Introduction
This topic covers brain contusion, a focal bruising of brain tissue caused by head injury, and traumatic encephalopathy, the chronic, progressive brain dysfunction that may follow severe or repeated traumatic brain injury. The acute lesion is discussed here; the diffuse, short-term post-concussive state belongs to the previous topic, and subdural and epidural haematomas belong to the next.
Brain contusion: definition and mechanism
A contusion is a bruise of the brain parenchyma with small haemorrhages (petechiae), oedema and, in severe cases, necrosis. Unlike concussion, it is a structural lesion that can be seen on imaging. It is most often caused by a blow to the head or by acceleration and deceleration forces, for example in road traffic accidents and falls.
- Coup injury: the lesion lies directly under the point of impact.
- Contrecoup injury: the lesion lies on the opposite side, where the brain strikes an uneven skull base or wing of the sphenoid.
- Typical sites are the frontal and temporal poles, the orbital surfaces of the frontal lobes and the temporal lobe base, because these lie against the bony irregularities of the anterior and middle cranial fossae.
- Shearing forces at the grey-white matter junction can add small haemorrhages, which may merge into larger lesions.