Another Rare Cause of Hypertrophic Olivary Degeneration Following Cavernous Malformation Hemorrhage: A Case Report

Introduction: Hypertrophic olivary degeneration (HOD) is a rare form of trans-synaptic
degeneration involving the Guillain–Mollaret triangle, characterized by enlargement of
the inferior olivary nucleus—unlike the atrophy typical of most neurodegenerative pro-
cesses. It is usually associated with stroke, surgical injury, or demyelination, but rarely
follows hemorrhage from a cavernous malformation (CM). This report presents a case
of HOD secondary to a mesencephalic CM hemorrhage, with emphasis on imaging find-
ings and diagnostic considerations. Case Description: A 55-year-old woman presented
with acute-onset, right-sided facial, torso, and limb hypoesthesia, along with gait insta-
bility. Neurological examination revealed sensory impairment in the right maxillary (V2)
and mandibular (V3) trigeminal territories, as well as diminished pain and temperature
sensation throughout the right hemibody. MRI revealed a hemorrhage in the posterior
mesencephalon near the left red nucleus, leading to the diagnosis of a CM with an asso-
ciated venous angioma. She was managed conservatively and improved clinically. Six
months later, MRI showed hypertrophy and T2/FLAIR hyperintensity of the left infe-
rior olive, consistent with developing HOD. At 1.5 years follow-up, olivary enlargement
had progressed—now consistent with stage 2 HOD—and a bilateral palatal tremor was
observed, more pronounced on the right side. DTI revealed asymmetric volume loss in
the left brainstem fiber pathways at the level of the medulla oblongata, confirming trans-
synaptic degeneration. Conclusions: This case highlights HOD as a rare but important
complication of mesencephalic CM hemorrhage. Recognition of its characteristic imaging
features—olivary hypertrophy with persistent T2/FLAIR hyperintensity—is essential for
accurate diagnosis. DTI supports the trans-synaptic mechanism, helping distinguish HOD
from other pathologies and preventing unnecessary investigations.