L e t t e r s t o t h e e d i t o r 1 Concussion To The ediTor: We read the review of Zuckerman et al. 5 on structural brain injury in sports-related concussion (Zuckerman SL, Kuhn A, Dewan MC, et al: Struc tural brain injury in sports-related concussion. Neurosurg Focus 33(6):E6, December 2012), which suggests a number of interesting issues. In spite of the uncertainty that has arisen from the difference in the perspectives, it is a worthwhile contribution consistent with the literature. Aside

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... from reviewing published cases of isolated head injuries, probably the most valuable contribution is inclusion of comments about unpublished cases from the authors' own institutional experience. The paper offers a different vantage point from which subarachnoid hemorrhage (SAH), subdural hemorrhage (SDH), epidural hemorrhage (EDH), malignant edema, and second-impact syndrome can be viewed vis-à-vis the blood-brain barrier damages of various intensity, mechanism, or location. These are all manifestations of extravasation, regardless of whether focal or diffuse, per rhexis or per diapedesis bleeding took place. The term edema, in the context of malignant cerebral edema, is generally used to indicate an increase in brain volume due to an increase in tissue water. 4 Brain swelling and cerebral edema are the common reactions of the brain to injury of whatever etiology. While generally considered to occur most commonly in infants and children, malignant cerebral edema also occurs in adults. In practice the most common type of edema is vasogenic edema, in which there is a breakdown of the blood-brain barrier. This occurs locally around mass lesions and also more diffusely in the cerebral white matter. The second most common type of edema is cellular edema. It is most often seen in association with ischemic conditions and is more prominent in gray matter, as cellular components are found in this location. 1 It seems that blood hyperdensity could not be the only criterion that the authors used, taking into account the edema's hypodensity and the loss of normal gray-white matter differentiation. As concussion is a functional rather than structural change, we believe that it primarily disturbs endothelial functioning of the blood vessel's wall. This is involved in the formation of the blood-brain barrier. Tight junctions of the nonfenestrated endothelium and the thick basement membrane restrict the diffusion of microscopic objects and large or hydrophilic molecules into the CSF. Its disruption causes extravasation of blood elements. Therefore, we suggest that edema and hemorrhage should be regarded as two extremes in a broader spectrum, where disruptions of endothelial continuity can be found microscopically or as evident to the naked eye. Since the literature recognizes a concussion as physiological (functional) rather than a morphological disrup-tion, its severity is not measured by CT or MRI findings but by the duration of transient memory loss or disorders that interfere with the qualitative character of consciousness. The long-term effect of these functional disorders sometimes results in posttraumatic chronic encephalopathy (a combination of motor, cognitive, and psychiatric symptoms). 2 While CT and MRI sometimes suggest encephalopathy or cerebral atrophy, confirmation of a diagnosis is not possible until postmortem. Thus, we doubt the appropriateness of the use of radiological criteria in assessing mild traumatic brain injury (TBI). This only highlights the importance of bridging full clinical details including radiological results with results of other investigative tests. We would like to clarify that we are responding to follow up in a constructive manner and hopefully produce a creative debate on the subject. Zuckerman and colleagues were apparently looking at isolated head injuries, where the structural injury is the focus of the presentation. However, it is possible that there is an exponentially greater number of more dramatic injuries that present first, and the mild TBI is ignored. 3