What are haematomas?
As I mentioned in the page Traumatic Injuries, haematomas (also spelled as hematomas, depending on dialect) are injuries to the blood vessels within the brain as a result of trauma. There are three different types of haematomas, two of which (epidural and subdural haematomas) are shown on the picture alongside. The other type of haematoma is intracerebral haematoma. These injuries to blood vessels often lead to haemorrhaging (bleeding) in the brain. More information can be found about this in Brain Haemorrhage.
Epidural (or above the dura) haematomas happen when vessels within the dura rupture due to skull fractures or other types of head injury. This leads to the separation of the dura from the skull: in normal circumstances, these two structures are fused together. The extent of the injury can differ depending on the age of the person: this can happen because the skull is fused in adulthood but in kids, the different skull bones are held together purely by cartilage, which is much more flexible. Epidural haematomas are considered as medical emergencies because unless the blood is drained out within a matter of hours, it may accumulate to a point where the brain can no longer tolerate it and shuts down. Symptoms may appear straight away, however it may be several hours because the person with the injury shows any symptoms, depending on the rate of leakage.
Subdural (or under the dura) haematomas happen when trauma tears the bridging veins, leading to bleeding within the subdural space. The bridging veins are the ones that extend through the cerebral hemispheres as well as the subarachnoid and subdural space within the meninges to finally empty within the dural sinuses. Both the elderly and infants are more prone to this type of injury than the age groups in between, because their veins are either stretched out due to shrinkage of the brain or thin, respectively. Subdural injuries lead to flattening of the brain similar to that of epidural haematoma: however, unlike epidural haematoma which can bleed constantly until either the blood is drained or the brain dies, subdural haematomas are self-limiting i.e. the blood breaks down over time.
Intracranial haematomas happen when the brain slides against the inner part of the skull: this leads to the brain becoming ‘bruised.’ These tend to happen in conjunction with contusions and lacerations, as discussed in Traumatic Injuries. Intracranial haematomas are often life-threatening and are considered as medical emergencies.