Last reviewed dd mmm yyyy. Last edited dd mmm yyyy
Cranial nerves are frequently damaged in head injury. The ones affected depend on the type of injury.
Overall, the olfactory nerve is most affected, resulting in anosmia. Probably, this is because the fine olfactory fibres passing through the cribriform plate are easily sheared by movements of the brain and olfactory bulb.
The facial and vestibulo-cochlear are another group commonly involved and are associated with fractures of the petrous temporal bone. The facial palsy may be immediate or delayed. Vertigo, tinnitus, and sensorineural deafness are common.
Cranial nerves II, III, IV, and VI are less frequently damaged. The optic nerve may be damaged by a fracture passing through the orbit, or secondary to prolonged intracranial pressure. There is visual loss or a field defect in one eye. Bitemporal hemianopia results from chiasmal damage.
The third, fourth and sixth cranial nerves may be damaged by an anterior or middle cranial fossa fracture as a result of herniation for the third. The pupils may be unequal, and there may be ptosis and disturbance of ocular movements. Oculomotor function is an important localising sign in the more immediate management of head injury.
Damage to the trigeminal nerve occasionally follows petrous or sphenoid fractures. It results in facial anaesthesia.
The other cranial nerves are rarely damaged.
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