MRI and neurological presentation of hypertrophic olivary degeneration

Background and purpose Hypertrophic olivary degeneration (HOD) is a rare transsynaptic degeneration that usually appears at around 3–4 weeks following an injury to the Guillain–Mollaret triangle, resulting in three possible patterns. Our purpose was to describe those MRI features linking them to their corresponding neurological manifestations and possible prior location of brain insults based on our own experience compared to the review of the literature. Methods Six patients with clinically evident new neurological symptoms not explained by the initial brain insult were included. All patients were subjected to complete neurological assessment by neurologist or neurosurgeon accordingly. Review of their prior and recent MRI studies as well as CT if available was carried out by two neuroradiologists who picked up the different but classical patterns of HOD on the latest imaging studies. Results The 6 patients had old brain insults including old hematomas (1 patient), old infarctions (3 patients) and hemorrhagic vascular malformation (2 patient) involving the afferent components of the Guillain–Mollaret triangle with development of new movement disorders including ataxia (4 patients), palatal myoclonus (4 patients), tremors (1 patient) and nystagmus (2 patients). MRI clearly showed the nature of the initial lesions. High T2 signal intensity was noticed at the inferior olivary nucleus (ION) in all patients representing olivary degeneration. The size of the ION was enlarged with rounded configuration in 5 cases thus considered hypertrophic, while the size of the ION was shrunken in one case and considered atrophic. The examined ION showed no restricted diffusion excluding recent infarction, blooming on T2∗ excluding hemorrhage or post contrast enhancement excluding inflammation or neoplasm. Unilateral HOD was seen in 3 cases involving the contra-lateral ION while bilateral HOD was seen in 3 cases. Conclusion HOD is an infrequent neurological pathology, sequel to Guillain and Mollaret triangle affection that involves a wide range of symptomatology. It manifests as enlargement of the ION with high T2 and FLAIR signal without enhancement, restricted diffusion or blooming on T2∗ or SWI.