A RARE CAUSE OF HYPERTROPHIC OLIVARY DEGENERATION FOLLOWING CAVERNOUS MALFORMATION HEMORRHAGE: A CASE REPORT

Objectives
Hypertrophic olivary degeneration (HOD) is an uncommon form of trans-synaptic degeneration involving the
dentato-rubro-olivary pathway, also known as the Guillain–Mollaret triangle. Unlike most neurodegenerative conditions,
HODis characterized by neuronal hypertrophy of the inferior olivary nucleus rather than atrophy. While it is most frequently
associated with ischemic or hemorrhagic stroke, surgical trauma, or demyelinating disease, its occurrence following
hemorrhage from a cavernous malformation (CM) is rare and underreported. This case report describes a patient who
developed HOD after hemorrhage from a mesencephalic CM, with emphasis on neuroimaging features and diagnostic
considerations.
Materials and Methods
This case report is based on a combined retrospective and prospective analysis of a single patient’s clinical course and
neuroimaging findings. Previous brain MRI studies were reviewed in conjunction with recent follow-up imaging and ongoing
clinical evaluation. Data were obtained from the patient’s medical records and magnetic resonance imaging, including
diffusion tensor imaging (DTI), to document the progression and radiological characteristics of hypertrophic olivary
degeneration.
Results
A 55-year-old female presented in December 2023 with acute-onset neurological symptoms, including left-sided facial and
limb hypoesthesia, central facial paresis, and gait instability. Neurological examination revealed sensory deficits in the V2
and V3 branches of the trigeminal nerve on the left, as well as decreased sensation in the left extremities. Consciousness
was preserved. Brain MRI performed during this initial episode revealed a hemorrhage in the dorsal aspect of the left
mesencephalon and led to the first-time diagnosis of an underlying cavernous malformation with an associated venous
angioma. The patient was managed conservatively and experienced gradual clinical improvement. A follow-up MRI
performed six months after the hemorrhage demonstrated hypertrophy of the left inferior olivary nucleus with T2 and FLAIR
hyperintensity, consistent with developing HOD. At that time, the patient reported no specific neurological complaints. At a
subsequent follow-up 1.5 years after the initial hemorrhagic event, repeat MRI showed progression of olivary hypertrophy,
now measuring approximately 1.6 cm CC and 0.5 cm AP. The signal intensity on T2-weighted and FLAIR sequences
remained elevated, without evidence of atrophy. These findings were consistent with stage 4 of HOD, according to the
five-stage radiological classification. Clinically, a palatal tremor was noted for the first time during this evaluation. DTI
tractography showed partial disruption and volume reduction of the left central tegmental tract, confirming trans-synaptic
degeneration within the Guillain–Mollaret triangle.
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Conclusions
This case highlights hypertrophic olivary degeneration as a rare complication of mesencephalic cavernoma hemorrhage.
Recognition of characteristic imaging features—persistent T2/FLAIR hyperintensity and olivary hypertrophy without
atrophy—is essential. DTI tractography supports the trans-synaptic mechanism. Accurate identification of HOD is critical to
prevent misdiagnosis, avoid unnecessary investigations, and ensure correct interpretation of delayed-onset neurological
symptoms.