Qualitative assessment of brain anomalies in adolescents with mental retardation

The neural basis of mental retardation is poorly understood. This study aimed to characterize structural anomalies of the brain in mental retardation and the relationship between them and the degree of mental retardation.

Eighty adolescents receiving educational support and 40 controls underwent MR brain imaging and intelligence quotient (IQ) assessment. MR images were evaluated according to a checklist of qualitative brain anomalies by a neuroradiologist blind to group membership. All scans were assessed by a second neuroradiologist to measure interobserver agreement. Ten percent of the studies were randomly selected for assessment of intraobserver agreement.

Evaluation of MR images by using the checklist generated results with a high degree of interobserver and intraobserver agreement. Intraclass correlations were 0.93 and 0.75 for interobserver agreement on the total abnormality score and the entire checklist, respectively, and 0.97 and 0.85 for intraobserver agreement on the total abnormality score and the entire checklist, respectively. IQ is negatively correlated with the total abnormality score (P < .001). Subjects with an IQ <70 have a significantly greater total score (P = .003) and a significantly greater score for 12 specific anomalies, including thinning of the corpus callosum (P = .001) and abnormalities of the lateral ventricles.

Mental retardation is associated with demonstrable brain anomalies, particularly thinning of the corpus callosum and ventricular abnormalities, and with a high total abnormality score. Greater levels of brain anomalies are associated with greater levels of mental retardation as evidenced by IQ.