18 F-DOPA PET Silence in High-grade Glioma Subtype F : A Distinct Metabolic Phenotype

Area of Science:

• Neuro-oncology
• Molecular Pathology
• Diagnostic Imaging

Background:

• The 2021 WHO classification categorizes adult diffuse gliomas into astrocytoma, oligodendroglioma, and glioblastoma.
• A newly identified epigenetic subtype, high-grade glioma IDH-wildtype, subtype F (HGG-F), exhibits gliomatosis-like infiltration, low proliferation, and prolonged survival.
• HGG-F presents a unique profile, including a grade 4 methylation status despite its indolent clinical behavior.

Purpose of the Study:

• To report the first evaluation of the HGG-F subtype using 18F-DOPA Positron Emission Tomography (PET).
• To characterize the imaging features of HGG-F, particularly its amino acid uptake patterns.
• To establish diagnostic considerations for HGG-F based on combined MRI and PET findings.

Main Methods:

• Case report of a patient diagnosed with HGG-F.
• 18F-DOPA PET imaging was performed to assess amino acid uptake.
• Magnetic Resonance Imaging (MRI), specifically FLAIR sequences, was used to evaluate lesion extent.

Main Results:

• Despite extensive FLAIR-hyperintense lesions on MRI, 18F-DOPA PET showed entirely normal tracer distribution.
• This finding represents "amino acid PET silence," a stark contrast to the typical intense uptake seen in other high-grade gliomas.
• The gliomatosis-like appearance on MRI combined with absent PET uptake is characteristic of this emerging subtype.

Conclusions:

• The HGG-F subtype presents a unique diagnostic challenge due to its indolent behavior and distinct imaging characteristics.
• "Amino acid PET silence" on 18F-DOPA PET, in conjunction with gliomatosis-like MRI findings, should raise suspicion for HGG-F.
• Recognition of these features is crucial for accurate diagnosis and appropriate patient management of this rare glioma subtype.