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Abstract
The treatment of basilar apex aneurysms has progressively become more minimalistic in nature. Although initial coil embolizations were geared towards those aneurysms with a favorable neck to dome ratio, wide necked aneurysms have also been increasingly treated by the endovascular route. Several techniques have been described in the stent assisted coiling of basilar apex aneurysms, including the Y stent formation, waffle cone technique and horizontal stenting. Thus far, horizontal stenting has required access from a retrograde approach—namely, the posterior communicating artery. The authors describe a novel antegrade technique, through the basilar artery, for the deployment of a Neuroform-EZ stent (Boston Scientific, Natick, Massachusetts, USA) in a horizontal configuration across the neck of a basilar apex aneurysm. This approach allowed for the complete coil embolization of a wide necked basilar apex aneurysm.
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Introduction
Endovascular neurosurgery has seen a dramatic evolution in the treatment of intracranial aneurysms. Results of prospective trials have demonstrated the durability of coil embolization in the treatment of ruptured and unruptured intracranial aneurysms.1 2 However, for the treatment of wide necked aneurysms, primary coil embolization has progressively become augmented by the use of balloon assistance techniques,3 stent technologies,4–7 liquid embolic agents8 or a combination thereof.9 This has especially been the case with wide necked basilar artery (BA) aneurysms.
Endovascular techniques for occlusion of these aneurysms, such as primary coil embolization, have been dramatically favored over traditional open microsurgical techniques because of the morbidity and mortality associated with open procedures. Unfortunately, the geometry of BA apex aneurysms may not be amenable to primary coiling without the use of the adjunctive technologies mentioned above. Balloon assisted techniques may not adequately prevent herniation of the coils into the parent vessels whereas Y stent configurations have added technical complexity, increased cost and an elevated risk of thromboembolic complications.6 10 A technique designed to mitigate these risks was recently described by Cross et al, as well as Fitzpatrick et al, for the treatment of unruptured and ruptured BA apex aneurysms, respectively.11 12 The authors of these studies reported their experience with the placement of a stent in a horizontal configuration across the neck of the aneurysm, from one posterior cerebral artery (PCA) to the other, in a retrograde fashion with access via a posterior communicating artery (PCoA). Unfortunately, if no ‘retrograde’ access is available, the approach must be modified to deploy a stent horizontally across the neck of the aneurysm. We present a novel technique applied in the treatment of a wide necked BA apex aneurysm in a patient who could not undergo retrograde stent placement because of unfavorable PCoAs. To our knowledge, this represents the first report of an intracranial stent deployed from and across the BA terminus in a horizontal configuration via an antegrade approach.
Case presentation
A patient in their mid-60s initially presented to our institution with transient left arm hemiparesis and paresthesias. Imaging, including CT angiography and digital subtraction angiography, confirmed a likely symptomatic right internal carotid artery (ICA) stenosis of approximately 95%. The patient was also found to harbor several incidental intracranial aneurysms—a 10 mm right PCoA segment ICA aneurysm, a 7 mm basilar apex aneurysm (figure 1A) and an approximately 5 mm contralateral carotid artery aneurysm. At that time, the patient underwent right carotid artery stent placement on an urgent basis, along with primary coil embolization of the right PCoA aneurysm. The patient tolerated the procedure well and without complication and returned 6 months later for treatment of the BA apex aneurysm.
(A) Angiographic injection of the left vertebral artery in the anteroposterior plane demonstrates a 7 mm wide necked basilar artery (BA) apex aneurysm. Note the angle and tortuosity of the left posterior cerebral artery (PCA) and its short pedicle from the BA. The previously coiled right internal carotid artery aneurysm can also be visualized in this image. (B) Angiographic view in the anteroposterior plane obtained after the deployment of the Neuroform-EZ stent (Boston Scientific, Natick, Massachusetts, USA). Note the stent markers (arrows) at the ostia of the left PCA and left superior cerebellar artery. (C) Final angiographic run, in the anteroposterior plane, demonstrating complete occlusion of the aneurysm and its neck at the basilar apex.
Given the wide necked nature of this aneurysm, the patient underwent bilateral Alcock testing to assess the potential for trans-PCoA stent placement. However, no obvious PCoA vessels were visualized, thus precluding this possible treatment strategy. Nonetheless, owing to the considerable risk of surgical treatment and the patient's preference, endovascular treatment of the aneurysm was pursued.
Prior to the intervention, the patient was neurologically intact. Platelet aggregation testing confirmed adequate responses to both aspirin and clopidogrel, which the patient had been taking on a daily basis. After sedation and a local anesthetic were administered, femoral artery access with a 6 French sheath was obtained. A 6 French Envoy guide catheter (Codman & Shurtleff Inc, Raynham, Massachusetts, USA) was carefully introduced into the left vertebral artery over a guidewire and a combination of a Marksman microcatheter (ev3/Covidien Vascular Therapies, Mansfield, Massachusetts, USA) and Glidewire Gold microwire (Terumo, Somerset, New Jersey, USA) were used to selectively catheterize the right PCA. The distal tip of the Marksman microcatheter was placed into the P2 segment, after which the microwire was removed. A 4 mm×30 mm Neuroform-EZ stent (Boston Scientific, Natick, Massachusetts, USA) was inserted into the Marksman microcatheter and carefully deployed into the right PCA. By providing some forward pressure on the microcatheter during its deployment, the stent was released in such a way as to abut the proximal stent markers to the wall of the BA, with the stent markers at the ostia of the left PCA and left superior cerebellar artery (SCA). Angiographic runs after stent deployment confirmed good placement of the stent across the base of the wide necked BA apex aneurysm (figure 1B). As a result, the stent's left-sided orifice was therefore open to the left PCA and left SCA.
After removal of the Marksman microcatheter, a Prowler LP ES microcatheter (Codman & Shurtleff Inc) and a Synchro-2 microwire (Boston Scientific) were used to catheterize the aneurysm through the interstices of the stent. Subsequent coil embolization ensued to completion with the placement of an initial framing coil (Axium, ev3/Covidien Vascular Therapies) followed by three additional three-dimensional coils (Orbit Galaxy, Codman & Shurtleff Inc) into the aneurysm (figure 1C). There was no evidence of coil herniation into any of the local parent vessels—namely, the BA or bilateral PCAs. The microcatheter was then removed and neurologic examination of the patient demonstrated no deficits. The patient was subsequently discharged home the following day, neurologically intact.
Discussion
The risks of open microsurgical clip ligation of BA apex aneurysms have driven neurosurgeons and neurointerventionists to seek durable and less invasive techniques for their obliteration. Wide necked BA aneurysms were once thought to be formidable lesions to tackle because of the number and proximity of parent vessels at the base of their necks, as well as the direct inflow of blood into the aneurysm dome through the basilar trunk. Recently, however, neurointerventionists have seen a dramatic evolution in terms of the treatment techniques and technology.
Strategies described for the treatment of wide necked intracranial aneurysms include the use of balloons or the deployment of stents, in a variety of configurations, to aid in the placement of coils within the aneurysm. Balloon assisted coil embolization, first described by Moret et al,13 relies on the ability of the balloon to remodel the shape of the aneurysm, specifically at its neck, after inflation within the parent vessel. Unfortunately, balloons neither provide a permanent barrier against coil herniation nor do they help divert blood flow away from the aneurysm. Therefore, herniation of coils into the parent vessel or distally can occur, as well as coil compaction. In an effort to circumvent this problem, stent(s) can be deployed to ‘stent remodel’ the neck of the aneurysm as well as provide a buttress to prevent coil migration. Unfortunately, the deployment of a single stent across the BA apex, from the PCA to the mid-BA, may allow coil herniation because of its limited approximation to and less than perpendicular angle with the axis of the aneurysm dome. If deployed in a Y configuration at the BA apex, the two stent technique has the added advantage of diverting blood flow away from the aneurysm and into the bilateral PCAs. However, using two stents increases the cost of the procedure as well as the risks of thromboembolic complications.6 10 Additionally, a combination of the above techniques, the balloon in stent technique, has also been described for the adjunctive coil embolization of basilar apex aneurysms.14 Unfortunately, this procedure carries a risk of significant neurologic deficit or brainstem infarct and should only be used in select cases.
The most recent technique described in the treatment of wide necked BA apex aneurysms involves the placement of a single stent in a horizontal fashion across the neck of the aneurysm, spanning one PCA to the contralateral PCA. This technique, reported in the treatment of both unruptured and ruptured aneurysms,11 12 requires the catheterization of a PCA via the ICA and an approach through the contralateral PCoA. Needless to say, if the anatomy of the PCoA is unfavorable (too small in caliber or highly tortuous), alternative techniques must be used in the treatment of the offending aneurysm. In the present case, we were able to deploy a Neuroform-EZ stent into the PCA via an antegrade approach, with the markers at the end of the stent anchored against the walls of the contralateral PCA and SCA. The advantages of the single stent technique have been previously described with the retrograde approach. Namely, this single stent technique is preferable to the Y stent configuration because theoretically it causes less flow disturbance at the aneurysm neck, may decrease the risk of thromboembolic complications resulting from using fewer stents and provides better approximation and is perpendicular to the axis of the dome.12 It is important to note that the length of the stent is critical, as a stent that is too short would be unstable and flap within the lumen of the BA, failing to provide adequate support to prevent coil mass herniation.
Ubiquitously described within the literature, the use of intracranial stents also necessitates the administration of dual antiplatelet agents.4 6 7 11 Unfortunately, in the setting of subarachnoid hemorrhage, the need for placement, management and removal of a ventriculostomy can represent contraindications for aspirin and clopidogrel. Resultantly, stent use in the treatment of aneurysms, especially when placed horizontally via a retrograde or antegrade approach, should be restricted to a highly selected group of patients.
Conclusion
The treatment of wide necked aneurysms continues to remain difficult, despite the use of balloon remodeling or stent assistance techniques. The antegrade placement of a single horizontally placed stent across the BA for the treatment of wide necked aneurysms should be reserved for clinically appropriate cases with optimal anatomy when a retrograde approach is unobtainable.
Acknowledgments
The authors thank Paul H Dressel, BFA, for assistance with preparation of the illustrations and Debra J Zimmer, AAS CMA-A, for editorial assistance.
References
Footnotes
Competing interests EIL receives research grant support (principal investigator: Stent-Assisted Recanalization in acute Ischemic Stroke, SARIS), other research support (devices) and honoraria from Boston Scientific and research support from Codman & Shurtleff Inc and ev3/Covidien Vascular Therapies; has ownership interests in Intratech Medical Ltd and Mynx/Access Closure; serves as a consultant on the board of Scientific Advisors to Codman & Shurtleff Inc; serves as a consultant per project and/or per hour for Codman & Shurtleff Inc, ev3/Covidien Vascular Therapies and TheraSyn Sensors Inc; and receives fees for carotid stent training from Abbott Vascular and ev3/Covidien Vascular Therapies. EIL receives no consulting salary arrangements. All consulting is per project and/or per hour.
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