Diagnostic value of Tl-201-single-photon emission computerized tomography studies in cases of posterior fossa hemangioblastomas

Object. The Tl-201 uptake index was evaluated for its usefulness in formula ting a diagnosis of hemangioblastoma. Thallium-201-single-photon emission c omputerized tomography (SPECT) studies were performed in nine patients harb oring hemangioblastomas in the posterior fossa and in five patients (six le sions) with gliomas in the posterior fossa. Methods. The Tl-201 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 Tl-201 uptake indices of the ea rly image (Tl-E) and that of the delayed image (Tl-D) were calculated. The isotope retention index (RI) was calculated as (Tl-E - Tl-D)/Tl-E The Tl-E was 2.7 +/- 0.7 in hemangioblastomas and 2.9 +/- 1.7 in gliomas (mean stand ard deviation). The Tl-D was 1.5 +/- 0.4 in hemangioblastomas and 2.4 +/- 1 .6 in gliomas. There were no significant differences between hemangioblasto mas and gliomas when Tl(E)s and Tl(D)s were compared. The isotope RI was 0. 43 +/- 0.07 in hemangioblastomas and 0.15 +/- 0.1 in gliomas, showing a sig nificantly higher RI in hemangioblastomas compared with gliomas (p < 0.01). Conclusions, Thallium-201 washout is significantly faster in hemangioblasto mas. 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 di agnosis of hemangioblastoma. Thallium-201 SPECT studies can be used to dist inguish hemangioblastomas from gliomas in the posterior fossa.