These occur due to stretching and shearing injury, often due to impaction of the brain against the skull on the side opposite to the injury. Thus they may be seen directly opposite the impact site, subcutaneous haematoma, fracture, or extradural haematoma (contre coup injury). The inferior frontal lobes and anterior temporal lobes are common sites after a blow to the back of the head.
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.
(aka multifocal haemorrhagic contusion)
Multiple contusions may be present throughout the cerebral hemispheres. They are often very small and visible at the grey/white matter interface. They are due to a shearing injury with rupture of small intracerebral vessels, and in a comatose patient with no other obvious cause they imply a severe diffuse brain injury with a poor prognosis. Larger haemorrhages may occur in severe trauma, and they may not be apparent on a scan performed immediately after the injury, only becoming prominent after a day or two. MRI is more sensitive to diffuse brain injury, particularily in the absence of haemorrhage.
This image demonstrates a small petechial haemorrhage in a typical location at the grey-white matter interface (arrow). As is often the case, there were multiple such lesions on other slices.
This may occur alone or in association with other intracerebral or extracerebral haematomas. Increased attenuation is seen in the CSF spaces, over the cerebral hemispheres (look closely at the Sylvian fissure), in the basal cisterns or in the ventricular system. SAH may be complicated by hydrocephalus. Confusion can sometimes arise between SAH due to trauma and due to a ruptured aneurysm or arteriovenous malformation (AVM); the patient may collapse and hit their head as a result of a bleed and the history (from the patient or a witness) is important.
This patient has an acute extradural haematoma on the right side, and acute traumatic subarachnoid haemorrhage on the left side.
This patient was semiconcious with subarachnoid bleeding. The filling in of the sulci over the cerebral hemispheres was subtle (not shown), but the clue is visible on this image; there is abnormal increased attenuation due to fresh blood in the 4th ventricle, which has settled posteriorly. The prepontine cistern is also indistinct and may contain blood.
There is a further example of post traumatic subarachnoid haemorrhage under "Intracranial Air".
Focal oedema may be seen as localised poorly defined areas of low density; MRI is more sensitive to such abnormalities.
Diffuse oedema may develop, especially in children. This may be difficult to detect on CT.
Infarction in a typical vascular territory may suggest dissection of a vessel, such as the carotid artery after a direct blow to the neck.
Continue | Contents | Tutorials
Dr A C Downie
Victoria Infirmary, Glasgow
andrew@radiology.co.uk