小児の閉鎖性頭部外傷のMR所見—特に中心性shearing forceについて

MRI Findings of Closed Head Injury in Children;with spedal reference to the effect of central shearing force

I．はじめに

　頭部外傷における脳損傷の基盤となるshearing forceはHolboun^10）によりacceleration, rotation movementにより生じることが証明された．shearing forceが強くなれば，その力は正中部に集中しやすくなり，diffuseaxonal injury（以下DAI）の病理所見からも正中，傍正中構造物の広範囲なaxonの断裂損傷として示されている．このshearing forceの程度や方向により様々な病態が生じる．その中にはcerebral concussion, diffusebrain swelling, DAIが招来すると考えられる．

　今回われわれは38例の小児の閉鎖性頭部外傷（Glasgow coma scale 4-15）のうちMR, T2Wで正中部および傍正中部に異常high intensityを呈した8例を経験した．これら小児の8例のMR，CT所見を比較検討し，各種の病態，特に小児の特殊性についても考按したので報告する．

It is considered that shearing effect as introduced by Ho!bourn may produce central concussion, diffuse brain swelling and diffuse axonal injury according to its grade of force.

MRI was performed in 38 children who had been admitted to our hospital during the previous 1 year for the treatment of closed head injury of varying severity.

In 8 out of 38 cases, abnormal high signal intensity was observed in the medial and para-medial brain par-enchyma on MRI. All of these 8 cases suffered from head trauma caused by motor vehicle accidents. They included 2 cases of cerebral concussion, 1 of diffuse brain swelling, and 5 cases of diffuse axonal injury. In 2 cases of cerebral concussion, MRI (T2 weighted) re-vealed only localized high intensity in the corpus callo-sum, while CT showed normal and subarachnoicl hemorrhage only at the interposium. These two child-ren had been unconscious for periods of 20 to 30 mi-nutes.

In one case of diffuse brain swelling, MRI (T2W) showed a slightly obscure border between gray and white matter due to generally increased intensity. In 5 cases of diffuse axonal injury, most of thesecases manifested lesions at the corpus callosum, deep white matter, periventricular gray matter, pons, mid-brain and the cerebellum as demonstrated by high sig-nal intensity on MRI (T2W) while CT in the acute stage showed small hemorrhage at the corpus callosum, corticomedullary junction and mid-brain and in the ven-tricles. Among these, two cases also demonstrated sub-dural hematoma and cortical contusional hemorrhage. At 3 - 4 weeks after injury, the area of high intensity previously demonstrated in the deep white matter and the corpus callosum on MRI (T2W) was reduced. These results may suggest that high intensity area:. on MRI (T2W) are clue to secondary edema induced by the release of vasoactive substances, catecholamine and calcium ion during the axonal injury.

Based on the outcome of our cases (vegetate state 1. dead 1), the extent of the brain-stem injury and hypox. is brain damage due to axonal injury seemed to effect the morbidity and mortality in children with closed head injury, while the extent of supratentorial axonal injury did not.