[¹⁸F]FAA-guided re-operative surgery for recurrent differentiated thyroid cancer

A 41-year-old male presented for restaging due to new cervical lesions detected by ultrasound, with elevated thyroglobulin levels (suppressed: 23.2 ng/mL; stimulated: 416.8 ng/mL) ten months after total thyroidectomy for differentiated thyroid cancer (DTC) (T2N1bM0). Contrast-enhanced CT and MRI revealed a cystic lesion with a solid component in right level II (red arrow) and enlarged lymph nodes in levels VI (yellow arrow). [¹⁸F]FDG PET/CT showed uptake only in the thyroid bed (white arrow). 6-Deoxy-6-[¹⁸F]fluoro-L-ascorbic acid ([¹⁸F]FAA) PET/CT revealed uptake in the solid component of the level II nodule (red arrow) and in three lymph nodes at level VI (yellow arrow). Fine-needle aspiration biopsy of the right level II lesion was nondiagnostic, while thyroglobulin (101.2 ng/mL) in the washout fluid indicated metastasis. The patient underwent selective neck dissection guided by [¹⁸F]FAA PET/CT. Histopathology confirmed metastases in levels II, IV, and VI, with [¹⁸F]FAA PET/CT detecting metastases in levels II and VI, while the level IV lymph node was missed by all imaging modalities (arrowhead). One month after surgery, the stimulated thyroglobulin level was 3.6 ng/mL. The patient received radioiodine therapy (100 mCi), with a post-therapeutic scan showing uptake confined to the thyroid remnant. …