Background Autism spectrum disorder (ASD) is defined on a clinical basis by impairments in social interaction, verbal and non-verbal communication, and repetitive or stereotyped behaviours. Voxel based morphometry (VBM), a technique that gives a probabilistic measure of local grey matter (GM) and white matter concentration, has been used to study ASD patients: modifications in GM volume have been found in various brain regions, such as the corpus callosum, brainstem, amygdala, hippocampus and cerebellum. However, the findings are inconsistent with respect to the specific localisation and direction of GM modifications, and no paper has attempted to statistically summarise the results available in the literature.

Methods The present study is a quantitative meta-analysis of the current VBM findings aimed at delineating the cortical regions with consistently increased or reduced GM concentrations. The activation likelihood estimation (ALE) was used, which is a quantitative voxel based meta-analysis method which can be used to estimate consistent activations across different imaging studies. Co-occurrence statistics of a PubMed query were generated, employing ‘autism spectrum disorder’ as the neuroanatomical lexicon.

Results Significant ALE values related to GM increases were observed bilaterally in the cerebellum, in the middle temporal gyrus, in the right anterior cingulate cortex, caudate head, insula, fusiform gyrus, precuneus and posterior cingulate cortex, and in the left lingual gyrus. GM decreases were observed bilaterally in the cerebellar tonsil and inferior parietal lobule, in the right amygdala, insula, middle temporal gyrus, caudate tail and precuneus and in the left precentral gyrus.