Hounsfield unit value has null effect on thyroid nodules at 18F-FDG PET/CT scans

ABSTRACT Objectives: Detection rate of thyroid nodules is increasing with the use of new imaging modalities, especially in screening for malignancies. Positron emission tomography/computed tomography (PET/ CT)-positive thyroid nodules should be differentiated for malignancy to avoid unnecessary operations and further follow-up. Most trials evaluate the role of SUVmax, but there is no definitive information about the utility of Hounsfield unit (HU) values for prediction of malignancy. This study aimed to evaluate the HU values beside SUVmax for detecting malignancy risk of PET/CT-positive thyroid nodules. Subjects and methods: Results of 98 cancer patients who had fine needle aspiration biopsy (FNAB) for thyroid nodules detected on PET/CT between January 2011 and December 2015 were assessed. The FNABs and surgical pathological results were recorded. Results: FNABs revealed benign results in 32 patients (32.7%), malignant in 18 (18.4%), non-diagnostic in 20 (20.4%), and indeterminate in 28 (28.5%). Twenty-four patients underwent thyroidectomy. The mean HU values were not significantly different in benign and malignant nodules (p = 0.73). However, the mean SUVmax was significantly higher (p < 0.001) in malignant ones. Area under curve (AUC) was 0.824 for SUVmax; the cut-off value was over 5.55 (p < 0.001), with 80% sensitivity, 84.5% specificity. Conclusions: Our current study demonstrated that HU value does not add any additional valuable information for discriminating between malignant and benign thyroid nodules. We also defined a SUV cut-off value of 5.55 for malignant potential of thyroid nodules detected on PET/CT Arch Endocrinol Metab. 2018;62(4):460-5

Incidental papillary microcarcinoma of the thyroid.

Papillary microcarcinoma (PMC) is a thyroid tumor measuring 10mm or less in maximum diameter and comprise up to 30% of all papillary thyroid cancers. Most of them are detected incidentally and defined as incidental papillary microcarcinoma (IPC<or=10mm). The incidence of such incidental cancers found in surgical specimens of benign thyroid diseases is high. Although most PMC are incidental, all incidental papillary cancers cannot be classified as microcarcinoma, owing to their size that may be larger than 10mm. Not much is known about the biological behavior and clinical course of IPC<or=10mm. There is an ongoing discussion among endocrinologists, endocrine surgeons and nuclear medicine specialists about the optimal therapeutic strategy for the patients with IPC<or=10mm. Some investigators advocate in favor of not performing further treatment in addition to initial thyroid surgery, whereas others suggest an aggressive surgical approach followed by radioiodine ablation therapy. Randomized prospective trials of observation versus standard thyroid cancer care are required to high-lighten this dilemma.