Primary paragangliomas(PGs) are rare neuroendocrine tumors, and PGs in thyroid being an especially uncommon subset. We present a case of an upper thyroid PG that could easily be mistaken for a parathyroid adenoma, contributing to the limited existing knowledge in this field.

A 59-year-old woman presented with a noticeable mass on the left side of her neck that had been bothering her for several months. A neck ultrasound revealed an enlarged and irregular nodule, situated behind the upper pole of the left thyroid. Within this nodule, certain areas exhibited hypo-echogenicity, while other sections shared an iso-echogenicity to the adjacent thyroid gland. Uniformly hypervascularity distributed throughout the region surrounding the nodule. The potential diagnoses encompassed a parathyroid adenoma, a paraganglioma, or, although less probable, a medullary thyroid carcinoma. From a surgical perspective, the well-encapsulated tumor was situated between the upper pole of the thyroid gland and the recurrent laryngeal nerve. The reddish vascular tumor exhibited strong adherence to the surrounding tissues but did not extend beyond its capsule into adjacent organs. Careful resection of the thyroid gland allowed us to completely remove the entire tumor, and it was observed that the recurrent laryngeal nerve passed through the base of the tumor.

Microscopically, the pathological specimen was characterized by polygonal tumor cells with eosinophilic cytoplasm and uniform nuclei. [Fig. A] These cells were organized in nested and zellballen patterns, and they were separated by a delicate fibrovascular stroma. [Fig. B] In the immunohistochemical stains, biomakers such as S-100, synaptophysin, chromogranin-A, insulinoma-associated protein 1(INSM-1) exhibited positive results for tumor cells, while parathyroid hormone showed a negative result. [Fig. C, D] The final diagnosis is a primary paraganglioma in thyroid.

The primary PG of upper thyroid gland is a rare disease. The correct diagnosis is rarely established preoperatively due to generalized characteristic in clinical symptom, radiographic examination and cytology. If a nodule lesion at posterior side of thyroid demonstrating hypervascularity in doppler sonography, paraganglioma should be taken into consideration. We present a case with primary PG of upper thyroid gland which might help clinician to make the decision in such cases.