Acute obstructive hydrocephalus due to a large posterior third ventricle choroid plexus cyst

We present the case of a child in whom acute hydrocephalus developed secondary to obstruction of the foramen of Monro by a choroid plexus cyst. The patient was seen in the emergency department with fevers, acute onset of headaches, and lethargy. Computed tomography demonstrated dilated lateral and third ventricles with a relatively normal-sized fourth ventricle. An external ventricular drain was placed. Despite decompression of the lateral ventricles, follow-up magnetic resonance imaging demonstrated a dilated third ventricle with a possible thin-walled mass extending from the foramen of Monro into the posterior portion of the third ventricle. The patient subsequently underwent endoscopic fenestration of the cyst with endoscopic third ventriculostomy. Although two other cases of symptomatic choroid plexus cysts of the third ventricle have been previously reported in children, our paper highlights the possibility of endoscopic cyst fenestration together with a third ventriculostomy as a treatment option in cases where the cyst extends into the posterior third ventricle. Despite adequate decompression, we were concerned that due to CSF pulsations the remnant cyst wall could result in acute aqueduct obstruction and subsequent hydrocephalus.