CD4⁺ T cells as a missing mechanistic link in post-hemorrhagic hydrocephalus

Post-hemorrhagic hydrocephalus (PHH) is a complex secondary condition that develops from several types of brain bleeds, specifically germinal matrix-intraventricular hemorrhage (GMH-IVH) in neonates, and IVH, aneurysmal subarachnoid hemorrhage (SAH) and intracerebral hemorrhage (ICH) in adults. PHH pathophysiology is multifactorial, involving impaired cerebrospinal fluid (CSF) circulation and/or absorption and neuroinflammation. Current management of PHH relies on surgical CSF diversion, which carries high complication rates and does not directly target underlying neuroinflammation. Increasing evidence implicates innate and adaptive immune mechanisms-particularly T cells-as critical drivers of secondary injury. This review synthesizes the role of CD4⁺ T cells in driving the neuroinflammatory cascade, barrier dysfunction, and neural injury across various forms of intracranial hemorrhage including GMH, IVH, ICH, and SAH-ultimately culminating in the development of PHH. By examining CD4⁺ T cell subsets, routes of entry into the brain, derived cytokine release, and the resulting crosstalk with resident neural cells, we elucidate how these immune mediators facilitate the pathogenesis of PHH after both pediatric and adult hemorrhages. It also reviews emerging pharmacologic strategies that modulate T cell trafficking and effector function in similar neurological conditions and highlights key mechanistic gaps and future directions. Understanding how CD4⁺ T cell subsets orchestrate neuroinflammation after a hemorrhage may enable development of targeted, non-surgical therapies to prevent or mitigate the development of PHH.