Hypertrophic olivary degeneration

Changed by Bruno Di Muzio, 20 Jul 2015
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Hypertrophic olivary degeneration (HOD) is a rare condition characterised by 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:

Clinical presentation

Palatal myoclonus is a classically described feature.

Pathology

Interruption of either of the connections 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. 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 HOD, as anatommically 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 brain

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 3-4 years, whereas hypertrophy occurs later (at about one year), and resolves by 3-4 years.

Clinically lesions in the triangle of Guillain and Mollaret, present as palatal tremor.

Differential diagnosis

General imaging differential considerations include:

  • -<li>infection, including <a href="/articles/cns-tuberculosis-1">tuberculosis</a>
  • +<li>infection, including <a href="/articles/tuberculosis-of-the-central-nervous-system-1">tuberculosis</a>

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