence of symptoms
Patient’s medical condition and how well they would withstand surgery (clipping)
Size, morphology and location of the aneurysm - The following are problematic:
— Large ill-defined or fusiform necks
— Atherosclerotic or distended vessels
— Major brain bifurcations
— Partially within cavernous sinus
— Midportion of the basilar artery
Surgeon’s experience

According to the AHA statement, factors that favor surgery include:

Young age with long life expectancy
Previously ruptured aneurysms
Family history of aneurysm rupture
Large aneurysms
Symptomatic aneurysms
Documentation of aneurysm growth and low associated risk with treatment

The major factors in deciding whether to use coiling are the structure and location of the aneurysm. If the sac has a wide neck where it attaches to the blood vessel, there is a danger that either a coil or some clotted blood will escape the sac, drift down the vessel and block a capillary further down the circulation system. However, the development of supple, more flexible stents and balloons has allowed stent-assisted and balloon-assisted coiling of irregular (fusiform) and wide-necked aneurysms.

Rupture Rates and Risks to Consider

The ISUIA study reported a 3.8% mortality (death) and 12.0% morbidity (injury to brain function) rate for surgery on unruptured aneurysms with no prior history of SAH (Weibers et al, Lancet. 2003 Jul 12;362(9378):103-10). The rupture rate during the surgical clipping operation has been reduced with the use of temporary clipping (Levy et al. Rupture of intracranial aneurysms during endovascular coiling: management and outcomes. Neurosurgery. 2001 Oct;49(4):807-11; discussion 811-3) to approximately 2.4% according to one source (comments to Levy). In case of rupture surgery has the advantage of direct access to the blood vessels surrounding the aneurysm for control and to drain any blood.

The rupture rate of aneurysms during coiling is between 2 and 4% in the published literature (Levy et al., 2001). Risk factors for rupture during a coiling include: recent prior rupture and the presence of a daughter aneurysm. However, previously ruptured aneurysms are likely more fragile and may be more likely to rupture irrespective of the procedure used. Furthermore, techniques are available to address rupture during coiling (Levy et al., 2001). Possible causes of rupture during the coiling procedure include:

Catheter punctures the aneurysm wall
Guidewire punctures aneurysm wall
Diversion of blood flow by coils towards weaker part of aneurysm wall
Inflation of balloon across aneurysm neck
Overpacking of aneurysm
Oversizing the coils
Increase in blood pressure against aneurysm wall due to: stiff 3D GDCs, contrast injection

One study done on aneurysm rupture during coiling found: rupture because of microcatheter use resulted in death whereas rupture due to coil herniation outside the aneurysm dome resulted in good recovery to moderate disability (Levy et al., 2001). As with airplanes, the most dangerous time appears to be the take-off and landing, the insertion and withdrawal. This study did not conclusively point to size being a risk factor.

Smaller aneurysms might be at higher risk for rupture during initial catheter placement, as the margin of error for catheter tip positioning relative to the aneurysm wall is smaller. When the wire is removed after placement of the coils, potential energy may build in the catheter’s loops and propel the tip of the catheter forward.

Conversely, larger aneurysms may rupture if the catheter gets wedged between the numerous coils it deposited and the aneurysm wall. Rupture during initial coil placement is more dangerous, as there is still high blood pressure flowing into the aneurysm. Thus, most studies show ruptures towards the end of coil placement yield patients with no symptoms.

Coiling has an advantage over surgery in that there are fewer alterations (brain damage) in the first and subsequent years after treatment.

Ultimately, many of the factors impairing the success of a surgical clipping are the same ones that impair the success of a coiling procedure; these factors favor no intervention, if possible. The characteristics of the aneurysm, in particular location and structure, dictate which procedure should be used.

Johns Hopkins University participated in the first large-scale global randomized trial of both treatments. This means that both an interventional radiologist and a neurologist consulted on each patient’s case. The cases wherein both doctors concluded that the estimated success rate of both coiling and clipping were exactly the same (either operation would have the same risk associated) were used in the randomized trial (where they alternated between clipping and coiling).

Of the 250 patients treated over the course of the 3-year study, only 2 patients were included in the randomized trial. This means that in 247 cases, both the interventional radiologist and the neurosurgeon agreed that one or the other procedure was preferable with less associated risk. This demonstrates the fact that one procedure is not "better" than the other; but each one should be used in the context best suited to it.