Department of Pathology, University of Oklahoma Health Sciences Center

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Answer:  1, 2, and 3; i.e. A (Partial agenesis of corpus callosum. Probst bundle is usually present; the timing of critical events that lead to this change happens between 9th to 20th weeks of gestation; it is often but not always associated with Aicardi syndrome.)   Level of difficulty: 3 NeuroTest NeuroLearn NeuroHelp

Discussion: 

• Pathology: Agenesis of the corpus callosum should be reserved to the cases when mechanism(s) by which the axons of the corpus callosum cross the midline in the usual position are absent or deficient (i.e., the agenesis is a primary event but not secondary to other damage or malformation of the neurons or axons up stream to the callosal axons). 

• Discussion of the case: In this case of partial agenesis of corpus callosum, a small portion of the residual corpus callosum is present (à). Since the corpus callosum develops in an anterior to posterior fashion, partial agenesis usually involves the posterior part while complete agenesis involves both anterior and posterior portions. If the anterior part of the corpus callosum is absent but the posterior part is present, a destructive mechanism should be seriously considered. Complete or partial agenesis of the corpus callosum rarely exists as an isolated entity. The cingulate gyrus overlying the residual portion of the corpus callosum has normal development. The more occipital portion of the cingulate gyrus, however, has vertical arrangement and is normal. Abnormal configuration of the cingulate gyrus is a constant assoiation with agenesis of corpus callosum.

• Probst bundle,  also called longitudinal corpora callosa. They are abnormal prominent bundle of fibers in median sagittal directions (longitudinal callosal fibers) in the lateral part of the roof of the lateral ventricles in cases of agenesis of corpus callosum. The volume of Probst bundle is significantly smaller than that of the corpus callosum. The Probst bundle is identified by the arrow in the figure below.