Koos grading scale

A common classification system known as the Koos grading scale is frequently used for vestibular schwannoma.

The Koos classification of vestibular schwannomas is designed to stratify tumors based on extrameatal extension and compression of the brainstem.

Grade 1 tumors involve only the internal auditory canal.

Grade 2 tumors extend into the cerebellopontine angle, but do not encroach on the brainstem.

Grade 3 tumor fills the entire cerebellopontine angle.

Koos Grade 4 Vestibular Schwannoma displaces the brainstem and adjacent cranial nerves.

A cross-sectional group of the Magnetic Resonance imagings of 40 patients with vestibular schwannomas varying in size comprised the study sample. Four raters were selected to assign a Koos grade to 50 total scans. Inter- and intra-rater reliability were calculated and reported using Fleiss' kappa, Kendall's W, and Intraclass correlation coefficient (ICC).

Inter-rater reliability was found to be substantial when measured using Fleiss' kappa (.71), extremely strong using Kendall's W (.92), and excellent as calculated by ICC (.88). Intrarater reliability was perfect for 3 out of 4 raters as assessed using weighted kappa, Kendall's W and ICC, with the intrarater agreement for the fourth rater measured as extremely high.

Erickson et al. demonstrated that the Koos classification system for vestibular schwannoma is a reliable method for tumor classification. This study lends further support to the results of current literature using Koos grading system. Further studies are required to evaluate its validity and utility in counseling patients with regard to outcomes 1).

Erickson NJ, Schmalz PGR, Agee BS, Fort M, Walters BC, McGrew BM, Fisher WS 3rd. Koos Classification of Vestibular Schwannomas: A Reliability Study. Neurosurgery. 2018 Aug 30. doi: 10.1093/neuros/nyy409. [Epub ahead of print] PubMed PMID: 30169695.
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