Trapped fourth ventricle (TFV) also known as isolated fourth ventricle (IFV) is a rare clinico-radiologic entity with only a few cases reported in the literatures. Most are detected incidentally without significant neurological deficit. It occurs when there is obstruction of both the aqueduct of Sylvius and exit foramina i.e. Magendie and Luschka or basal cisterns of the fourth ventricles. This will lead to progressive accumulation of cerebrospinal fluid (CSF), which initially produces mass effect on the cerebellum behind similar to posterior fossa space occupying lesion and subsequently the brain stem anteriorly.