Aim:Arachnoid dissection is a basic step during facial nerve microvascular decompression (MVD). However, the literature focusing on the arachnoid microstructure in this region is scarce, and there are different views on how to handle the arachnoid around the cochlea nerve in order to protect the cochlea nerve. To provide a valuable reference for minimal invasion during facial nerve MVD, the arachnoid microstructure during the infrafloccular approach was studied in this paper.Material and Methods:This study recruited 55 patients with hemifacial spasm who underwent MVD. Retrospective analyses of the MVD surgical videos were performed to reveal the arachnoid microstructure during the procedures. Cadaveric head specimens (n = 8, on 16 sides) were dissected for observation of the microstructure of the arachnoid in the cerebellopontine angle.Results:The arachnoid membrane surrounding the facio-cochleovestibular and lower cranial nerves forms two arachnoid sheaths. Both arachnoid sheaths contain two parts: the outer membranous and inner trabecular part. The membranous part is an intact and translucent membrane that wraps around nerves. The inner trabecular part is located beneath the membranous part and forms a trabecular network that connects the membranous arachnoid, nerves, and blood vessels to form a physical structure.Conclusion:The arachnoid connects the facio-cochleovestibular and lower cranial nerves, blood vessels, and cerebellum as a complex physical entity. Therefore, during MVD surgery, sharply dissecting the arachnoid before retracting the flocculus and relocating the offending vessels helps reduce nerve injury.