Rare Case of Hypertrophic Olivary Degeneration

52 year male with history of giddiness for one month presented to the ear, nose and throat outpatient department of our institution .On further examination he was also complaining of palatal tremors for the same duration. There was no evidence of vision problems/gait impairment. No prior history of stroke or trauma was present. Patient was not a known hypertensive.

MRI was done and showed increased signal intensity and enlargement of bilateral inferior olive seen on proton density-weighted and T2/FLAIR . Gradient recalled echo images shows areas of suspectibility effect suggestive of chronic haemorrhage in the mesencephalon ,no significant surrounding edema was noted . Neither enhancement was seen following contrast administration, nor restriction on diffusion-weighted imaging. Based on the radiologic findings and clinical symptoms, a diagnosis of hypertrophic olivary degeneration was made. The etiology of this case could be due to haemorrhage in the mesencephalon, although he was not a known hypertensive. The patient was treated symptomatically and is asked to return for a follow up MRI.

Hypertrophic degeneration of the inferior olive is mainly observed in patients developing palatal tremor (PT) or oculopalatal tremor (OPT). It is associated with hypertrophic inferior olivary degeneration that is characterized by enlarged and vacuolated neurons, increased number and size of astrocytes, severe fibrillary gliosis, and demyelination.[1] It appears on MRI as an increased T2/FLAIR signal intensity and enlargement of the inferior olive. T2 hyperintensity and hypertrophy is due to vacuolar degeneration, neuronal enlargement and astrocyte hypertrophy .The most frequent, studied, and reported condition is the development of PT/OPT and hypertrophic degeneration of the inferior olive in the weeks or months following a structural brainstem or cerebellar lesion.[2] This “symptomatic” condition requires a destructive lesion in the Guillain–Mollaret pathway, which spans from the contralateral dentate nucleus via the brachium conjunctivum and the ipsilateral central tegmental tract innervating the inferior olive. The most frequent etiologies of destructive lesion are stroke (hemorrhagic more often than ischemic), brain trreturn fauma, brainstem tumors, and surgical or gamma knife treatment of brainstem cavernoma. [3] Hypertrophic Olivary Degeneration (HOD) is due to trans-synaptic degeneration by lesions) in the Guillain-Mollaret triangle [dentato-rubro-olivary pathways] and presents as palatal tremors. HOD depict classical MRI findings in inferior olivary nucleus at 3 different phases. [4] (i) Before 6 months only T2 hyperintensity. (ii) From 6 months to several years T2 hyperintensity and hypertrophy ( due to vacuolar degeneration, neuronal enlargement and astrocyte hypertrophy]. (iii) From 3-4 years resolution/ atrophy with T2 hyperintensity . It is important to recognize this pattern of injury so that the changes in the medulla are not ascribed to a more serious cause, e.g. tumor, demyelination or infarct . The most important clue to the correct diagnosis is the association of a remote lesion along the pathway.Only anterior medullary involvment without restricted diffusion rules out infarct. Glioma /tumefactive demyelination shows heterogenous signal intensity, altered morphology and enhancement.