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Contusions are present on the right frontal tip (left side of image) orbital surface. |
2. Location: In general the most common sites are orbital surfaces, (inferior surface of frontal lobe) temporal lobes and occipital lobes. Contusions can be produced by rotation of the brain or by linear forces through the site of impact. The exact location may depend on conditions of the trauma. Contusions may be coup lesions (directly adjacent to the site of impact) or contrecoup lesions (on the opposite side of the brain from the impact). In the case of linear acceleration or deceleration injuries (i.e. a single blow to the unsupported head), contrecoup lesions are a common sequelae. A blow to the well supported head results in severe skull fractures, often with absence of coup and contre-coup lesions (the head does not accelerate or decelerate and the skull absorbs much of the force).
3. Pathology: In the most typical form of contusion, the summit of a cerebral gyrus is smashed, and the lesion has a wedge shape with its base toward the pia and the apex toward the white matter. All layers of cortex are regularly affected. In its early stage the hemorrhage remains bright red, and the surrounding brain tissue is edematous. When the lesion is older it becomes brick-red and finally golden orange-brown (due to deposition of hemosiderin), with a floor of glial tissue, covered by leptomeningeal fibrosis. The most chronic stage is sometimes called plaque jaune. Dura arachnoidal adhesions (meningocerebral cicatrix - scar involving meninges & cerebral cortex) later form on the surface, and frequently cause post-traumatic epilepsy.