Volumetric MRI brain analyses were compared in 15 male ADHD subjects without comorbidity (mean age, 12.4 years) and 15 normal controls at the University of California, Irvine, CA. ADHD children had smaller volumes of the following structures: left caudate, right anterior-superior (frontal) hemispheric region, bilateral anterior-inferior (peri-basal ganglia) hemispheric region, and bilateral retrocallosal (posterior parieto-occipital) region white matter. The caudate size was correlated with response to stimulant medication; responders had the smallest and symmetric caudate volumes, whereas nonresponders had reversed caudate asymmetry and the smallest retrocallosal white matter volume. 
COMMENT. Localized hemispheric structural anomalies may occur in children with ADHD, consistent with abnormal frontal-striatal function, and possibly correlated with response to stimulant medication. A neurodevelopmental process is suggested because the hemispheric volumes are similar to controls, and the changes are not associated with ventricular enlargement or the result of atrophy.
Temporal lobe arachnoid cyst - ADHD syndrome. A cerebral developmental anomaly and syndrome is reported in three children with ADHD found on MRI to have left sided temporal lobe arachnoid cysts . The diagnosis by MRI was determined following EEGs obtained because of headaches, language delay, or episodes suggestive of partial seizures. EEGs showed focal epileptiform or slow wave abnormalities involving the left temporal region and correlating with the location of the structural temporal fossa lesions. A causal association was considered plausible because of coincidental learning and language disabilities explained by temporal lobe and sylvian region pathology.