¹⁸F-FDG PET of Thyroid Nodules with Inconclusive Cytologic Results

TO THE EDITOR: We read with great interest the paper by Lioe-Fee de Geus-Oei et al. (1). There is no doubt that the main objective of preoperative evaluation of patients with thyroid nodules is to avoid unnecessary surgery. This will pose no problem for patients with a positive result for cancer on fine-needle aspiration biopsy (2). However, fine-needle aspiration biopsy will fail to give either a clearly positive (malignant) or clearly negative (benign) result in an important percentage of patients; the result will instead be inconclusive. For these patients, diagnostic/therapeutic surgery may be indicated as the next step (3,4), but for most the final diagnosis will be that of a benign lesion. Therefore, a large number of unnecessary surgical interventions are still being performed around the world, adding to the morbidity and mortality of thyroidectomy.

Lioe-Fee de Geus-Oei et al. (1) reported a negative predictive value of 100% for ¹⁸F-FDG PET in 44 patients (only 6 with cancer). Recently, our group addressed this problem using ^99mTc-methoxyisobutylisonitrile (MIBI) thyroid scanning (5), which is a less expensive and more readily available diagnostic test than ¹⁸F-FDG PET.

Our results on 130 consecutive patients who had hypofunctioning thyroid nodules and underwent thyroidectomy (50 patients with proven thyroid cancer) showed that lack of ^99mTc-MIBI uptake in the nodules always ruled out thyroid cancer (negative predictive value of 100%).

Lioe-Fee de Geus-Oei et al. (1) concluded that ¹⁸F-FDG PET reduces the number of futile hemithyroidectomies and outweighs the costs of unnecessary thyroid surgery, but ^99mTc-MIBI thyroid scans are considerably less expensive than ¹⁸F-FDG PET studies. We believe that ^99mTc-MIBI scans should be the first study to be performed in the diagnostic algorithm of patients with thyroid nodules and inconclusive cytologic results to avoid unnecessary thyroid surgeries.

However, because of the higher resolution of PET over conventional γ-cameras, research with ¹⁸F-FDG PET should be undertaken on patients with small-size incidentalomas to determine if the diagnostic test can help in the diagnostic algorithm of those patients.