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Structures at risk.
| Level I |
| No relevant risks |
| Level II |
| Ossicular chain |
| Level III |
| Ossicular chain, facial nerve, labyrinth |
| Level IV |
| Facial nerve, labyrinth, Jugular bulb, carotid artery |
| Level V |
| Facial nerve, jugular bulb, carotid artery, lower cranial nerves, vessels of CPA (AICA), brainstem. Risk of post-operative CSF leak |
