F18-FDG PET/CT imaging for pre-operative detection of nodal disease in pediatric differentiated thyroid cancer

Objectives Identification of thyroid cancer metastases to lateral cervical lymph nodes (LcLNs) can be useful for preoperative evaluation to optimize the surgical procedure. The aim of this study was to evaluate the value of pre-operative F18-Fluorodeoxyglucose Positron Emission Tomography (F18-FDG PET/CT) scan to diagnose differentiated thyroid cancer (DTC) and detect LCLNs metastases.

Methods Thirteen PET/CT scans performed preoperatively in 13 consecutive pediatric patients (10 females, 3 males; mean age: 13.4 years) with thyroid nodules were reviewed retrospectively. Abnormal increased activity in thyroid nodule is considered positive for malignancy. Focal increased uptake corresponding to LcLNS is called positive for metastatic disease. The diagnosis of thyroid nodule was confirmed by surgical pathology in 11 patients and by fine needle aspiration biopsy in two patients.

Results Seven out of 13 patients were ultimately diagnosed with thyroid carcinoma. The sensitivity and specificity of FDG-PET/CT for malignant thyroid nodule were 85% and 67% respectively. In 4 cases thyroid metastases were found in the LcLNs (proved by surgical pathology). F18-FDG-PET scan correctly detected LcLNs in two patients, was borderline in one and falsely negative in one subject. Interestingly ultrasound didn’t detect involved lymph nodes in one of the subjects with true positive FDG-PET results.

Conclusions FDG-PET/CT scan may identify metastatic lymph node involvement in the lateral compartment of the neck and could be considered as a complementary imaging modality to ultrasound in selected cases. It may also have a role in increasing the suspicion of malignancy in thyroid nodules. Future prospective study with a larger number of subjects will be helpful to clarify the exact role of pre-operative FDG-PET/CT in pediatric thyroid cancer