Pathogenesis and biomechanics of traumatic intracranial haemorrhages.

Intracranial haemorrhage is frequently seen by the general pathologist in the context of neural trauma. Thus, the differential diagnosis, pathogenesis and biomechanics are of practical interest in the routine work. Extradural haematomas are produced when branches of the middle meningeal vessels are lacerated. They are commonly located in the temporal fossa, and other intracranial haematomas may be present. Skull fractures occur in a high percentage of cases and play a key role in the pathogenesis of this type of bleeding. Acute subdural haematomas commonly arise from tearing of the bridging veins. They are often located in the temporal and frontal regions, and the morbidity and mortality are related to the extent of the underlying brain damage. The visco-elastic behaviour of the bridging veins and their lack of reinforcement by arachnoid trabecula in the subdural space explains why they tear under high rates of acceleration during trauma. Subacute and chronic subdural haematomas are weakly correlated with trauma. The less striking onset of symptoms may be related to the rate of blood accumulation and the capacity of the brain to accommodate the mass effect of the bleeding. Intracerebral haematomas are probably due to the direct rupture of the intrinsic cerebral vessels. The mortality rate shows no correlation with location, but those located in the basal ganglia are compatible with a good recovery when occurring in isolation. Traumatic subarachnoid haemorrhage, when in isolation, is usually associated with evidence of injury elsewhere, such as the neck muscles or the ligamentary system of the cervical spinal column. It may be secondary to intraventricular bleeding due to tearing of the tela choroidea, or associated with contusions.