Cody Lehe had a great life and a bright future. A tall, handsome, strapping young man, the 17-year-old was a high school senior and captain of the football team. Lehe was also a smart student with his sights set on college. Buoyed by the support of a loving, well-to-do family, he had everything going for him. Tragically, Lehe's life was to take a sharp turn that not only derailed his potential, but also was very nearly fatal. It began on the football field. American football is a game that demands teamwork, strategy, skill and a tougher-than-nails attitude. If you want to play the game, pain is to be expected - and ignored. During a Friday night game, Lehe received a helmet-to-helmet hit from an opponent during a tackle. Although he was able to get back up, he told a teammate that it was the hardest hit he had ever received. The impact left Lehe dizzy and unable to see clearly. But true to the macho code of football, he gritted his teeth, shook off the discomfort, and finished the game. The next night, Lehe went to watch a college football game. But the following day, he complained of a severe headache and felt extremely tired. On Monday morning, he told his mother he wanted to see a doctor. A computerised tomography (CT) scan showed that all appeared normal in Lehe's head. Nevertheless, the doctor told him to stop playing football until all his symptoms subsided. But an important game was coming up. As team captain, Lehe was determined to set an example and get back on the field of play. Moreover, his CT scans were completely normal, meaning there was no evidence that anything was seriously wrong. The teenager did not tell his coach that he was still suffering the effects of Friday night's hit to the head. Despite searing headaches and finding it difficult to concentrate, Lehe attended practice and participated in hitting drills - exercises where players run at each other at full speed with the intention of knocking the other player down. After taking a few hits, Lehe stepped to the side and told a friend: "My head is killing me, and I can't feel my legs." He then collapsed in a seizure before falling into a deep coma. Lehe was rushed to a local hospital where CT scans showed small subdural haematomas, the pooling of blood on the surface of the brain. He was airlifted to the Goodman Campbell Brain and Spine Centre at Indiana University Health Methodist Hospital in Indianapolis. Doctors there, including neurosurgeon Dr Michael Turner, found that the pressure inside his head was dangerously high. Normal levels should be between 5 and 15mmHg (millimetres of mercury). Lehe's brain was under a whopping 25 to 30mmHg of pressure. Magnetic resonance imagining (MRI) scans showed that there were small blood clots, but they were not the cause of Lehe's problems. The real problem was cerebral swelling. Lehe was a victim of second impact syndrome (SIS) whereby his brain suffered another trauma before it had fully recovered from injuries caused by a first impact, leading to catastrophic - and often fatal - swelling of the brain. SIS is a relatively rare condition, with only 30 or so reported cases in the United States to date. But the mortality rate is extremely high at 90 per cent, says Turner. The condition has only ever been reported in young athletes. Turner hypothesises that teenage brains are susceptible to SIS because they are still developing, and the immature brain responds differently than the mature one to trauma. The initial impact probably affects the brain's ability to regulate the amount of blood reaching the organ, says Turner. When this cerebral autoregulation is impaired and a second jolt to the brain is delivered, the brain overreacts, causing the cerebral arteries to widen, enabling more blood to flood the brain, and therefore leading to massive cerebral swelling. The swollen brain creates intense pressure inside the fixed confines of the skull. This pressure was so great in Lehe's case that it pushed his brain and upper spinal cord downwards, and damaged parts of his brain. Turner and his team battled for the next 55 days to save Lehe's life. They used everything in their medical arsenal to bring down the cerebral swelling and intracranial pressure, while trying to balance his blood flow, volume and pressure; respiratory rate; oxygenation levels; and other vital functions. During this critical time, Lehe's body suffered hypotension (low blood pressure), renal failure, sepsis, pneumonia and even temporary cardiac arrest. When Lehe was finally stable enough to leave the intensive care unit, he faced disabling changes and a long road to recovery. Lehe was no longer able to walk or talk. He spent the next 43 days in rehabilitation before he could finally go home. Six years later, Lehe still cannot walk without support. He has regained much of his speech, but struggles with his short-term memory. Given the rarity of this condition and the resulting dearth of data, SIS is not well understood. Medical experts had long thought that SIS was brought about by blood clots that form after the first impact, thereby causing headaches. However, Lehe's case was a particularly instructive one for medical researchers because the CT scan after his first hit was clean, which debunked this long-standing theory. More importantly, says Turner, it shows that a clean CT scan does not prevent one from a devastating syndrome, and does not clear a player to return to the game. Instead, severe and persistent headaches, such as those suffered by Lehe, might be a better predictor of the dangers of SIS.