Interventional Neuroradiology ~ GDC Coils Endosaccular Coiling of Cerebral Aneurysms Christopher M. Putman,M.D., Frank Huang-Hellinger, M.D. Ph.D, and Christopher Ogilvy, M.D.
The Interventional Neuroradiology service at Massachusetts General Hospital and the MGH Brain Aneurysm & AVM Center.

The primary goal of treatment of cerebral aneurysms is to prevent future rupture. What can we tell patients about their risk of future rupture? The best available data suggest that previously unruptured aneurysms carry a risk of hemorrhage of about 1-2 %/year. If subdivided by size, the risk is probably slightly lower for small aneurysms (< 1cm) and slightly higher for large aneurysms (1-2.5cm). The presence of multiple aneurysms and a family history of subarachnoid hemorrhage probably also raise the risk of rupture. Once an aneurysm has ruptured, the chance of re-hemorrhage dramatically increases. Of those patients who survive an initial subarachnoid hemorrhage, approximately 20 % re-bleed in the first 2 weeks and 35% over the first month if the aneurysm is left untreated. After the first 30 days the risk falls back to 1-2 % per year.

Surgical clipping is the mainstay of treatment of both ruptured and unruptured cerebral aneurysms. In this approach, the affected artery must be exposed and the aneurysm visualized directly. The surgeon can then carefully apply a metal clip to the base of the aneurysm thereby blocking blood flow into the aneurysm. Once the aneurysm is eliminated from the flow of blood the risk of hemorrhage is eliminated. The advent of microneurosurgical techniques and advancements in cerebrovascular surgery (temporary clipping, neuroprotection, etc.) have extended the applicability of aneurysm surgery and improved surgical outcomes. In spite of these advancements, there remain aneurysms which are difficult to clip even in the best of hands.

In 1991, Guglielmi detachable coil (GDC) embolization was introduced as an alternative method for treating selected aneurysm patients. The GDC system consists of a very soft and flexible microcoiled paltinum wire with intrinsic helical memory that is attached to a delivery mandrel. The coil is attached to the mandrel by a special soldered joint and can be "detached" once in the aneurysm by electrolysis. GDC embolization involves transarterial delivery of these platinum coils into the lumen of the aneurysm by way of a microcatheter placed into the aneurysm. The goal of the treatment is prevent the flow of blood into the aneurysm sack by filling the aneurysm with coils and thrombus. It has been shown in animals that this approach leads to organization of the thrombus in the aneurysm and with further healing to formation of a membrane across the neck of the aneurysm. This completes exclusion of the aneurysm from the flow of blood. Using the analogy of the surgical treatment, the technique is in effect placing an endosacular "clip".

Theorectically, there are several advantages of GDC over surgery. These procedures are performed under general anesthesia in the neuroangiography suite utilizing the standard transfemoral approaches used in diagnostic angiography. Potentially, the treatment could be combined with the initial diagnositic cerebral angiogram thereby reducing the period of risk of re-rupture. Because the approach is transarterial, multiple aneurysms can be treated during a single procedure, or GDC treatment could be combined with treatment of co-morbid conditions such as vasospasm (intra-arterial papaverine or angioplasty). Also, since there is no scarring of the route of approach to the aneurysm as there is in the case of surgery, staged or multiple procedures can be performed without added difficultly. Finally, since the approach is endovascular, the issues which make any particular location relatively straightforward or more difficult are entirely different. Therefore, some locations which are relatively difficult for surgery (basilar tip) are straightforward for GDC. (Of course, the opposite is also true of other sites-e.g. middle cerebral.)

Despite these potential advantages, surgery remains the primary treatment modality for most aneurysms. Surgical clipping has been successfully applied to intracranial aneurysms for many years and the durability of the treatment has been proven. This minimizes the need for post procedure angiographic studies which are required for any patient treated with GDC. Surgery also provides controlled access to areas of difficult anatomy and allows for arterial reconstruction for aneurysms with complex shapes and wide necks in which GDC could not be applied.

Massachusetts General Hospital was one of the sites in the multicenter trial involving a total of some 1200 patients that ultimately achieved FDA approval for the GDC technology. Since the beginning of the trial, we have developed an increasing practice in GDC therapy here at the MGH such that we are currently treating 20-30 aneurysms per year we this technique. The results so far indicate that more than 80% of GDC-treated aneurysms with a relatively narrow neck (arbitrarily defined as

Since its inception GDC embolization has evolved as a result of both clinical experience and the introduction of improvements in the technology. We are now much better at selecting aneurysms appropriate for treatment. Recently published work (Malisch 1997) confirms our experience that giant aneurysms are less likely to have a completely successful outcome after GDC embolization. Such aneurysms have a significant likelihood of coil compaction into the aneurysm, causing a recurrence of the aneurysm lumen and, more concerning, an alarmingly high hemorrhage rate after embolization (33% of such patients in one small series with an average follow-up interval of 3.5 years). We also now know that aneurysms that project along the direction of blood flow in the parent artery (e.g., superiorly directed basilar tip) are at increased risk for coil compaction into the aneurysm. Finally, there is the suggestion from autopsy data that thick-walled, calcified giant aneurysms are less likely to undergo clot organization and ultimate exclusion of the aneurysm from the circulation than is thought to be the case for small, thin walled aneurysms. Certainly, we have the best results with small aneurysms which also have small necks.

Technological advances in GDC technology have also improved this method of treatment. Over the last several years, the number of coil sizes has been increased, multi-dimensional coils allowing safer initial coil placement have become available, and more recently, much softer coils have been introduced. The manufacturing process which forms the attachment of the platinum coil with the stainless steel introducing wire has also been improved such that this detachment zone dissolves much quicker during the electrolytic process than previously. This improvement has dramatically reduced the time needed to detach each coil from up to several hours to almost always less than 10 minutes. Another significant technical refinement has been in the area of microcatheters. We now have braided, hydrophilically coated microcatheters which allow improved access to many aneurysms thereby increasing our chances of obtaining a complete aneurysm obliteration.

Our current approach is to consider GDC treatment as a complement to the surgical treatment of cerebral aneurysms. We consider using GDC in any patient in which surgery may carry an increased risk. These typically include patients with co-morbid medical conditions, with high Hunt and Hess Grades (³4), or with increased intracranial pressure following SAH. Aneurysms in which surgical exposure carries an unacceptable risk ( i.e. posteriorly directed basilar tip aneurysms or paraclinoid aneurysms which are partially within the cavernous sinus) or those which may not easily hold a surgical clip such as calcified atherosclerotic aneurysms GDC becomes the primary treatment option. GDC is also consider in patients who wish to have treatment but desire not to have a craniotomy.

References:

• Guglielmi G, Vinuela F, Sepetka I, et al. Electrothrombosis of saccular aneurysms via endovascular approach. Part 1: Eletrochemical basis, technique and experimental results. J Neurosurg, 75:1-7, 1991.
• Guglielmi G, Vinuela F, Dion J, et al. Electrothrombosis of saccular aneurysms via endovascular approach. Part 2: Preliminary clinical experience. J Neurosurg 75:8-14, 1990.
• Malisch TW, Guglielmi G, Vineula F, Duckwiler G, Gobin YP, Martin NA, Frazee JG. Intracranial aneurysms treated with the Guglielmi detachable coil: midterm clinical results in a consecutive series of 100 patients, J Neurosurg 87:176-183 (1997).

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