In previous studies of supratentorial gliomas with positron emission tomography (PET) and computed tomography (CT), high uptakes of L-methyl-11C-methionine (11C-L-methionine) were found even in astrocytomas without blood-brain barrier defects as judged by CT or 68Ga-EDTA PET. In a number of patients examined after radiation therapy, there were no consistent changes in the high uptake values. In the present investigation PET and CT were compared with regard to their abilities to visualize and delineate recurrent tumors and treatment-induced brain defects and to differentiate between them. The study was undertaken on four patients who were long-term survivors after treatment for high-grade gliomas. For PET, 11C-L-methionine and 68Ga-EDTA were used. In two patients recurrent/residual tumors appeared considerably larger with 11C-L-methionine PET than with CT or 68Ga-EDTA PET. In one patient, no signs of recurrence were seen with any of these three methods, and in a fourth patient, whose condition was clinically stable, the findings at PET with 11C-L-methionine were non-specific. In areas corresponding to the surgical parenchymal defects, the 11C-L-methionine uptake and, except in one case, the local blood volume was markedly reduced. PET with 11C-L-methionine thus has a potential for distinguishing between postoperative brain lesions and tumor recurrence with a higher accuracy than CT.

The regional kinetics of intravenously injected L-methyl-11C-methionine (11C-L-methionine) in the brain was investigated by positron emission tomography (PET) in 14 patients with gliomas. In both tumor and unaffected brain the tracer uptake reached a nearly constant level in 5 min or less. The ratio between the uptake of 11C-L-methionine by high-grade tumors and the uptake by unaffected brain was 1.9-4.8. In two cases of low-grade astrocytoma the ratio was 0.8-1.0. High uptakes of 11C-L-methionine occurred in gliomas even in the absence of blood-brain barrier defects as observed by other methods. This indicates that besides active transport of amino acid, a larger extracellular space in tumor as compared with unaffected brain tissue may also contribute to the increased uptake of 11C-L-methionine--derived radioactivity. In some patients delineation of the tumors was improved by use of PET with 11C-L-methionine as compared with computed tomography, angiography, and, in some instances, PET with 68Ga-EDTA. PET with 11C-L-methionine permits better evaluation of the tumor extent and may affect preoperative grading.

A new method was developed whereby close comparisons can be made between components of a computed tomography (CT) image and neuropathological findings. This was achieved by a combination of intravital (terminal) CT, postmortem CT, and whole brain sectioning of formalin-fixed tissue. The method was applied in seven cases of malignant supratentorial astrocytic gliomas (Kernohan Grades III and IV) and in one case of thalamic ependymoma. The glioblastoma-like parts of the astrocytic gliomas were usually correctly delineated by postcontrast CT, although there were exceptions to this rule. Tumor components consisting of diffusely growing malignant astrocytoma were difficult or impossible to delineate by CT. Necrotic areas within the tumors were accurately outlined by postcontrast CT. Peritumoral edema was correctly delineated by CT, but growth of diffuse astrocytoma or the presence of astrocytic gliosis within this edematous area seems difficult or impossible to evaluate by current CT techniques.