Table 5 Common cranial nerve injuries after head injury

Cranial Nerve

Features

I—Olfactory Possibly the most common cranial nerve injury. May be due to traction on olfactory bulbs during deceleration injury or to fracture of the cribiform plates.

II—Optic Direct traction or compression injury of the optic nerve may cause pupillary abnormalities. These abnormalities may also be due to third nerve injury from brain herniation. Orbital injury may also cause pupillary or extraocular movement abnormalities. The neurosurgeon must decide if pharmacological pupillary dilation is safe in the acute trauma setting.

III—Oculomotor Direct compression of the IlIrd nerve by the displaced uncus of the temporal lobe.

IV and VI—Trochlear May be due to immediate traction injury or as an indirect and Abducens sign of raised intracranial pressure.

VII and VIIII—Facial and

Vestibulocochlear

May be due to brainstem injury or temporal bone fracture. Otolaryngology evaluation and hearing tests before discharge are mandatory for patients with petrous temporal-bone fractures.

children with a skull fracture should be examined 3 months after injury to look for a pulsatile mass over the fracture site. These slowly expanding masses may contain a pseudomeningocele with or without herniated cerebral tissue. Infarct, seizure disorder, CSF leak or new neurological deficit may result. Surgery requires excision of the pseudomeningocele and dural repair.

Skull-base fractures can produce clinical signs such as raccoon's eyes (frontal fossa fractures) or Battle's sign, and hemotympanum (petrous temporal bone fractures). Clinical evidence of CSF leak should be sought (CSF otorrhea or rhinorrhea). Careful examination of all cranial nerves is mandatory to rule out injury within their skull-base foramina (see Table 5). Surgery is rarely indicated for skull-base fractures. Persistent CSF leak and/or meningitis from presumed CSF leak are exceptions.

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