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Radiology for Traumatic Brain Injury

The advent of CT scanning has had a huge impact for the treatment for traumatic brain injury. It is rapid, non-invasive and allows identification of surgically treatable lesions as well as diffuse injury. Plain skull -rays have no place in the management of severe blunt head injury. The indications for CT scanning in severe head trauma are not in question - all patients will require a CT scan (unless other injuries prevent this).

In general, indications for CT Scan in mild/moderate head injury are:

  1. Neurological signs
  2. Decreased level of consciousness
  3. Mental state difficult to evaluate
    (anaesthesia, drugs & alcohol, young children)

The patient with minimal external signs of injury who is fully alert & orientated (GCS 15) with a normal neurological examination and no symptoms other than headache may not need a CT scan. However they do need close observation for the next 24 hours by reliable observers. Should they require anaesthesia for treatment of other injuries they should have a CT scan prior to surgery.

Non-contrast CT scans are performed using contiguous 5mm slices for the skull base and 10mm slices for the rest of the brain. Bone and brain tissue windows should be examined. For severe brain injury where the patient is intubated, the upper cervical spine should be included in the scan (occiput - C2) as plain AP/odontoid films are difficult and may miss significant spine injury.

Epidural (extradural) haematoma

An epidural haematoma occurs when there is a tear in a vascular structure, usually arterial, in the potential space between the dura and the skull. The haematoma strips the dura off the skull vault and appears on CT as a biconvex lesion. Around 75% are associated with skull fractures. If there are no other brain injuries the patient may remain conscious until the haematoma expands to such a point that brain structures become compressed (the classic lucid interval). There is then rapid deterioration after this point. Surgical evacuation via a craniotomy is necessary and if performed early, before damage to brain structures occurs, can have an excellent outcome.

Subdural haematoma

Subdural haemorrhage usually occurs due to disruption of bridging veins between the brain and the dura. Blood can track around the brain and between the leaves of the falx. The presence of a subdural haematoma is an indication of underlying brain injury, and acute subdurals are associated with a worse outcome than epidural haematomas. On CT the subdural appears as a crescentic extra-axial collection. While surgical evacuation is usually indicated, the underlying brain injury will dictate the subsequent clinical course and functional outcome.

Cerebral contusion

Parenchymal contusions are a manifestation of direct injury to brain tissue. Contusions appear as bright signals within brain tissue, usually in areas abutting the skull or in areas near the zone of impact. Again contusions are more a reflection of underlying brain injury than clinically significant themselves and unless they are large, easily accessible and exert a significant mass effect surgical evacuation will not be of benefit. Multiple pin-point contusions are a sign of diffuse brain injury.

Diffuse Injury

Diffuse injury (or diffuse axonal injury) is due to acceleration and decelaration occurring at different rates across the brain as shear forces are applied during the moment of impact. There is a diffuse, non-focal pattern of injury. CT appearances vary, from a mild appearance with loss of grey-white differentiation, effaced ventricles and a small amounts of intra-ventricular blood, to a more severe picture with multiple contusions, diffuse swelling with loss of the basilar cisterns and brain stem involvement.

The initial CT scan appearance often underestimates the actual brain injury and the patients clinical condition may be much worse than the CT scan would suggest. Diffuse injury evloves and becomes more prominent on CT during the next 48-72 hours after injury. A diffuse injury grading system has been developed based on compression of the basal cisterns and the degree of midline shift apparent.

Diffuse Injury Grade CT appearance Mortality
I Normal CT scan 9.6%
II Cisterns present. Shift < 5mm
III Cisterns compressed/absent.
Shift < 5mm.
IV Shift > 5mm 56.2% 5:1 2000


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