SUN-415 - Paraganglioma Presenting as A Thyroid Nodule

Introduction:
Paragangliomas are rare neuroendocrine tumors that arise from parasympathetic or sympathetic ganglia. Since that initial report, just over 50 cases have been documented in the literature, highlighting the extreme rarity of this entity.
Radiographically, these tumors are typically well-circumscribed, hypoechoic, and hypervascular, measuring between 1.8 and 3.0 cm. Fine-needle aspiration findings are often nonspecific, frequently demonstrating loosely cohesive epithelioid cells with clear-to-eosinophilic cytoplasm.
Despite their often indolent clinical presentation and lack of symptoms related to catecholamine excess, thyroid paragangliomas are considered locally aggressive and may invade surrounding structures.

Hospital course:
The patient is a 57-year-old male who with an incidentally discovered thyroid nodule on a CT chest scan following a skiing accident, with subsequent ultrasound revealing a well-circumscribed solid nodule measuring 2.4 cm in the thyroid isthmus. The nodule had characteristics consistent with TR 4, indicating the need for further evaluation with fine-needle aspiration (FNA).
The patient's thyroid-stimulating hormone level was within normal limits at 1.84 mIU/L. Notably, there was no history of radiation exposure to the head or neck, no familial thyroid disease, and no symptoms related to swallowing, speech, or breathing.
He underwent FNA which showed follicular cells with nuclear enlargement suspicious for thyroid cancer. Following the FNA, the patient was referred to ENT for surgery and underwent a thyroid isthmusectomy. Intra-operatively a superior isthmus thyroid nodule located within the pyramidal lobe was resected.
The pathology confirmed the presence of a paraganglioma (2.0 cm) within the excised tissue.
The surgical margins were negative for the tumor, suggesting complete resection.


Conclusion:
Immunohistochemical staining is essential for establishing the diagnosis of thyroid paragangliomas. Thyroid paragangliomas are exceedingly rare and frequently misdiagnosed as thyroid carcinoma, in part because several key immunohistochemical stains are not routinely performed during standard thyroid nodule evaluation.
Accurate diagnosis is clinically significant, as the management of paragangliomas differs substantially from that of primary thyroid cancers with respect to surgical extent, postoperative surveillance, hormone secretion evaluation, and the need for germline mutation screening.
Given the extreme rarity of thyroid paraganglioma and its diagnostic similarities to more common thyroid neoplasms, improved recognition of characteristic ultrasound features, combined with identification of patients at increased genetic or clinical risk for paraganglioma, may allow for more targeted use of immunohistochemical testing in selected cases and ultimately increase diagnostic accuracy.

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