Usefulness of Positron Emission Tomography With Fludeoxyglucose F 18 and With Carbon 11–Tagged Methionine in the Diagnosis of Hippocampal Lesions

Abstract

A 78-year-old man presented in a confused state with short-term and autobiographical memory impairment and visuospatial disorientation. The neurological examination revealed right temporal superior quadrantanopia. Magnetic resonance imaging (MRI) performed 48 hours after symptom onset (Figure 1) showed hyperintensity and diffuse swelling of both hippocampi on T2-weighted fluid-attenuated inversion recovery sequences, restricted free-water diffusion on diffusion-weighted images, and small hemorrhages on susceptibility-weighted images. These findings suggested a vascular ischemic process and, less probably, paraneoplastic syndrome, infectious encephalitis, or space-occupying lesions. Cerebrospinal fluid analysis showed normal biochemical and cytological measures. Images from positron emission tomography (PET) with fludeoxyglucose F 18 (FDG) and with carbon 11–tagged methionine (Met) were coregistered to the original MRI using a 3-dimensional advanced image fusion tool (Syngo 3D, eSoft; Siemens Medical Solutions) that is based on multimodal volume registration by maximization of mutual information.¹ The FDG-PET image showed hypometabolism, whereas the Met-PET image exhibited low to moderate uptake in the corresponding MRI hyperintense areas, suggesting the presence of neuronal damage with mild inflammatory activity (Figure 2). The acute clinical presentation allowed us to establish a stroke of cardioembolic origin as the most likely cause, supported by the presence of paroxysmal atrial fibrillation. The patient's condition remains stable with anticoagulant treatment.