DIFFERENT TL-201 SINGLE-PHOTON EMISSION TOMOGRAPHIC PATTERNS IN BENIGN AND AGGRESSIVE MENINGIOMAS

To evaluate the possibility of preoperatively obtaining an index of ag gressiveness for intracranial meningiomas, we prospectively studied 22 patients with computed tomographic or magnetic resonance imaging evid ence of meningeal tumour using single-photon emission tomography (SPET ) of the brain and thallium-201 (Tl-201), On a brain-dedicated SPET sc anner, a rapid acquisition protocol with early, short scans was starte d simultaneously with the intravenous administration of 111 MBq Tl-201 , covering the initial intratumoral distribution of the tracer, Twenty minutes post injection, a delayed SPET scan was also obtained, On the reconstructed and attenuation-corrected images we calculated the Tl-2 01 concentration in tumour and normal contralateral brain tissue, and compared intratumoral tracer concentration In the initial and the fina l part of the rapid acquisition protocol. Benign and malignant meningi omas were classified as such based on histological examination. In mal ignant lesions, the ratio of the Tl-201 concentration at 2-4 min post injection to that at 14-16 min was found to be significantly higher th an in non-aggressive neoplasms (mean+/-1 SD: 1.14+/-0.31 and 0.56+/-0. 13, respectively: P <0.01), Conversely, in the delayed scan, most lesi ons showed high tracer concentration, and the two groups could not be distinguished. In addition, three recurrent meningiomas displayed the same Imaging behaviour as the malignant group, i.e. had similar Tl-201 concentration values at 2-4 and at 14-16 min. Our findings suggest th at the comparative assessment of intratumoral Tl-201 concentration at 2-4 and at 14-16 min post injection could provide a fast, simple metho d to differentiate preoperatively intracranial meningiomas with differ ent biological behaviour.