Occult Papillary Thyroid Carcinoma without Detection of the Primary Tumor on Preoperative Ultrasonography or Postoperative Pathological Examination: A Case Report.

Herein, we report a case of an occult thyroid cancer that was not detected as a primary tumor on preoperative ultrasonography or postoperative pathological examination, although a diagnosis of papillary thyroid carcinoma metastasis was made owing to the presence of a mass in the right upper neck. Needle biopsy of the mass in the right upper neck revealed positive results for thyroglobulin and TTF-1 on immunostaining, and a papillary thyroid carcinoma was observed with papillary and follicular patterns. We suspected papillary thyroid carcinoma (T0N1bM0) or ectopic papillary thyroid carcinoma. Accordingly, we performed total thyroidectomy, central lymph node dissection, right lateral neck dissection, and resection of the superficial lobe of the right parotid. A postoperative pathological examination of 5-mm slices of the specimen revealed no primary tumor in the thyroid. However, a hyalinized image of the thyroid indicated that a micropapillary thyroid carcinoma might have spontaneously disappeared. As there was no normal thyroid tissue in the metastasis to the superior internal jugular lymph node, the tumor was unlikely to be an ectopic papillary thyroid carcinoma. Therefore, we made a diagnosis of a papillary thyroid carcinoma (pT0N1bM0). After surgery, we determined that the tumor belonged to a high-risk group of papillary thyroid carcinomas and a poor-prognosis group of symptomatic papillary thyroid microcarcinomas; accordingly, ablation was performed with 30 mCi iodine-131. There was no recurrence or metastasis 24 months after the first surgery.