Development of profound Chiari I malformation and cerebellar tissue loss and resolution following shunting of posterior fossa extra-axial cyst. Case report.

INTRODUCTION: Chiari I malformation can be due to a multitude of etiologies such as craniosynostosis or hydrocephalus. A posterior fossa extra-axial cyst (PFEAC) appears to be an extremely rare cause of this form of hindbrain herniation. CASE REPORT: Herein, we report a case of PFEAC that presented with no Chiari I malformation and then presented months later with a significant Chiari I malformation. Following shunt placement of a PFEAC, striking reversal of the Chiari malformation as well as reconstitution of the cerebellum was noted. CONCLUSIONS: Patients with PFEAC might develop a Chiari I malformation and this might be treated with shunting of the PFEAC alone.