subdural haemorrhage
subdural haematoma
Subdural haematoma, aetiologyAcute SDH
Caused by tearing of communicating veins which traverse the subdural space, or more rarely the sinuses, due to a change of velocity of the head (acceleration or deceleration), often with some rotational movement. The site of original haemorrhage is not usually identified.
Sites
Lateral surface of a cerebral hemisphere, often in a parasagittal position. After blunt impact, the SDH may not be situated under the site of impact. The blood may move following accumulation.
Chronic SDH
May expand due to rebleeding or osmosis of CSF into the centre of the heamatoma; it may also be resorbed or stay the same size. The colour changes from dark red to brown between days 5 and 12.
Cellular infiltration occurs within a few hours; a neomembrane formed adjacent to dura which is a few cells thick in 4 days. Fibroblasts from the membrane enter the clot at 5–8 days.
Day 15: Membrane is present under the clot.
1–3 months: Hyaline appearance to membrane.
6–12 months: Thick, fibrous membrane, like dura.
Trauma
• Rapid acceleration/deceleration (with tearing of dural bridging veins);
• Minor trauma in setting of cerebral atrophy;
• Birth trauma in neonates.
Dural neoplasms
• Meningiomas
• Metastases
Abnormal haemostasis.