- A – Tumors limited to the middle ear space
- B – Tumors limited to the middle ear or mastoid without involvement of the intralabyrinthine space of the temporal bone
- C – Tumors involving the intralabyrinthine and apical spaces of the temporal bone, with extension into the apex
- D1 – Tumors with intracranial extension < 2 cm in diameter
- D2 – Tumors with intracranial extension > 2 cm in diameter
Reference:
Fisch U MD. Microsurgery of the skull base. Stuttgart: Thieme; 1988