What is the recommended imaging protocol for a patient with suspected grade II astrocytoma?

From the Guidelines

The best PET scan for a full body check of a patient with suspected grade II astrocytoma seen in MRI is PET imaging using amino acid tracers like FET or MET, as it provides additional diagnostic value compared to anatomical MRI and is superior to FDG-PET for patients with brain tumors, including astrocytomas 1.

Key Considerations

• MRI with and without contrast is the primary diagnostic tool for suspected grade II astrocytoma, including T1-weighted images before and after gadolinium contrast administration, T2-weighted images, FLAIR sequences, diffusion-weighted imaging (DWI), and perfusion imaging.
• Grade II astrocytomas typically appear as hyperintense lesions on T2-weighted and FLAIR sequences, with minimal or no enhancement on post-contrast T1-weighted images.
• Advanced techniques such as MR spectroscopy may be added to evaluate metabolite concentrations, particularly looking for elevated choline and reduced N-acetylaspartate levels, which suggest tumor presence.
• Diffusion tensor imaging (DTI) can help assess white matter tract involvement for surgical planning.

PET Imaging

• PET imaging using amino acid tracers like FET or MET can be considered as a complementary study to better delineate tumor boundaries and assess metabolic activity.
• The use of PET imaging in gliomas can provide additional insight beyond MRI into the biology and treatment response of gliomas, including noninvasive grading, differential diagnosis, delineation of tumor extent, surgical and radiotherapy treatment planning, posttreatment surveillance, and prognostication 1.
• The sensitivity of MRI for the detection of brain metastases depends on the technique employed, and PET imaging can be used to improve the accuracy of staging by detecting more extracranial metastases than CT, especially in patients with cancers of unknown primary (CUP) 1.

From the Research

Recommended Imaging Protocol for Suspected Grade II Astrocytoma

• The choice of PET scan for a full body check of a patient with suspected grade II astrocytoma depends on various factors, including the need to evaluate the histological grade and extent of the tumor.
• According to a study published in 1998 2, carbon-11 methionine (MET) PET was found to be highly useful for detecting astrocytomas, differentiating between benign and malignant astrocytomas, and evaluating the extent of astrocytomas.
• However, the same study found that MET was not sufficiently useful for evaluating the histological grade of astrocytomas, and that thallium-201 (201Tl) was more useful for this purpose.
• A meta-analysis published in 2019 3 found that both MET PET and 18F-fluoroethyltyrosine (FET) PET had higher sensitivities than fluorodeoxyglucose (FDG) PET for differentiating low- from high-grade gliomas.
• Another study published in 2015 4 highlighted the potential of FDG-PET/CT imaging for primary brain tumors, including its use in initial staging and risk stratification, therapy planning, response evaluation, and recurrence detection.
• A study published in 1999 5 used PET with 11C methionine (MET) and 18F fluorodeoxyglucose (FDG) to evaluate the effect of radiotherapy on operated low-grade astrocytomas, and found that malignant progression occurred at a similar rate in both patient groups, regardless of whether radiotherapy was applied or not.

PET Tracers for Glioma Grading

• The performance of different PET tracers, including FDG, MET, and FET, has been evaluated in various studies for glioma grading.
• A meta-analysis published in 2019 3 found that both MET PET and FET PET had higher sensitivities than FDG PET for differentiating low- from high-grade gliomas.
• However, the same meta-analysis found that FDG PET had a higher specificity than both MET PET and FET PET.
• The choice of PET tracer ultimately depends on the specific clinical context and the goals of the imaging study.

Clinical Applications of PET/CT and PET/MR

• PET/CT and PET/MR imaging have been used in various clinical applications, including the diagnosis and monitoring of adult-onset Still's disease 6.
• These imaging modalities have been found to be useful in assessing disease activity and monitoring response to therapy.
• However, the use of PET/CT and PET/MR in the diagnosis and management of suspected grade II astrocytoma is not well established, and further research is needed to determine their clinical utility in this context.