Symptomatic subdural hygroma as a complication of foramen magnum decompression for hindbrain herniation (Arnold-Chiari deformity).

Pseudomeningocele is a well known complication of foramen magnum decompression. Symptomatic subdural hygroma has not previously been described. We discuss a case of Arnold Chiari malformation type 1 in a 55-year-old Caucasian woman who underwent foramen magnum and upper cervical decompression and who developed a symptomatic subdural hygroma 2 weeks following surgery. This complication was most likely due to a technical error during surgery. It responded favourably to conservative therapy.