2025 Poster Presentations
P171: TWO CASES OF VESTIBULAR NERVE HYBRID NERVE SHEATH TUMOURS AND LITERATURE REVIEW
Celine D Hounjet, MD, BSc; John Maguire, MB, BCh, FRCPC; Brian D Westerberg, MD, MHSc, FRCSC; Ryojo Akagami, MD, BSc, MHSc, FRCSC; University of British Columbia
Introduction: Since the 2016 WHO classification of central nervous system tumours, hybrid nerve sheath tumours (HNST) have been recognized as tumours containing elements of more than one type of nerve sheath tumour. 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 centre, there have been two documented cases of hybrid tumours arising on the CN VII/VIII complex. Here we describe these cases of presumed vestibular schwannoma that ultimately were diagnosed as hybrid tumours on pathological analysis. Additionally, a literature review on this topic was completed.
Methods: Chart reviews including imaging and neuropathological assessments were reviewed for two cases of HNST of CN VII/VIII tumour that occurred at a single tertiary care referral centre. 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-Brackman 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 tumour located in the auditory canal has previously been reported. We have identified two further cases of hybrid tumour in this location at our centre. 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 phenomena to the list of WHO pathologies or due to insufficient tissue samples being provided to pathologists for tumours in this region.
