Chronic subdural hematomas (CSDH), with an incidence of 20/100,000/year, often necessitates surgical intervention. Recurrence requiring redo surgery occurs in 12% of patients. This study aims to assess the presence of bacteria in CSDH by systematically collecting multiple tissue samples and analyzing the association between positive cultures, prognosis, and recurrence.

This prospective single-center study was conducted at Henri Mondor University Hospital, France, between January 2023 and June 2024. Adult patients operated for CSDH were included. Clinical, radiological, and microbiological data were analysed with a 6-months follow-up. Surgery involved burr-hole or mini-craniotomy with systematic postoperative drainage. Three independent subdural samples were collected intraoperatively.

Eighty patients were included. Recurrence occurred in 20% of patients, with a median time to redo surgery of 15 days. Subdural germs were detected in 21% of patients, with a majority of positive samples in 53% and a majority of negative samples in 47%. The most common bacteria were Cutibacterium acnes and Staphylococcus species. No correlation was found between germ detection and hematoma recurrence or death. No patient developed postoperative empyema.

This study is the first to report systematic bacteriological testing of subdural collection. Detection of skin microbiota bacteria was not uncommon, but there was no significant increase in recurrence if bacteria were detected. The findings suggest that bacterial contamination rather than infection is more likely.

Clinically inapparent infection of subdural hematoma is not common and should not be explored systematically. The decision to treat with antibiotics should be based on multiple positive bacterial samples and clinical data.