Head Circumference and Brain Volume Trends in Autism Spectrum Disorder

Background: Head circumference (HC) and total brain volume (TBV) studies have consistently concluded Autism Spectrum Disorder (ASD) diagnosis to influence head size and TBV, respectively. Yet because HC and TBV findings are usually based upon small to moderate samples, the clarity of the overall picture is lost.

Objectives: To address this issue, an atlas of HC and TBV studies has been developed, based upon and comparing studies within ASD against each other, and against studies of typically developing (TD) individuals. It was hypothesised that HC and TBV would both be enhanced by ASD diagnosis.

Methods: Criteria for inclusion in to the atlas necessitated that the authors had provided raw data, or that it could be obtained from a publication using data capture techniques (Data Thief v.III; http://www.datathief.org; Tummers, 2006). Alternatively, where only means, SDs, and sample sizes were reported, we statistically modelled the data in two ways. First, we model the data with the mean value weighted by the sample size. In a second analysis, we statistically inferred a random sample within 1 SD of the reported mean for either or both age and HC or TBV of the participant. Additionally, ANCOVA's were performed on the raw HC and TBV data, controlling for age.

Results:  Nineteen HC studies (N=3,051) and 22 TBV studies (N=1,210) of participants with ASD were obtained. Twelve HC studies and 19 TBV studies of TD individuals (N=1,434) were also included. Ages ranged from 0 to 51 years. Results found loglinear fits to account for the most variance in the HC data, and second order polynomial fits to be most appropriate for TBV data. As hypothesised, ANCOVA's highlighted HC, between ages 0 and 4 years, to be greater in individuals with ASD compared to TD participants. Furthermore, TBV was larger in those with ASD compared to TD individuals between ages 1 to 4 years, 5 to 12 years, and 19 years and above. However, no significant difference in TBV was found in individuals between 13 and 18 years of age.

Conclusions: The present study supports the position that ASD diagnosis influences HC and TBV. This is the first instance where this amount of data has been collected and while examining the variance in the data, establishing the trend of HC and TBV across a substantial range of age. Nonetheless, it is apparent that the publication of raw data in the literature would be of great assistance in future evaluations of this issue.