Needle biopsy is the gold standard for diagnosing tumors. The incidence of needle implantation metastasis in malignancies caused by needle biopsy is extremely low about 0.003%-0.009%[1]. It is commonly reported in cases of pancreatic, hepatocellular, and prostate carcinomas[1] and thyroid carcinoma-related reports were extremely rare[2]. The incidence rate of NTS was only 0.14% among 4912 patients who had undergone FNA and were diagnosed with papillary thyroid carcinoma.
In our case, it is supposed that recurrent masses were caused by FNA for the following reasons: (1) The location of the mass was anterior to the sternocleidomastoid muscle, which was an atypical site of thyroid carcinoma metastasis. (2) On CT, the four masses around the sternocleidomastoid muscle were correlated with the pathway of FNA needle. (3) The pathology showed that the masses were papillary thyroid carcinoma and not lymph node tissue or normal thyroid tissue. (4) FNA may cause tumor metastasis.
Among the 11 relevant case reports reviewed[3-13], we found that 8 of all 17 lesions were located in skin, 4 ones in sternocleidomastoid muscle, 2 ones in strap muscle, 1 in platysma muscle, 1subcutaneous mass, 1 anterior neck mass with skin ulceration and hemorrhage. The location of the seedings caused by RFA were mostly located in the skin, while the number of seedings located around the sternocleidomastoid muscle was mostly small. However, unlike other cases, in our case the four masses located around the sternocleidomastoid muscle were highly suspicious of NTS caused by FNA. At the same time, the primary tumour also underwent invasion of the recurrent laryngeal nerve, causing hoarseness.
Currently, there is no literature reporting a clear association between NTS and thyroid pathological types. Of the 11 cases we reviewed, 7 patients had PTC, 3 patients had follicular thyroid carcinoma (FTC), and 1 patient had anaplastic thyroid carcinoma (ATC). According to the pictures of the patients provided in the literature, the 2 patients with PTC[9, 10] had more severe NTS occurring in the skin compared with the more malignant and aggressive ATC patients[7]. And our patient's postoperative pathology confirmed classic papillary thyroid carcinoma without high-grade histology. Therefore, we consider that the occurrence of NTS may not be associated with different pathological types of thyroid carcinoma, but more likely due to non-standard procedures. For the treatment of the implanted masses, surgery was used in all 11 cases reviewed. We recommend that the mass metastasizing from the FNA be removed, along with the surrounding tissue invaded by the mass. Postoperative radioactive iodine supplementation is also given to facilitate the patient's prognosis. In the 7 cases that were followed up, the patients had an excellent prognosis with no recurrence. Although NTS could be treated with secondary surgery and the prognosis was good, further research is needed on how to safely perform FNA and reduce the incidence of NTS.