Neuroanatomic Imaging in Autism

In the last decade, neuroimaging research has established that neuroanatomical abnormalities often occur in autistic individuals, but no single type of reported abnormality is ubiquitous in autism. Abnormalities in cerebral cortex, thalamus, basal ganglia, and brainstem have been inconsistently found or infrequently reported, but definitive studies remain to be done. Enlargement of cerebrospinal fluid spaces is present in some autistic people.1-10 One of the most frequently found abnormalities in autism with and without mental retardation is a reduction of cerebellar tissue.1,2,4,5,11-22 The reduction in cerebellar tissue appears to be greatest in neocerebellar regions within the vermis and hemispheres.4,11,12,15,16,18-22 The reduction appears to be the result of developmental hypoplasia rather than damage following full development, and so it may serve as a temporal marker to identify the events that damage the developing brain in autism, including other neural structures that may be concomitantly damaged.11 CEREBRAL HEMISPHERES, THALMUS, BASAL GANGLIA, AND LATERAL AND THIRD VENTRICLES Quantitative Imaging Studies Early quantitative computed tomography (CT) studies reported unusual parietooccipital and frontal asymmetries in autistic patients.23 Fourteen recent CT and magnetic resonance (MR) studies involving 283 autistic subjects have quantitated the size, volume, night-left asymmetry, and radio density on signal intensity of either the cerebral hemispheres, thalamus, basal ganglia, limbic structures, lateral ventricles, or third ventricle (Tables 1 and 2). In addition, these structures have been microscopically examined at autopsy in several cases of autism (Table 1). As seen in Tables 1 and 2, in quantitative neuroimaging studies there is no substantial evidence of abnormality in the cerebral hemispheres, corpus callosum, thalamus, basal ganglia, brain volume, lateral ventricles, and third ventricles.