Question: Following a fall at work in which his head hit machinery; a patient was admitted unconscious and observed for neurological problems and other injuries. The patient returned to his pre-existing conscious level within two hours of admission complaining of a headache, especially on moving his head. Total length of loss of consciousness was 20 minutes. No other injuries were identified by x-ray or CT brain scan. The patient was discharged home the next day with a final diagnosis of concussion with loss of consciousness. The principal diagnosis code is