Evaluation of malignancy in ring enhancing brain lesions on CT by thallium-201 SPECT

Objective-To investigate patients with cystic enhancing lesions on CT and to determine whether thallium-201 (Tl-201) SPECT adds to further preoperative information in differential diagnosis between gliomas and abscesses. Methods-Twenty one patients with cystic ring enhancing CT findings were studied and uptake indices were compared with CT enhancement volumes, histopathology, and survival times. Results-Fourteen high grade gliomas, three low grade gliomas, and four abscesses were found. Uptake was higher in the highly malignant glioma group (median thallium index (TI)=2.1), than in the low grade glioma group (median TI=1.4) or among the abscesses (median TI=1.6). Overlapping indices were found between high and low malignant cystic gliomas as well as between either one of the glioma groups and the infectious lesions, and there were no significant differences between groups. There was a level at the value 2, where TI greater than or equal to 2 correlated with tumour diagnosis. One low grade tumour had an extremely high index and a very high enhancement volume. Indices correlated significantly with CT enhancement volumes (P=0.005). There was no significant correlation between Tl indices and patient survival times among the high grade gliomas. One patient with a highly malignant tumour but low Tl uptake <<2, had a survival > five years. Conclusions-It is concluded that high Tl-201 uptake in enhancing cystic lesions is an indicator of highly malignant glioma. However, the differentiation between the high malignant gliomas and abscesses or low malignant gliomas by (TL)-T-201 SPECT is only partial with an overlap between these groups.