Object: The 201Tl uptake index was evaluated for its usefulness in formulating a diagnosis of hemangioblastoma. Thallium-201-single-photon emission computerized tomography (SPECT) studies were performed in nine patients harboring hemangioblastomas in the posterior fossa and in five patients (six lesions) with gliomas in the posterior fossa.
Methods: The 201Tl uptake index was defined as the ratio of mean counts of isotope per pixel in the tumor to mean counts of isotope per pixel in the homologous region of the healthy brain. The 201Tl uptake indices of the early image (TlE) and that of the delayed image (TlD) were calculated. The isotope retention index (RI) was calculated as (TlE - TlD)/TlE. The TlE was 2.7 +/- 0.7 in hemangioblastomas and 2.9 +/- 1.7 in gliomas (mean +/- standard deviation). The TlD was 1.5 +/- 0.4 in hemangioblastomas and 2.4 +/- 1.6 in gliomas. There were no significant differences between hemangioblastomas and gliomas when TlEs and TlDs were compared. The isotope RI was 0.43 +/- 0.07 in hemangioblastomas and 0.15 +/- 0.1 in gliomas, showing a significantly higher RI in hemangioblastomas compared with gliomas (p < 0.01).
Conclusions: Thallium-201 washout is significantly faster in hemangioblastomas. Hemangioblastoma is biologically benign, but contains a rich capillary network that forms a hypervascular tumor bed. Variations in its appearance on magnetic resonance images may cause difficulties in the differential diagnosis of hemangioblastoma. Thallium-201 SPECT studies can be used to distinguish hemangioblastomas from gliomas in the posterior fossa.