Recurrent subdural hygromas after foramen magnum decompression for Chiari Type I malformation.

A paediatric case of foramen magnum decompression for Chiari Type I malformation complicated by recurrent subdural hygromas (SH) and raised intracranial pressure without ventriculomegaly is described. SH pathogenesis is discussed, with consideration given to arachnoid fenestration. We summarise possibilities for treatment and avoidance of this unusual consequence of foramen magnum decompression.