Endocrine Abstracts

Background: Thyroid incidentaloma are asymptomatic thyroid nodules that are discovered on an imaging study performed to evaluate other structures. Clinically unrecognized thyroid nodules are common and can be found in up to 50–60% of patients at autopsy.¹ Increased use of imaging modalities of better quality in the modern era has resulted in an increased detection of incidental thyroid nodules. The prevalence rate is 67% with ultrasonography (US) imaging, 15% with computed tomography (CT) or magnetic resonance imaging (MRI) of the neck, and 1–2% with fluorodeoxyglucose (FDG) positron emission tomography.² Their clinical importance is primarily related to the need to exclude thyroid cancer. In this study we report on thyroid incidentaloma found on non-FDG functional imaging.

Clinical cases:

1. A 70-year old man was referred for hypercalcemia and nefrolithiasis. He was diagnosed with primary hyperparathyroidism. As ultrasound and scintigraphy could not detect a localization, 18F-fluorocholine PET/CT was performed. It showed 2 spots of uptake, one measuring 16 mm below the right thyroid lobe and another one inside the right thyroid lobe. The latter corresponded to a 9 mm hypoechogenic intrathyroidal nodule on ultrasound. The patient underwent right hemithyroidectomy and parathyroid exploration. Anatomopathological examination revealed a parathyroid adenoma and a papillary thyroid carcinoma, which had been removed completely.

2. A 76-year old man was referred for a thyroid incidentaloma on a 68Ga-DOTATATE PET/CT.The scan was performed for diagnosis of a pancreatic neuroendocrine tumor (NET) and revealed a spot of high somatostatine receptor (SSTR) expression in the left thyroid lobe, in a hypoechogenic 2.5 cm nodule on ultrasound. Fine-needle aspiration cytology (FNAC) of this nodule showed a Bethesda VI result. After recovery from a Whipple procedure, the patiënt underwent a total thyroidectomy. Pathology showed a 24 mm papillary thyroid carcinoma with largely follicular growth pattern, which had been removed completely. Postoperative thyroglobuline was low (1,37 ng/ml). The patient received 30 mCi radioiodine, with no distant uptake at the post-therapy scan.

3. A 65-year old man was diagnosed at our Department of Endocrinology for a papillary thyroid carcinoma (T3r1N0) in 2016. He underwent total thyroidectomy, followed by radioiodine therapy (100 mCi). One year later the stimulated thyroglobuline was below the detection limit and there was no uptake at the iodine-123 scan. In 2018 he was diagnosed with a bilateral cervical lymph node recurrence for which he underwent surgery followed again by 100 mCi radioiodine. There was no uptake at the post-therapy scan. The patient also had a history of prostate adenocarcinoma in 2008. In his urologic follow up a 68Ga-PSMA PET/CT was performed in 2019, and showed 2 spots of Prostate Specific Membrane Antigen (PSMA) accumulation in cervical lymph nodes. Ultrasound, FNAC and eventually surgical reintervention confirmed local recurrence of papillary thyroid carcinoma, which did not take up radioiodine. Adjuvant external radiation therapy was applied.

4. A 42-year old man was referred for a hotspot in the isthmus of the thyroid observed on a 99mTc-diphosponate scintigraphy. This bone scan had been performed for mid-thoracic back pain and was negative for bone metastasis. Ultrasound evaluation showed a normal homogenous thyroid.

Conclusion: We report four cases of thyroid incidentaloma on (no-FDG) functional imaging modalities. Not all but some may be malignant. All patients with a thyroid incidentaloma, independent of the mode of detection, need a dedicated neck US with risk stratification, followed by fine needle aspiration if necessary. Apart from FDG-PET, Choline, Somatostatin receptor (SSTR) and Prostate Specific Membrane Antigen (PSMA) imaging are other molecular nuclear techniques which can potentially identify radioiodine-refractory differentiated thyroid cancer (RAIR-DTC).³

References: 1. Mortensen J. D., Woolner L. B., Bennett W. A. Gross and microscopic findings in clinically normal thyroid glands. The Journal of Clinical Endocrinology & Metabolism. 1955;15(10):1270–1280. doi: 10.1210/jcem-15-10-1270.

2. Russ G, Leboulleux S, Leenhardt L, Hegedues L. Thyroid incidentalomas: epidemiology, risk stratification with ultrasound and workup. Eur Thyroid J. 2014;3:154–163. doi: 10.1159/000365289.

3. Zhuan-Zhuan M, Xin Z, Yan-Song L. Identification of Radioactive Iodine Refractory Differentiated Thyroid Cancer. Chonnam Med J. 2019 Sep;55(3):127–135. doi: 10.4068/cmj.2019.55.3.127. Epub 2019 Sep 24.