Teaching NeuroImages: acquired Chiari malformation with syringohydromyelia caused by posterior fossa tumor.

A 28-year-old man was admitted due to progressive headache and blurred vision. Neurologic examination showed bilateral papilledema. Brain MRI showed a cystic posterior fossa tumor compressing the fourth ventricle with tonsillar herniation and cervical syringohydromyelia (figure 1). The tumor was removed through a suboccipital craniectomy and pilocytic astrocytoma was diagnosed histologically. One month later, his symptoms had improved with shrinkage of syringohydromyelia by postoperative MRI (figure 2). Acquired Chiari malformation with syringohydromyelia is a rare disease with the incidence of 3% in posterior fossa tumors.1 The pathogenesis is thought due to blockage of CSF flow at the foramen magnum, causing disruption of the blood–brain barrier with syringohydromyelia formation most often at the cervical spine level. Acquired Chiari malformation with syringohydromyelia caused by posterior fossa tumors is usually asymptomatic.1 Early diagnosis by brain MRI and prompt decompressive suboccipital craniectomy may prevent disease progression and improve prognosis.2