LAUSR

Hypertrophic olivary degeneration (HOD) following a lesion of the dentato–rubro–olivary pathway (DROP) is a well‐known imaging finding and has extensively been described in the recent literature. We reviewed our patients with HOD as a result of a lesion of the DROP in order to analyze the disruption of the DROP and the resulting HOD in comparison with the literature. We observed unusual imaging findings in four patients. In two patients it concerned new observations related to the timing and imaging appearances of HOD. HOD became only visible 6 years after a lesion in the red nucleus in one patient and a cystic degeneration of the olivary nucleus was seen 3 years after the HOD in a second patient. In two patients we found HOD that could only be explained by the existence of an afferent feedback loop between the dentate nucleus and the inferior olivary nucleus and by the knowledge that these fibers run through the ipsilateral olivary nucleus before ending in the contralateral olivary nucleus. In one of these patients the lesion was located in the inferior cerebellar peduncle. In the other patient the lesion was located on the midline in the medulla oblongata. The imaging findings in these patients reveal new observations in the stages of imaging appearances in HOD and shed light on the forgotten dentato–olivary afferent feedback loop of the DROP. Clin. Anat. 30:543–549, 2017. © 2017 Wiley Periodicals, Inc.