PRIMARY BRAIN-STEM LESIONS CAUSED BY CLOSED-HEAD INJURIES

Traumatic lesions of the brain stem are of two types: primary, which a re considered to be caused at the moment of impact, and secondary, ass ociated with supratentorial mass lesion. Of the 239 patients with a se rious head injury who showed a severe disturbance of consciousness upo n admisision and who had CT scan carried out immediately, 21 cases wer e considered to have a primary brain stem lesion with initial CT scan. A primary brain stem lesion was found in 21 of 239 (8.8%) of patients with serious head injury. Their injuries were caused primarily by tra ffic accidents. Sixteen of the 21 cases showed not only brain stem les ions but also other brain injuries such as cerebral contusion of the w hite and gray matter, callosal injury, intraventricular hemorrhage, an d subarachnoid hemorrhage, which are considered to be caused by a diff use shearing injury. Five cases who showed a single injury to the brai n stem with no other brain lesions were considered to have a pure brai n stem lesion. Primary brain stem lesions were observed on the dorsal side of the midbrain, where they can be differentiated from secondary brain stem lesions. These lesions are considered to result from the sh earing mechanism in and around the brain stem very close to the tentor ial edge, or to an injury of the lower brain stem by hyperextension of the cervical vertebrae. The prognosis of patients with a primary brai n stem lesion was usually unfavorable, except in those with a single b rain stem lesion.