Contribution of brain 99mTc-sestamibi SPECT for the differential diagnosisof tumoral recurrence and radionecrosis of subtentorial glial tumors in adults

CT scan and MR imaging are plot always reliable in the differential diagnos is between radionecrosis and recurrence of brain tumor. We describe the results of a prospective study using Tc-99m Sestamibi. 22 p atients were included The histology of the tumor was astrocytoma (grade 2-4 ) oligodendroglioma (grade 2-3) or mixted (grade 2-3). SPECT was performed rising a Tomomatic 564, 1 h after the injection IV of 370 MBq of Tc-99m Ses tamibi. Ten slices parallel to the orbitomeatal plane were obtained Two ind ex were calculated i) CI: ratio of the mean counts in the lesion to the mea n counts in the controlateral choroid plexus and ii) MI : ratio of the mean counts in the lesion to the controlateral mirror area The results were com pared to stereotactic biopsies or to clinical course at 6 months. Twelve pa tients oat of 22 showed an increased uptake of the tracer and 11/12 present ed with a recurrence. In 10 patients without fixation, 4 were false negativ e. The sensitivity SOP the detection of tumor recurrence was 73 % and speci ficity was 85 %. The positive predictive value was 91 % and the negative pr edictive value was 60 %. The use of a cut-off value superior to 2 for MI an d superior to 0.5 for CI appears to be a good criterion for helping the dia gnosis of relapse according to the analysis of Receiver Operating Character istic curves (ROC). A positive SPECT was conclusive for the diagnosis of re currence but a negative SPECT did not allow to assess the absence of recurr ence. Limits of methods have to be stressed and searched for a better under standing of false negatives.