Study of subarachnoid spaces in children with idiopathic mental retardation.

The aim of this study was to assess quantitatively the size of the subarachnoid space in children with "idiopathic" mental retardation. The extent of various cerebrospinal fluid compartments was measured in 106 brain computed tomographic examinations of children with idiopathic mental retardation, and the results were compared with the corresponding normative data. The third ventricle was enlarged in 77% of the cases. A mild degree of diffuse widening of the subarachnoid spaces was found in about 30% of the patients. These morphologic alterations are additional observations supporting the hypothesis that "idiopathic" mental retardation has a biologic basis.