Acute foramen magnum syndrome caused by an acquired Chiari malformation after lumbar drainage of cerebrospinal fluid: report of three cases.

OBJECTIVE AND IMPORTANCE: The perioperative use of lumbar drainage of cerebrospinal fluid (CSF) is relatively common in neurosurgery, and the development of "acquired" Chiari malformations (tonsillar herniation) with lumbar CSF diversion procedures has been reported. CLINICAL
PRESENTATION: We describe the history of three patients who developed a foramen magnum syndrome, attributable to acquired Chiari I malformations, after perioperative lumbar drainage of CSF.
CONCLUSION: We propose that the mechanism responsible for Chiari I malformations involves a negative pressure gradient between the cranial and spinal regions, created by CSF drainage. Theories regarding the formation of acquired Chiari I malformations, the possible synergistic roles of intracranial pathological conditions and CSF drainage in the development of this entity, and the implications for the use of perioperative lumbar drainage are discussed.