Specific Imaging Findings

Epidural (or extradural) hematomas (EDH) appear as well-defined, frequently biconvex extra-axial collections, associated with skull fractures in the vast majority of cases. Acute EDHs are hyperdense on CT. EDHs may be isodense to gray matter if they are imaged in the hyperacute stage before a clot has formed. The presence of a swirled appearance formed by alternating crescentic regions of varying densities generally indicates active hemorrhage, which may be confirmed by post-contrast enhancement within a hematoma. The MRI signal intensities will vary depending on the age of blood products similar to other intracranial hemorrhages; however, this occurs much more rapidly so that most EDHs are bright on all sequences. Unlike subdural hematomas, EDHs can cross the midline but usually respect suture lines (unless the fracture line crosses the suture). In some cases the acute blood products may be resorbed into the exposed bone marrow of the adjacent fracture, leading to rapid (within hours) decrease in size or even complete disappearance of the hematoma.

Pertinent Clinical Information

Head trauma due to traffic accidents, falls, and assaults accounts for over 90% of EDHs. Non-traumatic (spontaneous) EDHs are rare and associated with infections, coagulation disorders, vascular malformations, and neoplasms involving the dura or skull. Approximately half of patients with EDH are comatose on admission or immediately before surgery, and roughly half of patients may have the classic “lucid interval” characterized by a patient who is initially unconscious, wakes up, and secondarily deteriorates.