Non-Operative versus Neurosurgical Treatment of Brain Abscess: An Emulated Trial Nested within a Nationwide, Population-Based Cohort.

Background: Uncertainty about the role of neurosurgery in brain abscess treatment is reflected in surveys and observational studies.

Methods: Nationwide population-based cohort study of all adults (≥18 years) diagnosed with brain abscess in Denmark from 2007 until 2023. Inverse probability weighting was applied to balance covariates according to neurosurgical treatment strategy. Outcomes included risks of mortality, rupture, and unfavourable outcome (Glasgow Outcome Scale 1-4) six months after discharge and were assessed using modified Poisson and Cox regression with 95% confidence intervals (CI). Unbalanced covariates were included in regression models for doubly robust estimations.

Results: The cohort comprised 558 patients (median age 59 years [interquartile range 49-69], 367/558 [66%] males). A non-operative strategy was assigned to 234/558 (42%) and neurosurgery to 324/558 (58%). Predisposing meningitis, diameter and deep location of abscess were included in doubly robust estimations.Analyses of treatment strategy showed that a non-operative approach was associated with adjusted relative risks of 2.47 (95%CI 1.50-4.04) for mortality, 2.25 (95%CI 1.26-4.01) for rupture, and 1.24 (95%CI 0.95-1-61) for unfavourable outcome compared with neurosurgery. Additionally, 85/234 (36%) patients assigned to the non-operative strategy required subsequent neurosurgery.Compared with neurosurgery at any time, maintained non-operative treatment was associated with adjusted hazard ratios of 1.53 (95%CI 0.84-2.76) for mortality, 2.00 (95%CI 1.17-3.42) for rupture, and 1.62 (95%CI 1.12-2.34) for unfavourable outcome.

Conclusions: Non-operative strategy was associated with twice the risks of mortality and rupture, and one-third required subsequent neurosurgery. These results support recommendations for neurosurgical drainage of brain abscess.