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 counseling patients at different stages of their follow-up, as the risk
of tumor growth is likely to be less following each subsequent year that a tumor 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-center study was performed using patients diagnosed with sporadic
unilateral VS and 5-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 with 10 years of surveillance MRI, there was no growth
in the first 5 years. Conditional probabilities of growth were calculated according
to Bayes’ theorem, and nonlinear regression analyses allowed modeling of growth. A
multidisciplinary 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 tumor 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 vs. 13%, p = 0.01). By 10 years, the risk of growth was 0.28% (95% CI: 0.00–2.37%). Modeling
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.
