Role of FDG-PET in Characterizing Adrenal Mass Lesions

Summary of the Article

1. Title of the article:

Performance of 18F-FDG PET/CT in the Characterization of Adrenal Masses in Noncancer Patients: A Prospective Study

2. First two Authors followed by et al:

Carole Guerin, François Pattou, et al.

3. One-line summary of the article:

This prospective multicenter study evaluates the diagnostic performance of 18F-FDG PET/CT in differentiating benign and malignant adrenal masses in noncancer patients.

4. Six key points from the article:

1. Study Design: A prospective multicenter study including 87 patients with adrenal masses ≥40 mm or indeterminate nature based on CT findings.
2. Diagnostic Findings: Malignant adrenal masses were larger, had higher unenhanced densities, lower relative washout, and higher 18F-FDG uptake compared to benign lesions.
3. Optimal Diagnostic Threshold: A Tumor SUVmax to Liver SUVmax (Tmx:Lmx) ratio >1.5 had a sensitivity of 86.7% and specificity of 86.1% for malignancy.
4. Clinical Implications: 18F-FDG PET/CT demonstrated high negative predictive value (96.9%) and can complement adrenal washout CT in characterization of adrenal masses.
5. Limitations: Small sample size, multiple PET/CT camera models across centers, and lack of long-term follow-up for benign cases.
6. Conclusion: 18F-FDG PET/CT should be recommended for evaluating large and/or indeterminate adrenal masses, improving malignancy detection.

5. Practical take-home message:

18F-FDG PET/CT serves as a valuable adjunct to adrenal washout CT in the workup of large or indeterminate adrenal masses, helping to refine surgical decision-making and reduce unnecessary resections.

6. Citation in Vancouver format:

Guerin C, Pattou F, Brunaud L, Lifante JC, Mirallié E, Haissaguerre M, et al. Performance of 18F-FDG PET/CT in the characterization of adrenal masses in noncancer patients: A prospective study. J Clin Endocrinol Metab. 2017 Jul;102(7):2465–2472. doi: 10.1210/jc.2017-00254.

Additional Notes on the Topic

Q. What is the role of 18F-FDG PET/CT in adrenal lesion evaluation?

18F-FDG PET/CT is highly valuable in distinguishing benign from malignant adrenal lesions by assessing metabolic activity. Malignant tumors typically exhibit higher glucose metabolism, which is reflected in increased FDG uptake.

Q. What is the diagnostic performance of 18F-FDG PET/CT?

• Sensitivity: 93% to 100%
• Specificity: 80% to 94%
• Overall accuracy: Up to 96%

These high values indicate strong reliability in characterizing adrenal masses, particularly in patients with known or suspected malignancies.

Q. How is 18F-FDG PET interpreted for adrenal lesions?

The scan is typically evaluated by comparing FDG uptake in the adrenal mass to that of the liver:

• Benign lesions: FDG uptake ≤ liver uptake
• Malignant lesions: FDG uptake > liver uptake

A tumor SUVmax to liver SUVmax ratio >1.5 has been shown to have high sensitivity (86.7%) and specificity (86.1%) for detecting malignancy.

Q. What are the advantages and limitations of 18F-FDG PET/CT?

Advantages

1. High negative predictive value, making it useful for ruling out malignancy.
2. Whole-body evaluation, helpful in detecting primary tumors or metastases.
3. Complements CT and MRI, especially for indeterminate adrenal masses.

Limitations

1. False positives: Some benign lesions (pheochromocytomas, certain adenomas) can show increased FDG uptake.
2. False negatives: Some malignant neuroendocrine tumors may have only mild FDG uptake.

Q. What are the clinical applications of 18F-FDG PET/CT for adrenal lesions?

1. Cancer patients: Detects adrenal metastases in patients with known malignancies.
2. Non-cancer patients: Useful in evaluating adrenal masses even in those without malignancies.
3. Indeterminate adrenal lesions: Helps characterize masses that cannot be definitively diagnosed by CT or MRI.
4. Surgical decision-making: Differentiating lesions needing surgery from those requiring surveillance.

Q. What is the take from the research being from the KEM Mumbai ?

• The current expert opinion from KEM Mumbai is that there is often an overlap of SUVmax values of benign and malignant adrenal lesions. Hence, the interpretation of FDG-PET must not be done in isolation and must be done looking at other characteristics of the lesion.
• Additionally, pheochromocytomas may also show an uptake on FDG-PET making the interpretation difficult

Q. How do pheochromocytomas appear on 18F-FDG PET?

Some Pheochromocytomas demonstrate high avidity for 18F-FDG

Q. What is the intensity of FDG uptake in pheochromocytomas?

• Pheochromocytomas show intense FDG uptake, with SUVmax values ranging from 2.3 to 29.3 (mean 9.7 ± 8.4).

Q. Why do pheochromocytomas have increased FDG uptake?

The increased glucose metabolism in pheochromocytoma cells is due to:

1. Upregulation of hexokinases (HK-2 and HK-3)
2. Activation of aerobic glycolysis (Warburg effect)
3. Increased expression of glucose transporters

Q. How does FDG PET compare to other imaging modalities?

• FDG PET is superior to 123I-MIBG SPECT in detecting pheochromocytoma, particularly in metastatic disease.
• 18F-FDOPA PET may be better than FDG PET for detecting well-differentiated pheochromocytomas.

Q. Do genetic mutations influence FDG uptake in pheochromocytomas?

• SDHx-related pheochromocytomas (especially SDHB mutations) show higher FDG uptake due to:
  • Compromised oxidative phosphorylation
  • Pseudohypoxic response
• SDHB-positive tumors tend to have greater FDG avidity than SDHB-negative tumors.

Conclusion

18F-FDG PET/CT is an effective and useful tool in evaluating adrenal lesions. While it should be interpreted alongside clinical data and other imaging techniques, its high sensitivity and specificity make it valuable in addition in distinguishing between benign and malignant adrenal masses.