Syndrome of primary transtentorial cerebellar displacement--"inverse Chiari type II syndrome".

Transtentorial upward displacement of parts of the cerebellum and the brain stem into the supratentorial space, a condition which has occasionally been described in the literature since 1958 in children with hydrocephalus and spina bifida, is demonstrated in one case together with a discussion of its pathogenesis. A former hypothesis regarding the condition as a result of long standing shunt treatment of the hydrocephalus with supratentorial decompression is opposed. Different findings in the present and in two formerly recorded observations point out that the cerebellar upward displacement must be a prenatally originated malformation complex associated with hydrocephalus. The main criteria of the syndrome, which seems to be very much related to the Arnold-Chiari malformation, are summarized.