The lateral angiogram in the differentiation of extracerebral hematomas.

The pathophysiology of epidural hematomas is considerably different from that of subdural hematomas. Epidural hematomas are well-localized intracranial masses under high pressure, whereas subdural hematomas are more widespread collections of blood under lower pressure. The underlying small cortical vessels are normal in both acute and chronic subdural hematomas but are severely distorted in epidural hematomas. The appearance of these vessels, seen best in the lateral projection, can help differentiate the various types of extracerebral hematomas.