The importance of diffuse brain swelling in the pathophysiology of pediatric severe and moderate traumatic brain injury (TBI) has long been touted as a distinct feature compared with adults. 1 Seminal studies carried out between 1979 and 1981 by Bruce and collagues 2 reported on the importance of this phenomenon in pediatric TBI, calling it "the syndrome of malignant brain edema." That early work suggested that the etiology of diffuse brain swelling after severe and moderate pediatric TBI was largely due to hyperemia, based on groundbreaking assessments of cerebral blood flow (CBF) quantified by xenon 133 in a small sample of children. Hyperemia was purported to increase cerebral