Vanishing cerebellum in myelomeningocoele.

Reduced hindbrain herniation observed after intrauterine myelomeningocoele repair suggests that posterior fossa changes in myelomeningocoele are secondary results of prolonged prenatal spinal cerebrospinal fluid leak. Exceptionally, this transforaminal herniation results in 'degeneration' of cerebellar tissue, presumably due to mechanically induced ischaemia. This phenomenon was called 'vanishing cerebellum in Chiari II malformation'. We report three similar cases of this apparently rare finding. Pregnancies were normal. Cerebellar hypoplasia was already recognized in one instance by prenatal ultrasound at gestational week 25. Postnatal imaging was similar in all three patients showing small posterior fossa, beaked midbrain tectum, small brainstem without pontine prominence, reduced cerebellar tissue with virtual absence of one hemisphere and supratentorial hydrocephalus. Our series is too small to draw firm conclusions about predisposing risk factors for and consequences of vanishing cerebellum. Cerebellar damage can interfere with cognitive development, as shown in children with cerebellar agenesis/ hypoplasia, congenital ataxia and small cerebellum following prematurity. A final conclusion on the cognitive consequence of vanishing cerebellum cannot be drawn on the available literature and our limited observations, as one of our patients died at 3 months and another is still too young for appropriate testing. However, the third (aged 15 years) is very severely retarded.