Authors: Reo Kawaguchi; Koji Osuka, MD, PhD; Masahiro Aoyama, MD, PhD; Shigeru Miyachi, MD, PhD; Masakazu Takayasu, MD, PhD (Nagakute, Japan)

Introduction: Eosinophils induce inflammation by releasing cytokines and cytotoxic granule proteins. Infiltration of eosinophilic granulocytes occurs in the outer membrane of chronic subdural hematomas (CSDHs). Eosinophils play an important role in the growth of CSDHs. However, the manner in which eosinophils accumulate within CSDH fluid remains undetermined. In the current study, we assessed the expression of eosinophil chemoattractants in CSDH fluids according to the growth stage of the CSDHs and examined the correlation between the two. Methods: CSDH fluids were obtained from 38 patients during trepanation surgery. Ecalectin, eotaxin-3, interleukin-5 (IL-5) and eosinophil-derived neurotoxin (EDN) concentrations were measured using ELISA kits. For use as controls, serum samples were collected from five healthy adults, and cerebrospinal fluid (CSF) samples were collected from five adults with unruptured aneurysms. The percentage of eosinophils (%eosinophil) in the CSDH fluids was calculated using Giemsa staining. Results: The concentrations of ecalectin, eotaxin-3, IL-5 and EDN were nearly equivalent in the serum and CSF samples; however, their concentrations were high in the CSDH fluids. In particular, the ecalectin and EDN levels in the CSDH fluids were significantly higher than those in the serum and CSF. The levels of eotaxin-3, IL-5, EDN and %eosinophil were significantly higher in the laminar type of CSDH, while that of ecalectin was not. The correlations between eotaxin-3 and IL-5, IL-5 and EDN, and EDN and %eosinophil were statistically significant (p<0.01). Conclusion: Our data suggest that eotaxin-3 is a chemoattractant of eosinophils.IL-5 induces the activation of eosinophils following the degranulation of EDN into CSDH fluids. These factors may serve as novel therapeutic targets for managing CSDH.