A rare case of arachnoid cyst of the fourth ventricle resulting in an Isolated fourth ventricle: Case report and review of the literature

Introduction: Post-hemorrhagic or post-infectious isolated or trapped fourth ventricles are rare occurrences associated with cystic lesions of the V4. However, the even less frequent arachnoid cyst of the fourth ventricle poses a differential diagnosis challenge and may be easily overlooked during initial medical assessments of V4 cystic lesions. Case Report: An 11-year-old child, previously healthy, presented with symptoms indicative of intracranial hypertension syndrome, including headaches, vomiting, and bilateral Grade II papilledema. Neuroradiological examination revealed a significantly enlarged fourth ventricle (V4) alongside small lateral and third ventricles. Initially suspected as a V4 arachnoid cyst, the patient underwent surgical intervention with a sub-occipital approach for cyst marsupialization, showing positive progress in the first postoperative month. However, one month later, intracranial hypertension symptoms recurred, and imaging indicated cyst recurrence within V4. A second procedure involved a V4-peritoneal shunt, resulting in a favorable postoperative outcome for one month. One month later, headaches and vomiting without papilledema reappeared, and imaging revealed moderate ventricle dilation. The therapeutic approach included ventriculocisternostomy alongside the V4 peritoneal shunt, leading to a favorable outcome with no signs of intracranial hypertension during follow-up consultations and a normal clinical examination. Conclusion: Trapped fourth ventricle is a rare clinico-radiologic entity, with limited cases reported. Treatment options encompass direct microsurgical approaches, fourth ventricle outflow fenestration, and alternative treatments like fourth ventriculoperitoneal shunts. Additionally, the combination of ventriculoperitoneal shunt and endoscopic treatment (VCS) may be considered for comprehensive management.