Literature ReviewMicrosurgical Clipping of Basilar Apex Aneurysms: A Systematic Historical Review of Approaches and their Results
Introduction
Two landmark studies, ISAT (International Subarachnoid Aneurysm Trial)1 and BRAT (Barrow Ruptured Aneurysm Trial),2 have shown that, when technically feasible, endovascular treatment of posterior circulation aneurysms offers a significantly better immediate neurologic outcome compared with open microsurgery. According to these findings, the overall rare basilar apex (BA) aneurysm (BAA), which accounts for only 7% of all intracranial aneurysms, is preferably treated by an endovascular route.3 However, there are factors that favor microsurgical occlusion of BAAs: large aneurysm size, wide neck, young patient age, and complex morphology, such as partial thrombosis or incorporation of branching vessels.4, 5, 6 Overall, the difficulty for the vascular neurosurgeon has increased, because the absolute number of BAAs operated on has decreased to roughly 1/4 to 1/3,4, 7 whereas the percentage of complex lesions has increased.
Among the surgical techniques developed for the treatment of BAAs within the past 40 years, the major ones include the transsylvian, subtemporal, pretemporal, and petrous approaches. Skull base adjuncts, such as the orbitozygomatic craniotomy and transcavernous approach, have been applied as well. Although a rationale for each individual technique was designed to fit a specific subset of BAAs, most aneurysms of the BA can be reached via more than 1 of the 4 major approaches. Our systematic review of the literature discusses specific indications for the 4 most common approaches by comparing results for microsurgical BAA occlusion, influencing anatomic factors, rates of good surgical outcomes, occlusion, morbidity, and mortality.
Our review aims at summarizing the techniques and results of the past decades to pass on this knowledge to future vascular neurosurgeons at a time when endovascular therapies have dramatically changed our work.
Section snippets
Methods
A systematic search was performed of the PubMed database (January 28, 2017) using the Boolean operator “OR” of the following search criteria (key words): “basilar apex aneurysm,” “basilar top aneurysm,” “basilar tip aneurysm,” “basilar bifurcation aneurysm,” and “basilar head aneurysm.” Inclusion criteria were peer-reviewed articles, original studies (no reviews, letters, or conference abstracts), minimum of 5 patients, description of surgical approach, report of neurologic outcome, and English
Results
The 35 retrospective studies identified through our search algorithm were reported between 1976 and 2015 and included 2041 patients with BAAs who underwent surgical treatment (Table 1). In these 35 studies, numbers ranged from 5 to 233 patients and rates of unruptured aneurysms ranged from 0% to 100%.
Approach variants consisted of 1131 transsylvian, 241 pretemporal, 375 subtemporal, and 17 petrosal approaches (Figure 4A). The remaining 277 patients were reported on in articles descripting
Discussion
Our literature review of 35 articles published between 1976 and 2015, which represented 2041 patients with BAAs, systematically compared outcomes for 4 commonly used approaches. Because BAA can show considerable variance of important morphologic features, each of the approaches was designed to fit a certain subset of BAA.
Conclusions
The transsylvian approach was most frequently used overall and for ruptured aneurysms. If the most suitable approach is chosen for a given BAA depending on morphologic anatomic and clinical factors, similar good neurologic outcomes are reported for transsylvian, subtemporal, and pretemporal approaches. Aneurysm-neck-to-PCP distance in those 3 approach groups showed considerable overlap at a range between −1 mm and +7 mm from the PCP. In this range, all 4 approaches have proved useful. Large and
Acknowledgments
We would like to thank Mr. Koehler and his colleagues from Atelier Guido Koehler, Basel, Switzerland, for their graphic illustrations. No funding was received for this research.
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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.