Objective: Infantile autism is a neurologic disorder that severely disrupts the development of many higher cognitive functions. The most consistent abnormal neuroanatomic findings in autism are loss of Purkinje neurons in the posterior cerebellum as detected by autopsy studies and hypoplasia of the posterior cerebellar vermis and hemispheres as detected by in vivo neuroimaging. Evidence of developmental arrest has also been detected in limbic structures in autopsy studies of autistic patients with mental retardation. Neither in vivo neuroimaging nor autopsy studies of autistic persons have reported abnormalities in the cerebrum. Because the cerebrum mediates many higher cognitive functions, such as social communication, language, abstract reasoning, planning, and organization, that are known to be deficient in patients with autism, a closer examination of the neuroanatomy of the cerebrum in infantile autism is warranted.
Materials and methods: MR images of 21 healthy autistic patients (6-32 years old) were mixed with MR images of control subjects and reviewed on four separate occasions by a neuroradiologist for any neuroanatomic abnormalities. Autism was diagnosed on the basis of criteria for autism as defined by the Diagnostic and Statistical Manual of Mental Disorders, and the autistic patients did not have any other concurrent neurologic disorders. To control for systematic bias in judging the type and location of abnormalities in the autistic population, three control groups were used: a normal control group of 12 subjects, a control group of 23 nonautistic patients with a variety of brain abnormalities for the first review, and another control group of 17 nonautistic patients for the second review. Control patients with brain abnormalities were selected from patients' files on the basis of MR findings of a variety of brain abnormalities. All MR images were coded for anonymity, randomly mixed, and examined by a neuroradiologist blinded to the purpose of the study and to the group membership of each subject. All normal and abnormal findings seen on the MR images of each subject were described on a standard form listing all major brain structures to ensure an examination of each structure in turn. To test for reliability, three subsequent reviews were performed by the same neuroradiologist.
Results: Parietal lobes were abnormal in appearance in 43% (9/21) of autistic patients. Cortical volume loss in the parietal lobes was seen in seven autistic patients; in four of these cases, cortical volume loss extended either into the adjacent superior frontal or occipital lobe. Additional abnormalities detected with MR in these nine patients included white matter volume loss in the parietal lobes (three patients) and thinning of the corpus callosum, especially along the posterior body (two patients). Abnormalities were bilateral. The mesial, lateral, and orbital regions of the frontal lobes; temporal lobes; limbic structures; basal ganglia; diencephalon; and brainstem were normal in all autistic patients. No abnormalities were found in the 12 normal control subjects. The control subjects with neurologic abnormalities had various abnormal findings consistent with their medical conditions.
Conclusion: Our results indicate that the parietal lobes are reduced in volume in a portion of the autistic population. Possible origins for this localized cerebral abnormality include early-onset altered development and late-onset progressive atrophy.