Skull x-rays: are used occasionally in the evaluation of penetrating head trauma to provide a rapid assessment of the degree of foreign body penetration in nonmissile penetrating head injuries (eg, stab wounds) or in gunshot wounds to screen for retained intracranial bullet fragments.
- A CT scan is the diagnostic study of choice in the evaluation of TBI.
- The standard CT scan for the evaluation of acute head injury is a noncontrast scan, from the base of the occiput to the top of the vertex in 5-mm increments.
- Each intracranial structure has a characteristic density, which is expressed in Hounsfield units. On this scale, CSF has a density of (+) 4 to (+) 10 units, white matter has a density of (+) 22 to (+) 36 units, and gray matter has a density of (+) 32 to (+) 46 units. Extravascular blood has a density of (+) 50 to (+) 90 units, and calcified tissue and bone have a density of (+) 800 to (+) 1000 units.
- Extra-axial hematomas include epidural (extradural) and subdural hematomas. Epidural hematomas are located between the inner table of the skull and the dura.
- They typically are biconvex in shape.
- Epidural hematomas usually are caused by injury to an artery, although 10% of epidural hematomas may be venous in origin. Q
- Subdural hematomas are located between the dura and the brain.
- Their outer edge is convex, while their inner border is usually irregularly concave. Q
- Subdural hematomas usually are venous in origin, Q although some subdural hematomas are caused by arterial injuries.
- The classic cause of a posttraumatic subdural hematoma is an injury to one of the bridging veins that travel from the cerebral cortex to the dura.
- Intra-axial hematomas are defined as hemorrhages within the brain parenchyma.
- These hematomas include intraparenchymal hematomas, intraventricular hemorrhages, and subarachnoid hemorrhages. Q
- Subarachnoid hemorrhages that occur because of trauma typically are located over gyri on the convexity of the brain.
- The subarachnoid hemorrhages that occur as the result of a ruptured cerebral aneurysm usually are located in the subarachnoid cisterns at the base of the brain.
Frontal contusions on head CT scan (arrow)
There is a focal area of haemorrhagic contusion in the right frontal lobe, with surrounding low density due to infarction or oedema. This is a frequent location for a contre-coup injury following a blow to the back of the head.