Flexible Endoscopic Transaqueductal Fenestration of Fourth Ventricular Arachnoid Cysts Combined with Endoscopic Third Ventriculostomy: A Technical Note.

Fourth ventricular arachnoid cysts are rare and optimal surgical management remains unclear. We describe a flexible endoscopic trans-third ventricular technique for the treatment of fourth ventricular arachnoid cysts associated with obstructive hydrocephalus. Through a frontal approach, a flexible neuroendoscope is advanced via the foramen of Monro and third ventricle into the dilated cerebral aqueduct, allowing access to the fourth ventricle. Cyst fenestration is performed using biopsy forceps and a balloon catheter, and communication with surrounding cerebrospinal fluid spaces can be established. Endoscopic third ventriculostomy is performed concomitantly to ensure cerebrospinal fluid diversion. In selected cases, additional caudal fenestration toward the cisterna magna can be achieved to enhance cerebrospinal fluid circulation. This minimally invasive technique avoids posterior fossa craniotomy and enables simultaneous treatment of hydrocephalus. The approach is particularly suitable for cases with sufficient aqueductal dilation and offers a safe and effective alternative in selected patients.