Imaging Features of Hypertrophic Olivary Degeneration

Abstract

Hypertrophic olivary degeneration (HOD) is a unique form of transneuronal degeneration caused by a disruption of the dentato-rubro-olivary pathway, also known as the triangle of Guillain-Mollaret. The triangle of Guillain-Mollaret is involved in fine voluntary motor control and consists of both the inferior olivary nucleus and the red nucleus on one side and the contralateral dentate nucleus. Clinically, patients classically present with symptomatic palatal myoclonus. Typical magnetic resonance imaging findings include T2-hyperintensity and enlargement of the inferior olivary nucleus evolving over time to atrophy with residual T2-hyperintensity. In this article, we provide a case-based illustration of the anatomy of the Guillain-Mollaret-triangle and the typical imaging findings of hypertrophic olivary degeneration.

Palato-pharyngo-laryngeal myoclonus with recurrent retrograde feeding tube migration after cerebellar hemorrhagic stroke: a case report and review of hypertrophic olivary degeneration

“…The efferent fibers of the red nucleus then descend via the central tegmental tract and reach the ipsilateral inferior olivary nucleus. The inferior olivary nucleus completes the triangle by sending decussating efferent fibers via the inferior cerebellar peduncle to the original dentate nucleus within the cerebellum [7,9].…”

“…When a pathologic lesion interrupts this inhibitory modulation, inferior olivary neurons enlarge and develop abnormal soma-somatic gap junctions within weeks to months [11]. It has been established that HOD occurs with lesions involving the dentato-rubral pathway in the superior cerebellar peduncle or the rubro-olivary pathway in the central tegmental tract, but not in nearby areas [9]. This supports the theory that it is the loss of inhibitory input from the dentate nucleus to the ION that causes overactivity in the latter [11].…”

“…As a result, the ION may become an autonomous oscillator due to its intrinsic rhythmic capabilities leading to hyperkinetic movement disorders [11]. Symptoms can present anywhere from 1 month to 8 years after lesion to the Guillain-Mollaret triangle, though most commonly onset is within the first year [9,[12][13][14][15].…”

Idiopathic bilateral hypertrophic olivary degeneration

“…Focal lesions like infarction, haemorrhage, demyelination  and trauma involving this neuronal pathway lead to interruption, and following sequential pathological changes are described (table 1). 1…”

Development of Hypertrophic Olivary Degeneration following Pontine Hemorrhage

“…Hypertrophic olivary degeneration is a rare disorder that typically develops in the weeks to months following a structural brainstem or cerebellar lesion in the Guillain–Mollaret triangle (ipsilateral inferior olivary and red nuclei and contralateral dentate nucleus) . On MRI, this appears as an increased T2/FLAIR signal intensity and enlargement of the inferior olive due to enlarged and vacuolated neurons, increased astrocytes, gliosis, and demyelination.…”