Endoscopic Transfontanellar Approach of a Cyst Anterior to the Brainstem Crossing the Foramen Magnum-Part I: Failure of Unique Fenestration: 2-Dimensional Operative Video.

Premature infants with severe germinal matrix intraventricular hemorrhage (IVH) are at high risk of posthemorrhagic ventricular dilation and hydrocephalus (Video 1). We report the case of a 3-month-old premature infant referred for posthemorrhagic multilocated hydrocephalus. He presented with somnolence, hypotonia, and a bulging fontanelle. His past medical history included an IVH grade III with hydrocephalus initially treated by temporary ventriculosubgaleal shunting. Magnetic resonance imaging (MRI) showed persistent hydrocephalus associated to a cyst extending anteriorly from the mesencephalon to the posterior wall of the sixth cervical vertebra, causing severe brainstem and spinal cord compression. A two-step surgery was performed, consisting of an endoscopic procedure and a ventriculo peritoneal shunt placement, to achieve hydrocephalus treatment and cyst fenestration. A right transfontanellar approach with the head flexed was chosen, using a straight 30-degree endoscope. The procedure and surgical technique are explained in a step-by-step fashion in the original conditions. A large unique fenestration was performed with no postoperative complications and improvement of the neurological status. One month later the patient presented again with symptomatic intracranial hypertension with compatible clinical and imagery findings. MRI showed cyst recurrence and hydrocephalus. We therefore revised our strategy and performed an additional procedure, which is detailed in the second part of the video (Part II: Success of Multiple Fenestrations). Our report underlines the high risk of recurrence of such cysts in post-hemorrhagic arachnoiditis. Cyst recurrence may be explained by the absence of crossing flow when a unique perforation is made.