Koos grading scale

The Koos grading scale  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 proved its inter- and intra-reliability, demonstrating that the Koos classification system is a reliable method.