J Korean Thyroid Assoc.  2015 May;8(1):67-74. 10.11106/cet.2015.8.1.67.

Ultrasonographic Classification of the Metastases to the Thyroid Gland

• Lee KH
• Shin JH
• Han BK
• Ko EY
• Ko ES
• Hahn SY
• Ryu JH

• KMID: 2149622
• DOI: http://doi.org/10.11106/cet.2015.8.1.67

Abstract

BACKGROUND AND OBJECTIVES
To classify the metastases to the thyroid gland arising from non-thyroidal malignancies on ultrasound (US).
MATERIALS AND METHODS
We enrolled 45 consecutive patients with metastases to the thyroid gland from 2005 to 2012. We classified metastases into 4 types; type I: diffuse non-mass forming lesion, type II: a solitary suspicious nodule, type III: multiple suspicious nodules, and type IV: nodule(s) with no suspicion. We subcategorized type I into two subtypes; type IA: diffusely infiltrative lesion, type IB: diffuse micronodulation.
RESULTS
The most frequent primary malignancy of thyroid metastases was lung cancer. The patients with thyroid metastases were 26 (57.8%) in type I; type IA: 16 (35.6%), type IB: 10 (22.2%), 14 (31.1%) in type II, 3 (6.7%) in type III and 2 (4.4%) in type IV. Type I metastasis included 18 of 25 patients with lung cancer and all 3 patients with stomach cancer. Thirty patients (73.3%) having type IA, II or III revealed malignant findings on US, in contrast, 12 (26.7%) patients having type IB or IV revealed no suspicious findings.
CONCLUSION
Type I (diffuse non-mass forming lesion) was the most common in thyroid metastases. A quarter of thyroid metastases revealed no suspicious findings on US. Thyroid metastases can be considered as a differential diagnosis, when diffuse non-mass forming lesions or nodules with no suspicion are revealed on thyroid US.

Keyword

Thyroid metastases; Ultrasound; Micronodulation

MeSH Terms

Classification*
Diagnosis, Differential
Humans
Lung Neoplasms
Neoplasm Metastasis*
Stomach Neoplasms
Thyroid Gland*
Ultrasonography

Figure

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  Fig. 1. Type IA thyroid metastases in a 61-year-old male with lung cancer. Diffuse infiltrative hypoechoic lesion is demonstrated in the entire thyroid gland with multiple microcalcifications (white arrowhead). Diffuse infiltrative lesion reveals mild hypervascularity on color Doppler examination. Normal thyroid parenchyma is entirely replaced by the infiltrative lesion. On histology, obtained by core needle biopsy, malignant cells of metastatic adenocarcinoma with stromal fibrosis replace normal follicular structures entirely on the biopsy specimen (A: transverse plane, B: color Doppler examination, C: Hematoxylin & Eosin stain, ×40, D: cytokeratin stain, × 100).

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  Fig. 2. Type IB thyroid metastases in an 86-year-old male with lung cancer. US demonstrates diffuse micronodulation (white arrowheads), which reveals innumerable small linear or curvilinear hypoechoic lesions in entire thyroid gland. Thyroid gland demonstrates marked hypervascularity in color Doppler examination. Histology, obtained by core needle biopsy, demonstrates relatively preserved follicular structures, in which the component of metastatic adenocarcinoma (arrowheads) is less than 10% areas of total biopsy specimen on microscopic evaluation (A: transverse plane, B: color Doppler examination, C: Hematoxylin & Eosin stain, ×100, D: thyroid transcription factor-1 stain, ×100).

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  Fig. 3. Type II thyroid metastases in a 54-year-old female with head and neck cancer. A 2 cm suspicious malignant mass is demonstrated in the right mid-thyroid lobe on US. An additional probable benign nodule is observed in the ipsilateral thyroid lobe. Fine needle aspiration revealed metastatic squamous cell carcinoma (A: transverse plane, B: longitudinal plane).

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  Fig. 4. Type III thyroid metastases in a 55-year-old male with lung cancer. Three suspicious malignant nodules are demonstrated in the right mid-thyroid lobe (A: transverse plane, arrow), left upper thyroid lobe (B: transverse plane, arrowhead) and left mid-thyroid lobe (C: transverse plane, arrowhead). Fine needle aspiration of a suspicious malignant nodule in the right thyroid lobe (arrow) shows metastatic carcinoma.

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  Fig. 5. Type IV thyroid metastases in an 84-year-old male with renal cell carcinoma. Two thyroid nodules in left lobe don't demonstrate suspicious findings. Fine needle aspiration for the larger mass located superiorly (arrow) revealed metastatic carcinoma (A: transverse plane, B: longitudinal plane).

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