SOMATOSTATIN RECEPTOR IMAGING IN CNS TUMORS USING IN-111-OCTREOTIDE

This study evaluates the in vivo visualization of somatostatin (SS) re ceptors in central nervous system (CNS) tumours using In-111-octreotid e imaging and discusses the clinical implications. Ninety-five patient s with histologically confirmed diagnosis of CNS tumours were imaged 2 -4 and 24 h after the intravenous injection of 111-185 MBq of In-111-o ctreotide. An uptake index was computed using tumour/ non-tumour ratio s evaluated using a standard region-of-interest method. Semi-quantitat ive immunohistochemical studies of SS binding sites were performed on frozen tumour sections. All meningiomas, most pituitary adenomas and m any glial tumours showed a positive scan, whereas all neurinomas, cran iopharingiomas and ependymomas had negative receptor scans. Radio-octr eotide uptake varied among the SS receptor positive CNS rumours: very intense in meningioma, intermediate in pituitary adenoma and of a low grade in glioma. The results of immunohistochemical studies confirmed the scintigraphic findings in all cases. We believe In-111-octreotide is a suitable radiopharmaceutical for characterizing CNS tumours in vi vo as SS receptor positive or negative. This new neuronuclear imaging technique may be useful for differential diagnosis in selected cases, for post-surgical follow-up and in the assessment of differentiation i n glial tumours.