Vestibular schwannoma: dissection of the tumor and arachnoidal duplication.

ABSTRACT

INTRODUCTION: In vestibular schwannoma (VS) surgery, the arachnoidal duplication, based on an epiarachnoidal origin of the tumor, is reputedly induced by medial growth of tumor and helpful in atraumatic dissection. This study was intended to verify the epiarachnoidal origin of VS. MATERIALS AND METHODS: We studied 49 human temporal bones (TBs) specimens. Twenty-two TBs from 18 patients with VS were selected. An additional series of 27 TBs without any tumor within the internal auditory meatus were also included. We identified the location of the meninges and the position of the transition zone inside the meatus and described the lateral extension of the subarachnoid spaces. RESULTS: In VS specimens, psammoma bodies were seen at the fundus along the arachnoidal layer. No connective tissue or protrusion of a psammoma body was observed between the nerves and the VS. High magnification failed to demonstrate any meningeal cleavage plane between the facial or cochlear nerve and the tumor. The subarachnoid space was visible within the internal auditory meatus and extended from the porus to the fundus. In every case, the transition zone, the vestibular ganglion, or the VS was located in the subarachnoid fluid space. CONCLUSION: We were not able to identify any layer between tumor and the intrameatal contents and did not observe any conjunctive-tissue capsule surrounding the intrameatal VS, as an epiarachnoidal tumor origin would suggest. These observations are in contradiction with the descriptions concerning the epiarachnoidal origin of VS.