In vivo tractography of fetal association fibers

Abstract

Association fibers connect different cortical areas within the same hemisphere and constitute an essential anatomical substrate for a diverse range of higher cognitive functions. So far a comprehensive description of the prenatal in vivo morphology of these functionally important pathways is lacking. In the present study, diffusion tensor imaging (DTI) and tractography were used to visualize major association fiber tracts and the fornix in utero in preselected non-motion degraded DTI datasets of 24 living unsedated fetuses between 20 and 34 gestational weeks (GW). The uncinate fasciculus and inferior fronto-occipital fasciculus were depicted as early as 20 GW, while in vivo 3D visualization of the inferior longitudinal fasciculus, cingulum and fornix was successful in older fetuses during the third trimester. Provided optimal scanning conditions, in utero DTI and tractography have the potential to provide a more accurate anatomical definition of developing neuronal networks in the human fetal brain. Knowledge about the normal prenatal 3D association tract morphology may serve as reference for their assessment in common developmental diseases.

Fig 1. In utero tractography of the UF in subjects 3 (a), 16 (b) and 24 (c) (22, 28 and 34 GW respectively).

Fiber tracts are projected on axial T2-weighted images.

Fig 2. In utero tractography of the IFOF (yellow) in subjects 1 (a), 9 (b) and 23 (c) (20, 24 and 33 GW respectively) and its relation to the UF (red).

Fiber tracts are projected on axial T2-weighted images.

Fig 3. In utero tractography of the ILF (orange) in subjects 4 (a), 19 (b) and 24 (c) (23, 33 and 34 GW respectively) and its relation to the IFOF (yellow).

Fiber tracts are projected on axial T2-weighted images.

Fig 4. In utero tractography of the cingulum (pink) in subjects 15 (a), 20 (b) and 23 (c) (27, 33 and 33 GW respectively) and its relation to the corpus callosum (dark blue).

Tractography of the corpus callosum was performed according to the methods described in Kasprian et al. (2008) [26]. Fiber tracts are projected on axial T2-weighted images.

Fig 5. In utero tractography of the fornix (light blue) in subjects 14 (a), 17 (b) and 23 (c) (27, 30 and 33 GW respectively) and its relation to corticospinal/ corticopontine fibers (green).

Tractography of corticospinal/ corticopontine fibers was performed according to the methods described in Kasprian et al. (2008) [26]. Fiber tracts are projected on axial T2-weighted images.

Fig 6. In utero tractography of association and limbic fiber tracts in subjects 1 (a) and 20 (b) (20 and 33 GW respectively) and their relation to the corpus callosum (dark blue) and corticospinal/ corticopontine fibers (green).

Fiber tracts are projected on axial T2-weighted images. Visualized association fiber tracts include the UF (red), the IFOF (yellow), the ILF (orange) and the cingulum (pink). The limbic fiber bundle of the fornix is color-coded in light blue.