Glossary of Terms in Otolaryngology

Koos Classification

  • The Koos Classification System is a widely used radiographic grading scale for assessing the size of vestibular schwannomas.1
    • Grade I tumours are purely within the internal auditory canal.
    • Grade II tumours extend into the cerebellopontine angle without contacting the brainstem.
    • Grade III tumours occupy the cerebellopontine cistern and contact the brainstem but do not displace it.
    • Grade IV tumours displace the brainstem and cranial nerves.

Koos Classification of Vestibular Schwannomas Koos Classification of Vestibular Schwannomas, on MRI imaging

Koos Classification for Vestibular Schwannomas

Grade Features
I Intracanalicular tumour.
II Tumour extends into the cerebellopontine angle but does not extend to the brainstem.
III Tumour occupies the cerebellopontine cistern and contacts the brainstem but does not displace it.
IV Tumour displaces the brainstem and cranial nerves.

Koos Classification Table

  1. Koos, Wolfgang T., et al. “Neurotopographic considerations in the microsurgical treatment of small acoustic neurinomas.” Journal of neurosurgery 88.3 (1998): 506-512. ↩

Last updated May 26, 2024
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