201Tl-SPECT in low-grade gliomas:: diagnostic accuracy in differential diagnosis between tumour recurrence and radionecrosis

Purpose. The aim of this work was to describe the usefulness of a simple Tl-201 single-photon emission computed tomography (SPECT) technique in the differential diagnosis between tumour recurrence and radionecrosis during the follow-up of patients treated for low-grade gliomas. Methods. The study population comprised 84 patients treated for low-grade gliomas who showed suspicion of tumour recurrence during their follow-up. All patients were examined by neuro-anatomical imaging procedures (CT, MRI) and Tl-201-SPECT. Tl-201-SPECT images were assessed by visual analysis based only on the information on the prescription form and by estimation of the uptake index (ratio of mean counts in the lesion to those in the contralateral mirror area). Examiners were blinded to the results of other tests. Results. Under these conditions, the neuro-anatomical procedures yielded 26.2% inconclusive reports, with a global diagnostic accuracy of 0.61, a sensitivity of 0.63 and a specificity of 0.59. The global diagnostic accuracy for Tl-201-SPECT was 0.83, with a sensitivity of 0.88 and a specificity of 0.76. Diagnostic pitfalls were observed in regions with physiological Tl-201 uptake, i.e. the posterior cranial fossa, diencephalon, lateral ventricles and cavernous and longitudinal venous sinuses. An uptake index cut-off value of 1.25 showed a sensitivity of 0.90 and specificity of 0.80 for detection of tumour activity. Conclusion. Tl-201-SPECT has adequate diagnostic accuracy to be part of routine algorithms in the follow-up of patients with low-grade glioma suspected of tumour recurrence, as an alternative to neuro-anatomical procedures and not solely as a complementary test.