PurposeThe cerebellopontine angle (CPA) is a frequent region of skull base pathologies
and therefore a target for neurosurgical operations. The outer arachnoid is the key
structure to approach the here located lesions. The goal of our study was to describe
the microsurgical anatomy of the outer arachnoid of the CPA and its pathoanatomy in
case of space-occupying lesions.MethodsOur examinations were performed on 35 fresh
human cadaveric specimens. Macroscopic dissections and microsurgical and endoscopic
examinations were performed. Retrospective analysis of the video documentations of
35 CPA operations was performed to describe the pathoanatomical behavior of the outer
arachnoid.ResultsThe outer arachnoid cover is loosely attached to the inner surface
of the dura of the CPA. At the petrosal surface of the cerebellum the pia mater is
strongly adhered to the outer arachnoid. At the level of the dural penetration of
the cranial nerves, the outer arachnoid forms sheath-like structures around the nerves.
In the midline, the outer arachnoid became detached from the pial surface and forms
the base of the posterior fossa cisterns. In pathological cases, the outer arachnoid
became displaced. The way of displacement depends on the origin of the lesion. The
most characteristic patterns of changes of the outer arachnoid were described in case
of meningiomas, vestibular schwannomas, and epidermoid cysts of the CPA.ConclusionThe
knowledge of the anatomy of the outer arachnoid of the cerebellopontine region is
essential to safely perform microsurgical approaches as well as of dissections during
resection of pathological lesions.
