2025 Proffered Presentations
S270: BRITISH SKULL BASE SOCIETY EVIDENCE-BASED CONSENSUS ON VESTIBULAR SCHWANNOMA SURVEILLANCE BASED ON CONDITIONAL PROBABILITY OF TUMOUR GROWTH
James Tysome; Cambridge University Hospitals
Aims: Surveillance plays a crucial role in managing patients with Vestibular Schwannomas (VS). Most studies refer to the risk of VS growth over time; however, this is not useful for counselling patients at different stages of their follow-up, as the risk of tumour growth is likely to be less following each subsequent year that a tumour does not grow. We investigated the conditional probability of VS growth at particular time-points, given a patient has not grown thus far. This was used to inform a British Skull Base Society (BSBS) consensus on the optimal duration and frequency of imaging.
Methods: Initially a single centre study was performed using patients diagnosed with sporadic unilateral VS and five year follow up. An International multicenter retrospective analysis of prospectively collected databases from five tertiary care referral skull base units was then performed. In patients with10 years of surveillance MRI where there was no growth in the first 5 years. Conditional probabilities of growth were calculated according to Bayes' theorem, and nonlinear regression analyses allowed modelling of growth. A multi-disciplinary Delphi consensus was then conducted at a British Skull Base Society Meeting.
Results: A total of 341 patients met the inclusion criteria. At 1 year, the probability of growth given that the tumour had not grown to date was seen to be 21%, at 2 years 12%, at 3 years 9%, at 4 years 3%, and at 5 years 2%. The conditional probability of growth of extracanalicular VS was only significantly higher in the first year when compared with intracanalicular VS (29% versus 13%, p = 0.01). By 10 years, the risk of growth was 0.28% (95% CI 0.00%-2.37%). Modelling determined that the remaining lifetime risk of growth would be less than 1% at 7 years 7 months, less than 0.5% at 8 years 11 months. Consensus was for for VS managed by surveillance to stop discontinued when the remaining lifetime risk of VS growth is <0.5%.
Discussion: The use of conditional probability of VS growth from combining databases arising from different populations gave robust data to facilitate a BSBS consensus statement on frequency and length of imaging in patient with VS.