Central nervous system lymphoma characterization by diffusion-weighted imaging and MR spectroscopy

PURPOSE: The characterization and differentiation of central nervous system (CNS) lymphoma has important diagnostic, therapeutic, and prognostic significance. The purpose of this study is to characterize the diffusion-weighted imaging (DWI) and MR spectroscopic (MRS) findings in CNS lymphoma. MATERIALS AND METHODS: Twenty consecutive patients (male [n = 12], female [n = 8]) with histopathologically proven CNS lymphoma were retrospectively evaluated during this study from July 2005 to April 2007. Patients included immunocompromised (n = 9) and immunocompetent (n = 11) individuals. MR Imaging (pretreatment n = 13), pre- and post-treatment (n = 7) included DWI (n = 20) (b = 1000s/mm2) and ADC (apparent diffusion coefficient) maps of all patients. MRS was performed (n = 10) with PRESS (point-resolved spectroscopy) sequence (multivoxel n = 8, single voxel n = 2) with a TE of 144 msec. All patients were histopathologically confirmed to have lymphoma by biopsy. RESULTS: Areas of restricted diffusion were observed in 90 % (n = 18/20) on pretreatment scans. The diffusion restriction was variable on post-treatment scans. Median metabolite ratios in 10 patients were Cho/Cr- 2.12, NAA/Cho -.49, and NAA/Cr - 1.64. Presence of lactate or lipid was noted in 90 % (n = 9/10). Sites of lesion location were subcortical white matter (n = 6), basal ganglia (n = 4), corpus callosum (n = 3), extra-axial space including cavernous sinus (n = 5), cerebellum (n = 1), and lateral ventricle (n = 1). CONCLUSION: Restricted diffusion is a consistent imaging finding in CNS lymphoma in immunocompetent patients. Spectroscopy is helpful in initial imaging diagnosis and post-treatment surveillance. These lesions are usually paraventricular in location. MR imaging appearances differ among immunocompetent and immunosuppressed individuals in most cases.