SPECT Thallium Imaging in Meningiomas: Early Functional Indications in Neovascularity and Tumor Recurrence

Introduction: Skull base meningiomas pose complex postoperative management issues. Increased T2 signal has been shown to correlate with tumor recurrence potential and neovascularity. SPECT-T1 imaging provides exquisite characterization of meningiomas and when used in conjunction with conventional MR imaging could provide clinical utility.

Methods: Ten consecutive cases of skull base meningiomas were selected from our database. SPECT thallium-201 imaging was performed in all patients. A 5 mCi (185MBq) dose of thallium-201 was administered and delayed sequences obtained of 30 minutes using a low-energy parallel-hole collimator. MRI T2 signal images were then obtained and compared to SPECT reconstructed images with filtered back projection. The “thallium index” was defined as the ratio of counts per pixel value in the lesion to the counts per pixel value in the control. This index was statistically analyzed with tumor volume, patient age, contrast enhancement, and T2 signal change. Long-term follow-up results were recorded.

Results: Quantitative thallium indices performed in all cases correlated most significantly with T2 signal changes (mean ± 1 SD:1.14 ± 0.31, p < 0.01). There was no statistically significant correlation with patient's age, tumor volume, or contrast enhancement. This was maintained in long-term follow-up after a mean of 1 year.

Conclusions: SPECT thallium imaging has shown consistent high specificity for detecting meningiomas. Quantitative thallium index has the statistically highest correlation with MRI T2 signal. SPECT imaging may provide a means with which to quantify the amount of tumor neovascularity and thereby recurrence. This may have further clinical utility in applications with newer targeted therapies.