Head Injury
General
There are two major concerns following head trauma resulting in loss of consciousness. One is the
neuropsychological consequences of the trauma in patients who have not had any focal deficits. The
other is the possibility of seizure secondary to the trauma.
The neuropsychological consequences are secondary to the effects of acceleration/deceleration forces on
the skull and brain. Because of the anatomy involved, these forces cause their greatest focal damage to the
orbital, frontal and anterior temporal areas of the brain. Associated with the cortical damage there is
diffuse white matter damage.
The result of this is dysfunction in a number of functional executive activities of the brain. These
frequently are, 1) slowing of reaction time, impaired memory and deficient ability to perform constantly at
a high level over time, particularly in settings of complex activities and choices. 2) A high propensity
for further mental decline with fatigue. Other problems include attention, initiation and proper
sequencing of tasks, difficulty in planning and anticipating the future, and difficulty establishing
automatic responses to a trigger. The affected individual may not notice or care that the task is
being poorly performed. Problems are exacerbated by stress, fatigue and pain and the handling of
simultaneous emergency tasks is particularly affected. Although the problems may be severe,
routine IQ and mental status testing may be within normal limits. Fortunately there is a natural tendency
for deficits to improve.
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Prediction of Neuropsychological Outcome
Sufficient data to accurately predict the outcome of most types of head injury is unfortunately
unavailable. There are a number of ways to predict the outcome of head injury and the most commonly
used to date has been the duration of post-traumatic amnesia (PTA). Most individuals who have had a
PTAof less than 30 minutes are likely to be fit within three months. Older individuals and/or those who have a history of previous concussion are of greater
concern. A person with PTA lasting more than 30 minutes but less than 24 hours will likely be fit from
a neuropsychological point of view after a longer time, probably one year.
Those with focal neurological deficits, those who have focal abnormalities on CT scanning or a more
prolonged PTA require neuropsychological assessment with particular attention to frontal lobe
functioning before medical certification. Flight simulator testing may be useful. Magnetic resonance
imaging (MRI) is more sensitive than CT scanning in defining areas of frontal lobe and white matter
abnormality and is therefore an important diagnostic adjunct in those who have had brain injuries. These
people clearly require a more prolonged period off work than those with simple concussion.
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Prediction of Posttraumatic Epilepsy
The probability of epilepsy is greater in those with penetrating skull injuries. Even with full physical and
neuropsychological recovery there is an increased probability of seizures for over ten years. In general,
of those who develop post traumatic seizures, 50% will occur within one year and 70 - 80% within two
years. Thereafter the incidence is 3 - 5% per year up to ten years. The probability of seizures has been
correlated with CT scan findings as illustrated in Table 1.
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Table 1 - Risk Factors for Late Posttraumatic Epilepsy
|
Incidence of Late Seizures (%) |
Penetrating injury caused by missile |
53 |
Intracerebral haematoma – laceration |
39 |
Focal brain damage on early CT scan |
32 |
Early seizures |
25 |
Depressed fracture – torn dura |
25 |
Extradural or subdural haemorrhage |
20 |
Focal signs (hemiplegia, aphasia, ..) |
20 |
Depressed skull fracture |
15 |
Loss of consciousness > 24 hours |
5 |
Linear fracture |
5 |
Mild concussion |
1 |
Pagni C.A. (1990) Post-traumatic Epilepsy and
Prophylaxis: Acta Neurochirurgica, Suppl. 50, 38-47 (1990) |
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Aeromedical Status
- Those with PTA lasting 30 minutes or less, who after the event, have a normal neurological
examination without sequlae, may be medically certified in three to four months if the CT scan is
normal.
- Those with PTA lasting from 30 minutes to 24 hours but with a normal MRI and EEG, may be
medically certified by one year. If a seizure occurred in the first week after trauma in an
adult, a longer interval before medical certification is indicated.
- Those with PTA greater than 24 hours but who have normal neuroimaging and neuropsychological testing, may be
medically certified by two years. Flight simulator testing may provide additional valuable information in
these cases.
- Those with closed head injury with extracerebral haemorrhage, but without dural tear or
intracerebral involvement may return to full duties by five years. An EEG and neuroimaging
should be undertaken at that time.
- Those with closed head injuries with associated intracerebral haemorrhage or focal deficit, but
whose neuropsychological testing does not show significant residua 7 years post trauma, may be
considered at that time. Those who demonstrate abnormal neuropsychological residua have been
more seriously injured and should be considered individually.
- Those with penetrating skull injuries from a missile are unfit for 15 years even if
neuropsychologically normal because of the continuing excess risk of posttraumatic epilepsy.
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Chronic Subdural Hematoma
These can occur at any age, though they are more common in the older age group. Individuals
frequently are unaware of significant head trauma.
Postevacuation if the applicant has;
- no sequelae and
- no seizures in the year following surgery and
- no significant abnormality on CT scanning and sleep deprived EEG, they may be considered for
medical certification.
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