Master of the “push-pull” technique is essential.
Patient selection for treatment must conform to the current literature and to clinical observations.
The tools needed to solve intraoperative complications must be readily available before starting the treatment.
Not every aneurysm is best treated with coiling. A low threshold for deciding to clip the aneurysm is recommended.
The treatment of intracranial aneurysms has been revolutionized over the past two decades with the advent of endovascular treatment and technologies. Although open craniotomy for clip ligation and bypass surgery are still required for certain aneurysms, technologic advancements have been decreasing the need for such invasive therapies. The prevalence of intracranial aneurysms ranges from 0.2 to 9% depending on the study, the study population, and the treatment center. Based on interpretation of the data, it is more likely that the true prevalence is closer to 1% of the adult population in young adults and 4% in the elderly.1
The natural history of intracranial aneurysms remains a controversial subject. The retrospective International Study of Unruptured Intracranial Aneurysms (ISUIA)2 found that the risk of rupture of aneurysms smaller than 10 mm was much lower (by a factor of 10 to 20) than reported in previous studies or in the experience of most large centers. The prospective arm of this study reported yearly rupture rates of 1.2%, 3.1%, and 8.6% for aneurysms 7 to 12 mm, 13 to 24 mm, and greater than 25 mm, respectively.3 This study also had significant selection bias and did not effectively combine data for aneurysms less than 7 mm. Of the 1692 patients, 534 patients were switched from observation to treatment (410 clipped and 124 coiled), and of the 193 patients who died of causes other than aneurysmal subarachnoid hemorrhage (aSAH), 52 died of intracerebral hemorrhage.4
Rinkel et al4 performed a literature review between 1955 and 1996 of nine studies evaluating 3907 patients. They found an overall risk of rupture of 0.7% for aneurysms less than or equal to 10 mm and 4% for aneurysms larger than 10 mm. In a landmark study, Juvela et al5 studied all unruptured intracranial aneurysms at their institution in Finland prior to 1979 and had 100% follow-up. In 142 patients with 181 aneurysms the cumulative rates of aSAH were 10.5% at 10 years, 23% at 20 years, and 30.3% at 30 years. Significant predictors of aSAH were aneurysm size, patient age (inverse relation), and cigarette smoking.
With a greater collecting and understanding of data, we now know that certain locations of aneurysms (posterior communicating artery aneurysms and those in the posterior circulation) have a higher risk of rupture. Irregular shape, documented growth, family history, and cigarette smoking also play a major role. With this is mind, it is generally accepted that each individual patient have a specifically tailored treatment plan.
The development of the Guglielmi detachable coil and its Food and Drug Administration (FDA) approval in 1995 introduced a potential alternative treatment for intracranial aneurysms.6 , 7 Guglielmi himself must be astonished at the major paradigm shift in treatment in just the past 15 years largely based on the continual advancement of technology. The treatment paradigm for intracranial aneurysms, both ruptured and unruptured, varies wildly based on the institution and the “gatekeeper” of this patient population. At most centers the volume of clipping verses coiling is dependent on the gate-keepers’ treatment expertise. Initially, aneurysms that were relegated to endovascular treatment were those in elderly patients, with high-grade aSAH or with serious medical and surgical comorbidities. The major barrier to endovascular therapy has traditionally been a wide aneurysm neck (Fig. 35.1), higher recurrence rates, and absent long-term data on efficacy. The release of the International Subarachnoid Aneurysm Trial (ISAT) has dramatically changed treatment practice for ruptured aneurysms around the world.8 , 9 This prospective, randomized, international study looked at the comparison of outcomes at 1 year in ruptured aneurysms treated with either endovascular coiling or surgical clip ligation. The study found that independent survival at 1 year was superior in the endovascular cohort, and that the survival benefit continues for at least 7 years. The risk of rebleeding in the endovascular group was very low but higher than that of the surgical clipping group; long-term seizures were lower in the coiled group. Recently, the Barrow Ruptured Aneurysm Trial (BRAT) trial was completed, which eliminated the bias of experience.10 These very experienced open and endovascular neurosurgeons replicated the ISAT study at a single center and found similar results. Interestingly, rehemorrhage was more common in the surgical clipping group.
It is important to point out that endovascular therapy is in its infancy with regard to both operator experience as well as technology. The traditional reports of “recurrence” or “coil compaction” have been as high as 14 to 34%.11 , 12 These rates are often quoted but often taken out of context, as they reflect often minimal compaction with no clinical relevance and are from the pre-stent era. The ability to occlude adequately, a wide-neck aneurysm, and increased packing density with stent assistance have likely lowered this number. The pertinent question is, What amount of compaction is enough to warrant retreatment? Most experienced surgeons have many patients in both operative and endovascular treatments with small remnants at the neck that are stable and of no clinical concern. These patients must be differentiated from the ones with increased growth or any filling of the body or dome of the aneurysm. The introduction of “bioactive” coils has also shown early promise in lowering the recurrence rates.13 , 14 With improved delivery and embolization techniques as well as an increase in the use of endovascular technique at most centers, recurrence rates as well as outcomes will likely improve. With longer term follow-up it has now been well established that the risk of recurrence is also very high in cigarette smokers.15 , 16 This is important in that it is one of the only truly modifiable risks, and the surgeon should play a large role in this education in addition to the primary caregiver.
Training has also reflected this paradigm shift. Most neurosurgical residency programs now have a mandatory endovascular rotation as mandated by the Residency Review Committee and the American Board of Neurological Surgery. With more physicians training and performing less invasive techniques, as in other areas of medicine, improved outcomes will follow.
♦ Patient Selection
There was little variability in patient selection prior to the ISAT trial (level 1 data), but now the widespread acceptance of endovascular treatments by the neurosurgical community and the improved technology and outcomes have increased the number of variables to consider. Thus, there is currently a wide disparity between centers in who is treated with either endovascular therapy or open craniotomy. There is a general consensus that elderly patients, patients with medical comorbidities, and most patients with high-grade subarachnoid hemorrhage (SAH) are more suitable for coiling. For dual-trained neurosurgeons, the algorithm used to be “if I can’t clip them, they should be coiled”; the opposite is now true at many centers. Patients who require long-term anticoagulation are also excellent candidates in that they do not require any cessation of anticoagulation for treatment, with the caveat that anticoagulation may increase recurrence risk.
Patients should sign an informed consent form after a discussion of treatment options ideally with a surgeon who performs both coiling and clipping or who works with either a neurosurgeon or an interventionist. Too often patients are confused by the surgeon’s treatment bias. In our practice, which is exclusively staffed by dual-trained neurosurgeons, we explain to the patient (or family, in cases of SAH) that there are two treatment options available and that we perform both regularly. It must be clearly stated that they both carry risks and benefits, and that the risk/benefit ratio is what should determine the choice. Treatment centers and operators have different levels of experience and different comfort levels, and this should be a large factor in the ultimate recommendation.
Our treatment algorithm is based on our experience with both open and endovascular treatments. At our center, most posterior circulation aneurysms are treated via endovascular coiling. Posterior inferior cerebellar artery (PICA) aneurysms that are distal or wide necked are often better suited for clip ligation (Fig. 35.2). With stent- or balloon-assisted techniques, it is very rare that a basilar artery aneurysm requires clip ligation. Most wide-necked anterior communicating artery aneurysms and middle cerebral artery aneurysms are treated via craniotomy due to the relative ease and safety of this technique. All other anterior circulation aneurysms are generally treated with endovascular methods.
We tell patients that the benefit of open craniotomy is the immediate cure of the aneurysm, with only one angiogram needed at 5-year follow-up. It is imperative to tell the patient that clip ligation does not guarantee a cure, but that intraoperative angiography helps reduce the risk of leaving residual aneurysm.17 The risks of open surgery include retraction injury, wound infection, longer inpatient and outpatient recovery, and the need for antiepileptic medications postoperatively. Endovascular treatment is much less invasive, and usually entails only one night in the hospital and several days’ recovery time at home. The risk of thromboembolic events, however, is greater, and the recurrence rates are higher than with open surgery, but with proper surveillance the risk of SAH is very low.17 The patient is also counseled that they need to have at minimum one 6-month follow-up angiogram and periodic magnetic resonance angiography (MRA) thereafter.
Giant aneurysms remain a challenge to treat from an endovascular standpoint. The rate of recurrence has been reported to be as high as 50%, and surgical morbidity is higher for these aneurysms than for smaller aneurysms. The risk of recurrence and recoiling may be an acceptable trade-off for some patients. Hunterian ligation and trapping with endovascular techniques are also effective in select patients. The introduction of Onyx polymer (ev3, Irvine, CA) and closed cell stents may hold promise for this difficult aneurysm type.
♦ Technical Nuances
With the advent of endovascular treatment comes the development of new techniques and ideas, and greater understanding of the art of coil embolization. One would be hard pressed to find any two surgeons who have the exact (or even closely similar) technique and philosophy. So the following discussion reflects one surgeon’s experience. However, one tenet that should be considered inviolable is to treat the patient and not the films. One should ask not “Can I do this?” but rather “Should I do this?”; when all tools are at your disposal, decision analysis is more difficult and must always play the most important role.
As already discussed, with the advent of stent technology, complex coils, and liquid embolics, outcomes continue to improve. Most wide-necked aneurysms are now readily treated with such devices (Fig. 35.3). The improvement of stent delivery enables the treatment of aneurysms in distal locations as well as the ability to utilize new creative techniques. Although there have been major advances in stent design and safety, it must be cautioned that we still do not have longterm data on in-stent stenosis, durability, and safety, and the use of stents should be judicious. Indeed, there has been an increased interest in obviating the need for stent placement by using liquid polymers, complex coils, and bioactive coils (Fig. 35.4).
The first goal of endovascular treatment of aneurysms is to understand the angiographic anatomy. Just as there has been a whirlwind in the evolution of devices, so too has biplane angiographic technology advanced. Three-dimensional reconstruction is available on all new biplane units, and at a minimum, biplane two-dimensional images are a must for any neurointerventional procedure (Fig. 35.5). Once the anatomy is appreciated, the aneurysm must be entered via a microcatheter and microwire. Just as in angiography, the wire is used as a guide to navigate the catheter. Too stiff a wire will allow easy shaping and access to acute turns, but will inhibit the catheter from “following” over the wire around acute bends. Too soft a wire, in contrast, will not allow for navigation into these bends such as at the takeoff of the A1 segment. Catheters come in different configurations of shape, size, and stiffness. Many surgeons use a straight catheter tip and steam-shape it to fit a particular aneurysm and anatomy. In general, anywhere a wire can be navigated to, the catheter should be able to follow. Once the microwire is navigated into the aneurysm, the catheter is carefully threaded over the wire. This maneuver is one of the more common causes of difficulty and morbidity. Once the catheter is advanced, there is an immediate tension translated onto the wire, and when the wire is pulled back upon, the catheter will then automatically advance over the wire. This “push-pull” phenomenon is the hallmark of successfully and safely catheterizing an aneurysm. Once this step is mastered, most aneurysms can be entered, regardless of location.
Once the aneurysm is entered, our preference is for the catheter tip to be in midposition, which is position B in Fig. 35.6A . A catheter placed on the wall may increase the risk of coil protrusion, as all the kinetic force will be placed on the aneurysm wall. It is also difficult to distinguish resistance from pushing against the wall versus tension in the catheter system related to tortuous anatomy (Fig. 35.6B).
Likewise, a catheter placed too close to the neck may cause prolapse of the entire catheter system into the parent vessel. Every aneurysm has different anatomic features, and placement should be adjusted accordingly. Smaller aneurysms obviously have a closer apposition of the catheter tip to the dome, which makes them more dangerous and more prone to intraprocedural rupture. Care should be taken with irregularshaped aneurysms in that the catheter position should be away from any excrescence, as it is the weakest point. With adequate catheter placement, the decision of what size, shape, and type of coil must be made. Nomenclature of coil size is x mm × x mm, the first number being the diameter and the second being the length (Fig. 35.7). The diameter should be sized according to the largest dimension of the aneurysm. The length should be correlated with the volume of the aneurysm. For example, an elongated aneurysm with a length of 7 mm may have a smaller volume than a 7-mm spherical aneurysm. This is important in that although the initial loop of coil takes excellent shape, too long a coil will cause the aneurysm to be filled, but there will be coil remaining to be placed. This scenario then mandates either “forcing” the remainder in or pulling the entire coil out, both less than ideal situations. An angiographic run or roadmap can be done prior to detachment of the coil to ensure excellent placement and to rule out extravasation. Newer coils have been designed for giant aneurysms with much longer lengths.
A basic tenet is that the two most dangerous coil placements are the first and last, similar to the takeoff and landing of an airplane. Filling of the aneurysm is done with sequentially smaller sized coils and in general with “softer” coils towards the end. Packing of the aneurysm occurs from dome to neck. Judgment must be taken into account at this juncture. Poor filling at the neck promotes coil compaction and recurrence, but overly aggressive packing can increase the risks of rupture, prolapse of coils into the parent artery, and thromboembolism. Just as in intraprocedural rupture during open surgery, the most dreaded location of rupture is the neck, as this is much more difficult to control and repair, with significant risk to the parent arteries. A useful sign at this stage is catheter “kickback”; when the coil is advanced appropriately, the catheter should push back, as shown by arrow B in Fig. 35.8 , during coil deployment rather than translate the force of the coil onto the neck of the aneurysm, as shown by arrow A in Fig. 35.8 . At the completion of coiling, several views, including three-dimensional, when appropriate, can be performed to ensure complete obliteration. At this point in the mask technique the catheter should be slowly removed under direct fluoroscopic visualization to ensure no movement of coils. Once the catheter is removed from the neck, it should remain close to the neck for a final run. In case of any further filling or extravasations, the catheter can quickly be placed back in the aneurysm or be used for thrombolysis if needed.