Enhanced staging of differentiated thyroid carcinoma: integrating [F]FDG digital PET/CT with neck ultrasound.

Purpose: Accurate initial staging of differentiated thyroid carcinoma (DTC) is paramount to avoid disease persistence or relapses. Neck ultrasound (US) is the gold-standard examination for lymph node staging; however, it might miss the central compartment ones. [F]FDG PET/CT has been used to characterise unclear or suspicious thyroid nodules and can also identify nodal disease. This study tested the diagnostic efficacy of a combined approach, including digital [F]FDG PET/CT of the cervical region and neck US in DTC staging.

Methods: We retrospectively evaluated consecutive patients treated at our centre with high-risk thyroid who had had a neck US and a neck digital [F]FDG PET/CT before surgery and at least one year of follow-up. Diagnostic parameters, including sensitivity (Se) and accuracy (Acc), were compared across US alone, [F]FDG PET/CT alone, and the combined approach using a patient-based analysis (PBA); Se was also tested employing a lesion analysis (LBA). Clinical and SUV parameters were compared with the histology and the one-year outcome via a logistic regression model.

Results: Eighty-two patients (61 females) were included. At the PBA, the combined approach was superior to US alone regarding Se (44% vs 19%, p < 0.05) and Acc (80% vs 72%, p < 0.05) in the central compartment nodes. At the LBA, the combined approach was superior to either method overall (43%, 37%, and 36% for combined, [F]FDG, and US, respectively, p < 0.01) and to US in the central nodes (25% vs 14%, p < 0.01). SUVratio was an independent predictor of histologically aggressive DTC variants (p = 0.009), central compartment metastases (p = 0.04), and incomplete response at follow-up (p = 0.004).

Conclusions: The combined cervical [F]FDG PET/CT / US approach improves the initial staging and harbours valuable prognostic information for DTC patients.