Extradural vs subdural haematoma

The extradural (epidural) haematoma lies between the skull and the dura. On CT it is lentiform (biconvex) and does not cross the suture lines (the dura is tethered at the sutures). It is classically from the middle meningeal artery tear after a temporal bone fracture. The patient may have the lucid interval (concussion, recovery, then deterioration). The prognosis is excellent if evacuated before the herniation, because the underlying brain is often uninjured.^[2] The acute subdural haematoma lies between the dura and the arachnoid. On CT it is crescent-shaped and crosses the suture lines (but does not cross the midline falx). It is from the bridging-vein tear or the cortical laceration. There is usually no lucid interval (the patient is unconscious from the impact). The prognosis is worse because the underlying brain is injured (the contusion, the oedema), and the mortality is high even with the evacuation.^[3] An acute subdural over 10 mm thick or with shift over 5 mm is evacuated regardless of the GCS — and the comatose small subdural is evacuated if the GCS fell by 2 or more points, the pupils are asymmetric or fixed and dilated, or the ICP exceeds 20 mmHg. Both lesions need the urgent surgical evacuation when thick or shifting: the extradural is the more urgent because the rapid expansion from the arterial source can cause the herniation in minutes — coma with anisocoria is evacuated as soon as possible — while the subdural (often venous) expands more slowly.^[2][3]