The Rates of Incidental Perivascular Space (PVS) Findings on MRI Among Infants at High- and Low-Risk for ASD: Preliminary Results from the IBIS Study

Background: Prior research has highlighted an increased frequency of incidental findings in the MRI scans of children diagnosed with ASD. However, little research has explored the frequency of incidental MRI findings in infants who are at high familial risk for autism. While no differences in the frequency of incidental MRI findings have been reported in infants at high (HR) and low risk (LR) for ASD at 6 months of age, it is possible that differences in the frequency of incidental MRI findings between these groups become apparent later in infancy.

Objectives: We examined the frequency with which incidental findings occur in HR and LR infants at 6, 12, and 24 months of age. We examined how findings at different ages relate to subsequent diagnostic outcomes.

Methods: Participants are part of an ongoing multi-site study (The Infant Brain Imaging Study) and underwent MRI scans at 6, 12, and 24 months (Total N=324; 239 HR, 85 LR). Diagnostic outcome of ASD was determined at 24 months of age by expert clinicians.  The final sample was composed of three groups: N=49 HR infants who were diagnosed with ASD (HR-ASD); N=190 HR infants who were not diagnosed with ASD (HR-neg); and N=85 LR control infants (LR-neg). A neuroradiologist at each site (blind to risk status and diagnosis) reviewed and classified each scan, and each scan classification was confirmed by a second neuroradiologist. For the purposes of this study, each scan was classified as being either Abnormal or Typical by the presence and degree of perivascular spaces (PVS). The degree of  PVS was rated on a five-point scale: none, minimal, mild, moderate, and marked. The rate of Abnormal vs. Typical scans at 24 months was compared between groups using Chi-squared tests. 

Results: The rate of abnormal scans at 24 months was higher in the HR-ASD compared to the HR-neg and LR-neg groups: 63.27% of scans in the HR-ASD group were classified as abnormal, compared to less than 40% of scans in the HR-neg and LR-neg groups. The ratio of abnormal vs. normal scans in the HR-ASD group was significantly higher compared to both the HR-neg group (χ² = 11.15, p < .001) and LR-neg group (χ² = 7.44, p < .01). PVS were found in >60% of abnormal scans at 24 months across all groups.

Conclusions: The examination of MRI scans across diagnostic outcomes demonstrated that abnormal findings at 24 months were significantly more common in HR-ASD children, compared to HR-neg and LR-neg children. Interestingly, for all three diagnostic groups, PVS were the most frequent findings across all abnormal scans. Analyses of other incidental findings and correlations between MRI findings and clinical characteristics are currently underway and will be presented.