The neuropathology of infant subdural haemorrhage.

Subdural haemorrhage (SDH) in the infant has a different pattern from that seen in the older child and adult. It is usually a widespread, bilateral, thin film, unlike the thick, space-occupying and often unilateral clot seen in older children and adults after trauma. Whether both arise by the same mechanism is unknown, but it seems unlikely. Most SDH is said to be due to trauma but in infants there are other, atraumatic causes. Birth is also important; recent MRI studies show an incidence of almost 50% in asymptomatic neonates. Traumatic SDH is said to result from rupture of bridging veins but new insights into the anatomy of infant dura suggest a dural origin for thin film subdural bleeding in young babies. Acute SDH usually rapidly resolves, but sometimes develops into a chronic fluid collection. Healing of SDH is by formation of a granulating membrane which may confer vulnerability to rebleeding, either spontaneously or after an otherwise innocuous event. SDH has a particular significance as one of the features of the triad (together with retinal haemorrhage and encephalopathy) associated with non-accidental injury. As the possibility of non-accidental injury is often first raised by a radiologic report of subdural bleeding, it becomes critically important in the interpretation of the scan appearances to understand the unique physiology and anatomy of the infant dura.