Neuroendoscopic Fenestration of Quadrigeminal Cistern Arachnoid Cyst Presenting with Developmental Regression

arachnoid cyst is rare and not usually located in the tectal plate region. Such a cyst may extend to the surrounding area and compress adjacent structures due to cys-tic expansion. Arachnoid cysts occasionally are associated with hydrocephalus and produce related symptoms. In our case, a 20-month-old boy presented with developmental regression and macrocephaly. Image study of the brain demonstrated a large cyst on the superior portion of the posterior fossa with extension to the supratentorial space and a compressed cerebellum inferiorly and brain stem anteriorly. Lateral and third ventricles were enlarged severely. We performed lateral ventriculo-cystostomy by neuroendoscope via a precoronal approach. Additional third ventriculostomy was performed on the floor of the third ventricle. At 9 months after surgery, the patient showed restored development, and postoperative image showed a reduction of arachnoid cysts and lateral and third ventricles.