Insufficiency of positron emission tomography and magnetic resonance spectroscopy in the diagnosis of intravascular lymphoma of the central nervous system.

Intravascular large B-cell lymphoma (IVL) is a rare type of extranodal lymphoma with an aggressive clinical course characterized by the proliferation of lymphoma cells within the lumen of small vessels. Diagnosis is often difficult because of marked variability in clinical presentation and nonspecific laboratory and radiological findings, especially when central nervous system (CNS) symptoms are the only manifestation. Modern metabolic imaging techniques such as positron emission tomography (PET) and (1)H-magnetic resonance spectroscopy (MRS) have been reported to be useful in the diagnosis of conventional primary CNS lymphoma. We report the case of a 69-year-old man who presented with a progressive leukoencephalopathic syndrome. The patient was examined by (18)F-fluorodeoxyglucose and (11)C-methionine PET and MRS, but none of these examinations were able to show the presence of a tumor in the lesions or to clarify the tumor characteristics. Brain biopsy was the only way to obtain a definite diagnosis of IVL. The patient was treated intensively with standard immunochemotherapy but died 6 months after the diagnosis. Here, we discuss the insufficiency of modern metabolic imaging techniques, including PET and MRS, and recommend a rapid decision of brain biopsy in the diagnosis of IVL only involving the CNS.