Comparative Analysis of Anterior Petrosectomy and Retrosigmoid Approaches to Anterior Inferior Cerebellar Artery: A Cadaver Study

Introduction: Anterior inferior cerebellar artery (AICA) aneurysms are extremely rare and comprise less than 1.5% of intracranial aneurysms. A standardized neurosurgical treatment has yet to be formulated, and postoperative morbidity is significantly high—both in open and endovascular procedures. Several surgical approaches have been described to access the proximal AICA; however, there is insufficient data on exposure or control of the regional vascular anatomy. The objective of the present study is to compare the surgical freedom and vascular control that is afforded through an anterior petrosectomy approach (APA), or an extended retrosigmoid approach with and without inframeatal drilling (ERA and ERIA, respectively).

Methods: The APA, ERA, and ERIA were performed bilaterally in 6 latex-injected cadaveric specimens (12 sides). A navigation system was used to acquire measurements and subsequent statistical analysis conducted to compare the results of the three approaches. Linear distances measured include: 1) AICA origin to the most proximal/distal visible points of the basilar artery (BA), 2) AICA origin and from the crossing point with the cranial nerves VI and VII-VIII—to the proximal perforators, 3) a temporary clip was applied in the most proximal/distal visible points of the BA, and their distance from AICA origin measured to assess clippability. Lastly, the degree of surgical freedom at AICA’s origin from the BA and at the crossing points with VI and VII-VIII cranial nerves were evaluated.

Results: The AICA mean length was 43.8 ± 14.2 mm, and the distance from its origin to the first perforator was 8.7 ± 1.4 mm. The length of the AICA exposure was 4.4 ± 1.8 mm distally and 18.5 ± 6.9 mm proximally. Distance from the AICA origin to the clippable segment of the BA was proximally 2.8 ± 1.8 mm among the three approaches; distally the BA clippability increases with ERA and ERIA (mean: 1.1 ± 0.3 mm) compared with APA (0 ± 0.1 mm, p = 0.04). The perforators arising from proximal AICA and its bifurcation were mostly related to the crossing points with the VI and VII-VIII cranial nerves. As concerns SF, ERIA was comparable to APA and superior to ERA for AICA origin point (p = 0.0440). At the VI cranial nerve crossing point, EIRA SF was superior to the ERA (p = 0.0010) and APA (p = 0.0139). Both ERA and ERIA were superior to APA (p = 0.0011 and p = 0.0039, respectively) for the VII–VIII cranial nerves crossing point.

Conclusion: This study demonstrates that ERIA yields the most extensive degree of surgical freedom and affords optimal proximal vascular control for AICA exposure. ERIA is superior to the ERA in AICA exposure at the origin and at the crossing point with the VI cranial nerve. The APA did not improve surgical exposure and vascular control at the proximal AICA but allowed for access to the origin in all specimens. This study gives objective data that may help neurosurgeons in choosing the best approach when dealing with AICA aneurysms or other local pathologies.