Nerve origin of vestibular schwannoma: a prospective study.

OBJECTIVE: The origin of vestibular schwannoma has always been a matter of debate. The aim of our study was to identify the nerve origin of this tumour. STUDY DESIGN: Prospective case review. This study was conducted at Gruppo Otologico, a private referral centre for neurotology and skull base surgery. METHODS: A total of 200 cases of vestibular schwannoma were included in the study. All the tumours were removed surgically utilising the translabyrinthine approach. The origin of the tumour was sought at the fundus of the internal auditory canal. RESULTS: A total of 200 consecutive cases was included in the study. The origin of the tumour was limited to one nerve at the fundus in 152 cases (76 per cent). Out of these cases, the tumour originated from the inferior vestibular nerve in 139 cases (91.4 per cent), from the superior vestibular nerve in nine cases (6 per cent), from the cochlear nerve in two cases (1.3 per cent) and from the facial nerve in two cases (1.3 per cent). CONCLUSION: The vast majority of vestibular schwannomas originate from the inferior vestibular nerve; the incidence of involvement of this nerve increases as the tumour size increases. An origin of vestibular schwannoma from the inferior vestibular nerve can be considered as one of the explanatory factors for the poor functional outcome of the extended middle cranial fossa approach, and probably accounts also for the better hearing preservation rate reported in some series for the retrosigmoid approach.