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Hypertrophic olivary degeneration-MRI

 Case Report: 50 year old hypertensive with prior history of stroke, presents with loss of fine voluntary movements. MRI shows an ill defined, T2 low signal intensity foci in the lower pons suggesting hemosiderin and ferritin deposits with relatively well defined T2 hyperintensity and enlargement of the left anterior medulla in the inferior olivary nucleus region with no restricted diffusion, suggesting possible hypertrophic olivary degeneration (HOD) secondary to pontine haemorrhage.

Case submitted by Dr MGK Murthy, Mr Sentil & Mr Venkat

Teaching points :
- Is a form of trans-synaptic degeneration.  End result of the damage of the neuronal connections between dentate nucleus , red nucleus  &  inferior olivary nucleus (dentate-rubral-olivary pathway).
- Unique type of degeneration in view of enlargement of the effected inferior olivary
  neurons. Dentate nucleus is connected to contralateral red nucleus via ipsilateral inferior olivary nucleus and controls fine voluntary movement (called Gullain and Mollaret triangle).
- Red nucleus of one side is connected to the ipsilateral inferior olivary nucleus via
  different tract called central segmental tract. HOD can occur due to any focal lesion including ischaemia, demyelination & neoplasms.
- Typically seen within 4 to 6 months of the primary brain stem insult. Olivary hypertrophy usually resolves in 10 to 16 months, though T2 hyperintensity may persist for years, and the clinical symptoms rarely improve.
- If the primary lesion is in central tegmental tract, olivary hypertrophy is ipsilateral. If the primary lesion is in dentate nucleus / superior cerebellar peduncle, olivary
   hypertrophy is contralateral.  If the lesion involves both central tegmental tract and superior cerebellar peduncle, the olivary degeneration is bilateral.

- Pathologically is unusual vacuolar degeneration of cytoplasm leading to
  enlargement and increased number of astrocytes. Palatal myoclonus / dentatorubral tremor / ocular myoclonus are unusual clinical syndromes. Presence of olivary lesion associated with contralateral dentate nucleus / superior cerebellar peduncle / ipsilateral red nucleus / pontine tegmentum makes any other diagnosis highly unlikely     
Hypertrophic olivary degeneration-MRI Reviewed by Sumer Sethi on Monday, October 28, 2013 Rating: 5

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