I-123-IMP SPET in the diagnosis of primary central nervous system lymphoma

We reviewed N-isopropyl-p-[I-123]iodoamphetamine (I-123-IMP) single-photon emission tomography (SPET) images of brain tumours and assessed the usefuln ess of I-123-IMP SPET for the diagnosis of primary central nervous system ( CNS) lymphoma. We analysed 52 tumours that showed enhancement on magnetic r esonance imaging: 11 malignant lymphomas, 3 anaplastic astrocytomas, 17 gli oblastomas, 12 meningiomas, 4 metastatic brain tumours and 5 other brain tu mours. I-123-IMP uptake in the tumours on early (15-min) and delayed (4-h) scans was visually classified as high, moderate or low as compared with the contralateral brain cortex. Early and delayed I-123-IMP uptake ratios comp aring tumours with contralateral brain cortex (T/N ratio) were also calcula ted. In malignant lymphomas, the visual uptake of I-123-IMp was moderate to high on the delayed scans. The delayed T/N ratios were significantly highe r than the early ratios (P<0.05) and all lymphomas, with the exception of o ne small one, had delayed ratios greater than 0.9. In non-lymphomatous tumo urs, the visual uptake of I-123-IMP was low on the delayed scans. The delay ed T/N ratios were significantly lower than the early ratios (P<0.01) and a ll non-lymphomatous tumours had delayed ratios of less than 0.8. The T/N ra tios of lymphomas were significantly higher than those of nonlymphomatous t umours on both early and delayed scans (P<0.0001). These results suggest th at I-123-IMP SPET may be a useful tool in the differential diagnosis of pri mary CNS lymphoma.