Preoperative grading of gangliogliomas using FDG PET and Tl-201 SPECT: comments from a nuclear medicine view.

Gangliogliomas are rare tumors and the two papers by Patel et al and Kincaid et al along with my and other accompanying commentaries in this issue of the American Journal of Neuroradiology cover most of the facts a radiologist would need to know. I was invited to comment on the potential usefulness of scintigraphy (FDG PET or Tl-SPECT) in the evaluation of these tumors. The clinical behavior of this tumor does not appear to be directly related to the degree of its malignancy, but rather to its resectability (1). It appears, however, that if close follow up is decided in favor of resection, the degree of malignancy, if known, may be a crucial factor in determining the frequency of follow up radiologic studies. In addition, I believe that the degree of malignancy may also influence the decision for faster, if not immediate, resection. Therefore, if this information were provided by scintigraphy, at least for those tumors located in the brain, we could certainly accept its place in the original evaluation of the patient. The paper by Kincaid et al addresses this issue. The Preoperative Grading of Gangliogliomas Using FDG PET and T1-201 SPECT by Kincaid et al (page 801) is an interesting retrospective review of this unusual brain tumor. The authors reviewed 11 patients; eight were examined by FDG-PET, two by Thallium SPECT, and one by both studies. Of these 11 patients, nine had low grade and two had high grade gangliogliomas. The two malignant tumors were visible on Thallium scans; however, none of the patients with high grade tumors were examined by PET scans. On the other hand, all the PET studies done in patients with low grade tumors were true negatives, but only one patient with a low grade tumor was examined by a Thallium scan. Given these numbers, I cannot agree with the authors that FDG-PET or Thallium is 100% correct. These are different tests that cannot be combined to give the misleading interpretation of 100%.