Multimode Sonographic Features of Adenoid Cystic Carcinoma Metastasized to the Thyroid
Adenoid cystic carcinoma (ACC) is a rare malignant tumor, accounting for approximately 1% of all head and neck neoplasms. It typically originates in the major and minor salivary glands. Despite its slow growth, ACC is known for frequent local recurrence and late distant metastasis. The most common sites of metastasis include the lungs, bones, brain, and liver. Metastasis to the thyroid, however, is relatively uncommon. This article presents a detailed case study of a 42-year-old woman with ACC of the submaxillary gland, which metastasized to the bilateral thyroid lobes. The focus is on the multimode sonographic features of thyroid metastasis from ACC, emphasizing the role of ultrasonography as the primary diagnostic tool.
The patient, a 42-year-old female, presented with a 5-month history of a left neck mass. She had undergone surgery followed by radiation and chemotherapy two years prior for ACC of the left submaxillary gland. Physical examination revealed a hard, fixed, painless nodule on the left neck that was moderately growing and did not move during swallowing. Skin examination was normal. A contrast-enhanced computed tomography (CT) scan showed soft tissue density masses in the bilateral neck and multiple lung metastases. Additionally, two slightly low-density lesions of undetermined origin were noted in the thyroid.
Thyroid sonography revealed two homogeneous hypoechoic nodules located in the upper poles and middle of the gland. The sonographic features of these nodules included being solid, oval, well-circumscribed, wider than tall, non-calcified, and hypovascular. The maximum lengths of the left and right nodules were approximately 0.7 cm and 0.8 cm, respectively. Further examination using contrast-enhanced sonography and shear wave elastography (SWE) showed that the lesions were hypoenhanced and medium-to-hard in texture. SWE parameters for the right nodule included Emax of 81.1 kPa, Emin of 20.6 kPa, Emean of 46.3 kPa, and a ratio of 2.7. For the left nodule, these values were Emax of 88 kPa, Emin of 8.2 kPa, Emean of 47.4 kPa, and a ratio of 4.1.
In addition to the thyroid nodules, a 2.8 cm palpable nodule was noted in the operative area, and another 2.3 cm nodule was found beneath the sternocleidomastoid muscle. Lymphatic nodes at levels III and IV were also abnormal, with a maximum diameter of 0.8 cm. Following the ultrasonic examination, the patient underwent sonography-guided fine-needle aspiration of the thyroid nodule. Cytologic results confirmed ACC. Subsequently, she underwent a thyroidectomy and neck dissection. Histopathologic examination after surgery confirmed that all nodules in the thyroid, the operative area, and the lymphatic nodes were ACC metastases.
ACC is a rare tumor in the head and neck region, with distant metastasis being an important prognostic factor. Radiological investigations, such as CT scans, are crucial for identifying recurrence during postoperative follow-up. However, the study of conventional ultrasonic and elastographic features of thyroid metastasis from ACC is limited. Generally, malignant thyroid nodules originate from thyroid tissue, and thyroid metastatic cancers account for 1.4% to 3.0% of all thyroid malignancies, with renal cell carcinoma being the most common primary site. Thyroid metastasis from ACC is relatively rare.
In this case, the two metastatic nodules mimicked benign thyroid nodules on conventional ultrasonography. Their features included being solid, oval, well-circumscribed, wider than tall, and non-calcified, none of which indicated malignancy. However, SWE revealed that the nodules were significantly stiffer than the surrounding normal thyroid tissue, with maximum elasticity values of 88.0 kPa and 81.1 kPa. These values were also higher than those typically reported for benign thyroid nodules. Contrast-enhanced ultrasonography showed heterogeneous enhancement and hypoenhancement, consistent with malignant thyroid nodules rather than benign ones.
In conclusion, the combination of SWE and contrast-enhanced ultrasonography may provide valuable insights for diagnosing ACC metastasized to the thyroid. These advanced ultrasonography techniques can serve as supplementary methods to CT scans in confirming the diagnosis. The case highlights the importance of multimode sonographic evaluation in detecting rare metastatic lesions in the thyroid, particularly in patients with a history of ACC.
doi.org/10.1097/CM9.0000000000000033
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