Diffusion tensor imaging of midline posterior fossa malformations.

BACKGROUND

Diffusion tensor imaging and tractography have been used to evaluate a variety of brain malformations. However, these studies have focused mainly on malformations involving the supratentorial compartments. There is a paucity of data on diffusion tensor imaging of posterior fossa malformations.

OBJECTIVE

To describe the color vector maps and modified or abnormal tracts of midline posterior fossa malformations.

MATERIALS AND METHODS

Diffusion tensor imaging was performed in one patient with rhombencephalosynapsis and two with Joubert syndrome. Color vector maps of fractional anisotropy were used to place a region of interest for seed point of fiber tracking.

RESULTS

The vermis was severely hypoplastic or absent in rhombencephalosynapsis and Joubert syndrome. In rhombencephalosynapsis, vertically oriented fibers were visualized in the midportion of the cerebellum. The location of the deep cerebellar nuclei could be inferred from the amiculum and were medially located in rhombencephalosynapsis. In the two patients with Joubert syndrome, the horizontally arranged superior cerebellar peduncles were well demonstrated on the color vector maps. Failure of the superior cerebellar peduncles to decussate in the mesencephalon was also well demonstrated on both color vector maps and tractography. The deep cerebellar nuclei were more laterally located in Joubert syndrome.

CONCLUSION

The use of tractography in midline posterior fossa malformations expands our understanding of these malformations.