Mapping Corpus Callosum Deficits in Autistic Children using Novel Computational Anatomy Algorithms

Proc. Human Brain Mapping Conference, New York City, NY, USA, June 2003.

¹Christine N. Vidal, ³Timothy J. DeVito, ¹Kiralee M. Hayashi, ³Dick J. Drost PhD, ^2,3Peter C. Williamson MD, ²Beth Craven-Thuss, ¹David Herman, ¹Yihong Sui, ¹Arthur W. Toga PhD, ^2,3Rob Nicolson MD, ¹Paul M. Thompson PhD

¹Laboratory of Neuro Imaging, Dept. Neurology, UCLA School of Medicine, Los Angeles, CA, USA
²Dept. Psychiatry, University of Western Ontario, London, Canada
³Dept. of Medical Biophysics, University of Western Ontario, London, Canada

Fig. 1: (a): Witelson Partitioning Scheme; (b),(c): Significant Anatomical Differences (Autistics vs. Controls); (d) Percentage Thickness Reduction in Autism.

ABSTRACT

35 T1-weighted 3D MP-RAGE 3T MRI volumes (1.2-mm isotropic) were acquired from 15 autistic children (age: 9.9 yrs.+/-3.2SD), 7 matched Tourette syndrome subjects (10.5 yrs.+/-2.8SD), and 13 controls (10.0 yrs.+/-2.1SD) matched for age, height, and sex. In ICBM space, the CC was delineated as a surface extending 4 mm either side of the interhemispheric fissure. Traces were converted into 3D parametric surface meshes. Group average shape models were overlaid. A medial surface equidistant between each subject’s upper and lower surfaces was derived, and its distance to each boundary point was mapped. Group differences in the resulting thickness maps were assessed at each surface location, by ANOVA and permutation testing. Mean group differences in callosal anatomy were plotted as a percentage reduction in local thickness (see Fig. 1).

Average maps in autism revealed reduced callosal thickness in the genu, midbody and splenium (p<0.0002); midsagittal callosal area was 13.7% smaller, overall (604.8+/-37.2mm² versus 700.7+/-21.8mm² in controls; p<0.021). The Witelson partition, which divides the callosum into fifths (see Fig. 1a), identified similar reductions in the genu (14.8%; p<0.016), midbody (13.3%; p<0.047), and splenium (14.9%; p<0.036). No overall brain volume differences were detected (p>0.38). No shape or thickness differences were found in Tourette patients.

These anomalies suggest impaired frontal and occipital connectivity in autism. The fluctuating effect size, and lower power, of volumetric measures may explain why some prior studies have found anatomical reductions only in the genu and rostrum [2], or most prominent in the body or posterior sectors [3-5]. Here, shape mapping discriminates groups better (p<0.0002) than volumetry (p<0.02). Visualization of these deficit profiles may provide an MRI-based biomarker of autism, for genetic and behavioral studies.

References: [1]. Witelson S (1989). Brain 112:799-835. [2]. Hardan A (2000). Neurology 55:1033-1036. [3]. Egaas B et al. (1995). Arch. Neurol. 52:794-801. [4]. Piven J et al. (1997). Am. J. Psychiatry 154:1051-1056. [5]. Manes F et al. (1999). J Neuropsych. Clin. Neurosci. 11(4):470-4.

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