18F-FDG PET-CT is performed for staging of a 56-year-old man with newly diagnosed right lung adenocarcinoma. The SUVmax of the primary tumour is 8.2, and there is a solitary FDG-avid lesion in the right adrenal gland (SUVmax 6.5). A second primary adrenal adenoma is excluded. The staging implication is:
- A Stage IIIA — ipsilateral adrenal is a regional node
- B Stage IVA — single extrathoracic metastasis ✓
- C Stage IVB — multiple extrathoracic metastases
- D Stage IVA is only applicable for contralateral lung nodule
Correct answer: B. Stage IVA — single extrathoracic metastasis
Explanation
Per the 8th edition TNM staging for lung cancer, a single extrathoracic metastasis (M1b) places the patient in Stage IVA. Multiple extrathoracic metastases (M1c) classify as Stage IVB. The adrenal gland is an extrathoracic site. The right adrenal is not a regional lymph node for lung cancer. PET-CT is superior to CT alone for detecting adrenal metastases vs. adenomas (adrenal adenoma is typically cold on FDG PET).
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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