[Importance of cerebral tomoscintigraphy using technetium-labeled sestamibi in the differential diagnosis of current tumor vs. radiation necrosis in subtentorial glial tumors in the adult].

CT scan and MR imaging are not always reliable in the differential diagnosis between radionecrosis and recurrence of brain tumor. We describe the results of a prospective study using 99mTc Sestamibi. 22 patients were included. The histology of the tumor was astrocytoma (grade 2-4) oligodendroglioma (grade 2-3) or mixed (grade 2-3). SPECT was performed using a Tomomatic 564, 1 h after the injection i.v. of 370 MBq of 99mTc Sestamibi. Ten slices parallel to the orbitomeatal plane were obtained. Two index were calculated i) CI: ratio of the mean counts in the lesion to the mean counts in the contralateral choroid plexus and ii) MI: ratio of the mean counts in the lesion to the contralateral mirror area. The results were compared to stereotactic biopsies or to clinical course at 6 months. Twelve patients out of 22 showed an increased uptake of the tracer and 11/12 presented with a recurrence. In 10 patients without fixation, 4 were false negative. The sensitivity for the detection of tumor recurrence was 73% and specificity was 85%. The positive predictive value was 91% and the negative predictive value was 60%. The use of a cut-off value superior to 2 for MI and superior to 0.5 for CI appears to be a good criterion for helping the diagnosis of relapse according to the analysis of Receiver Operating Characteristic curves (ROC). A positive SPECT was conclusive for the diagnosis of recurrence but a negative SPECT did not allow to assess the absence of recurrence. Limits of methods have to be stressed and searched for a better understanding of false negatives.