Koos grading scale

Last revised by Yuranga Weerakkody on 23 Nov 2022

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

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Cases and figures

  • Case 1: left Koos 1
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  • Case 2: left Koos 2
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  • Case 3: right Koos 3
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  • Case 4: right Koos 4
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