Sonographic Evaluation of Intrathyroid Metastases

Intrathyroid metastases from extrathyroid primary tumors are rare. Clinical findings may be subtle, but detection of intrathyroid metastases has improved with sonography. The objective of this study was to evaluate the sonographic appearance of intrathyroid metastases.

Patients with thyroid masses with cytopathologic features matching those of an extrathyroid primary tumor were retrospectively identified. The appearances of intrathyroid metastases on sonography were reviewed for the following features: size, margin regularity, echogenicity, echotexture, vascularity on power or color Doppler ultrasonography, and the presence or absence of any associated cervical adenopathy.

The study included 52 patients. The most frequent primary tumor sites were lung, head and neck, and breast. Intrathyroid metastases presented as a discrete nodule in 34 patients and as diffuse infiltration of the gland in 18 patients. The discrete nodules ranged in size from 1.1 to 5.6 cm (mean ± SD, 2.5 ± 1.2 cm). Thirty-three lesions (63%) had irregular margins, and 19 (37%) had well-defined margins. Most of the lesions were heterogeneously hypoechoic (n = 50, 96%). Vascularity was present in 32 of 50 measured lesions (64%) that were evaluated with Doppler sonography. Cervical adenopathy was present in 37 patients (71%).

Intrathyroid metastases have sonographic characteristics similar to those described for both benign and malignant thyroid diseases. In patients with a previous or current extrathyroid malignancy, thyroid nodules or diffuse infiltration of the thyroid gland on sonography should be viewed as a potential intrathyroid metastasis and evaluated via ultrasound-guided fine-needle aspiration regardless of the site of the primary tumor.