ABSTRACT NUMBER: ESOC2026A345 WEBER: THE ISOLATED MIDBRAIN SYNDROME

Abstract Background and aims The incidence of solitary midbrain infarction causing Weber Syndrome is uncommon as infarctions in the vertebrobasilar system occur concurrently with infarctions in other locations. Weber is a unique brainstem syndrome characterized by crossed hemiplegia and ipsilateral third nerve palsy. Methods We highlight a case of a 63-year-old female with diabetes, hypertension, prior right corona radiata stroke with left hemiparesis and chronic kidney disease, who presented with new onset left facial droop, right arm weakness and dysarthria. Her NIHSS was 13 with three new points for the aforementioned symptoms. Results Neurological examination revealed left eye ptosis with inability to adduct and a 4 mm pupillary size compared to 3 mm on the right. Motor exam was significant for 4/5 strength in the right upper extremity, 5/5 in the left upper extremity and bilateral lower extremity strengths of 3/5. Blood pressure was 151/70 mmHg. Laboratory was significant for HBA1c of 8.1% and creatinine of 4 mg/dl. CT head, CT angiogram and perfusion were unremarkable. Subsequent MRI of the brain revealed punctate left paramedian pontine infarct. Interrogation of implantable mobile device was negative for atrial fibrillation. Conclusions In summary, our patient presented with oculomotor nerve palsy and contralateral hemiparesis consistent with the diagnosis of Weber syndrome secondary to small vessel disease stroke. It is frequently under-recognized when early CT scan is normal. Bedside localization can outperform early imaging. Recognition should prompt timely MRI to confirm the diagnosis and avoid misattribution to other etiology. Neuroanatomic vigilance remains essential for diagnosing rare brainstem stroke variants. Conflict of interest Marilou Ching: nothing to disclose