Wednesday, 15 April 2015

Bilateral Hypertrophic Olivary Degeneration MRI

A 50 y o was admitted after acute onset of unconsciousness. On admission MRI brain reveled hypertensive Pontine bleed extending in adjacent mid brain. His clinical condition gradually improved.

On follow up after 6 month pt was alert, dysartric, bilateral dysmetria of the arms without paresis, bilateral horizzontal gaze paresis. No palatal myoclonus.

During this 6mth follow, MRI  shows;
A resolved chronic Pontine bleed with,
New bilateral and symmetric T2 hyper intense foci with mild swelling in the region of inferior olivary nuclei of medulla suggestive of bilateral hypertrophic inferior olivary degeneration. 

Hypertrophic olivary degeneration ( HOD)

Hypertrophic olivary degeneration is a rare finding secondary to focal lesions of the brain stem involving Guillain–Mollaret triangle.

The three corners of the triangle are:
1.             Red nucleus.
2.             Inferior olivary nucleus
3.             Contralateral dentate nucleus.

In CNS the degeneration of an anatomical structure is usually characterized by neuronal loss replaced by proliferation of glial elements.
Unique to the inferior olivary nucleus is transneuronal degeneration resulting in hypertrophy.
Clinical presentation is Palatal myoclonus, a classically described feature.
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.
In short hypertrophic olivary degeneration can be caused by any lesion involving the above mentioned structures, it is typically seen with focal lesions involving the ipsilateral central tegmental tract, the contralateral superior cerebellar peduncle, or the dentate nucleus.
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.

Pathologically, cell body enlargement, vacuolation of the cytoplasm, astrocytic hyperplasia and proliferation, demyelination, and fibrillary gliosis have been described.

Hypertensive bleeding is a relatively common cause of pontine haemorrhages resulting in hypertrophic olivary degeneration.

Imaging wise the inferior olivary nucleus or nuclei 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.
On imaging DDs include infarction, demyelination, Neoplastic, metastases, lymphoma, infection, including tuberculoma.

T2 hyperintense non enhancing lesion that is accompanied by enlargement of the olivary nucleus, particularly if bilateral and symmetric, as our patient, can be explained only by hypertrophic olivary degeneration. Typically T 2  hyperintensity is evident on follow up imaging  the signal abnormality was absent in the on admission MR imaging. In the next few months the patient could complain palatal myoclonus which is not evident now.

Most commonly a lesion involving central tegmental tract causes unilateral olivary degeneration. Our patient is having bilateral hypertrophic degeneration from lesion located in the midbrain and Pons.

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