Objective: The aim of this study is to clarify the period of extraosseous accumulation of 99mTc-hydroxymethylenediphosphonate (HMDP) to radiation nephropathy mimicking recurrent or remnant neuroblastoma in the pararenal region. Methods: We reviewed five neuroblastoma and one ganglioneuroblastoma patients (2 boys and 4 girls aged 1-9 years) who underwent 99mTc-HMDP bone scintigraphies periodically before and after radiation therapy. Results: Increased renal uptake coincident with the radiation port appeared in 5 of 6 patients from O to 3 months (mean 1.7 months), and persisted up to 7 months after the completion of radiotherapy. Renal uptake of 99mTc-HMDP was gradually decreased, and eventually became accumulation defects in 5 of 6 patients from 6 to 17 months (mean 8.9 months) after radiotherapy. Conclusion: When extraosseous accumulation is found after radiation therapy in neuroblastoma patients, radiation nephropathy would be a candidate in the differential diagnosis besides recurrent or remnant tumor.
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