Sunday 12 February 2012

Hypertrophic Olivary Degeneration

A rare type of secondary degeneration of Inferior Olivary Nucleus (ION), usually caused by primary lesion in Dento Rubro Olivary pathway (Anatomical Triangle of Guillain and Mollaret)

Triangle of Guillain and Mollaret defined by three anatomical structures.
Dentate nucleus (DN) of Cerebellum.
Contra lateral Red Nucleus (RN).
Inferior Olivary Nucleus (ION), ipsilateral to RN.

Imagingwise Hypertrophic Olivary Degeneration seen as unilateral or bilateral enlargement of ventro medial portion of Medulla with T2 hyperintensity which corresponds to ION.

There patterns of HOD in relation to location of primary lesion.
Ipsilateal HOD, when primary lesion is in brain stem – central tegmental tract.
Contralateral HOD, when primary lesion is in DN of cerebellum.
Bilateral HOD, when primary lesion involves both central tegmental tract and superior cerebellar peduncle.

Case : A 60 yo male complaining of mild ataxia.
Gliosis confined to right half of mid brain, Pons and cerebellar peduncle. A Gliotic lesion in the region of dentate nucleus of right cerebellar hemisphere. Ventromedial portions of both half of Medulla show enlargement with T2 hyper intensity implies to Bilateral Hypertrophic Olivary Degeneration explained by involvement of central tegmental tract, cerebellar peduncle and dentate nucleus of cerebellum.
Clinically patient has no palatal myoclonus.

Histologically olivary enlargement is a vacuolar cytoplasmic degeneration.  Hypertrophy is related to local increase in astrocyte proliferation. Associated brain stem lesions are usually a focal Gliosis, may result from ischemia, bleed, demyelination, trauma including surgery.
Clinically characterised rhythmic palatal myoclonus, may affect any age group and gender.
Usually develop after 10 to 11 month after primary lesion.
Virtually all patient with clinically palatal myoclonus will show HOD on imaging but not necessary that all patient of HOD on imaging will show palatal myoclonus clinically.
Bilateral HOD

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