Presentation
Resection of anaplastic oligodendroglioma ten years prior. Possible tumor recurrence
Patient Data
Resection cavity in the left frontal lobe with adjacent FLAIR hyperintensity through the adjacent white matter. Patchy gadolinium enhancement in the left frontal lobe and temporal lobe posterior to the resection cavity on post-contrast imaging. Gyral thickening and FLAIR hyperintensity in the regions of enhancement.
On the 40-minute static acquisition, there is diffusely abnormal increased FET accumulation adjacent to the surgical cavity in the left frontal lobe inferiorly (corresponding to the regions of patchy enhancement on MR. SUVmax is 4.6. Abnormal uptake is also present in the region of the left caudate and also in the left thalamus. There is a focus slightly separated from the main area of uptake superiorly in the left frontal lobe.
Tumor: background ratio (max: mean): 3.7
Analysis of 40-minute dynamic imaging, reveals a type 3 time-activity curve that favors a grade 3/4 glioma.
Case Discussion
18F-FET (fluoroethyl tyrosine) PET scans are used in the imaging workup of brain tumors, with the tracer demonstrating an affinity for glial tumors. FET PET/CT scans are usually interpreted in conjunction with MRI brain scans and can be paired with F18-FDG PET scans in some cases to evaluate for the presence of high-grade glioma.
Dynamic FET PET imaging, where images are acquired between 0-40 minutes post-administration of tracer has shown value in helping delineate radiation necrosis and tumor recurrence. The EANM Guidelines 1 for interpretation of these studies relies on three types of time-activity curves:
Type 1 curve: favors inflammatory or low grade glioma
Type 2 curve: intermediate
Type 3 curve: favors grade 3/4 glioma
In this case, a type 3 curve (sharp upstroke with washout of tracer) is demonstrated which favors a higher grade glioma. The higher tumor to background ratio is also consistent with recurrent disease.
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