Presacral mass consisting of a meningocele and a Tarlov cyst: successful surgical treatment based on pathogenic hypothesis.

This illustrative case shows a meningocele created by erosion of the sacrum by a perineurial cyst. It is the first report of a large presacral mass consisting of a perineurial cyst and a meningocele simultaneously. We describe a hypothesis for the pathogenesis of this particular constellation of circumstances and present a successful surgical option based on the assumed pathogenesis.