[Papillary thyroid microcarcinoma diagnosed based on cyst-like mediastinal metastasis].

Papillary thyroid microcarcinoma (PMC) is defined as a papillary carcinoma 1 cm or less in size. PMC is a variant of papillary carcinoma, the most common thyroid cancer, which has a very good prognosis and in which distant metastases and death (0.4--1% per year) are exceptional.1 We report a patient who was diagnosed with metastasis of a papillary microcarcinoma as the result of an evaluation of a mediastinal mass. This was an asthmatic patient aged 38 years with no history of neck irradiation or family history of thyroid cancer. The surgery department referred the patient to the endocrinological department after surgery for a cystic tumor, 7 cm in diameter, in the posterosuperior mediastinum (Figs. 1 and 2) after the histological study reported the finding in an intraoperative biopsy of a cystic wall of fibrous tissue with thyroid follicles without atypia and associated lymphocyte infiltrate consistent with pharyngeal pouch abnormalities. The final pathological study showed a cystic formation with a wall consisting of fibrous stroma with thyroid follicles, many of them with involutive phenomena, while others showed slight anisonucleosis and some ‘‘frosted glass’’ nuclei. Lymphoid tissue sectors coexisted with histiocyte clusters and calcification foci. The final diagnosis was metastasis from a papillary carcinoma in the cyst-like lymph node. The patient was clinically euthyroid, with a normal thyroid gland on palpation and no adenopathies on physical examination. Ultrasound examination of the thyroid and neck showed a hypoechoic Image 5.7 mm × 3.1 mm in size in the left lobe with no pathological nodes. The functional thyroid study was within normal parameters, with negative antithyroid antibodies. Additional surgery performed in this case consisted of total thyroidectomy with bilateral level VI lymph node excision and the examination of both jugular