Hemiparkinsonism Secondary to Giant Aneurysm

An 81-year-old woman presented with progressive right levodopa-nonresponsive hemiparkinsonism for 6 months. Brain CT scan and MRI (Figure 1) showed a giant supraclinoid unruptured aneurysm of the left internal carotid artery, leading to severe left basal ganglia displacement and left cerebral peduncle compression. The patient underwent ioflupane SPECT (Figure 2) that showed decreased tracer binding exclusively in the left putamina and left caudate nuclei. The preserved presynaptic dopaminergic function of right basal nuclei ruled out an unmasked latent Parkinson disease.