Bilateral Hypertrophic Olivary Degeneration Following Brainstem Insult: A Retrospective Review and Examination of Causative Pathology

Abstract

Hypertrophic olivary degeneration is a rare condition caused by a lesion in the Guillain-Mollaret triangle which leads to trans-synaptic degeneration resulting in the degenerative hypertrophy of the inferior olivary nucleus. This condition presents clinically with palatal tremor but can also produce ocular myoclonus or cerebellar signs. While any lesion that occurs within the Guillian-Mollaret triangle and results in the deafferentation of the inferior olive can lead to hypertrophic olivary degeneration, the most common etiologies include ischemic and hemorrhagic stroke, vascular malformation, neoplasm, and iatrogenic injury related to surgery. We report a series of 7 patients who presented with this condition bilaterally on MRI imaging, including 1 case which represents the first report of toxoplasmosis leading to the development of bilateral hypertrophic olivary degeneration and only the third reported case, unilateral or bilateral, related to an infectious etiology.

Keywords: Guillain-Mollaret Triangle; Neuroanatomy; hypertrophic olivary degeneration; inferior olivary nucleus; palatal tremor.

Figure 1.

(a) A 57-year-old male who initially presented with restricted diffusion of territories consistent with a stroke involving the basilar artery and the artery of Percheron and (b) 1-month follow-up MRI demonstrated bilateral T2 hyperintensity of the ION.

Figure 2.

(a) Initial gradient echo sequence of a patient who presented with pontine cavernoma rupture demonstrating and (b) a 6-month follow-up MRI (FLAIR sequence) demonstrating bilateral T2 hyperintensity in the inferior olives.

Figure 3.

Initial (a) and 2 months follow-up MRI of a 52-year-old male with HIV and crack cocaine use who presented with sub-acute strokes and leukomalacia, demonstrating bilateral FLAIR hyperintensities and fullness of the bilateral ventral medulla (b).

Figure 4.

(a) A 26-year-old male who presented following remote trauma was found to have multiple lesions consistent with a history of high-grade diffuse axonal injury, including lesions best visualized on susceptibility-weighted sequences located in the right dentate nucleus and (b) increased T2 signal in the bilateral inferior olives.

Figure 5.

(a) A 44-year-old male presented with central pontine hemorrhage, extending into the bilateral middle cerebellar peduncles and (b) bilateral FLAIR hyperintensity of the ventral medulla in the same patient on 6-week follow-up MRI.

Figure 6.

(a) contrast-enhanced MRI of a 54-year-old, HIV positive female who presented with headache, demonstrating a contrast-enhancing lesion that appears to involve the posterior pons and both superior cerebellar peduncles, (b) T2 FLAIR sequence demonstrating significant edema associated with multiple contrast-enhancing lesions in a patient with CNS toxoplasmosis, and (c) follow-up MRI was obtained 6 weeks later that demonstrates bilateral fullness with associated T2 hyperintensity at the level of inferior olives.

Figure 7.

(a) A 28-year-old male underwent resection of medulloblastoma with initial post-operative MRI revealing trace blood products on susceptibility-weighted sequences and (b) 6-month follow-up MRI showed bilaterally increased T2 signal as well as increased fullness at the level of the ventral medulla, consistent with bilateral HOD.

Figure 8.

Triangle of Guillain-Mollaret.