Shifting subdural fluid collection and hydrocephalus after foramen magnum decompression for basilar invagination

Background: Postoperative hydrocephalus and subdural fluid collection (SFC) have been reported as the rare complications following foramen magnum decompression in patients with Chiari malformation.Case Description: The paper reports the case of a 63-year-old female patient who underwent foramen magnum decompression for basilar invagination. The patient developed a shifting, bilateral SFC and subsequent acute hydrocephalus. A ventriculoperitoneal shunting was performed and the clinical symptom resolved. The dramatic change in CSF distribution supported the diagnosis of external hydrocephalus, which was associated with a postoperative cervical pseudomeningocele.Conclusions: Postoperative SFC in patients underwent foramen magnum decompression may harbor different mechanisms. Subdural drainage for patients having external hydrocephalus may have a higher recurrence rate.