Covert orienting in three etiologies of congenital hydrocephalus: the effect of midbrain and posterior fossa dysmorphology.

Covert orienting is related to the integrity of the midbrain, but the specificity of the relation is unclear. We compared covert orienting in three etiologies of congenital hydrocephalus (aqueductal stenosis [AS], Dandy-Walker malformation [DWM], and spina bifida myelomeningocele [SBM]--with and without tectal beaking) to explore the effects of midbrain and posterior fossa malformations. We hypothesized a stepwise order of group performance reflecting the degree of midbrain tectum dysmorphology. Performance on an exogenously cued covert orienting task was compared using repeated measures analysis of covariance, controlling for age. Individuals with SBM and tectal beaking demonstrated the greatest disengagement cost in the vertical plane, whereas individuals with AS performed as well as a typically developing (TD) group. Individuals with SBM but no tectal beaking and individuals with DWM showed greater disengagement costs in the vertical plane relative to the TD group, but better performance relative to the group with SBM and tectal beaking. Individuals with AS, DWM, and SBM and tectal beaking demonstrated poorer inhibition of return than TD individuals. Impairments in attentional disengagement in SBM are not attributable to the general effects of hydrocephalus, but are instead associated with specific midbrain anomalies that are part of the Chiari II malformation.