As far as police can tell, the blunt force did not come from a weapon, or a wall, or a windshield, but only the fists of another young girl whom she fought hours earlier. While the specific circumstances of Joanna\'s death are especially tragic and extremely unusual, medical experts said a blow in just the right spot can often prove fatal. \"This is rare, in that I\'ve never seen it in a female, certainly not in a female adolescent,\" said Dr. Keith Black, a neurosurgeon at Cedars-Sinai Medical Center. Black, who was not involved in Joanna\'s medical care, sees such injuries all the time among older patients and said a blow to the head from one young girl to another could \"absolutely\" be sufficient to cause enough trauma to lead to death. Punches to the head can often lead to delayed bleeding if a vein is torn, and that can lead to a clot when blood collects on the surface of the brain. Coroner\'s Lt. Fred Corral said Ramos died of blunt force trauma to the head and said her death has been ruled a homicide, but he didn\'t immediately have further details about her injuries. The finding rattled the already shaken school community at Willard Elementary, where Joanna attended the fifth grade. She died Friday, about six hours after a brief fight with another girl in an alley near the school in a working-class neighborhood in the port city of Long Beach. Joanna, who would have turned 11 on March 12, was unconscious by the time she arrived at the emergency room and underwent emergency surgery for a blood clot on her brain late Friday after she began vomiting and complained of a headache, her older sister, 17-year-old Vanessa Urbina, told The Associated Press. \"After surgery the doctor said she was still alive, and then a few minutes later he comes back and tells us that her heart stopped and they couldn\'t bring her back,\" Urbina said, crying as she sat on the steps of the school near a memorial of flowers and balloons. Police said they have made no arrests and were conducting an investigation that will be presented to prosecutors when it\'s completed. Worried parents lingered as they dropped off their children Monday in a light rain and wondered aloud how the school, tucked a few blocks off a major city street, could have become the scene of such unexpected violence. \"I\'m just so confused at this moment, thinking should I take my daughter out of this school,\" said Victoria Pyles, whose daughter started classes at the school last week. \"If this is what is going on, I don\'t like it. It\'s very scary.\" School officials believe the fight occurred near the school in a 15-minute window between the time school let out and the start of Joanna\'s after-school program at 2:30 p.m., said Chris Eftychiou, a spokesman for the Long Beach Unified School District. Joanna didn\'t have any visible injuries or show any signs of distress for about an hour, but she eventually told staff she felt unwell and was picked up by a relative, he said. Urbina, the older sister, said Joanna\'s cousin picked her up. After her mother retrieved her, Joanna vomited in the car all the way home and told her mother she felt sleepy and wanted to go to bed. Symptoms — such as headache, nausea, lethargy — may not set in for hours and people can mistakenly think that they\'re fine, Black said. Typically, he said, the hit to the head would have to be fairly significant to cause a blood clot and often involves the head hitting walls or the ground, but a punch is enough. \"You can certainly get enough of an impact to get enough movement in the brain by a fist to tear a vein, if it\'s in the right location,\" Black said. Police have said the fight lasted less than a minute, did not involve weapons, and no one was knocked to the ground. A friend of Joanna\'s saw her as she reported to the after-school program after the fight and said she had blood on her knuckles from wiping at a bloody nose, said Cristina Perez, the friend\'s mother. Perez said her daughter, who is 10, heard about plans for the fight, apparently over a boy, during recess earlier in the day and knew to stay away from the alley after school. Fights involving young children, including girls, are increasing nationally, in part because of the wired world children now live in, said Travis Brown, a national expert on bullying and school violence. Children used to have a disagreement at school and would have a night or a weekend to cool down, but social media and text messaging mean students can continue their dispute 24 hours a day, he said. \"There was a time when a kid had a way to escape the things at school, but now there\'s no escape,\" Brown said. \"That stuff just escalates to a point where it gets out of hand. This is an everyday occurrence.\"