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Hypertrophic olivary degeneration in a child following midbrain tumor resection: longitudinal diffusion tensor imaging studies.

Hypertrophic olivary degeneration (HOD) is a dynamic process caused by disruptive lesions affecting components of the Guillain-Mollaret triangle (GMT). The authors applied diffusion tensor imaging (DTI) to investigate longitudinal changes of the GMT components in a child with HOD after neurosurgery for a midbrain tumor. Diffusion tensor imaging data were acquired on a 1.5-T MRI scanner using a balanced pair of diffusion gradients along 20 noncollinear directions 1 day and 3, 6, and 9 months after surgery. Measurements from regions of interest (ROIs) were sampled in the affected inferior olivary nucleus, ipsilateral red nucleus, and contralateral superior and inferior cerebellar peduncles and dentate nucleus. For each ROI, fractional anisotropy and the mean, axial, and radial diffusivities were calculated. In the affected inferior olivary nucleus, the authors found a decrease in fractional anisotropy and an increase in mean, axial, and radial diffusivities 3 months after surgery, while 3 months later fractional anisotropy increased and diffusivities decreased. For all other GMT components, changes in DTI scalars were less pronounced, and fractional anisotropy mildly decreased over time. A detailed analysis of longitudinal DTI scalars in the various GMT components may shed light on a better understanding of the dynamic complex histopathological processes occurring in pediatric HOD over time.