Background: Knowledge about meningioma growth characteristics is needed for
developing biologically rational follow-up routines. In this study of
untreated meningiomas followed with repeated MRIs, we studied growth
dynamics and explored potential factors associated with tumor growth.

Methods: In a single-center cohort study, we included 235 adult patients
with a radiologically suspected intracranial meningioma and at least three
MRI scans during follow-up. Tumors were segmented using an automatic
algorithm from contrast enhanced T1-series, and if needed manually
corrected. Potential meningioma growth curves were statistically compared;
linear, exponential, linear radial, or Gompertzian. Factors associated with
growth were explored.

Results: In 235 patients, 1394 MRI scans were carried out in the median
five-year observational period. Of the models tested, a Gompertzian growth
curve best described growth dynamics of meningiomas on group level. 59 % of
the tumors grew, 27 % remained stable, and 14 % shrunk. Only 13 patients(5%)
underwent surgery during the observational period and were excluded after
surgery. Tumor size at time of diagnosis, multifocality, and length of
follow-up were associated with tumor growth, whereas age, sex, presence of
peritumoral edema or hyperintense T2-signal were not significant factors.

Conclusion: Untreated meningiomas follow a Gompertzian growth curve,
indicating that increasing and potentially doubling of subsequent follow-up
intervals between MRIs seems biologically reasonable, instead of fixed time
intervals. Tumor size at diagnosis is the strongest predictor of future
growth, indicating a potential for longer follow up intervals for smaller
tumors. Although most untreated meningiomas grow, few require surgery.