What does a diffuse FDG (Fluorodeoxyglucose)-avid neoplasm indicate?

From the Guidelines

A diffuse FDG-avid neoplasm indicates a highly aggressive and metabolically active cancer with extensive involvement, suggesting a poor prognosis and the need for prompt and aggressive treatment. This finding is typically associated with malignancies that exhibit high glucose metabolism, such as lymphomas, aggressive carcinomas, and metastatic disease 1. The intensity of FDG uptake, measured as SUV or standardized uptake value, often correlates with tumor aggressiveness and can help determine prognosis.

Key Points to Consider

• Diffuse uptake patterns suggest that the cancer involves large areas of tissue or has spread throughout an organ or multiple sites in the body
• Common examples of diffuse FDG-avid neoplasms include lymphomas, certain aggressive carcinomas, and metastatic disease
• The pattern and degree of FDG avidity help oncologists determine appropriate treatment strategies and monitor response to therapy
• Further diagnostic workup, including biopsies, is usually necessary for definitive diagnosis and to guide treatment decisions

Diagnostic and Treatment Implications

• FDG-PET/CT can be useful in staging and surveillance of primary mediastinal lymphoma, but its value is limited in the initial assessment of mediastinal masses 1
• MRI can provide further tissue characterization of mediastinal masses and is superior to CT for detection of invasion of the mass across tissue planes and involvement of neurovascular structures 1
• Treatment strategies may include systemic therapy, such as chemotherapy or immunotherapy, and localized treatment approaches, such as surgery or radiation therapy, depending on the specific type and stage of cancer.

Recent Evidence

• A recent study published in 2021 in the Journal of the American College of Radiology highlights the importance of FDG-PET/CT and MRI in the evaluation of mediastinal masses 1.
• The study suggests that FDG-PET/CT can be useful in distinguishing between benign and malignant lesions, but its value is limited by the frequent FDG-PET/CT avidity of normal and hyperplastic thymus.
• MRI, on the other hand, can provide further tissue characterization and is superior to CT for detection of invasion of the mass across tissue planes and involvement of neurovascular structures.

From the Research

Definition of Diffuse FDG-avid Neoplasm

• A diffuse FDG-avid neoplasm refers to a type of cancer that exhibits increased uptake of Fluorodeoxyglucose (FDG) on positron emission tomography (PET) scans, indicating high metabolic activity 2, 3, 4.
• FDG is a glucose analog that is taken up by cells with high metabolic rates, such as cancer cells, and is phosphorylated by hexokinase to FDG-6-phosphate, which is then trapped in the cell 4.

Clinical Significance of Diffuse FDG-avid Neoplasm

• The presence of a diffuse FDG-avid neoplasm may indicate a malignant tumor, as cancer cells often exhibit increased glucose metabolism compared to normal cells 2, 3, 5.
• However, not all FDG-avid lesions are malignant, as some benign lesions, such as inflammation or infection, can also exhibit increased FDG uptake 5, 6.
• The positive predictive value (PPV) of FDG-PET/CT for malignancy is high, ranging from 98.7% to 100% in patients with a clinical suspicion of active malignant disease 2.

Diagnostic Considerations

• Biopsy remains the gold standard for diagnosing malignancy, even in cases with high FDG uptake on PET scans, as some benign lesions can mimic malignant tumors 2, 3.
• Further diagnostic workup is warranted in cases with unexplained focal FDG uptake, as this finding can be associated with both malignant and benign processes 3, 6.
• Knowledge of the patterns and risk of malignancy of FDG-avid lesions can facilitate the management of oncology patients and improve the interpretation of PET-CT scans by imaging specialists 6.