OBJECTIVE: This study aimed to investigate the immunologic profile of chronic subdural hematoma (CSDH) subtypes based on their radiologic appearances, with a focus on comparing the membranous CSDH to other subtypes. METHODS: We prospectively analyzed 170 CSDH cases from 138 patients, categorizing them into "Membranous" and 'Other' subtypes based on computed tomography scans. Samples were collected from the subdural fluid and systemic blood and analyzed for a panel of inflammatory markers. Demographic data, clinical characteristics, and time since trauma were also assessed. RESULTS: Time since trauma to diagnostic computed tomography was significantly longer for the "membranous" subtype (P = 0.001). 'Membranous" CSDH exhibited a distinct immunoprofile, including lower hemoglobin levels (P = 0.0002) and higher concentrations of matrix metallopeptidase 9 (P = 0.005) and interleukin-8 (IL-8) (P <
0.0001). Additionally, "Membranous" CSDH showed elevated levels of interferon gamma-induced protein 10, monokine induced by gamma interferon, and uPAR compared to 'Other' subtypes, with significant correlations between interferon gamma-induced protein 10 and monocyte chemoattractant protein-1 (P = 0.013), monokine induced by gamma interferon (P = 0.002), and urokinase-type plasminogen activator receptor (P = 0.006). IL-8 levels also correlated significantly with monocyte chemoattractant protein-1 (P = 0.02), suggesting distinct inflammatory pathways in the "Membranous" subtype. CONCLUSIONS: This study demonstrates that CSDH subtypes, particularly the "Membranous" subtype, possess a distinct immunologic profile. These findings provide novel insights into CSDH pathophysiology. The unique inflammatory landscape of "Membranous" CSDH, marked by elevated matrix metallopeptidase 9 and IL-8 levels, may contribute to its chronic nature.