Post-traumatic intradiploic leptomeningeal cyst of the posterior fossa in an adult.

Intradiploic cysts in the posterior fossa are rare. We report a post-traumatic intradiploic leptomeningeal cyst in an adult and review the diagnosis and pathogenesis of this lesion. A 28-year-old woman presented with a headache and a hard mass in the occipital region. She had a history of head injury as she had fallen from a height at the age of 18 months. CT scans and MRI revealed an expanding intradiploic cyst with the density of cerebrospinal fluid (CSF) and thinning of the inner and outer tables. A bony defect of the inner table connecting to the cisterna magna was also visualized. At surgery, we detected free communication of the CSF between the cystic cavity and the subarachnoid space of the posterior fossa via a defect in the dura and inner table. The dural defect was sutured primarily and covered with the autogenous outer table. An intradiploic cyst of the occipital bone can be detected in adults and might be caused by remote head injuries during childhood. Prompt surgical repair of the dural and bony defect in an adult patient has an excellent prognosis.