Histopathologic and immunohistochemical characterization of a primary papillary thyroid carcinoma in the lateral cervical lymph node.

Lymph nodes in the neck are known to occasionally contain benign epithelial inclusions and can be rare primary site of various tumors usually occurring in other organs. Papillary thyroid carcinoma in the lateral neck lymph node with co-existing ectopic thyroid inclusions has not been reported previously. A 41-year-old male patient, who had normal thyroid function and no history of neck irradiation, was seen with a slowly enlarging mass in the right lateral neck. At surgery the cervical mass was found to be separate from the thyroid proper without any attachments in between. Papillary thyroid carcinoma and co-existing thyroid inclusions were identified within the lateral cervical lymph node. Immunohistochemistry detected strong and diffuse cytoplasmic positivity with antibodies against CK19 and CK903 in papillary thyroid carcinoma. Benign thyroid follicles within the lymph node were only weakly and focally stained. Thorough examination confirmed no malignancy in the total thyroidectomy specimen. Furthermore, small foci of metastatic papillary carcinoma were identified in two ipsilateral lymph nodes from neck dissection specimen. These findings suggest development of primary papillary thyroid carcinoma from malignant transformation of benign intranodal thyroid inclusions.