Hemiballismus as the Initial Manifestation of Brain Metastasis: Diagnostic Discordance Between PET-CT and MRI in a Patient With Multiple Neoplasms.

Brain metastases are a frequent cause of intracranial tumors in adults and usually present with neurological deficits such as headache, seizures, or motor impairment. Hyperkinetic movement disorders, including hemiballismus, are exceptionally uncommon in this setting. Hemiballismus results from dysfunction within the subthalamic or neighboring basal ganglia regions and can occur secondary to various pathological processes. We report the case of an 80-year-old man with a history of ischemic stroke, myocardial infarction, multiple primary malignancies with hepatic metastases, and chronic kidney disease who presented with acute-onset left-sided hemiballismus predominantly involving the upper limb, accompanied by hematuria. A recent fluorodeoxyglucose positron emission tomography (FDG PET)-computed tomography (CT) revealed a new hypermetabolic focus in the right basal ganglia, along with progressive hepatic lesions. Magnetic resonance imaging (MRI) and angiography demonstrated diffuse cerebral atrophy, chronic microangiopathy, and old lacunar infarcts, but no new focal abnormalities. The discordance between PET-CT and MRI findings suggested a metabolically active lesion not yet detectable on structural imaging. During hospitalization, the patient developed transient delirium managed conservatively and was discharged clinically stable, without recurrence of involuntary movements. This case highlights the value of integrating functional and structural neuroimaging in the assessment of atypical neurological presentations in patients with multiple malignancies. PET-CT may reveal early metabolic alterations preceding MRI-detectable changes, emphasizing the importance of comprehensive clinicoradiologic correlation for timely diagnosis and individualized management.