Thallium-201 scintigraphy of neuroblastoma: different results for primary tumors and skeletal lesions.

Thallium-201 scintigraphy was performed in 8 children with neuroblastoma, and uptake by the tumors was evaluated in comparison with the results of 123I-MIBG scintigraphy. No primary tumors or metastatic lymph nodes showed 201Tl accumulation, but in 4 cases of bone marrow metastases accompanied by focal cortical invasion, the metastatic lesion was demonstrated more clearly on the early image than on the delayed image. In another case of bone metastases infiltrating cortical bone revealed by 123I-MIBG scintigraphy and biopsy before treatment, 201Tl scintigraphy performed after chemotherapy showed abnormal accumulation in the tibia, but the second 123I-MIBG scintigraphy performed 1 week after the 201Tl scintigraphy showed no abnormal uptake. 201Tl does not appear to have good affinity for neuroblastoma, but it accumulates in metastatic skeletal lesions. A reactive hypermetabolic bone marrow, and/or inflammatory process and periosteal reaction due to the presence of metastatic foci may have induced the 201Tl accumulation. It seems that 201Tl is not useful for the diagnosis. Nevertheless, the discordance between 201Tl uptake in primary tumors and skeletal lesions allows speculation on the mechanism of 201Tl accumulation in skeletons.