Evaluating vestibular schwannoma size and volume on magnetic resonance imaging: An inter- and intra-rater agreement study

Objectives: In the management of patients with vestibular schwannoma it is essential to reliably assess tumor size. In respect to volumetric and linear measurements of these tumors we evaluated a) the inter-rater reliability, b) the intra-rater variability, c) the concordance of volume measurements derived from axial versus those from coronal MRI datasets, and d) the correlation of one-dimensional and volumetric measurements.

Patients and methods: We selected gadolinium-enhanced T1-weighted MRI datasets from 20 patients who had both axial and coronal datasets available with the same slice thickness in each of these orientations. Tumor volumes and diameters were independently determined by two investigators.

Results: The inter-rater reliability was determined based on the intra-class correlation coefficient, which was 0.998 for volumetric measurements and 0.950 for diameters. The relative smallest detectable difference between both raters was 21.2% for volumetric and 21.2% for linear measurements. Regarding the intra-rater variability we found a relative smallest detectable difference of 17.5% (rater 1) and 24.3% (rater 2) for volumetric measurements. The correlation between measurements on axial and those on coronal datasets was ρ=0.999. In order to find a function that reliably predicts tumor volume from diameter, we fitted a series of equations based on linear and polynomial regression, with the highest regression coefficient being r(2)=0.79.

Conclusion: The longitudinal use of semi-automated volumetric measurements has the potential to accurately inform vestibular schwannoma disease management. We have quantified the reliability of this technique. A strict MRI protocol for follow-up investigations should be adhered to in order to minimize measuring errors.