AbstractObjectiveValidation of automated 2‐dimensional (2D) diameter measurements of vestibular schwannomas on magnetic resonance imaging (MRI).Study DesignRetrospective validation study using 2 data sets containing MRIs of vestibular schwannoma patients.SettingUniversity Hospital in The Netherlands.MethodsTwo data sets were used, 1 containing 1 scan per patient (n = 134) and the other containing at least 3 consecutive MRIs of 51 patients, all with contrast‐enhanced T1 or high‐resolution T2 sequences. 2D measurements of the maximal extrameatal diameters in the axial plane were automatically derived from a 3D‐convolutional neural network compared to manual measurements by 2 human observers. Intra‐ and interobserver variabilities were calculated using the intraclass correlation coefficient (ICC), agreement on tumor progression using Cohen's kappa.ResultsThe human intra‐ and interobserver variability showed a high correlation (ICC: 0.98‐0.99) and limits of agreement of 1.7 to 2.1 mm. Comparing the automated to human measurements resulted in ICC of 0.98 (95% confidence interval [CI]: 0.974; 0.987) and 0.97 (95% CI: 0.968; 0.984), with limits of agreement of 2.2 and 2.1 mm for diameters parallel and perpendicular to the posterior side of the temporal bone, respectively. There was satisfactory agreement on tumor progression between automated measurements and human observers (Cohen's κ = 0.77), better than the agreement between the human observers (Cohen's κ = 0.74).ConclusionAutomated 2D diameter measurements and growth detection of vestibular schwannomas are at least as accurate as human 2D measurements. In clinical practice, measurements of the maximal extrameatal tumor (2D) diameters of vestibular schwannomas provide important complementary information to total tumor volume (3D) measurements. Combining both in an automated measurement algorithm facilitates clinical adoption.