Precision in Practice: Inter- and Intra-rater Reliability of Linear Measurements and Tumor Growth in Vestibular Schwannoma

Objective The aim of this study is to compare and assess the inter- and intra-rater reliability of various linear measurement techniques for vestibular schwannomas (VS) and their impact on determining tumor growth in a multidisciplinary multicenter setting. Methods Six experts (neurosurgeons, otorhinolaryngologists, and radiologists) involved in VS management, from two tertiary referral centers, measured linear extrameatal VS tumor size parallel and perpendicular to the petrous ridge, and as maximum axial and maximum coronal diameter. Inter- and intra-rater reliability were evaluated using the intraclass correlation coefficient (ICC). The repeatability coefficient was computed for each measurement direction. Fleiss' kappa was used to determine the degree of agreement on tumor growth. Results Reliability between raters was significantly excellent (ICC >0.9) across all measurement directions, with the highest ICC observed for measurements parallel to the petrous ridge (ICC, 0.974; 95% CI, 0.957-0.986). Good or excellent reliability was achieved in 95.8% of all intra-rater measurements, with predominantly higher ICC scores for measurements in the coronal plane. Fleiss' kappa for interrater variability of determining tumor growth was highest and substantial for measurements parallel to the petrous ridge 0.672 (95% CI, 0.546-0.799). Conclusion Linear measurements of VS parallel to the petrous ridge yield excellent interrater reliability and the most favorable repeatability coefficient. Good to excellent intra-rater reliability across all measurement directions was observed. The most accurately defined tumor growth was obtained comparing measurements parallel to the petrous ridge. We recommend measurements parallel to the petrous ridge as the standard linear method for evaluating VS and growth.