Figure 6.

ST analysis of heterotopic corticospinal tract projections in Joubert syndrome. (A–E) Fetal MRI of subject 2 at GW21. Axial T2-weighted images through the brainstem demonstrate molar tooth malformation of the mesencephalon (A) and vermian hypoplasia (C). (D) A midsagittal T2-weighted image shows a nodular hypointense interpeduncular mass (arrow). (E) In utero tractography shows a discontinuity of most internal capsule streamlines at the level of the mesencephalon. (F) Neuropathological autopsy at GW22 demonstrated perpendicularly cut fibers in the cerebral peduncles at the level of the rostral mesencephalon, but showed a complete absence of the corticospinal tract in the medulla oblongata (G) between the arcuate nuclei (^*) and the inferior olive (^**). (H,I) Sections through the caudal mesencephalon show a heterotopic projection of the corticospinal tract from the cerebral peduncles medially into the interpeduncular cistern. (J,K) Sections through the pons visualize some transverse pontine fibers and abnormal fiber tracts in the pontine tegmentum and posterior right basis pontis. Note the absence of normal perpendicularly cut fibers of the corticospinal tract between the pontine nuclei. (F,H,J) HSB images, (I,K) Histology-based tractography, (G) H&E.