Hypertrophic olivary degeneration in a child following midbrain tumor resection: Longitudinal diffusion tensor imaging studies - Case report

Hypertrophic olivary degeneration (HOD) is a dynamic process caused by disruptive lesions affecting componentsof the Guillain-Mollaret triangle (GMT). The authors applied diffusion tensor imaging (DTI) to investigatelongitudinal changes of the GMT components in a child with HOD after neurosurgery for a midbrain tumor.Diffusiontensor imaging data were acquired on a 1.5-T MRI scanner using a balanced pair of diffusion gradients along20 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 inferiorcerebellar peduncles and dentate nucleus. For each ROI, fractional anisotropy and the mean, axial, and radial diffusivitieswere calculated. In the affected inferior olivary nucleus, the authors found a decrease in fractional anisotropyand an increase in mean, axial, and radial diffusivities 3 months after surgery, while 3 months later fractionalanisotropy increased and diffusivities decreased. For all other GMT components, changes in DTI scalars were lesspronounced, and fractional anisotropy mildly decreased over time. A detailed analysis of longitudinal DTI scalars inthe various GMT components may shed light on a better understanding of the dynamic complex histopathologicalprocesses occurring in pediatric HOD over time.