Even for those who do not suffer a hematoma (brain bleed) like Natasha Richardson did, symptoms from a MTBI or concussion can be delayed for a number of other factors.

The myelin sheath and schwann cells that surround the axons can continue to deteriorate after the original impact. This can go on for weeks and sometimes months. This deterioration leaves the axons unable to pass the messages on to the next neuron.

There is also a theory that the brain cells send out tRNA (transmitting or signaling RNA) to tell the neighboring cells to self-destruct, so that erroneous messages do not get processed. When this happens in a young person, the brain then just reroutes the messages via another route. In older persons, this rerouting is not as successful.