Neuroepithelial cyst of the posterior fossa: two case reports with radiologic-pathologic correlation.

The clinical, radiologic and pathological findings in two cases of neuroepithelial cyst of the posterior fossa are described. The first patient was a 43-year-old woman who presented with clumsiness of the hands, gait disturbance and slurring of speech. Magnetic resonance imaging (MRI) revealed a large cystic structure between the cerebellum and the brain stem on the left side, accompanied by compression of the medulla oblongata and displacement of the forth ventricle to the right. The second patient was an 11-month-old boy who presented with progressive bulbar dysfunction. He had previously undergone surgery for myelomeningocele and hydrocephalus associated with Arnold-Chiari type 2 malformation. MRI revealed a large cystic mass isointense with cerebrospinal fluid between the cerebellum and the midbrain, compressing the fourth ventricle and displacing the brain stem to the right. The cases were pathologically similar, the cyst containing a single layer of cuboidal epithelium and rims of neuroglial cells. Immunohistochemical staining was consistent with neuroepithelial cyst. It is important to distinguish this type of cyst from a malignant mass to ensure appropriate treatment and determine the prognosis. In addition, even though neuroepithelial cysts of the posterior fossa are benign, they are often symptomatic because of their mass effect. The second case was unusual because the cyst developed over a period of 2 months, which shows that this type of cyst can develop rapidly. To the authors' knowledge, the association with Arnold-Chiari type 2 malformation has not previously been reported.