TP 13312

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Head Injury

• General
• Prediction of Neuropsychological Outcome
• Prediction of Posttraumatic Epilepsy
• Table 1 - Risk Factors for Late Posttraumatic Epilepsy
• Aeromedical Status
• Chronic Subdural Hematoma

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. 

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. 

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.

Table 1 - Risk Factors for Late Posttraumatic Epilepsy

Aeromedical Status

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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. 

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;

1. no sequelae and
2. no seizures in the year following surgery and
3. no significant abnormality on CT scanning and sleep deprived EEG, they may be considered for medical certification.