SOMATOSTATIN RECEPTOR SCINTIGRAPHY IN CENTRAL-NERVOUS-SYSTEM TUMORS -ROLE OF BLOOD-BRAIN-BARRIER PERMEABILITY

Somatostatin receptors are expressed in meningiomas and low-grade glio mas, raising the hope that scintigraphy with In-111-DTPA-D-Phe1-octreo tide might be helpful in the in vivo localization, differential diagno sis and postoperative/postradiotherapy brain tumor follow-up. Methods: Indium-111-DTPA-D-Phe1-octreotide scintigraphy and brain scintigraphy using Tc-99m-DTPA as a nonspecific tracer for blood-brain barrier int egrity were simultaneously performed in 60 patients with CNS tumors us ing dual-isotope acquisition mode SPECT. For 23 patients, the scintigr aphic findings were also compared with in vitro somatostatin receptor autoradiography of surgical biopsy specimens. Results: In meningiomas (located outside the blood-brain barrier), the somatostatin receptor s can showed all tumors and scintigraphic signal intensity correlating w ith in vitro SSR density positive in all meningiomas. Less contrast wa s seen on Tc-99m-DTPA scans. In all tumors inside the blood-brain barr ier, the In-111-DTPA-D-Phe1-octreotide scan visualized the tumors with a disrupted blood-brain barrier, as seen by Tc-99m-DTPA scintigraphy. Discrepancies, however, were observed between somatostatin receptor s cintigraphy and in vitro receptor autoradiography. Conclusion: Combine d somatostatin receptor and Tc-99m-DTPA scintigraphy may be helpful fo r noninvasive differentiation between meningiomas and other CNS tumors . False-negative scans were observed as a result of shielding by the i ntact blood-brain barrier. Interpretation of negative and positive som atostatin receptor scans in CNS tumors must therefore be done with cau tion.