Usefulness of dual isotope 123I-IMP and 201Tl SPECT for the diagnosis of primary central nervous system lymphoma and glioblastoma.

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Preoperative differential diagnosis between primary central nervous system lymphoma (PCNSL) and glioblastoma (GBM) is important because these tumors require different surgical strategies. This study investigated the usefulness of dual isotope, iodine-123-labeled N-isopropyl-p-iodo-amphetamine (123I-IMP) and thallium-201 chloride single-photon emission computed tomography (201Tl SPECT) for the differential diagnosis. Twenty-five PCNSL patients and 27 GBM patients who underwent dual isotope imaging, 123I-IMP and 201Tl SPECT, are included. Tumor-to-normal (T/N) ratio was calculated from the ratio of maximum tracer counts in the lesion to the mean counts in the contralateral cerebral cortex. The mean and minimum apparent diffusion coefficient values (ADCmean and ADCmin, respectively) on magnetic resonance imaging were also analyzed. Delayed phase 123I-IMP SPECT was the most useful imaging examination for the differentiation between PCNSL and GBM compared with early phase 123I-IMP SPECT, early and delayed phase 201Tl SPECT, ADCmean, and ADCmin. However, the median T/N ratios of PCNSL and GBM were 1.32 and 0.83, respectively, in the delayed phase 123I-IMP SPECT. On the other hand, the median T/N ratios of PCNSL and GBM were 3.10 and 2.34, respectively, in the delayed phase 201Tl SPECT, with excellent tumor detection. Delayed phase 123I-IMP SPECT could differentiate between PCNSL and GBM with high accuracy, but T/N ratio was low and tumor detection was poor. 201Tl SPECT was useful for estimation of the malignancy and localization of the tumors with high T/N ratio. Dual isotope 123I-IMP and 201Tl SPECT was useful for the preoperative diagnosis of PCNSL and GBM.