Trigeminal neuropathy in vestibular schwannoma: a treatment algorithm to avoid long-term morbidity

Trigeminal neuropathy (TGN) can occur as a presenting feature of vestibular schwannoma (VS) or as an adverse effect of radiosurgery. This study was designed to evaluate a treatment algorithm for presenting symptoms of TGN in patients with VS, and a new radiosurgery dosimetric tolerance to avoid TGN after treatment. Outcome was measured after microsurgery (MS), stereotactic radiosurgery (SRS), hypofractionated stereotactic radiotherapy (HSRT), and fractionated radiotherapy (FRT).

A prospectively held VS database was retrospectively analysed from 2011 to 2016 at a tertiary university hospital. All patients who underwent MS from 2011 and all patients who underwent radiotherapy (SRS, HSRT, FRT) from 2015 were studied. Patients on surveillance and neurofibromatosis type 2 patients were not included. Patient demographic data, tumour characteristics, presenting symptoms, and post-treatment outcomes were analysed.

Eighty-eight patients were included in the study (43 microsurgery, 45 radiotherapy). Twenty-seven (31%) patients presented with TGN symptoms. The median age of patients included was 56.5 (range 6-72 years), with a median follow-up for MS and SRS of 38 and 20 months, respectively (range 10-80 months). All 27 patients with TGN were offered MS as per protocol. Three patients declined, or were not fit for surgery, and received FRT. Complete resolution of TGN symptoms was achieved in all 24 patients who underwent MS and 33% (1/3) of patients with FRT. Eleven patients experienced transient post-operative complications (pseudomeningocele (6), meningitis (3), venous sinus thrombosis, cerebellar haemorrhagic contusion, and posterior fossa haematoma). Of the 45 patients in the radiotherapy cohort, 36 were suitable for SRS, of which 30 patients who met the dose-volume constraints for trigeminal nerve underwent single-fraction SRS and 6 patients who did not meet the constraints received HSRT. Nine patients (20%) received FRT including three patients with pre-treatment TGN. None of the patients developed new TGN symptoms following SRS or HSRT.

Our algorithm to select the optimal treatment modality appears to achieve comparable or better long-term outcome. Microsurgical resection in our cohort resulted in complete resolution of symptoms in all patients. None of our SRS- or HSRT-treated patients developed TGN during the follow-up period. The adherence to strict trigeminal nerve dose-volume constraints for SRS remains critical to minimise TGN post treatment. Fractionated radiotherapy is an alternative for patients who refuse surgery or those who are unfit for surgery.