Brain injury is sometimes said to be part of whiplash associated disorder. The reason for this is undoubtedly the many problems the victims report, which could be explained by a structural injury to the brain. Nevertheless, there is little evidence that there is a brain injury, and therefore plausible mechanisms must be discussed.
The anatomy of the cervical spine admits a transient decrease in the brainstem circulation when the head is bent backwards. The vertebral arteries may be blocked during a very short period. This mechanism could be the reason why some victims report short amnesia (or even unconsciousness), but the lack of blood is of such a short duration that I find it impossible that this could cause tissue death with chronic symptoms. In rare cases dissection of the inner wall of the blood vessels can cause brain infarction or transient ischemic attacks.
Animal models have shown a tendency to small bleedings in the brain tissue after sudden movements. Some American studies have shown very small bleedings in whiplash victims. The results are uncertain and have not been confirmed in recent studies. The possibility remains, but it is probably a very uncommon condition.
This diagnosis applies when the head hits an unresilient surface. It does not in neck distorsion, and the diagnosis is not appropriate. If there is a direct trauma to the skull, there is one more injury mechanism, and we do not talk about whiplash associated disorder in such a case.
In a whiplash injury according to the classic definition – a straight impact from behind – the head will receive a movement pulse which causes a transition backwards in relation to the trunk, but also a rotation backwards (forehead up, occiput down). As the energy is transferred as a pulse, the rotation starts with a very powerful acceleration. In this process, the brain according to the law of inertia will remain in its position when the skull is struck in the rotation. This could be the equivalent of a concussion, and from that point of view we may retain the concussion as a possible mechanism despite the lack of direct trauma to the skull.
As microscopic blood vessels could rupture causing minor bleeding, so could the nerve fibers. This process is invisible on MRI and might occur despite normal neurophysiological examination of conduction velocities in the brain. New technique may give us the possibility to detect metabolites of nervous tissue. The injury can be local or diffuse, in both cases to little to give evident findings at routine examination but in some instances detectable with neuropsychological measuring methods. It is however uncertain to what extent such examination would give findings also in cases of psychological impairment.
So what is the mechanism causing victims with nothing more than a muscular distorsion to report symtoms of brain injury? Click here for explanation!
| Last update 31 August, 1997 visitors since 12 Sept. 1997. e-mail to the author |