Koos grading scale

Last revised by Arlene Campos on 7 May 2024

The Koos grading scale 1 is frequently used as a classification system for vestibular schwannomas.


  • grade 1: small intracanalicular tumor

  • grade 2: small tumor with protrusion into the cerebellopontine cistern (CPA); no contact with the brainstem

  • grade 3: tumor occupying the cerebellopontine cistern with no brainstem displacement

  • grade 4: large tumor with brainstem and cranial nerve displacement


A cross-sectional study 2 proved its inter- and intra-reliability, demonstrating that the Koos classification system is a reliable method.

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