Ibtissam El bqaq, Zaineb Ehirchiou, Lina Belkouchi, Nazik Allali, Latifa Chat, Siham El Haddad
Journal: Medpeer Publisher
ISSN: 3066-2737
Volume: 3
Issue: 7
Date of Publication: 2026/07/22
Arachnoid cysts of the fourth ventricle are exceedingly rare, benign, cerebrospinal fluid–filled developmental lesions accounting for only a small fraction of intracranial arachnoid cysts, with occurrence in early infancy being particularly uncommon. We report the case of a 5-month-old infant with hydrocephalus present since birth, who presented with hypotonia and feeding refusal. Standard brain MRI identified a large, well-defined, thin-walled cystic formation of the fourth ventricle with regular margins, measuring approximately 67 x 64 x 77 mm (AP x H x T), hypointense on T1-weighted images, hyperintense on T2-weighted images, and suppressed on FLAIR sequences, without diffusion restriction or enhancement following contrast administration, responsible for upstream triventricular dilatation and mass effect on the adjacent cerebellum, pontocerebellar space, and brainstem. This case illustrates an unusual presentation and age of onset for this rare entity and discusses the differential diagnosis of posterior fossa cystic malformations in infancy, as well as the diagnostic and management considerations specific to this age group.
Arachnoid cyst, Fourth ventricle, Infant, Hypotonia, Posterior fossa
Download PDF