[Idiopathic external hydrocephalus].

5 male children who had idiopathic external hydrocephalus are described; all were all in the first year of life. Macrocephaly and hypotonia were present in all, as well as mild to moderate delay in language and gross motor development; cognition was normal. CT-scan showed in all enlarged subarachnoid spaces but normal or mildly dilated lateral ventricles. Macrocephaly was present in the fathers of 4 of the 5 families. In all cases the course of this condition was benign. There was clinical and roentgenological improvement between the ages of 2 and 2.5 years; the developmental delay resolved at about age 4, at which time the CT pattern had become normal.