Sequelae of head impact include two situations: 1. There are no abnormal findings in the skull after head impact, but there are persistent clinical symptoms, such as dizziness, headache, nausea and vomiting. There are no abnormal findings in the subsequent repeated head CT and MRI examinations. If such symptoms persist for more than 3 months after the injury, it is called post-traumatic brain injury syndrome, also known as sequelae. There is no latency period because the corresponding clinical symptoms are manifested after the injury and persist.2. Head with intracranial hemorrhage, the sequelae of this type of patients may appear hydrocephalus, epilepsy, vegetative state of existence. For the occurrence of hydrocephalus and epilepsy, it may be manifested within one week after the injury, and some patients even occur within 24 hours after the injury, so the incubation period of this kind of patients is within 1 week. For vegetative state, it is defined as at least 3 months after the injury, so the incubation period is 3 months.