Abstract
A local shift of the brain stem and transtentorial herniation are studied in the state of increased intracranial pressure (ICP) induced by a supratentorial mass lesion. Analysis of ICP dynamics is based on the correlations between an increased ICP and the local shifts of the brain.
Simultaneous measurement of brain shifting, ICP, systemic blood pressure, respiration, cerebral blood flow (CBF), electroencephalogram, and the size of pupils were carried out using 18 mongrel dogs and 5 monkeys. In the initial phase of mass expansion, tentorial herniation was observed on the balloon side, and the midbrain shifted to the ventral and contralateral side with a gradual increase in ICP. The pons and the ponto-medullary junction were also dislocated to ventral direction. With further mass expansion, tentorial herniation was also observed on the contralateral side, and the midbrain altered its displacement to dorsal and to the balloon side, while the pons and the ponto-medullary junction continued to shift ventrally. At the steepest rise in ICP, dorsal shift of the midbrain reached a maximum, while irregular respiration, hypotension, and a decrease in CBF were observed, and the midbrain turned its shift to ventral direction again.
In conclusion, an acute deterioration of the brain stem was induced by the adverse shift of the brain stem between the midbrain and the pons during an acute increased ICP.
