Background & Importance: Idiopathic stenosis of the foramina of Magendie and Luschka is a rare cause of obstructive hydrocephalus involving the fourth ventricle.

Case Presentation: We reported the case of a 40-year-old woman who developed headaches and vertigo for several months and more recently gait disturbance. The CT scan showed quadri-ventricular hydrocephalus involving mainly the fourth ventricle with dilated lateral recesses. Craniocervical MRI confirmed hydrocephalus and also showed the brainstem and cerebellar tonsil herniation through the foramen magnum with hydromyelia and a hyperintense signal on T2 weighted MRI of cervical spinal cord. Biological analyses were normal. She underwent endoscopic third ventriculostomy (ETV). No complication was observed. The patient became asymptomatic during the weeks following the surgical procedure and remained stable at a mean follow-up interval of 20 months. Postoperative MR images demonstrated regression of the hydrocephalus; complete disappearance of brainstem and cerebellar tonsil herniation, hydromylia and the hyperintense signal on T2 weighted MRI of cervical spinal cord.

Conclusion: This case confirms the existence of hydrocephalus caused by idiopathic fourth ventricle outflows obstruction in adult and the efficacy of ETV for this rare indication.