Traumatic subdural hygroma and chronic subdural hematoma: A systematic review and meta-analysis

Recently, a relationship between traumatic subdural hygroma (SDG) and chronic subdural hematoma (CSDH) has been proposed. However, the role of traumatic SDG in development of CSDH has not been well characterized. This systematic review aimed to estimate the rate of evolution of traumatic SDG to CSDH, and to identify risk factors associated with traumatic SDG evolution to CSDH. We searched MEDLINE, EMBASE, and Cochrane Li-brary databases from inception to May 26, 2021, using the combination of the terms "subdural hygroma" and "chronic subdural hematoma." Using a random-effects model, we calculated a pooled estimate of rate of evo-lution of traumatic SDG to CSDH. In addition, we conducted a systematic review of studies of risk factors for traumatic SDG evolution to CSDH. Nineteen studies with 1,335 patients met the inclusion criteria for meta -analysis. The pooled estimate of evolution rate was 25.0 % (95 % CI, 19.3 %-30.7 %; I2 = 85.6 %), with signif-icant heterogeneity among studies (P < 0.01). Age >= 60 years was associated independently with traumatic SDG evolution to CSDH, after adjustment for study design using multivariate meta-regression. Risk factors associated with evolution of traumatic SDG to CSDH were radiological characteristics such as thicker SDG and higher SDG CT value. The rate of traumatic SDGs evolution to CSDH is approximately 25 %. Patients aged 60 or older with traumatic SDGs are at increased risk of CSDH development. Thicker SDG and higher SDG CT value, are commonly reported risk factors for traumatic SDG evolution to CSDH. However, higher quality studies are needed.