Fig. 1.

FDG PET/CT in a 52-year-old man who presented with a pathologically enlarged left cervical lymph node. Excision biopsy of the lymph node and subsequent histopathological examination indicated metastatic squamous cell carcinoma of unknown primary. Microdirect laryngoscopy and bronchoscopy were performed with (blind) biopsy and tonsillectomy; subsequent histopathological examination only showed reactive changes in the tonsils, pyriform sinus, and left tongue base, without any indication for the presence of primary tumor. FDG PET in the coronal (a) and axial plane (b) shows intense FDG uptake in the left supraglottic region (arrows), likely representing the primary tumor. Corresponding CT and fused FDG PET/CT images in the coronal (b, c, respectively) and axial plane (e, f, respectively) localize the lesion at the base of the tongue (arrows). Histopathological examination of a directed biopsy of the lesion revealed in situ squamous cell carcinoma of the tongue base (moderately to poorly differentiated)