structural:expansion
Pathophysiology

The break of the temporal bone causes bleeding from the middle meningeal artery, hence epidural bleeding is often rapid as arteries are high-pressure flow. In 10% of cases, however, it comes from veins and can progress more slowly. A venous hematoma may be acute (occurring within a day of the injury and appearing as a swirling mass of blood without a clot), subacute (occurring in 2–4 days and appearing solid), or chronic (occurring in 7–20 days and appearing mixed or lucent).