Inflammation plays an important role in the pathogenesis and growth of intracranial aneurysms (IAs). We investigated the clinical value of the neutrophil-to-lymphocyte ratio (NLR) as a marker of systemic subclinical inflammation in patients with IAs.

Consecutive patients with IAs who underwent endovascular treatment (EVT) were enrolled in the study. The evaluation indicators were aneurysm size and rupture, a poor outcome at 3 to 6 months, and delayed cerebral ischemia (DCI) during hospitalization.

In total, 532 patients with IAs underwent EVT (mean age, 54.0 years; 62.4% female). Among patients with ruptured IAs, those with a higher NLR had an increased risk of a poor outcome at 3 to 6 months and DCI during hospitalization than those with a lower NLR. A higher NLR was significantly more strongly associated with the size of unruptured aneurysms and aneurysm rupture than a lower NLR. The NLR and C-reactive protein concentration showed similar predictive ability for aneurysm size and treatment prognosis. The NLR was lower at discharge than admission for patients with ruptured IAs and DCI.

An elevated NLR was significantly associated with the size of unruptured IAs, an increased risk of a poor outcome, and DCI in patients with ruptured IAs.