Epidural hematoma is caused by tears of the middle meningeal artery or vein, or of a dural venous sinus. The blood accumulates in the interval between the inner table of the calvarium and the dura by gradually stripping the dura from its bony attachment. CT visualizes the epidural hematoma as a well-localized biconvex radiodense mass (83) (Fig. 6-88). It is commonly, though not invariably, associated with a skull fracture. It causes mass effect upon the adjacent brain parenchyma with effacement of the underlying sulci, compression of the brain and ventricles, and possible contralateral midline shift. It is important to note that midline shift is a secondary injury caused by subfalcine herniation, which is herniation of the cingulate gyrus under the falx cerebi, and can eventually lead to ipsilateral anterior cerebral artery infarction. When there is a question about whether the mass might be intraparenchymal, contrast injection enhances the dura, establishing the epidural position of the clot. As the clot lyses over the next few weeks, it shrinks and changes to isodense and then hypodense relative to the brain. The inner aspect of the clot vascularizes, and this may produce a thicker rim of enhancement on late contrast studies. The overlying dura may calcify. Epidural hematoma may be associated with subdural, subarachnoid, or intraparenchymal hemorrhages.