NQ-101a Answer: (A) Inferior olivary nucleus

NQ-101b Answer: (E) The hypertrophic change (thickening) is resulted from an abnormal increase in the number of neurons

Diagnosis: Partial hypertrophy of the inferior olivary nucleus

Pathology of the case: The salient feature here is the loss of the curvy contour of the inferior olivary nuclei with part of it getting broader than the rest. This is hyptertrophy of the inferior nuclei.

 

The inferior olivary nucleus (ION) is located in the medulla. It receives motor input from multiple sources including the red nucleus and the dentate nucleus, amongst others. The efferent projections (“climbing fibers”) extend to the Purkinje cells of the cerebellum. Given its close association with the cerebellum, lesions involving the inferior olivary nucleus result in motor incoordination. Hypertrophy of the of the ION occurs when the afferent projections from the red nucleus or dentate nucleus are interrupted. This results in trans-synaptic degeneration of the olivary neurons which appear as enlarged, vacuolated neurons surrounded by gliotic neuropil. The number of neurons is not increased. In fact, there is a loss of neurons. The increase in size is resulted from gliotic scarring and therefore the term hypertrophy may not be totally correct. It is more like a kind of pseudohyptertrophy.  [Click here to see high magnification in HE stain, immunohistochemistry for neurofilament proteins and GFAP]

 

The triangle of Guillain and Mollaret (also known as myoclonic triangle, dentatorubro-olivary pathway) represents the fibers extending from the red nucleus to the inferior olivary nucleus as well as the fibers between the red nucleus and the contralateral dentate nucleus. Damage to the red nucleus/ION fibers can result in hypertrophy of the ION.