Risk factors for chronic subdural haematoma formation do not account for the established male bias

•No study has validated a male bias for CSDH.•A male bias (M:F 97:58) for CSDH was confirmed in n = 155 patients.•The largest risk factor was cerebral atrophy.•A history of trauma and alcohol abuse was similar between genders.•A novel explanation for the male CSDH bias is required.

ObjectiveThe ‘subdural space’ is an artefact of inner dural border layer disruption: it is not anatomical but always pathological. A male bias has long been accepted for chronic subdural haematomas (CSDH), and increased male frequencies of trauma and/or alcohol abuse are often cited as likely explanations: however, no study has validated this. We investigated to see which risk factors accounted for the male bias with CSDH.MethodsRetrospective review of prospectively collected data.ResultsA male bias (M:F 97:58) for CSDH was confirmed in n = 155 patients. The largest risk factor for CSDH was cerebral atrophy (M:F 94% vs. 91%): whilst a male bias prevailed in mild-moderate cases (M:F 58% vs. 41%), a female bias prevailed for severe atrophy (F:M 50% vs. 36%) (χ2 = 3.88, P = 0.14). Risk factors for atrophy also demonstrated a female bias, some approached statistical significance: atrial fibrillation (P = 0.05), stroke/TIA (P = 0.06) and diabetes mellitus (P = 0.07). There was also a trend for older age in females (F:M 72 ± 13 years vs. 68 ± 15 years, P = 0.09). The third largest risk factor, after atrophy and trauma (i.e. anti-coagulant and anti-platelet use) was statistically significantly biased towards females (F:M 50% vs. 33%, P = 0.04). No risk factor accounted for the established male bias with CSDH. In particular, a history of trauma (head injury or fall [M:F 50% vs. 57%, P = 0.37]), and alcohol abuse (M:F 17% vs. 16%, P = 0.89) was remarkably similar between genders.ConclusionsNo recognised risk factor for CSDH formation accounted for the established male bias: risk factor trends generally favoured females. In particular, and in contrast to popular belief, a male CSDH bias did not relate to increased male frequencies of trauma and/or alcohol abuse.