Noninvasive differentiation of meningiomas from other brain tumours using combined (111)indium-octreotide/(99m)technetium-DTPA brain scintigraphy

We have studied prospectively 47 patients with CNS rumours including 16 meningiomas and 33 other tumours using combined In-111-octreotide and Tc-99m-DTPA brain scintigraphy. In-111-octreotide scintigraphy was used to image somatostatin receptors (SSR) and Tc-99m-DTPA scintigraphy was used to assess the integrity of the blood-brain barrier (BBB). A total of 32 tumours (65%) were detected. All SSR positive rumours also had positive Tc-99m-DTPA scans and all SSR negative tumours were negative on Tc-99m-DTPA scans. Among the tumours located outside the BBB, all meningiomas and two out of six schwannomas were positive on combined SSR/Tc-99m-DTPA scintigraphy. Among the rumours located inside the BBB, seven out of nine gliomas grade I-III were negatitve, whereas all glioblastomas were positive. Other positive tumours included one malignant non-Hodgkin lymphoma and two cerebral metastases. SSR scintigraphy alone was non-specific in the diagnosis of meningiomas, as 16 non-meningiomatous tumours also had positive SSR scans probably due to a breakdown of the BBB (excluding the malignant lymphoma). Measuring the tumour-to-background ratio on SSR scans improved specificity, but sensitivity was decreased below 70% because some meningiomas were only slightly positive. Only the ratio of SSR scintigraphy to conventional Tc-99m-DTPA brain scintigraphy (SSR-ro-BS index) allowed a reliable differentiation of meningiomas from other CNS tumours, most notably from schwannomas (sensitivity: 94%; specificity: 100%). Our results support the usefulness of combined SSR and conventional brain scintigraphy in the noninvasive pre-operative diagnosis of meningiomas.