Two Cases of Vestibular Nerve Hybrid Nerve Sheath Tumors and Literature Review

Introduction: Since the 2016 WHO classification of central nervous system tumors, hybrid nerve sheath tumors (HNST) have been recognized as tumors containing elements of more than one type of nerve sheath tumor. Although common peripherally and extracranially, few reports of intracranial HNST located on a cranial nerve have been published to date. At our tertiary care referral center, there have been two documented cases of hybrid tumors arising on the CN VII/VIII complex. Here we describe these cases of presumed vestibular Schwannoma that ultimately were diagnosed as hybrid tumors on pathological analysis. Additionally, a literature review on this topic was completed.

Materials and Methods: Chart reviews including imaging and neuropathological assessments were reviewed for two cases of HNST of CN VII/VIII tumor that occurred at a single tertiary care referral center. Both cases were completed by the same surgical team composed of a fellowship trained neurosurgeon, otolaryngologist, and neurophysiologist. The first case occurred in 2017 and the second occurred in 2022. Intraoperative findings were consistent with a vestibular Schwannoma and no atypical findings were identified. For both cases intraoperative monitoring was utilized in the typical fashion. Both patients had little hearing on the ipsilateral side at baseline. Both had gross total resections without new neurological deficit and were graded as House-Brackmann 1 post operatively. Additionally, a systematic literature search utilizing the search matrix (“hybrid” AND ((“vestibular schwannoma” OR “acoustic neuroma” OR “schwannoma” OR “neuroma” OR “cranial nerve”) AND (“intracranial” OR “CPA” OR “skull base” OR “cerebellopontine” OR “cranial nerve”))) was completed on July 11, 2024, resulting in 171 papers for screening. Ultimately 3 papers were included in the final analysis.

Results: Three cases of HNST affecting cranial nerves were identified in the literature. One case of HNST of the facial nerve and one case of HNST of the trigeminal nerve were identified. Only one case of hybrid tumor located in the auditory canal has previously been reported. We have identified two further cases of hybrid tumor in this location at our center. A total of 643 vestibular Schwannoma cases have been completed between 2001 and 2024 by this surgical team resulting in an institutional incidence rate of 0.31%.

Conclusion: HNSTs may be underreported in the cranial region. This may relate to the relatively recent addition as a recognized phenomenon to the list of WHO pathologies or due to insufficient tissue samples being provided to pathologists for tumors in this region.

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Artikel online veröffentlicht:
07. Februar 2025