What is concussion?
Concussion is a period of unconsciousness that follows a violent blow to the head. In severe cases concussion leads to a massive bleeding in the brain and causes permanent brain damage.
The brain weighs about three pounds and contains billions of nerve cells and a complexity of interconnecting fibres. The brain is well protected, being enclosed in a strong bony case (skull) and cushioned in a bath of water (cerebrospinal fluid). The living brain is a soft, jelly-like structure covered with a dense network of blood vessels.
A blow to the head causes the brain to rebound against the rigid bone of the skull. This may cause a tearing or twisting of the structures and blood vessels of the brain, which results a disturbance of function of the electrical activity of the nerve cells in the brain and a breakdown of the usual flow of messages within the brain.
This trauma to the brain causes an immediate brief period of unconsciousness, which starts at once and lasts for periods ranging from a few seconds to several hours or even days.
A blow to the head can cause multiple shearing injuries and multiple points of bleeding from small blood vessels. The shearing force stretches and tears the soft nerve tissue and the blood vessels associated with it. The bleeding may be minor and is re-absorbed with no lasting damage.
A single episode of minor concussion is unlikely to have permanent effects.
However in more serious concussion, it may lead to the production of an expanding accumulation of blood (a hematoma) that may slowly compress the brain. This condition is life threatening and neurosurgery will be necessary to open the skull.
Most patients in these cases also have a skull fracture. Repeated episodes of concussion, such as may be experienced by boxers, may cause major permanent brain damage (the ‘punch-drunk’ syndrome). If an individual is unconsciousness for a long time there is also the risk of the brain swelling, also a dangerous complication.
Symptoms of concussion
Loss of consciousness is immediate and lasts for a variable period. At the moment of impact the breathing briefly stops and the blood pressure drops. During this time, examination shows widespread loss of brain function.
Recovery is progressive. Consciousness returns before vision.
The individual may be able to respond to simple questions and commands on becoming conscious. However there may be some degree of memory loss including an inability to remember events immediately before the injury.
Causes of concussion
Concussion is caused by head injury, usually without skull fracture forces. This causes the brain to swivel and experience compression against the bony protrusions on the inside of the skull.
The injury is associated with some bleeding inside the brain, and destruction of nerve tissue may occur.
Concussion may be followed by:
- Fainting attacks
- Weakness and numbness of the legs
- Delayed paralysis on one side of the body
- A period of relative normality followed by a relapse into unconsciousness.
The last complication is the most important and is an acute and urgent emergency calling for immediate surgical action. It indicates continued bleeding (hematoma) inside the skull and progressive compression of the brain downwards.
Another complication of concussion is delayed fainting. The affected person may seem to be normal, but after a time, while standing or walking, will turn pale and fall to the ground, unconscious. Recovery is, however, rapid.
Rarely, a more serious form of post concussion collapse occurs. This condition occurs minutes or hours after the apparent recovery. The individual suddenly becomes unconscious and falls, and for a time remains unresponsive. A feature of this complication is a very slow pulse rate.
There is eventual recovery, often with vomiting, restlessness and headache.