Increased uptake of Tc-99m-HMPAO in necrosis area of brain tumor

Tc-99m-hexamethylpropylene amine oxime (Tc-99m-HMPAO) has been shown to localize in primary brain tumors with wide spectrum of Tc-99m-HMPAO uptake. The cause(s) of the wide spectrum of tumor uptake, however, has not been understood. Two patients with histologically proven glioblastoma with tumor necrosis, who had the central necrosis in MRI imaging, were studied after administration of 20 mCi of Tc-99m-HMPAO. SPECT imaging was performed 20 min and 3hr after administration. The SPECT images showed higher uptake of Tc-99m-HMPAO in tumor necrosis than the contralateral area. To confirm Tc-99m-HMPAO uptake in tumor necrosis, animal study was performed. Ten female Fischer rats were implanted with the 9L gliosarcoma cell line or C6 glioblastoma cell line into right cerebral hemisphere of the rats stereotactically. 15 days after tumor inoculation, two mCi of Tc-99m-HMPAO was injected into the rat via tail vein. Four hours after injection, the rats were sacrificed to remove their brains and the autoradiographic images were compared with the pathologic findings. Two out of 5 cases of the C6 implated group showed tumor necrosis but there were no evidence of hemorrhage. All of the 8 cases without tumor necrosis showed decreased uptake of Tc-99m-HMPAO in autoradiography (average T/N uptake ratio : 0.75, range : 0.40-0.90). On the other hand, the two cases with the tumor necrosis revealed an increased uptake of this agent (T/N uptake ratios: 1.23 and 1.42, respectively). This study indicates that the necrosis area of brain tumors can retain Tc-99m-HMPAO and cause an increased uptake