Contrecoup Injuries
This is the base of the brain showing the temporal and frontal poles, cerebellum and the brain stem. The frontal and temporal poles, especially the left temporal pole, show extensive bruising. This appearance is sometimes called 'burst lobe'. (Contusion of the brain ruptured into the subdural surface as a haematoma.)
Cotrecoup injury is important in forensic medicine as it helps the pathologist to differentiate a 'fall' from an 'assault'.
Striking the movable head with a small surfaced blunt weapon causes brain injury immediately beneath the site of impact as a result of the local deformation of the skull (inbending) causing compression of brain tissues and tensile stress caused by 'bouncing back' phenomenon of the inbended skull to the original position. This is called coup injury. The skull may not fracture as the kinetic energy is not enough to overcome the elastic limit of the skull bone.
A fall on the occiput causes contusions of the brain (some times lacerations and 'burst lobe') on the frontal and temporal poles. They are called contrecoup injuries as they occur in sites diametrically opposite to the site of impact, which is on the occiput.
Contrecoup injuries do not occur on occipital poles. Reason? The cause for these injuries is thought to be due to the rugged nature of the anterior and middle cranial fossa, where the frontal and temporal poles lie respectively. The appearance of the lesser wings of sphenoid, orbital plates are petrous temporal bones tells it all.
A fall on the temporal region may cause contrecoup injuries on ipsilateral brain, where it is in contact with the falx just as it caused contrecoup injuries on the contralateral brain.
Since there are exception to this rule each and every case should be properly evaluated before pronouncing that it was a fall and not an assault.
Priyanjith Perera
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