Mortality Reduction of Acute Surgery in Traumatic Acute Subdural Hematoma since the 19th Century: Systematic Review and Meta-Analysis with Dramatic Effect: Is Surgery the Obvious Parachute?

The rationale of performing surgery for acute subdural hematoma (ASDH) to reduce mortality is often compared with the self-evident effectiveness of a parachute when skydiving. Nevertheless, it is of clinical relevance to estimate the magnitude of the effectiveness of surgery. The aim of this study is to determine whether surgery reduces mortality in traumatic ASDH compared with initial conservative treatment. A systematic search was performed in the databases IndexCAT, PubMed, Embase, Web of Science, Cochrane library, CENTRAL, Academic Search Premier, Google Scholar, ScienceDirect, and CINAHL for studies investigating ASDH treated conservatively and surgically, without restriction to publication date, describing the mortality. Cohort studies or trials with at least five patients with ASDH, clearly describing surgical, conservative treatment, or both, with the mortality at discharge, reported in English or Dutch, were eligible. The search yielded 2025 reports of which 282 were considered for full-text review. After risk of bias assessment, we included 102 studies comprising 12,287 patients. The data were synthesized using meta-analysis of absolute risks; this was conducted in random-effects models, with dramatic effect estimation in subgroups. Overall mortality in surgically treated ASDH is 48% (95% confidence interval [CI] 44-53%). Mortality after surgery for comatose patients (Glasgow Coma Scale ≤8) is 41% (95% CI 31-51%) in contemporary series (after 2000). Mortality after surgery for non-comatose ASDH is 12% (95% CI 4-23%). Conservative treatment is associated with an overall mortality of 35% (95% CI 22-48%) and 81% (95% CI 56-98%) when restricting to comatose patients. The absolute risk reduction is 40% (95% CI 35-45%), with a number needed to treat of 2.5 (95% CI 2.2-2.9) to prevent one death in comatose ASDH. Thus, surgery is effective to reduce mortality among comatose patients with ASDH. The magnitude of the effect is large, although the effect size may not be sufficient to overcome any bias.