a specific area of tissue). Studies with PET scanning and transcranial Doppler imaging have shown that changes in cerebral blood flow, such as hypoperfusion and vasospasm, can follow penetrating head injury. These changes can last for two weeks. An ischemic cascade similar to the course of cellular and metabolic events that follow other head injuries may follow penetrating head injuries. Sometimes in penetrating injuries, the brain releases thromboplastin, which can lead to problems with blood clotting. While blunt trauma to the head does not present a risk of shock due to hemorrhage, penetrating head trauma does. Diagnosis and treatment A person with a penetrating head injury may be evaluated using X-ray, CT scan, or MRI (MRI can only be used when the penetrating object would not be magnetic, because MRI uses magnetism and could move the object, causing further injury). Surgery may be required to debride or repair the injury or to relieve excessive intracranial pressure. Intracranial pressure is monitored and attempts are made to maintain it within normal ranges. Intravenous fluids are given and efforts are taken to maintain high blood oxygen levels. Prognosis The highest-velocity injuries tend to have the worst associated damage. A study published in 1991, which documented 314 individuals who had had penetrating cranial injuries caused by gunshot wounds, found that 73% died from their injuries at the scene of the incident, and a further 19% ultimately died later, thus indicating a total mortality rate of 92%. Perforating injuries have an even worse prognosis. Penetrating head trauma can cause impairment or loss of abilities controlled by parts of the brain that are damaged. A famous example is Phineas Gage, whose personality appears to have changed (though not as dramatically as usually described) after a perforating injury to his frontal lobe(s). People with subarachnoid hemorrhage, a blown pupil, respiratory distress, hypotension, or cerebral vasospasm are more likely to have worse outcomes. People with penetrating head trauma may have complications such as acute respiratory distress syndrome, disseminated intravascular coagulation, and neurogenic pulmonary edema. Up to 50% of patients with penetrating brain injuries get late-onset post-traumatic epilepsy. See also Brain herniation Traumatic brain injury References External links Neurotrauma Injuries of head