Very late onset of chronic subdural hematoma. Case report.

A 56-year-old man developed subdural effusion after mild head trauma, which remained unchanged in volume and density on computed tomography during a follow-up period of 7 months. However, typical chronic subdural hematoma (CSDH) had developed by 9 months after the head trauma. The CSDH was successfully treated by irrigation and drainage. This unusually delayed onset of CSDH suggests that we should be aware of the possibility of very late onset of CSDH in patients with persistent asymptomatic subdural effusion.