The role of neutrophil-related indicators in aneurysmal subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a severe subtype of hemorrhagic stroke with a high rate of disability and mortality. With advances in diagnosis and treatment, early intervention for intracranial aneurysms (craniotomy clamping and interventional embolization) can effectively prevent rebleeding. However, early brain injury (EBI) and delayed cerebral ischemia (DCI) caused by aSAH still result in fatalities among hospitalized patients. Additionally, survivors often experience cognitive impairments that affect daily functioning, work ability, and quality of life, imposing a significant societal burden. Identifying prognostic markers for SAH and its related complications (i.e., DCI, rebleeding, and pneumonia) and conducting early interventions are the focus of current research. Recent evidence indicates that neutrophils play a key role in aSAH. The neutrophil-to-lymphocyte ratio (NLR) and neutrophil-to-albumin ratio (NAR) are peripheral biomarkers that provide information about the inflammatory load in both innate and adaptive immunity. Neutrophil extracellular traps (NETs) are special structures formed after neutrophil destruction or apoptosis, which have dual roles in bactericidal activity and promoting cell inflammation and apoptosis. In addition, the NLR, NAR, and neutrophil to platelet ratio (NPR) are considered peripheral biomarkers that reflect the inflammatory burden involving both innate and adaptive immunity. This review summarizes current studies on neutrophils in aSAH, including evidence on the role of NETs in the pathophysiological changes following SAH. We further discuss whether NLR, NAR, and NPR can predict clinical outcomes and complications after aSAH and serve as useful biomarkers for clinical management to support the development of new therapeutic strategies for aSAH.