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AJNR - American Journal of Neuroradiology

Published ahead of print on November 11, 2008
doi: 10.3174/ajnr.A1361

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American Journal of Neuroradiology 30:282-289, February 2009
© 2009 American Society of Neuroradiology

PEDIATRICS

Variability of Homotopic and Heterotopic Callosal Connectivity in Partial Agenesis of the Corpus Callosum: A 3T Diffusion Tensor Imaging and Q-Ball Tractography Study

M. Wahl^a,b, Z. Strominger^b, R.J. Jeremy^c, A.J. Barkovich^a,b,c, M. Wakahiro^b, E.H. Sherr^b and P. Mukherjee^a

^a Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, Calif
^b Department of Neurology, University of California, San Francisco, San Francisco, Calif
^c Department of Pediatrics, University of California, San Francisco, San Francisco, Calif

Please address correspondence to Pratik Mukherjee, MD, PhD, Department of Radiology, University of California, San Francisco, 505 Parnassus Ave, Box 0628, San Francisco, CA 94143-0628; e-mail: pratik{at}radiology.ucsf.edu; or Elliott H. Sherr, MD, PhD, Department of Neurology, University of California, San Francisco, 505 Parnassus Ave, M798, San Francisco, CA 94143-0114; e-mail: sherre{at}neuropeds.ucsf.edu

BACKGROUND AND PURPOSE: Little is known about the anatomic connectivity of callosal axons in individuals with partial agenesis of the corpus callosum (pAgCC). We used tractography based on both diffusion tensor imaging (DTI) and high angular resolution diffusion imaging (HARDI) to investigate interhemispheric white matter connectivity in pAgCC.

MATERIALS AND METHODS: DTI and HARDI were performed at 3T on 6 individuals with pAgCC and 8 control subjects. For HARDI analysis, a Q-ball reconstruction method capable of visualizing multiple intravoxel fiber orientations was used. In both DTI and HARDI, whole-brain 3D fiber tractography was performed by using deterministic streamline algorithms. Callosal fibers were then segmented to identify separately connections between homologous cortical regions (homotopic fibers) and nonhomologous regions (heterotopic fibers) by using manually drawn regions of interest.

RESULTS: In control individuals, we observed densely connected homotopic fibers. However, in individuals with pAgCC, we identified not only homotopic connections but also heterotopic connections in 4 of 6 subjects. Furthermore, the observed homotopic connections in pAgCC did not necessarily correlate with the position or size of the residual callosum. The nature of homotopic and heterotopic connectivity varied considerably among subjects with pAgCC, and HARDI recovered more callosal fibers than DTI.

CONCLUSION: Individuals with pAgCC demonstrate a remarkable diversity of callosal connectivity, including a number of heterotopic tracts that are absent in healthy subjects. The patterns of their callosal connections cannot be predicted from the appearance of their callosal fragments on conventional MR imaging. More tracts and more extensive fibers within tracts are recovered with HARDI than with DTI.

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				D. Rubinstein Partial Development of the Corpus Callosum AJNR Am. J. Neuroradiol., June 1, 2009; 30(6): e81 - e81. [Full Text] [PDF]

				P. Mukherjee, M. Wahl, and A.J. Barkovich Reply: AJNR Am. J. Neuroradiol., June 1, 2009; 30(6): e82 - e82. [Full Text] [PDF]