Development of Infants With Idiopathic External Hydrocephalus.

External hydrocephalus in an infant is a condition in which the rate of growth of head circumference exceeds the expectations of the Nellhouse curve together with increased size of the subarachnoid spaces. Developmental milestones of 20 infants (aged 0-16 months) with external hydrocephalus were studied by the Mullen Scales of Early Learning. The areas of development that were studied were visual reception, fine motor, expressive language, receptive language, and total Mullen score. There were no significant differences between the study group and the general population in all 5 scores. The only prominent feature of our external hydrocephalus patients was hypotonia (transient in 9 [45%] and persistent in 2 [10%]). Although the term external hydrocephalus describes a roentgenographic presentation, the term benign enlargement of subarachnoid space is preferred in infants similar to our group by better describing the benign nature of the phenomenon in appropriately selected infants.