The causes of epilepsy: traumaDamage to cerebral nerve cells may occur through physical trauma. In war time, head injuries due to penetrating injuries from shrapnel are a potent source of epilepsy. About 45 per cent of survivors develop later seizures. In civilian life most head injuries are closed—that is to say there is no penetration of the skull. However, the impact of the head with the dashboard or road in road traffic injuries may cause the later development of post-traumatic epilepsy. Professor Bryan Jennett of Glasgow has done a great deal to sort out the factors in a head injury that are most likely to cause later epilepsy. The first is the duration of the post-traumatic amnesia. This is the name given to the period after a head injury when patients, although conscious, are not recording in their memory on-going events, even though they may seem to be behaving rationally at the time. A typical story is for a man to have no recollection of relatives visiting him in hospital, even though he talked and joked with them. The duration of post-traumatic amnesia may vary from a few minutes, when the term 'concussion' is often loosely applied, to many weeks or even months. The mechanism of the amnesia is not known, but a useful analogy is to consider a blancmange in a mould (the brain on the skull). A vigorous tap or shaking of the mould may cause oscillations so violent within the blancmange that cracks appear within its structure, even though the mould remains intact. Such shearing forces can be demonstrated within the brains of animals subject to experimental head injuries. The longer the duration of post-traumatic amnesia, the greater the chance of the development of later epilepsy. The second factor which Professor Jennett found to be important was the presence of focal neurological signs, such as changes in the reflexes, after the injury. Presumably these just reflect a greater degree of disruption of the brain. The third factor was the presence of local damage to the cortical surface of the brain, as judged by the presence of a tear in the dura—the membrane covering the brain. The impact of the head on a sharp corner may cause a depressed fracture, with fragments of bone tearing the dura and becoming embedded in the cortex. Professor Jennett found that if all three factors were present in one case (a prolonged amnesia of more than 24 hours after the head injury, focal neurological signs, and a dural tear), then there was a 40 per cent chance of developing epileptic seizures later. If none of these factors was present the risk was about two per cent. Professor Jennett also noted that some head-injured patients had a seizure in the first week after the injury. The occurrence of such an event perhaps the marker of an inherited low convulsive threshold or of extensive cortical damage—was a potent predictor of late post-traumatic epilepsy. A seizure in the first week, accompanied by a long post-traumatic amnesia and focal neurological signs was followed by later seizures in 60 per cent of cases, even if the dura were not torn. There are other types of brain injury apart from those caused by the ubiquitous road traffic and industrial accidents. Cerebral trauma also occurs, unavoidably, during cranial operations. For example, small balloon-like swellings called 'aneurysms' on arteries at the base of the brain are never, by themselves, responsible for epilepsy. In order to avoid the risk of haemorrhage, operation may be advised. The surgeon, in approaching the aneurysms in order to clip the neck of the 'balloons', has to handle and retract, albeit very gently, normal brain. Unfortunately seizures may follow such handling of cerebral tissues. *20\188\2* Epilepsy «Viagra no Prescription» |
|
Total 1153 articles Articles © www.ipeerx.com 2012 |