Brain Abnormality Findings in F18-FDG PET/CT Imaging and its Role in the Clinical Diagnosis of Autism

Objectives: Autism is a spectrum of neurodevelopmental disorders that affects one in every 68 children. Currently, the only way to diagnose autism is through behavioral and psychological evaluation. Hybrid Positron Emission Tomography (PET) and Computed Tomography (CT) have recently been evaluated as a diagnostic tool for identifying patients with autism. The purpose of this study is to evaluate abnormal findings on F18-FDG PET/CT brain scans of autistic patients and determine if F18-FDG PET/CT scans demonstrate the ability to assess autism.

Methods: Two studies were reviewed to assess the effectiveness of F18-FDG PET/CT imaging used in diagnosing autism. A total of 38 autistic patients and nine control patients were evaluated. All patients were injected with F18-FDG and scanned after an incubation period. Study one’s purpose was to evaluate 23 patients with autism and all were injected with 7mCi of F18-FDG. The second study evaluated 15 autistic patients and nine control (non-autistic) patients all injected with 0.15mCi of F18-FDG. In both studies, abnormal findings for each patient on the PET/CT scan were compared to the results of a baseline MRI.

Results: Areas of increased and decreased brain metabolic activity were evaluated for each patient. Neither study reported specific areas of normal uptake in the patients with autism. Study one found that 22 patients (95%) had reduced uptake in the hippocampus, 19 patients (82%) had decreased uptake in the amygdala, 9 patients (39%) had diminished uptake in the parahippocampal region, 15 patients (65%) had reduced uptake in the mesial temporal region, and 13 patients (56%) had decreased uptake in the cerebellum. It was also discovered that 17 patients (74%) had hypermetabolic uptake in the frontal lobes. Study two found 13 patients (86.7%) had hypometabolic activity in the temporal regions, nine patients (60%) had reduced uptake in the frontal area, and seven patients (46.7%) had reduced uptake in the parietal area. The study also found that out of the nine control patients, three patients (33%) had findings of low uptake in the frontal lobes.

Conclusion: Both studies found hypometabolic activity in the temporal lobes; however contradicting results of metabolic activity in the frontal lobes were found. The patients with autism vastly differed in the areas of abnormal metabolic activity. The mixed results found in the participants could be due to the differences in doses used in the studies, the inconsistency of imaging parameters, or a possible misdiagnosis in autistic patients. Further research should be completed to demonstrate the true ability of F18-FDG to diagnose autism.