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case_images: A timeline of the patient's diagnosis and treatment process. US, ultrasound; CEUS, contrast-enhanced US; ACR-TIRADS, American College of Radiology-Thyroid Imaging and Reporting Data System; SSCCT, secondary squamous cell carcinoma of the thyroid.
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case_images: A 69-year-old woman presented at the Affiliated Hospital of Guangdong Medical University in October 2022 with a painless right-sided neck mass that had been rapidly enlarging for the last 2 months (Fig. 1).
case_images: Combined US and CEUS findings of Lesion A before treatment. (A) US showed a mixed cystic-solid mass with irregular margins, macrocalcifications and microcalcifications inside. (B) Color Doppler flow imaging showed abundant blood flow signals inside. (C) One of the arteries demonstrated a PS of 7.4 cm/sec, an ED of 1.5 cm/sec, a S/D of 4.9 and an RI of 0.80. (D) CEUS showed an inhomogeneous hypo-enhanced thyroid nodule with a broad central area of non-enhancement and unclear boundaries. US, ultrasound; CEUS, contrast-enhanced US; RI, resistive index; PS, peak systolic velocity; ED, end diastolic velocity; S/D, systolic-to-diastolic ratio.
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case_images: Lesion A, a mixed cystic-solid mass measuring 5.7x4.3x5.6 cm, was situated in the lower middle region of the right lobe of the thyroid gland (Fig. 2A). Color Doppler flow imaging (CDFI) displayed abundant blood flow signals inside the lesion (Fig. 2B), with a resistive index (RI) of 0.80 in one of the arteries (Fig. 2C). Lesion A presented as an inhomogeneous hypo-enhanced thyroid nodule with a broad central area of non-enhancement and blurred borders (Fig. 2D).
case_images: US and color Doppler findings of Lesion B before treatment. (A) US showed a solid slightly hyperechoic nodule with unclear boundaries. (B) Color Doppler flow imaging showed abundant blood flow signals in and around the nodule. US, ultrasound; CEUS, contrast-enhanced US; RI, resistive index; TIS, thermal index for soft tissue; TIB, thermal index for bone; TIC, thermal index for cranial bone; MI, mechanical index.
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case_images: Lesion B was a solid, slightly hyperechoic nodule measuring 2.6x1.7x2.3 cm, occupying the upper part of the ipsilateral lobe (Fig. 3A). CDFI (Fig. 3B). CEUS was performed after injecting 2.0 ml SonoVue  (Bracco).
case_images: Combined US and CEUS findings of Lesion A after treatment. (A) US revealed that the size had significantly reduced. (B) Color Doppler flow imaging showed abundant blood flow signals inside. (C) The resistive index value was decreased to 0.65. (D) CEUS findings revealed that the percentage of non-enhancing areas within the nodule was higher than the percentage before treatment. US, ultrasound; CEUS, contrast-enhanced US.
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case_images: Lesion A was smaller (3.5x2.6x3.3 cm) than its initial size, and the RI (0.65) was decreased compared with its initial value (Fig. 4A-C). CEUS still showed heterogeneous hypo-enhancement of the nodule with blurred boundaries, but the percentage of internal non-enhancing areas was higher than the initial percentage (Fig. 4D).
case_images: Combined US and CEUS findings of Lesion B after treatment. (A) US revealed that the boundary was clearer, and a uniform and continuous hyperechoic thin halo was present in the periphery. (B) Color Doppler flow imaging showed an increase in the internal blood flow signal of the nodule, and the periphery appeared to have a circumferential blood flow signal. (C) CEUS showed a uniformly high enhancement of the nodule with clearer boundaries. US, ultrasound; CEUS, contrast-enhanced US.
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case_images: The boundary of Lesion B became clearer with a uniform and continuous hyperechoic thin halo visible around it, and there was no marked change in its size (Fig. 5A). CDFI showed an increase in the internal blood flow signal of the nodule, and the periphery appeared to have a circumferential blood flow signal (Fig. 5B). Correspondingly, CEUS showed a uniformly high enhancement of the nodule with a clearer boundary (Fig. 5C).
case_images: Pathological findings. (A) Hematoxylin and eosin staining of Lesion A (original magnification, x200). (B) Hematoxylin and eosin staining of Lesion B (original magnification, x100).
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case_images: Postoperative pathology revealed Lesion A as an SCCT, with mostly coagulative necrosis, and Lesion B as nodular goiter, with adenomatous nodule formation (Fig. 6).