Unusual co-occurrence of hypertrophic inferior olivary degeneration with infratentorial cavernomatosis and orbital cavernous hemangioma.

Hypertrophic olivary degeneration (HOD) is a rare condition resulting from a lesion in the Guillain-Mollaret triangle (GMT), causing transsynaptic degeneration and hypertrophy of the inferior olivary nucleus (ION). The GMT is composed of the dentate nucleus, red nucleus, and ION, and is commonly affected by ischemic and hemorrhagic strokes, vascular malformations, neoplasms, or surgical trauma. Cavernomas are a frequent type of cerebral vascular malformation associated with HOD, while orbital cavernous hemangiomas are another rare vascular malformation. The association of these two malformations is scarcely reported, with only one case previously documented. We report the case of a 26-year-old male presenting with right exophthalmos and palatal myoclonus, where brain MRI demonstrated HOD secondary to infratentorial cavernomatosis, along with a right orbital cavernous hemangioma. This case highlights a rare co-occurrence of infratentorial cavernomatosis and orbital cavernous hemangioma, emphasizing the importance of recognizing vascular malformations as potential causes of HOD.