Non-neural parenchymal contributions to measures of macrocephaly in autistic participants: Orbital-frontal circumference measures and brain size revisited.

摘要

Increased prevalence of macrocephaly is a consistently replicated finding among individuals with autism. Several possible mechanisms have been proposed to explain increased macrocephaly, including increased production of non-neural tissues. The purpose of this study was to be the first to analyze the relationships between measures of occipital frontal circumference (OFC), ventricular space, brain parenchyma, surface subarachnoid cerebral spinal fluid (CSF) and meningeal volume, and extra-neural tissue volumes in a large group of autistic participants, some of which were selected for macrocephalic. Sixty male participants (34 Autistic; 26 Controls) who underwent volumetric magnetic resonance imaging (MRI) analysis were included in this study. They were divided into four groups based on head size; a normocephalic control group, a macrocephalic control group, a normocephalic autistic group, and a macrocephalic autistic group. Volumes of interest for this study included brain volume, surface CSF/meningeal volume, and non-neural tissue volume. Comparison between the diagnostic groups revealed a significant difference in brain volume when comparing the macrocephalic autistic and macrocephalic controls. No other significant differences were observed. Growth trends indicated similar growth patterns for brain volume and non-neural tissue volume when comparing autism and control participants across age. There appeared to be a trend toward significant differences for surface CSF/meningeal volume growth patterns with CSF increasing slightly faster across age. Additional analyses indicated significant predictable relationships between measures of non-neural tissue and OFC measures for all diagnostic groups. Only normocephalic controls demonstrated a significant relationship between brain volume and OFC. In contrast, there were no relationships between OFC and brain volume for autistic participants, but there was a significant relationship between OFC and surface CSF/meningeal volume. These findings appear to be consistent with theories of early abnormal neuronal development and explanations for these findings are discussed in the context of recent publications of brain growth in normal and autistic populations.