Intravascular large B-cell lymphoma (IVLBCL) is a rare and aggressive variant of diffuse large B-cell lymphoma with frequent involvement of the central nervous system. Its atypical presentation often delays the diagnosis and due to its aggressive behaviour, the diagnosis is made post-mortem in half of the cases. We report a case of a 67-year-old male patient presenting with speech difficulties and balance disturbances in whom a magnetic resonance imaging (MRI) scan showed multiple lesions of the white matter, denoted as embolic infarctions. He was treated for a suspected endocarditis with antibiotics, but deteriorated neurologically with persistent fever. A consecutive FDG -PET /CT revealed an increased uptake in the adrenals, of which a biopsy showed IVLB CL. The patient was successfully treated with systemic R-CHOP with intrathecal methotrexate and achieved complete remission after six cycles of chemotherapy. The potential role of FDG-PET/CT is illustrated by this case leading to an exceptional diagnosis of IVLBCL.