Functional and molecular thyroid imaging

Molecular imaging of thyroid and parathyroid diseases

INTRODUCTION

Molecular imaging of thyroid and parathyroid diseases has changed in recent years due to the introduction of new radiopharmaceuticals and new imaging techniques. Accordingly, we provided an clinicians-oriented overview of such techniques and their indications.

AREAS COVERED

A review of the literature was performed in the PubMed, Web of Science, and Scopus without time or language restrictions through the use of one or more fitting search criteria and terms as well as through screening of references in relevant selected papers. Literature up to and including December 2023 was included. Screening of titles/abstracts and removal of duplicates was performed and the full texts of the remaining potentially relevant articles were retrieved and reviewed.

EXPERT OPINION

Thyroid and parathyroid scintigraphy remains integral in patients with thyrotoxicosis, thyroid nodules, differentiated thyroid cancer and, respectively, hyperparathyroidism. In the last years positron-emission tomography with different tracers emerged as a more accurate alternative in evaluating indeterminate thyroid nodules [18F-fluorodeoxyglucose (FDG)], differentiated thyroid cancer [124I-iodide, 18F-tetrafluoroborate, 18F-FDG] and hyperparathyroidism [18F-fluorocholine]. Other PET tracers are useful in evaluating relapsing/advanced forms of medullary thyroid cancer (18F-FDOPA) and selecting patients with advanced follicular and medullary thyroid cancers for theranostic treatments (68Ga/177Ga-somatostatin analogues).

Integrated Diagnostics of Thyroid Nodules

Thyroid nodules are common findings, particularly in iodine-deficient regions. Our paper aims to revise different diagnostic tools available in clinical thyroidology and propose their rational integration. We will elaborate on the pros and cons of thyroid ultrasound (US) and its scoring systems, thyroid scintigraphy, fine-needle aspiration cytology (FNAC), molecular imaging, and artificial intelligence (AI). Ultrasonographic scoring systems can help differentiate between benign and malignant nodules. Depending on the constellation or number of suspicious ultrasound features, a FNAC is recommended. However, hyperfunctioning thyroid nodules are presumed to exclude malignancy with a very high negative predictive value (NPV). Particularly in regions where iodine supply is low, most hyperfunctioning thyroid nodules are seen in patients with normal thyroid-stimulating hormone (TSH) levels. Thyroid scintigraphy is essential for the detection of these nodules. Among non-toxic thyroid nodules, a careful application of US risk stratification systems is pivotal to exclude inappropriate FNAC and guide the procedure on suspicious ones. However, almost one-third of cytology examinations are rendered as indeterminate, requiring "diagnostic surgery" to provide a definitive diagnosis. 99mTc-methoxy-isobutyl-isonitrile ([99mTc]Tc-MIBI) and [18F]fluoro-deoxy-glucose ([18F]FDG) molecular imaging can spare those patients from unnecessary surgeries. The clinical value of AI in the evaluation of thyroid nodules needs to be determined.

Pitfalls of DualTracer 99m-Technetium (Tc) Pertechnetate and Sestamibi Scintigraphy before Parathyroidectomy: Between Primary-Hyperparathyroidism-Associated Parathyroid Tumour and Ectopic Thyroid Tissue

Diagnosis of primary hyperparathyroidism (PHP) is based on blood assessments in terms of synchronous high calcium and PTH (parathormone), but further management, particularly parathyroid surgery that provides the disease cure in 95-99% of cases, requires an adequate localisation of the parathyroid tumour/tumours as the originating source, with ultrasound and 99m-Technetium (99m-Tc) sestamibi scintigraphy being the most widely used. We aimed to introduce an adult female case diagnosed with PHP displaying unexpected intra-operatory findings (ectopic thyroid tissue) in relation to concordant pre-operatory imaging modalities (ultrasound + dual-phase 99m-Tc pertechnetate and sestamibi scintigraphy + computed tomography) that indicated bilateral inferior parathyroid tumours. A sudden drop in PTH following the removal of the first tumour was the clue for performing an extemporaneous exam for the second mass that turned out to be non-malignant ectopic thyroid tissue. We overviewed some major aspects starting from this case in point: the potential pitfalls of pre-operatory imaging in PHP; the concordance/discordance of pre-parathyroidectomy localisation modalities; the need of using an additional intra-operatory procedure; and the clues of providing a distinction between pathological parathyroids and thyroid tissue. This was a case of adult PHP, whereas triple localisation methods were used before parathyroidectomy, showing concordant results; however, the second parathyroid adenoma was a false positive image and an ectopic thyroid tissue was confirmed. The pre-operatory index of suspicion was non-existent in this patient. Hybrid imaging modalities are most probably required if both thyroid and parathyroid anomalies are suspected, but, essentially, awareness of the potential pitfalls is mandatory from the endocrine and surgical perspectives. Current gaps in imaging knowledge to guide us in this area are expected to be solved by the significant progress in functional imaging modalities. However, the act of surgery, including the decision of a PTH assay or extemporaneous exam (as seen in our case), represents the key to a successful removal procedure. Moreover, many parathyroid surgeons may currently perform 4-gland exploration routinely, precisely to avoid the shortcomings of preoperative localisation.

Evaluation of Thyroid Nodules in Patients With Fine-Needle Aspiration Biopsy

BACKGROUND

The incidence of thyroid nodules has increased in the last 50 years due to the widespread use of imaging methods and incidental detection of small thyroid nodules. Thyroid fine-needle aspiration biopsy (FNAB) is the most accurate, reliable, and cost-effective test to evaluate thyroid nodules.

AIM

In this research, we aimed to elucidate thyroid fine-needle aspiration cytology (FNAC) to understand how suspicious cases predict malignancy.

MATERIALS AND METHODS

Within this research's scope, 411 patients over 16 years old who were evaluated in Izmir Katip Celebi University, Ataturk Training and Research Hospital Internal Medicine (Izmir, Turkey) outpatient clinic for thyroid nodules between 2018 and 2022 and underwent thyroid FNAC followed by thyroid surgery were analyzed retrospectively. The age, gender, thyroid FNAC, operation type, and histopathology of all the patients were reviewed. Individuals with a history of head and neck cancer were excluded from the analysis.

RESULTS

No statistically significant relationship between the pathology results and demographic characteristics was found. A statistically significant correlation existed between the pathology and FNAB results (p<0.05). Although 84.5% of the patients were diagnosed as benign, 14.7% as suspicious, and 0.8% as malignant in FNAC, all of these cases were diagnosed as benign in final histopathology results. Similarly, 21.9% of the patients were diagnosed as benign, 58.8% as suspicious, and 19.4% as malignant in FNAC and all of these cases were diagnosed as malignant in final histopathology results. A correlation was determined between the two measurements (Cohen's kappa (κ)=0.557; p<0.001). The test's sensitivity was 47%, and the specificity was 99.1%. According to the FNAC results, the rate of being diagnosed with malignancy (positive predictive value (PPV)) was 93.9%, and the rate of being diagnosed as benign (negative predictive value (NPV)) was 85.8% for the individuals initially diagnosed as benign.

CONCLUSION

Although FNAB remains the most important diagnostic tool to identify benign cases with a high accuracy rate, the operation decision is not clear in suspicious atypia of undetermined significance/follicular lesions of undetermined significance (AUS/FLUS) cytology findings. In conclusion, this study highlights the importance of FNA results and helps in surgical decision-making by emphasizing that the possibility of malignancy in the post-operative final histopathology report is higher, especially in the presence of suspicious FNAC results.

Diagnostic Effectiveness of Dual Source Dual Energy Computed Tomography for Benign and Malignant Thyroid Nodules

Objective

To evaluate the diagnostic effectiveness of dual source dual energy computed tomography (DS-DECT) for benign and malignant thyroid nodules.

Methods

Between January 2019 and December 2021, 60 patients with surgically and pathologically verified thyroid nodules treated at our institution were recruited. DS-DECT was administered to all patients. The iodine content of lesioned and normal tissues, the normalized iodine concentration (NIC) and standardized CT values of benign and malignant nodules, the consistency of examination results and pathological findings, and diagnostic effectiveness were all investigated.

Results

The diagnosis accuracy was the same as that of surgical pathology, producing a 100% accuracy for the 60 patients with thyroid nodules (42 were benign and 18 were malignant). The iodine content of lesioned solid tissue differed significantly from that of normal tissue, as did the iodine content of malignant and benign nodules (P < 0.05). In the arterial phase, no significant difference was found in NIC and standardized CT values between benign and malignant nodules (P > 0.05). The optimal critical NIC for differentiating benign and malignant nodules in the venous phase was 0.74 and the standardized CT value was 0.79 HU according to the receiver operating characteristics (ROC) curve. Malignant nodules were diagnosed when the NIC was <0.74 and the standardized CT value was <0.79 HU, with AUC values of 0.89 and 0.93, respectively, where the sensitivity and specificity of the differential diagnosis of NIC were 90.48% (38/42) and 88.89% (16/18), respectively, and those of the differential diagnosis of standardized CT value were 92.86% (39/ 42) and 94.44% (17/18), respectively. The diagnosis accuracy of DS-DECT was 100%, and the diagnostic results of morphological characteristics and pathological testing were consistent. The sensitivity and specificity of the NIC values and standardized CT values in the venous phase differential diagnosis of benign and malignant nodules were compatible with the morphological differential diagnosis.

Conclusion

DS-DECT is highly accurate in determining the benignity and malignancy of thyroid nodules and has a strong potential for clinical promotion to allow for prompt treatment.