Traumatic acute subdural hematoma (TASH) is a life-threatening entity. 90% of cases undergo urgent surgery. Evacuation of the hematoma and decompression of the brain tissue are necessary. If the neurological status of the patient is good, conservative treatment for resolution of the hematoma is an option. In addition, spontaneous resolutions of TASHs have been reported, but their mechanism has not been investigated. An 85-year- old female was admitted to our emergency department with deterioration of mental status and vomiting after a traffic accident, diagnosed with bilateral frontoparietal TASH. Surprisingly, control computed tomography (CT) showed a remarkable reduction in the hematoma size and decrease in the midline shift preoperatively. There was an arachnoid injury at cranial CT and thoracolumbar magnetic resonance imaging (MRI) study was verified that blood in subarachnoid space at the lumbar region. Control CT revealed intraventricular hematoma 5 days after the initial cranial CT. The patient was discharged two weeks later without any neurological deficits. Rapid spontaneous evacuation of TASH into the intraventricular space via the thoracolumbar subarachnoid cerebrospinal fluid (CSF) circulation is presented and possible related mechanisms are discussed. TASH as an event of traumatic head injury or secondary to tearing of corticodural bridging vessels could occur incidentally. Arachnoid tears and the effect of CSF flow due to high pressure are responsible for redistribution and relocation of the TASH. Radiological investigation with thoracolumbar spine MRI and repeated cranial CT is necessary for rapid resolution.