Papillary thyroid microcarcinoma presenting as lymph node metastasis — a diagnostic challenge: case report and systematic review of literature

Papillary thyroid microcarcinomas (PTMCs) have an excellent prognosis, although a few may metastasize to cervical lymph nodes. However, an infiltrated palpable neck node without evidence of thyroid disease at presentation is uncommon. We report a patient with PTMC presenting as a solitary lymph node metastasis without evidence of primary thyroid tumor in thyroid imaging and with inconclusive lymph node fine-needle biopsy (FNB) cytology. In our case, node excision and histological examination set the diagnosis and immunocytochemical staining of the FNB specimens verified it. A systematic review of reported similar cases was performed; relevant diagnostic dilemmas were also summarized. The clinical presentation of this type of papillary carcinoma becomes evident at a relatively younger age and affects almost equally the two genders; the enlarged lymph node is almost exclusively ipsilateral to the primary tumor, which may be unifocal or multifocal and is difficult to detect by thyroid imaging modalities. Lymph node FNB cytology, thyroglobulin (Tg) measurement in the washout liquid of the FNB needle, FNB immunocytochemistry and lymph node excision accompanied by histological examination provide a stepwise diagnostic approach. We conclude that PTMC may present as a lymph node metastasis without evidence of a primary thyroid tumor. In such cases, thyroid malignancy should be suspected and, in the presence of negative or non-diagnostic lymph node FNB cytology, measurement of Tg in the fluid aspirate should be performed.