Performance of contrast-enhanced ultrasound in thyroid nodules: review of current state and future perspectives

Simple Summary: Ultrasound has been used as baseline imaging for thyroid nodules for decades; nevertheless, no single feature is sensitive or specific enough to exclude or confirm thyroid malignancy. Therefore, clinical practice and research still focus on less invasive diagnostic patterns to reduce unnecessary fine-needle aspiration biopsies or surgery. The main advantage of CEUS is the ability to assess the sequence and intensity of vascular perfusion and hemodynamics in the thyroid nodule, thus providing real-time characterization of nodule features, and considered a valuable new approach in the determination of benign vs. malignant nodules. In addition, contrast agents used in CEUS can help to guide treatment planning for minimally invasive procedures (e.g., ablation) and to provide accurate follow-up imaging to assess treatment efficacy in both benign and malignant nodules and associated lymph nodes. Examination protocol has almost reached standardization, although there are numerous controversies reported about the interpretation of qualitative and quantitative patterns that would require a systematic approach. This literature and current state review of CEUS in thyroid nodules address the existing concepts and highlights of the future perspectives.Ultrasound has been established as a baseline imaging technique for thyroid nodules. The main advantage of adding CEUS is the ability to assess the sequence and intensity of vascular perfusion and hemodynamics in the thyroid nodule, thus providing real-time characterization of nodule features, considered a valuable new approach in the determination of benign vs. malignant nodules. Original studies, reviews and six meta-analyses were included in this article. A total of 624 studies were retrieved, and 107 were included in the study. As recognized for thyroid nodule malignancy risk stratification by US, for acceptable accuracy in malignancy a combination of several CEUS parameters should be applied: hypo-enhancement, heterogeneous, peripheral irregular enhancement in combination with internal enhancement patterns, and slow wash-in and wash-out curve lower than in normal thyroid tissue. In contrast, homogeneous, intense enhancement with smooth rim enhancement and "fast-in and slow-out" are indicative of the benignity of the thyroid nodule. Even though overlapping features require standardization, with further research, CEUS may achieve reliable performance in detecting or excluding thyroid cancer. It can also play an operative role in guiding ablation procedures of benign and malignant thyroid nodules and metastatic lymph nodes, and providing accurate follow-up imaging to assess treatment efficacy.