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The Koos grading system69
| Koos Grade | Tumor Description |
|---|---|
| I | Small intracanalicular tumor |
| II | Small tumor with protrusion into the cerebellopontine angle; no contact with the brainstem |
| III | Tumor occupying the cerebellopontine cistern with no brainstem displacement |
| IV | Large tumor with brainstem and cranial nerve displacement |
