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Hypertrophic Olivary Degeneration

Summary

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  • Rare neurological condition characterised by enlargement of the inferior olivary nucleus
  • Results from disruption of the dentato-rubro-olivary pathway (Triangle of Guillain-Mollaret)
  • Presents with palatal tremor, dentatorubral tremor, and ocular myoclonus1

Pathophysiology

  • Caused by lesions in the dentato-rubro-olivary pathway
    • Pathway components: dentate nucleus, red nucleus, inferior olivary nucleus
  • Deafferentation of the inferior olivary nucleus leads to:
    • Neuronal hypertrophy
    • Vacuolation of neurons
    • Astrocytic proliferation
  • Typically unilateral, but can be bilateral if both pathways are affected

Demographics

  • Rare condition, exact prevalence unknown
  • No significant gender predilection
  • Can occur at any age, but more common in adults
  • Associated with various underlying conditions:
    • Stroke
    • Trauma
    • Tumours
    • Demyelinating diseases

Diagnosis

  • Clinical presentation:
    • Palatal tremor (most common symptom)
    • Dentatorubral tremor
    • Ocular myoclonus
  • Symptoms typically appear 1-6 months after the initial insult
  • Diagnosis based on clinical findings and imaging

Imaging

  • MRI is the modality of choice
  • T2-weighted and FLAIR sequences:
    • Hyperintense signal in the inferior olivary nucleus
    • Enlargement of the inferior olivary nucleus
  • T1-weighted sequences:
    • Normal or mildly hypointense signal
  • Diffusion-weighted imaging:
    • No restricted diffusion
  • Time course of imaging findings :
    • 0-6 months: Increased signal without hypertrophy
    • 6-18 months: Increased signal with hypertrophy

    • 18 months: Persistent increased signal with resolution of hypertrophy

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  • Right hemipontine cavernoma resected 1 year prior.
  • The right medullary olive became progressively hyperintense and swollen.

Treatment

  • No specific treatment. Recognising the T2-hyperintense, hypertrophied olive downstream of a Guillain-Mollaret triangle lesion avoids mistaking it for a tumour

Differential diagnosis

Differential Diagnosis Differentiating Feature
Infarction Restricted diffusion on DWI in acute phase; wedge-shaped; follows vascular territory; no T2 hypertrophy of the inferior olive
Demyelinating lesion Ovoid lesions; periventricular Dawson's fingers; no isolated inferior olive enlargement
Low-grade glioma Expansile mass with ill-defined margins; no correspondence to known Guillain-Mollaret triangle
Metastasis Multiple lesions; surrounding vasogenic oedema; ring or nodular enhancement
Infectious lesion Rim-enhancing abscess with restricted DWI; associated parenchymal oedema
Wallerian degeneration Linear T2 signal along specific white matter tracts; no isolated olivary hypertrophy
Neurodegenerative disease Bilateral and symmetric atrophy rather than hypertrophy
Vasculitis Multiple vascular territories affected
Radiation necrosis History of radiation therapy, contrast enhancement

  1. Wang et al. Hypertrophic olivary degeneration: A comprehensive review focusing on etiology. 2019. Brain research - Open in new tab. ↩