Diffusion abnormalities and reduced volume of the ventral cingulum bundle in agenesis of the corpus callosum: a 3T imaging study

Abstract

Background and purpose: Patients with agenesis of the corpus callosum (AgCC) exhibit cognitive and behavioral impairments that are not replicated by surgical transection of the callosum, suggesting that other anatomic changes may contribute to the observed clinical findings. The purpose of this study was to determine whether the ventral cingulum bundle (VCB) is affected in patients with AgCC by using diffusion tensor imaging (DTI) and volumetry.

Materials and methods: Twelve participants with AgCC (8 males and 4 females; mean age, 30 +/- 20) and 12 control subjects matched for age and sex (mean age, 37 +/- 19) underwent MR imaging and DTI at 3T. 3D fiber tracking of the VCB was generated from DTI and the average fractional anisotropy (FA) was computed for the tracked fibers. Additionally, the volume, cross-sectional area, and length of the VCB were measured by manually drawn regions of interest on thin-section coronal T1-weighted images. The Student t test was used to compare these results.

Results: Compared with controls, subjects with AgCC demonstrated significantly reduced FA in the right VCB (P = .0098) and reduced volume and cross-sectional areas of both the left and right VCB (P < .001 for all metrics). The length of the VCB was also significantly reduced in the complete AgCC subgroup compared with controls (P = .030 in the right and P = .046 in the left, respectively).

Conclusions: Patients with AgCC have abnormal microstructure and reduced volume of the VCB, suggesting that abnormalities in intrahemispheric white matter tracts may be an important contributor to the clinical syndrome in patients with AgCC.

Figures

Fig 1.

Reconstructed fiber tracts of VCB are overlaid on reconstructed coronal and midsagittal sections of the color map in a healthy control (A−C) and a patient with AgCC (D−F). A and D, An anterior region of interest (white line) is drawn on the coronal section immediately anterior to the pons. B and E, A posterior region of interest (white line) is placed on a coronal section aligned with the point of intersection of the external capsule and the posterior limb of the internal capsule. C and F, Fiber tracking of the VCB is then generated from a posterior region of interest to an anterior region of interest. Coronal sections in which an anterior region of interest and a posterior region of interest are manually drawn are shown in relation to each other on a sagittal section (white lines).

Fig 2.

VCB on the color map and 3D-T1WI in a healthy control (A−D) and a patient with AgCC (E−H). A and E, In the reconstructed sagittal sections of color map, the VCB is identified as a green and blue area (arrows) in the inferomedial aspect of the temporal lobe. B and F, Multiple regions of interest are overlaid on a reconstructed sagittal section of 3D-T1WI (small white lines). Arrow indicates the gray matter of the hippocampal tail. C and G, Reconstructed fiber tracts of VCB are overlaid on a reconstructed coronal section of the color map (red area). D and H, A region of interest is drawn manually in each coronal section (white line) by visually identifying the anatomic boundaries and referring to the fiber tracts of VCB on reconstructed coronal sections of the color map.