Introduction: The natural course of post traumatic acute thin SDH is different among various patients. Most thin SDH resolve spontaneously, a few progress into chronic subdural hematomas requiring surgical treatment. The causative factors for progression of ASDH to CSDH in not fully studied. Objectives: The objectives of this study were to analyse the occurrence of subacute or chronic SDH preceded by the traumatic acute thin SDH and their various presenting symptoms, risk factors, time of presentation, surgical interventions and outcomes. Material and methods: This was a retrospective study conducted at the Institute of Neurosurgery, Madras Medical College. Patients with symptomatic sub acute or chronic SDH following acute post traumatic thin SDH, who were managed conservatively, in the past were included and analysed by database. Results: Totally 20 patients were analysed. All patients underwent burrhole evacuation. Mean age was 47. 75% were alcohol consumers. 10% of patients were on anticoagulants. Presenting symptoms before surgery were headache (70%), dysarthria (20%), hemiparesis (20%), seizure (25%), and drop in GCS (15%). Mean duration between injury and onset of new signs and symptoms was 14 days. Mortality was 10%. Conclusion: Acute thin SDH without surgical treatment liquefies and may later progressively enlarge, so that new symptoms develop in the subacute stage. Furthermore, this pathological process may contribute to the subsequent development of chronic SDH. Mean onset of symptoms was 14 days from our study. Hence, follow up imaging at end of 2nd week is advisable to identify the enlarging SDH which leads to help in early surgical intervention and prevent irreversible brain damage.

Keywords: Acute Subdural hematoma; Chronic subdural hematoma.