Ultrasound findings of diffuse metastasis of gastric signet-ring-cell carcinoma to the thyroid gland

Abstract

It has been shown that metastases to the thyroid from extrathyroidal malignancies occur as solitary or multiple nodules, or may involve the whole thyroid gland diffusely. However, diffuse metastasis of gastric cancer to the thyroid is extremely rare. Here, we report a case of a 74-year-old woman with diffuse infiltration of gastric adenocarcinoma (signet-ring-cell carcinoma/poorly differentiated adenocarcinoma) cells in the thyroid. The pathological diagnosis was made based on upper gastrointestinal endoscopy with biopsy and fine-needle aspiration cytology of the thyroid. An 18F-FDG PET/CT revealed multiple lesions with increased uptake, including the bilateral thyroid gland. On thyroid ultrasound examination, diffuse enlargement with internal heterogeneity and hypoechoic reticular lines was observed. On color Doppler imaging, a blood-flow signal was not detected in these hypoechoic lines. These findings were similar to those of diffuse metastases caused by other primary cancers, such as lung cancer, as reported earlier. Therefore, the presence of hypoechoic reticular lines without blood-flow signals is probably common to diffuse thyroid metastasis from any origin and an important diagnostic finding. This is the first report to show detailed ultrasound findings of diffuse gastric cancer metastasis to the thyroid gland using color Doppler.

Keywords: Color Doppler ultrasonography; Neoplasm metastasis; Signet-ring-cell carcinoma; Stomach neoplasm; Thyroid gland.

Fig. 1

Histopathology of the primary gastric tumor. a Hematoxylin and eosin stain; original magnification ×100. Atypical cells with cytoplasmic mucin are diffusely invading the gastric mucosa. b Hematoxylin and eosin stain; original magnification ×400. Round-shaped cells with cytoplasmic mucin vacuoles and eccentrically placed nuclei are components of signet-ring-cell carcinoma (rectangle). Cells with a high nuclear-to-cytoplasmic ratio are components of poorly differentiated adenocarcinoma (oval)

Fig. 2

a Coronal maximum intensity projection (MIP) of 18F-FDG PET imaging before admission. Accumulation was found in the stomach, in the right hepatic lobe, in the extensive lymph node metastases, and in the whole thyroid gland. b Transverse section of the thyroid on 18F-FDG PET/CT imaging before admission. Diffuse uptake in bilateral thyroid lobes was observed. c Transverse section of the thyroid on CT imaging after admission. The thyroid gland was diffusely swollen. Its size enlarged and its CT value decreased after hospitalization. In addition, the adipose tissue concentration in the surrounding area increased

Fig. 3

Thyroid ultrasonography after admission. a Transverse section of the thyroid gland on B-mode (brightness mode) ultrasound imaging. The thyroid was diffusely enlarged, with a 10-mm-thick isthmus. No nodular lesion was observed. The thyroid parenchyma was not of uniform echogenicity, with many hypoechoic reticular lines scattered in it. b Longitudinal section of the right lobe of the thyroid on color Doppler ultrasound imaging. c Longitudinal section of the left lobe of the thyroid on color Doppler ultrasound imaging. A Doppler signal was not detected in the hypoechoic reticular lines

Fig. 4

Cytology specimen that was obtained by fine-needle aspiration from the right lobe of the thyroid gland (Papanicolaou stain; original magnification ×400). Discohesive atypical cells with irregular hyperchromatic nuclei containing prominent nucleoli were present. Round-shaped cells with cytoplasmic mucin vacuoles and eccentrically placed nuclei were signet-ring-cell carcinoma cells (arrow). Cells with a high nuclear-to-cytoplasmic ratio were thought to be poorly differentiated adenocarcinoma cells (arrowhead). There were numerous mitotic figures (big arrowhead). Based on these findings, the thyroid lesion was defined as “malignant” (metastatic carcinoma) by TBSRTC