On the day she was admitted, the 18-year-old's head CT showed a subarachnoid hemorrhage and nothing else remarkable. No skull fracture. No air inside the skull. She had arrived at the emergency department in cardiopulmonary arrest after a crushing injury to her chest and abdomen.
By hospital day 19, the follow up scan showed gas distributed through the frontal, temporal and occipital lobes. By day 32, it had spread throughout the intracranial cavity. She had never had a neurosurgical procedure. Serial imaging found no cerebrospinal fluid leak, no pneumothorax, and no pneumomediastinum, which ruled out the usual explanations.
