Thyroid Incidentalomas: Practice Considerations for Radiologists in the Age of Incidental Findings

Due to increased use of computed tomography (CT), prevalence of thyroid and adrenal incidentalomas is rising. Yet, previous studies on the outcomes of diagnostic work-up of incidentalomas are subjected to inclusion bias. Therefore, we aimed to investigate prevalence and outcomes of diagnostic work-up of thyroid and adrenal incidentalomas detected on chest CT in a less selected population of COVID-19 suspected patients.

A retrospective, observational cohort study.

We included all COVID-19 suspected patients who underwent chest CT between March 2020 and March 2021. Radiology reports and medical records were reviewed for the presence and subsequent diagnostic work-up of thyroid and adrenal incidentalomas.

A total of 1,992 consecutive COVID-19 patients were included (59.4% male, median age 71 years [IQR: 71–80]). Thyroid and adrenal incidentalomas were identified in 95 (4.8%) and 133 (6.7%) patients, respectively. Higher prevalence was observed with increasing age, among female patients and in patients with malignancy. Forty-four incidentalomas were further analyzed, but no malignancies were found. Only three lesions were hormonally active (1 thyrotoxicosis and 2 mild autonomous cortisol secretion). Diagnostic work-up did not lead to any change in clinical management in 97.7% of the analyzed patients.

Prevalence rates of thyroid and adrenal incidentalomas on chest CT in a less selected COVID-19 cohort were 4.8% and 6.7%, respectively. Yet, as all incidentalomas turned out to be benign and only three lesions were (mildly) hormonally active, this raises the question whether intensive diagnostic work-up of incidentalomas is necessary in all patients.

Thyroid cancer is the most common endocrine malignancy. Thyroid cancer typically manifests as a thyroid nodule, although the majority of thyroid nodules are benign. Several strategies exist to diagnose cancer in a thyroid nodule, including ultrasound evaluation, fine needle aspiration (FNA) with cytology evaluation and/or molecular testing. Cancer-associated molecular alterations occurring in the majority of thyroid cancers have been uncovered, with the most common being mitogen-activated protein kinase (MAPK) pathway gene mutations or fusions. Several molecular panels are available for the evaluation of thyroid FNA samples and may help to refine the probability of cancer, predict histologic cancer type, estimate risk of cancer recurrence, and identify potential therapeutic targets. This chapter reviews the molecular alterations characteristic of thyroid cancer and available molecular technologies along with their clinical utility and limitations.

Increasingly use of PET/CT leads to discovery of incidental findings. Hypermetabolic thyroid nodules are one of the unexpected lesions in PET/CT imaging with an increased risk of thyroid cancers. Our study aims to determine the malignant potential of incidentally detected 18F-FDG avid thyroid nodules by using Tc-99m MIBI imaging.

PET/CT scans were performed for nonthyroidal purposes and were evaluated for the presence of hypermetabolic thyroid nodules. Tc-99m MIBI scans and ultrasonography-guided fine needle aspiration biopsies were subsequently performed for all patients.

Primary thyroid malignancies were identified in 25% of patients with increased focal FDG uptake at definitive diagnosis. Among the patients with FDG avid thyroid nodules, Tc-99m MIBI scan showed true-positive results in all thyroid carcinomas (n:7) with a 36.3% (4/11) false-positivity rate. In three patients with indeterminate cytology results, Tc-99m MIBI scan findings were also negative. The sensitivity, specificity, positive predictive value of Tc-99m MIBI scan in predicting the malignancy of FDG-positive thyroid nodules were 100%, 77%, 63.6%, respectively.

The implementation of ^99mTc-MIBI scan performed by dual phase and SPECT/CT modality might be a helpful cost-effective approach in addition to FNAB in patients with ¹⁸F-FDG-positive thyroid nodules and indeterminate cytology to improve the patients’ prognosis and reduce unnecessary thyroid operations with associated use of FNAB.

L’utilisation croissante de la TEP/TDM conduit à des découvertes fortuites. Les nodules thyroïdiens hypermétaboliques sont l’une des lésions inattendues en imagerie TEP/TDM avec un risque accru de cancers de la thyroïde. Notre étude vise à déterminer le potentiel malin des nodules thyroïdiens avides de ¹⁸F-FDG détectés accidentellement en utilisant l’imagerie MIBI au Tc-99m.

Des tomodensitogrammes TEP/TDM ont été réalisés à des fins non thyroïdiennes et ont été évalués pour la présence de nodules thyroïdiens hypermétaboliques. Une scintigraphie MIBI au Tc-99m et une biopsie par aspiration à l’aiguille fine guidée par échographie ont ensuite été réalisées pour tous les patients.

Des tumeurs malignes thyroïdiennes primitives ont été identifiées chez 25 % des patients présentant une augmentation de la fixation focale du FDG au moment du diagnostic définitif. Parmi les patients atteints de nodules thyroïdiens avides de FDG, l’analyse MIBI au Tc-99m a montré des résultats vrais positifs dans tous les carcinomes thyroïdiens (n:7) avec un taux de fausse positivité de 36,3 % (4/11). Pour 3 patients avec des résultats cytologiques indéterminés, les résultats du Tc-99m MIBI étaient également négatifs. La sensibilité, la spécificité, les valeurs prédictives positives, prédictives négatives et la précision de la scintigraphie MIBI au Tc-99m pour prédire la malignité des nodules thyroïdiens positifs au FDG étaient respectivement de 100 %, 77 % et 63,6 %.

La mise en œuvre de l’analyse au 99mTc-MIBI réalisée en double phase et en modalité TEMP/TDM pourrait être une approche rentable, utile en plus du FNAB chez les patients présentant des nodules thyroïdiens positifs au 18F-FDG et une cytologie indéterminée, pour améliorer le pronostic des patients et réduire les opérations thyroïdiennes inutiles avec l’utilisation associée de la FNAB.