Teaching NeuroImages: hemorrhagic cavernoma with secondary development of hypertrophic olivary degeneration.

Hypertrophic olivary degeneration (HOD) is secondary degeneration of the inferior olivary nucleus (ION) due to a primary lesion in the dento-rubro-olivary pathway. This pathway is known as the Guillain and Mollert triangle, containing the dentate nucleus and the contralateral red and inferior olivary nuclei (figure e-1 on the Neurology® Web site at www.neurology.org). The commonest presenting symptom is palatal myoclonus occurring 8-12 months after the primary insult. MRI of the ION initially has normal results (figure 1). Three phases of HOD exist on MRI: hyperintense signal change without hypertrophy, hyperintense signal change with hypertrophy (figure 2), and regression of hypertrophy with persistent hyperintense signal.(1.)