Infants with subdural haematoma constitute a medical emergency, but they also immediately trigger thoughts of possible inflicted injury. Two articles in this issue highlight once again the incidence, aetiology, and neuroimaging of infantile subdural haematomas/effusions (SDH/E).

Hobbs et al report an incidence of subdural haematoma/effusion in infancy from all causes of 24.1 per 100 000 children less than 12 months of age (and 12.54 per 100 000 aged 0–2) in the largest UK study to date.¹ Cases of SDH/E diagnosed on brain imaging or at postmortem examination were reported to the BPSU, through the monthly reporting card system, over a 12 month period (April 1998–March 1999) from all specialists likely to have contact with infantile subdural haematoma/effusion. Because a subdural haematoma/effusion is a dynamic pathology and can be due to trauma or infection etc, the authors have very appropriately defined case entry as any child under 2 years with subdural haemorrhage, haematoma, or effusion, and have reported the aetiology that was ascribed by local reporter personnel.

A traumatic acutesubdural haemorrhage is a venous haemorrhage resulting from vascular shearing of cortical surface and interhemispheric bridging veins when motion of the brain within the skull stretches and tears the weakest of some 15–20 small bridging veins as they cross the subdural space. In the acute haemorrhage the brain is covered with a layer of undiluted blood clot with a high haematocrit. It is temporally considered acute if within three days of the injury.²

As the acute bleed breaks down by fibrinolysis, water is drawn into the collection, haemodilution occurs, and the haematocrit falls to less than 10%. There is subsequently a marked expansion after about one week. Denaturation of the …