Figure 3. CT and MR appearance of epidural hematoma.

Noncontrast CT (A,B) performed on a 26-year-old man who was “found down” with altered mental status. Note the classic biconvex hyperdense epidural hematoma with an overlying nondisplaced calvarial fracture (arrows). Axial T2WI (C) from a “rapid” MR protocol in a different patient (3-month-old accidentally dropped on her head) reveals a right parietal biconvex low signal epidural collection. Note the position of the dura, seen as the thin black line deep to the collection (arrows); this allows confident determination that the collection is located in the epidural space. Sagittal (D) and axial (E) reformatted images from a noncontrast CT performed in a different patient (13-year-old male after a skateboard accident) show a heterogeneous epidural hematoma in the occipital region. Areas of lower density within the hematoma likely represent hyperacute unclotted blood concerning for active bleeding and predictive of continued expansion of the hematoma. This is confirmed on the CTA of the head performed minutes later (F) where dense contrast material extravasates (F, arrow) into the area of low density on the earlier noncontrast study (E, arrow). The sagittal reformatted images (D) best demonstrate how the hematoma crosses the plane of the tentorium cerebelli (arrow) into the posterior fossa, characteristic of epidural hematomas (unlike subdural hematomas) as they are not constrained by dural boundaries. In contrast to arterial epidural hematomas, venous epidural hematomas bleed under lower pressure and are therefore less likely to increase in size. Noncontrast CT (G), axial FLAIR (H) and sagittal T1WI (I) performed on a 52-year-old victim of assault reveal a right sphenoparietal venous epidural hematoma (arrows). CT on the day of the injury (G) shows the characteristic well-defined, crescentic, high-density extra-axial collection (white arrow) along the anterior margin of the middle cranial fossa. On MRI performed 2 days later (H,I), the same venous epidural hematoma (arrow) appears isointense to adjacent anterior temporal contusion on FLAIR (H) and hyperintenseT1WI (I), consistent with intracellular methemoglobin blood products and it has not increased in size. In cases of trauma, multiple pathologic entities often are seen in the same examination. Notably, foci of subarachnoid hemorrhage (white arrowhead) and temporal lobe contusions (black asterisk) are much more visible on MRI (H) than CT.

In contrast to arterial epidural hematomas, venous epidural hematomas bleed under lower pressures and are less likely to expand. Noncontrast CT (G), axial FLAIR (H) and sagittal T1WI (I) performed on a 52-year-old victim of assault reveal a right sphenoparietal venous epidural hematoma (arrows). CT on the day of the injury (G) shows a characteristic lobular high-density extra-axial collection (white arrow) along the anterior margin of the middle cranial fossa. On MRI performed 2 days later (H,I), the same venous epidural hematoma is seen adjacent to an anterior temporal contusion (H (I). In cases of trauma, multiple pathologic entities often are seen in the same examination. Notably, linear foci of subarachnoid hemorrhage (white arrowhead) and temporal lobe contusion (asterisk) are much more visible on MRI (H) than CT (G).