18F-FDG PET-CT is performed for staging of non-small cell lung cancer (NSCLC). Which of the following physiological uptake patterns can mimic mediastinal nodal metastasis and lead to a false-positive reading?

• A Physiological brown adipose tissue (BAT) uptake in the neck and paravertebral regions
• B Oesophageal peristaltic uptake
• C Right ventricular myocardial uptake
• D Thymic rebound following chemotherapy ✓

Explanation

Thymic rebound (thymic hyperplasia) following chemotherapy causes diffuse FDG uptake in the anterior mediastinum and can be mistaken for anterior mediastinal lymph nodal disease on PET-CT. It occurs more commonly in younger patients 3–6 months after chemotherapy cessation. The key to differentiation is the smooth, triangular/arrowhead shape of the thymus on CT corresponding to the FDG uptake. Brown adipose tissue (BAT) uptake is paravertebral/neck/supraclavicular — not mediastinal nodal distribution. Oesophageal uptake is linear along the oesophagus.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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