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.