The Role of SPECT/CT and PET/CT Hybrid Imaging in the Management of Ectopic Thyroid Carcinoma—A Systematic Review

Abstract

Background and Objectives: Thyroid ectopy represents a rare disease with an incidence of 0.3–1/100,000. It occurs due to the defective embryological process of the thyroid gland development. The thyroid ectopic tissue may suffer malignant transformation. This review aims to shed light on the roles that I-131 SPECT/CT (radioiodine 131 single-photon emission tomography fused with computed tomography) and F-18 PET/CT (fluorodeoxyglucose F18 positron emission tomography fused with computer tomography) may play in managing patients with ectopic thyroid carcinoma. Materials and Methods: A total number of 47 articles were identified on the PubMed and Google Scholar databases, and 3 other articles were selected from articles identified in the references cited in the retrieved articles. After refining the selection, the inclusion and exclusion criteria were applied, resulting in 10 articles that were included in the review. Results: The cases of ectopy included in this review were localised as follows: four cases in the thyroglossal duct, two cases in the mediastinum, one case in the oesophagus, one case in the thorax, one case with a pre-tracheal location, and one case with a latero-cervical location. In all the cases, F-18 FDG PET/CT was used as a diagnostic tool. In one case, F-18 FDG PET/CT was combined with I-131 SPECT/CT and MRI (magnetic resonance imaging). In one case, it was combined with 68 Ga-FAPI PET/CT (Ga-68 radiolabelled FAP inhibitor positron emission tomography fused with computer tomography). The maximum SUVs (standardised uptake values) ranged from 5.5 to 25 g/mL. Conclusions: F-18 PET/CT and I-131 SPECT/CT hybrid nuclear imaging is of great value in assessing ectopic thyroid carcinoma. F-18 FDG PET/CT plays an important role in the primary tumour evaluation and distant disease detection. Ga-68 FAPIs are a promising alternative. I-131 SPECT/CT adds important information related to the anatomical characterization of primary and distant iodine-avid lesions.