Satoshi Tateshima, MD, D.M.Sc., Assistant Professor-Director of the Aneurysm Program, Division of Interventional Neuroradiology, Ronald Reagan UCLA Medical Center.
Gary Duckwiler, MD, Director of Clinical Affairs and Fellowship Director, Division of Interventional Neuroradiology, Ronald Reagan UCLA Medical Center
Flow diversion stents and endoluminal flow-disrupting devices are new therapeutic approaches to treat challenging intracranial aneurysms [1,2]. The first generation Pipeline Embolization Device (PED) has already been used in clinical practice. The reported results of PED treatment of intracranial aneurysms appear to be promising and very encouraging for the neuro-endovascular field [1,2]. However, there has always been a lingering concern associated with any intracranial stent that they may compromise the blood flow in small side branches coming from the stented segment of artery. After the introduction of low profile, self-expandable intracranial stents such as Neuroform, Wingspan, and Enterprise, we started to realize that eloquent perforators could sustain their patency with an approximately 10% area-coverage stent [3]. Unfortunately, with a low coverage stent, the likelihood of aneurysm occlusion without adjunctive treatment is very low. Finding the “sweet spot” of neck coverage versus side branch occlusion is the ultimate target to prevent aneurysm recurrence. The introduction of PED has expanded this envelope in that we may be able to put a stent that has 30% area coverage while maintaining the patency of perforating arteries, although the long-term patency of stented artery including perforating arteries still needs to be evaluated carefully.
Masuo et al introduced a very unique experimental method to access the patency of perforating arteries coming off a major intracranial artery after the stent placement [4,5]. They used a rabbit abdominal aorta and lumbar artery to simulate the relationship between a major intracranial artery and its perforating arteries. Their studies published in AJRN 2002 (healthy aorta) and 2005 (atherosclerotic aorta) suggest that risks of perforator occlusion may increase when a stent is placed in an atherosclerotic artery [4,5]. The safety and biocompatibility of PED and PED2 were tested utilizing the same methodology except that the abdominal aortae were as healthy as a human pediatric case. Thus, the indication of PED placement for a challenging intracranial aneurysm associated with atherosclerotic change must be planned with extra caution.
Another open question is the interim effect of flow diversion on the stability of cerebral aneurysms. Intra-aneurysmal flow and its relationship to growth and rupture of aneurysms is a highly debated topic [6]. From the landmark ISAT trial, it was proven that intra-aneurysmal coiling reduced the rerupture rate compared to historical rates [7]. Whether or not high-coverage stents will provide the same benefits predictably, without causing a negative impact of intra-aneurysmal flow dynamics remains to be seen, especially given the need for coagulation management in the acute phase. In this study, both side branch preservation and aneurysm occlusion were obtained, which is a great first step.
The PED seems to be a promising potential solution in wide neck and possibly fusiform aneurysms that are not treatable by conventional surgery or endovascular embolization. Certainly, any efforts to further delineate the safety profile and outcome predictability of high coverage stents is valuable and necessary.
References
1. Fiorella D, Woo HH, Albuquerque FC, Nelson PK. Definitive reconstruction of circumferential, fusiform intracranial aneurysms with the pipeline embolization device. Neurosurgery 62: 1115-1121: 2008
2. Lylyk P, Miranda C, Ceratto R, Ferrario A, Scrivano E, Luna HR, Berez AL, Tran Q, Nelson PK, Fiorella D. Curative endovascular reconstruction of cerebral aneurysms with the pipeline embolization device: the Buenos Aires experience. Neurosurgery 64: 632-643: 2009
3. Biondi A, Janardhan V, Katz JM, Salvaggio K, Riina HA, Gobin YP. Neuroform stent-assisted coil embolization of wide-neck intracranial aneurysms: strategies in stent deployment and midterm follow-up. Neurosurgery 61: 460-469: 2007.
4. Masuo O, Terada T, Walker G, Tsuura M, Matsumoto H, Tohya K, Kimura M, Nakai K, Itakura T. Study of the patency of small arterial branches after stent placement with an experimental in vivo model. AJNR Am J Neuroradiol 23: 706-710: 2002
5. Masuo O, Terada T, Walker G, Tsuura M, Nakai K, Itakura T. Patency of perforating arteries after stent placement? A study using an in vivo experimental atherosclerosis-induced model. AJNR Am J Neuroradiol 26:543-548: 2005
6. Tateshima S, Tanishita K, Omura H, Villablanca JP, Vinuela F. Intra-aneurysmal hemodynamics during the growth of an unruptured aneurysm: in vitro study using longitudinal CT angiogram database. AJNR Am J Neuroradiol. 28: 622-627: 2007
7. Molyneux AJ, Kerr RS, Yu LM, Clarke M, Sneade M, Yarnold JA, Sandercock P; International Subarachnoid Aneurysm Trial (ISAT) Collaborative Group. International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion. Lancet. 366: 809-817: 2005
