Hypertrophic olivary degeneration
Updates to Article Attributes
Hypertrophic olivary degeneration (HOD) is a rare condition characterised by a unique pattern of trans-synaptic degeneration. It is caused by a lesion in the triangle of Guillain and Mollaret, resulting in hypertrophy of the inferior olivary nucleus. The three corners of the triangle are:
- red nucleus
- inferior olivary nucleus
- contralateral dentate nucleus
Clinical presentation
Palatal myoclonus, rhythmic involuntary movement of the soft palate, uvula, pharynx, larynx and upper extremity are classically described clinical features.
Palatal myoclonus may not always be present, but when it is present, it's pathognomonic.
Pathology
The connection between the red nucleus, ipsilateral inferior olivary nucleus and the contralateral dentate nucleus forms the triangle of Guillain and Mollaret. Interruption of either connection between the dentate nucleus and contralateral red nucleus (dentatorubral tract, superior cerebellar peduncle) or the connection between the red nucleus and ipsilateral inferior olivary nucleus (central tegmental tract) leads to changes in the olive. The olive receives inhibitory (GABAergic) signals within the dentato-rubro-olivary pathway, with trans-neuronal degeneration causing enlargement rather than atrophy.
Pathologically, this is characterised by "trans-synaptic degeneration resulting in vacuolation of the neurons" and an increase in astrocytes. Isolated lesions of the inferior cerebellar peduncle do not cause hypertrophic olivary degeneration, as anatomically there are no direct connections between the inferior olivary nucleus and the contralateral dentate nucleus (fibres from the inferior olivary nucleus project to the cerebellar cortex via the olivocerebellar tracts and then to the dentate nucleus).
Radiographic features
It is often seen several months after the original insult.
MRI
In radiology laymen terms, the inferior olivary nucleus gets larger and increases in T2 signal intensity.
Typically, within a few months, T2 signal increases and lasts for 3-4 years, whereas hypertrophy occurs later (at about one year), and resolves by 3-4 years. There are three stages:
-
Firstfirst stage:T2W hyperintensityT2: hyperintense without olivary swelling -
Secondsecond stage:T2W hyperintensityT2 hyperintense and olivary swelling occuring concomitantly. Develops; develops after 6 months and persists for nearly 3-4 years. -
Thirdthird stage: oOlivarylivary swelling subsides, however, T2W and FLAIR hyperintensity persist.
Differential diagnosis
General imaging differential considerations include:
- infarction
- demyelination
- astrocytoma
- metastases
- lymphoma
- infection, including tuberculosis
-<strong>First stage: </strong>T2W hyperintensity without olivary swelling</li>- +<strong>first stage: </strong>T2: hyperintense without olivary swelling</li>
-<strong>Second stage: </strong>T2W hyperintensity and olivary swelling occuring concomitantly. Develops after 6 months and persists for nearly 3-4 years. </li>- +<strong>second stage: </strong>T2 hyperintense and olivary swelling occuring concomitantly; develops after 6 months and persists for nearly 3-4 years. </li>
-<strong>Third stage: </strong>Olivary swelling subsides, however, T2W and FLAIR hyperintensity persist.</li>- +<strong>third stage: o</strong>livary swelling subsides, however, T2W and FLAIR hyperintensity persist.</li>
Image 2 MRI (T2) ( update )
Image 3 Diagram ( update )
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