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FIGURE 4. HNSCC metastasis from unknown primary tumor. Patient had enlarging 3-cm left neck mass felt on physical examination. (A) Contrast-enhanced CT depicted space-occupying lesion (red arrows) in left neck. Biopsy of lesion was obtained by fine-needle aspiration, and lesion was proven to be lymph node metastatic squamous cell carcinoma. There was no clear evidence of primary tumor except for subtle asymmetry at left tonsillar fossa (blue arrow) that was of uncertain significance. 18F-FDG PET (B) and fusion PET/CT (C) clearly identified primary tumor at left tonsillar fossa (yellow arrows); finding was confirmed by endoscopic biopsy.
