BACKGROUND AND OBJECTIVES: Supratentorial herniation is traditionally described as a mechanical shift of brain structures due to elevated intracranial pressure. However, this model inadequately explains the stepwise physiological decline observed in patients with progressive brainstem dysfunction. We aimed to propose and support a novel conceptual model of herniation based on a vertically oriented compaction gradient and the emergence of a “demarcation line of tissue compaction” as a physiological boundary between viable and irreversibly failing neural tissue. METHODS: A prospective observational study was conducted between 2022 and 2025, involving 287 patients with traumatic supratentorial brain herniation admitted to the neurosurgical departments of 3 urban hospitals. Clinical staging was based on consciousness, pupillary reactivity, brainstem reflexes, motor responses, respiratory pattern, and the Kerdo Vegetative Index. Postmortem morphological analysis was conducted in 129 cases to determine the rostrocaudal extent of brainstem injury. RESULTS: Five distinct stages of herniation were identified, each correlated with specific clinical features and anatomic damage. A progressive downward pattern of neurological deterioration and structural destruction was observed from the diencephalon to the medulla. The progression was often preceded by a physiological cluster—Hyper-H triad—manifesting as hyperthermia, hypertonia, and hormonal dysregulation. Clinical signs and autonomic shifts consistently mirrored this descent. The findings support the presence of a transitional frontier—termed the demarcation line of compaction—separating salvageable function from collapse. CONCLUSION: Supratentorial herniation represents not only spatial displacement but also a structured physiological degradation. The compaction model provides a dynamic framework for understanding herniation progression and may assist in bedside assessment, staging, and early intervention. The Hyper-H triad may serve as an early physiological indicator of impending herniation. Further prospective and imaging-based studies are warranted to validate this approach.
Mustafayev et al. (Mon,) studied this question.