Clinical relevance of 111In-octreotide scans in CNS tumors

Sixty-six patients with a clinical and neuroradiological diagnosis of CNS tumors were evaluated by 111In-octreotide scintigraphy. Planar images were acquired at 2-4 and 24 hours after the injection of 111-185 MBq of 111In-octreotide (Octreoscan, Byk-Gulden). In the positive scans the tumor/non-tumor ratio was evaluated using a standard ROI method, and an uptake index (U.I.) of the lesion was determined. In vitro binding assays were performed on frozen sections from surgical specimens from 17 patients. All 32 meningiomas demonstrated a positive 111In-octreotide scan with a high U.I. Only 13 of 21 gliomas showed a positive scan, but the U.I. was significantly lower (p < 0.001 by "t"-test); one lymphoma showed a faint tracer uptake. All the other histotypes evaluated yielded negative scans. In all cases the receptorial pattern shown by the immunohistochemical staining technique was concordant with the scintigraphic results. 111In-octreotide scintigraphy allowed a differential diagnosis of meningioma versus other CNS tumors in 6 patients (4 neurinomas, 1 brain metastasis of melanoma, 1 lymphoma). In conclusion, 111In-octreotide scintigraphy is a promising tool to evaluate the SS receptorial pattern of CNS tumors and to increase the diagnostic specificity of conventional imaging providing useful information in selected cases for the therapeutic strategy.