Sinking bullet syndrome: A unique case of transhemispheric migration

Background Spontaneous migration of retained intracranial bullet fragments is an increasingly recognized phenomenon. However, such migration is usually limited in extent, since it occurs along the bullet tract or cerebrospinal fluid (CSF) spaces. Transhemispheric migration through an intact cerebral hemisphere has not been previously reported. Observations A 20-year old man sustained a gunshot wound (GSW) to the head with a left parieto-occipital entry point, resulting in retained bullet fragments within the anterior right frontal lobe. The patient developed medically refractory intracranial hypertension, necessitating a left decompressive hemicraniectomy. He exhibited a favorable postoperative course, with gradual neurologic recovery, and was ultimately discharged to a rehabilitation facility. Notwithstanding, serial head CT scans during the first 2 weeks revealed gradual transhemispheric migration of bullet fragments from the right frontal pole to the right occipital pole, traveling through largely intact, uninjured brain tissue. Lessons Transhemispheric migration of bullet fragments via intact brain tissue may rarely occur. While the exact mechanisms underlying this phenomenon remain unclear, potential factors may include: bullet weight, CSF pulsations, dissection through white matter tracts, and biomechanical effects of large skull defects. Bullet migration does not necessarily delay or prevent neurologic recovery.