Isolated fourth ventricle associated with treated hydrocephalus and chiari type 2 malformation

Isolated fourth ventricle is a rare condition seen as a result of anatomical or functional occlusion of the inlet and outlet holes of the fourth ventricle. It may be seen in cases with Chiari type 2 malformation, too. We report a 20-month-old boy with isolated fourth ventricle presenting with weakness in his arms. He had been treated for myelomeningocele and hydrocephalus in the neonatal period and followed for Chiari type 2 malformation. The isolated fourth ventricle developed in the presence of a well-functioning lateral ventricle shunt. He was treated with a new shunt into the fourth ventricle.