Case Report: Primary Fourth Ventricle Outlet Obstruction in Childhood - New Clinical Insights and Long-Term Outcome

Primary fourth ventricle outlet obstruction (PFVOO) is a rare cause of obstructive hydrocephalus in children. Diagnosis often requires high clinical suspicion and advanced magnetic resonance imaging (MRI) sequences, and the optimal management remains a matter of debate.

We report a 3-year-old girl with unexplained tetraventricular hydrocephalus who presented with progressive macrocephaly, intermittent headaches, and atypical stereotyped head movements. She had previously undergone ventriculoperitoneal shunting in infancy, which failed after 18 months. High-resolution 3D-CISS MRI confirmed a patent aqueduct and a membranous obstruction at the foramen of Magendie, establishing the diagnosis of idiopathic PFVOO. An endoscopic third ventriculostomy (ETV) was performed uneventfully, and postoperative MRI confirmed ventricular size reduction. The patient remains clinically stable 2 years later, representing one of the longest pediatric follow-ups reported after ETV for PFVOO.

PFVOO should be included in the differential diagnosis of unexplained tetraventricular hydrocephalus in children when conventional imaging is inconclusive. Advanced MRI sequences such as 3D-CISS are valuable for identifying subtle outlet obstructions. This case, extending the pediatric follow-up to 2 years, reinforces ETV as a safe and durable first-line treatment option in selected patients with PFVOO.