Combined transpetrosal-transtentorial approach with occipital artery - anterior inferior cerebellar artery bypass and aneurysm clipping for a lower basilar artery aneurysm involving anterior inferior cerebellar artery: Two-dimensional operative video.

Background: Aneurysms of the lower basilar artery (BA) are rare, accounting for <1% of all intracranial aneurysms. This location has been described as "No man's land" since it poses a potential challenge for microsurgery. Recently, endovascular treatment has become an alternative option; however, there are some disadvantages regarding the obliteration rate, patency of the parent, and perforating arteries. Case Description: We present the case of a 69-year-old female with an incidentally found lower BA aneurysm. The imaging examinations revealed a wide-neck aneurysm size of 8.5 mm arising just distal to the vertebrobasilar junction, with involvement of the left anterior inferior cerebellar artery (AICA). After a discussion with the patient, she opted to undergo the surgical treatment. We described the detailed steps of our surgical techniques in performing a combined transpetrosal-transtentorial approach. First, the occipital artery (OA) was harvested. Then, the posterior transpetrosal (retrolabyrinthine) and a far-lateral suboccipital approach were conducted with tentorial sectioning to expose the aneurysm. After AICA was confirmed to arise from the aneurysm sac, the OAAICA bypass was established to ensure AICA patency, followed by complete aneurysm clipping. The approach provided both the presigmoid and retrosigmoid corridors for bypass and clipping procedures, respectively. The patient tolerated the procedure well. Postoperative imaging examinations showed complete aneurysm obliteration and bypass patency without complications. She was discharged without neurological deficits (modified Rankin Scale 0). Conclusion: The combined transpetrosal approach is safe and effective for revascularization and clipping procedure for a lower BA aneurysm.