Brain anatomy and development in autism: review of structural MRI studies

Abstract

Autism is a neurodevelopmental disorder that severely disrupts social and cognitive functions. MRI is the method of choice for in vivo and non-invasively investigating human brain morphology in children and adolescents. The authors reviewed structural MRI studies that investigated structural brain anatomy and development in autistic patients. All original MRI research papers involving autistic patients, published from 1966 to May 2003, were reviewed in order to elucidate brain anatomy and development of autism and rated for completeness using a 12-item check-list. Increased total brain, parieto-temporal lobe, and cerebellar hemisphere volumes were the most replicated abnormalities in autism. Interestingly, recent findings suggested that the size of amygdala, hippocampus, and corpus callosum may also be abnormal. It is conceivable that abnormalities in neural network involving fronto-temporo-parietal cortex, limbic system, and cerebellum may underlie the pathophysiology of autism, and that such changes could result from abnormal brain development during early life. Nonetheless, available MRI studies were often conflicting and could have been limited by methodological issues. Future MRI investigations should include well-characterized groups of autistic and matched healthy individuals, while taking into consideration confounding factors such as IQ, and socioeconomic status.

Introduction

Autism is a complex disease characterized by impairment of social interaction, language, behavior, and cognitive functions [61]. Autistic phenotype is a behavioral syndrome described by the DSM-IV [3] based on the presence of at least 6 of 12 symptoms related to impairment in social interaction, verbal and nonverbal communication deficits, restricted interests, and repetitive behaviors, which are present by the age of 3 years [60]. Clinical features and cognitive impairments persist throughout life and are associated with mental retardation in the majority of patients [50]. Although the causation of autism is still largely unknown, it has been suggested that genetic, developmental, and environmental factors could be involved alone or in combination as possible causal or predisposing effects toward developing autism 7., 51., 69..

In the last 15 years, several magnetic resonance imaging (MRI) studies examined the brain anatomy in patients with autism in order to identify structural abnormalities. MRI has become the method of choice for investigation of brain morphology, because of its high contrast sensitivity and spatial resolution, in the absence of radiation exposure. This is particularly important in research studies involving children and adolescents 21., 40..

The goal of this review was to summarize morphometric brain investigations involving patients with autism, in order to examine structural brain anatomy and development in autism. Additionally, we discussed specific methodological issues that should contribute to improve the design of future MRI investigations in this field.