Quantitative analysis of the shape of the corpus callosum in patients with autism and comparison individuals

Abstract

Multiple studies suggest that the corpus callosum in patients with autism is reduced in size. This study attempts to elucidate the nature of this morphometric abnormality by analyzing the shape of this structure in 17 high-functioning patients with autism and an equal number of comparison participants matched for age, sex, IQ, and handedness. The corpus callosum was segmented from T1 weighted images acquired with a Siemens 1.5 T scanner. Transformed coordinates of the curvilinear axis were aggregated into a parametric map and compared across series to derive regions of statistical significance. Our results indicate that a reduction in size of the corpus callosum occurs over all of its subdivisions (genu, body, splenium) in patients with autism. Since the commissural fibers that traverse the different anatomical compartments of the corpus callosum originate in disparate brain regions our results suggest the presence of widely distributed cortical abnormalities in people with autism.

Figure 1

Mapping the surface of the corpus callosum. In the pseudocylindrical coordinate system, the z coordinate is the arc length along the centerline from the splenium (left). Radius and polar angle are then measured within the plane orthogonal to the centerline at z.

Figure 2

The map of Δρ = ρ_autism(ϕ, z) – ρ_control(ϕ, z), i.e. the mean deficit or excess in ρ(ϕ, z) in the autistic cases compared with controls. Differences are statistically significant (for q^* = 0.05) in the outlined areas.

Figure 3

Regions where autistic and control CC appear to differ, as in Figure 2, projected back into anatomical space and viewed from above and from below. The CC in those with autism is significantly larger (resp. smaller, insignificantly different) than the CC in comparison clients where Δρ > 0 (resp. Δρ < 0, Δρ ≈ 0).

Figure 4

Mean Δρ as a function of z, averaging over ϕ, within sections of the CC body encompassing those regions where Δρ was significantly less than 0. These sections are outlined in the inset, upper left (compare Figure 2). On the left body (L), as z increases toward the genu, so does mean Δρ (95 % confidence interval on the slope of the line: [−0.004, 0.045]). There is no evidence of such a trend on the right (R), where the slope is consistent with zero (95 % confidence interval [−0.017, 0.025]). Confidence intervals were estimated via bootstrap resampling of autism/comparison client case pairs.