The source of bleeding is typically from a torn meningeal artery, usually the middle meningeal artery. An associated skull fracture is present in ~75% of cases 3. Pain (often severe headache) is caused by the stripping of dura from the bone by the expanding haemorrhage. The posterior fossa is a rare location for traumatic injury, in general, including EDH 3-4.
Occasionally, an EDH can form due to venous blood, typically a torn sinus with an associated fracture.
Young patients being affected is not only a result of the prevalent demographics of patients with head injury but also relates to the changes that occur in the dura in older patients, as the dura is much adherent to the skull.
It is important to realise that in the setting of sutural diastasis extradural haematomas can cross sutures, as the continuation of the parietal (periosteal) component of the dura through the suture - which usually limits spread - is likely also to be disrupted.