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Do coated or expanding coils optimize treatment of brain aneurysms, compared with bare platinum coils?


Coil embolization with bare platinum coils (BPCs) has been proved to be a safe, effective, and durable means of treating aneurysms, with outcomes superior to clipping in selected patients. In the last 15 years, however, coiling with BPCs resulted in higher short-term risks and lower long-term durability for large or giant aneurysms with wide necks and those with intraluminal thrombi. Newer coil geometries and remodeling devices such as balloons and intracranial stents have been developed, and "coated coils" are the latest innovation.

Coated coils generally consist of a platinum coil that carries material located either on the outer surface or within the coil or as "inbraided" microfilaments. Of the five types of coated coils on the market, several utilize a polyglycolic-polylactic acid polymer, a bioactive material that promotes healing by enhancing the transformation of intraaneurismal thrombus into fibrous tissue. Another option, the HydroCoil, is covered by a hydrogel, which swells and reduces the space between coils, thereby improving durability by increasing overall packing density up to two to three times, compared with BPCs.

Clinical experience with coated coils has been positive. At a symposium at a meeting sponsored by the American Society of Interventional and Therapeutic Neuroradiology held in Oahu, Hawaii, John Chaloupka, M.D., of the University of Iowa Hospitals in Iowa City reported only 16% of 232 patients required retreatment within 6 months after coiling with Matrix (Boston Scientific) coils, which declined to 7% in those who also received adjunctive stenting. Johnny Pryor, M.D., of Massachusetts General Hospital, Boston, reported a 92% success rate with Cerecyte (Micrus) coils in treating complex and wide-necked aneurysms in patients considered too risky for surgery.

At the University of Illinois at Chicago, we have found coiling with HydroCoils (Microvention) decreased by one-third both the recurrence rate (from 26% to 17%) and retreatment rate (from 15% to 10%), compared with BPCs in a series of size- and shape-matched aneurysms. In a series of 50 aneurysms that were initially filled with HydroCoils and then "finished" with either BPCs or HydroCoils, the use of bare finishing coils was associated with greater coil usage, increased procedural costs, and higher recurrence and retreatment rates than those finished with HydroCoils. Similar trends were seen in a larger, multicenter series of 200 patients.

In an informal survey at the ASITN meeting, about 40% of the audience of 150 neuroradiologists responded that inflammation, edema, or hydrocephalus was of "great concern" with bioactive coated coils. Worldwide, the HydroCoil's manufacturer, reports rates of 0.3% for meningitis, 0.5% for edema, and 2.1% for hydrocephalus in large or giant aneurysms.

While we look forward to the results of large-scale controlled randomized trials now underway, I believe coated coils allow us to effectively and safely treat larger aneurysms with wider necks and more complex anatomy than was possible with BPC, with the least likelihood of regrowth and need for retreatment.

Tim Malisch, M.D., is an associate professor in the departments of neurosurgery and radiology at the University of Illinois at Chicago.


Bare platinum coils have been used in more than 150,000 patients worldwide since 1990. Use of this technique is supported by excellent clinical data in more than 500 published papers showing that endovascular coiling with BPC is safe, effective, and durable in treating both ruptured and unruptured brain aneurysms.

While some advocate the use of newer coils to optimize outcomes, there are currently no good, prospective, multicenter papers or clinical trials that have been published with long-term data to demonstrate improved safety, efficacy, or cost savings with biologically active and/or coated coils, compared with BPCs.

From our experience at the University of California San Francisco Medical Center, where more than 1,500 patients have been treated using conventional bare platinum coils, we have found BPCs easy to use and widely available for all different types of aneurysms. Recent advances have made coils softer and more conformable, with complex, concentric 2-D and 3-D shapes with larger internal diameters to better fit aneurysms of different sizes and shapes. Concentric packing has improved the volume and filling of aneurysms, and the increased coil diameters have enhanced long-term aneurysm occlusion. BPCs are also compatible with intracranial stent devices and balloon remodeling techniques, and these adjunctive treatments can improve outcomes for larger wide-necked aneurysms.

These modifications have had excellent clinical results. Better packing and neck coverage with larger-diameter coils have resulted in less than 10%-12% recanalization rates at 6 months and 12 months in our own center. For the past 2.5 years, we have used only the larger-diameter 0.012-inch, more concentric, and complex-shaped bare platinum coils with excellent results.

In addition to being more expensive per unit coil than BPCs, biologically active coils are unable to pack as tightly as BPCs. Evidence also suggests that the majority of the polymer coatings are resorbed over time, so that only 30% of the surface volume of the BPC remains after 12 weeks. A presentation in May 2005 at the American Society of Neuroradiology meeting by David Fiorella, M.D., and Cameron G. McDougall, M.D., showed that 36% of 78 aneurysms treated with Matrix bioactive coils recanalized and 50% required retreatment; these numbers were higher for nine patients with larger aneurysms (larger than 10 mm), of which 64% recanalized and 78% required retreatment.

Expanding coils have other disadvantages, including longer and more difficult preparation prior to use and time constraints during placement within the aneurysm. They cannot be reused once they have been prepped or placed in the body and may cause delayed narrowing of the parent artery due to excessive tissue reaction at the aneurysm neck interface.

One of the most serious drawbacks to the use of coated or expanding coils is the risk of developing severe inflammatory responses, including aseptic chemical meningitis and hydrocephalus. Although infrequent, these reports are trouble-some and remain unresolved.

Randall T. Higashida, M.D., is chief of the division of interventional neuroradiology at the University of California, San Francisco.
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Title Annotation:PRO & CON
Author:Malisch, Tim; Higashida, Randall T.
Publication:Internal Medicine News
Date:Nov 1, 2005
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