"grade 1: small intracanalicular tumour"
"grade 2: small tumour with protrusion into the cerebellopontine cistern (CPA); no contact with the brainstem"
"grade 3: tumour occupying the cerebellopontine cistern with no brainstem displacement"
"grade 4: large tumour with brainstem and cranial nerve displacement"
"A cross-sectional study proved its inter- and intra-rater reliability, demonstrating that the Koos classification system is reliable 2."
"grade 2: small tumour with protrusion into the cerebellopontine cistern (CPA); no contact with the brainstem"