Thyroid-associated paragangliomas.

BACKGROUND: Paragangliomas in the region of the thyroid gland are rare tumors that can present a diagnostic challenge by mimicking follicular and c-cell derived thyroid tumors.
SUMMARY: Thyroid-associated paragangliomas are likely a subset of laryngeal paragangliomas and, although quite rare, should be considered in the differential diagnosis of a hypervascular thyroid nodule. The preoperative diagnosis of thyroid-associated paragangliomas can be challenging since the cytologic and histologic features overlap with more common primary thyroid neoplasms, in particular medullary carcinoma. Differential expression of a panel of immunohistochemical markers, including neuro-specific enolase, chromogranin A, synaptophysin, keratin, and S100, can be used to distinguish thyroid-associated paragangliomas from primary thyroid tumors. Intraoperatively, thyroid-associated paragangliomas may be associated with significant intraoperative bleeding and are often densely adherent to surrounding tissues, including the recurrent laryngeal nerve. Interestingly, the aggressive local behavior of these tumors does not correspond to potential for malignancy, as there are no patients with malignant thyroid-associated paragangliomas reported in the medical literature. Therefore, these tumors may be treated with limited resection. Postoperatively, patients with paragangliomas should receive hormonal evaluation for functional disease, imaging evaluation for multicentric and metastatic disease, and genetic counseling.
CONCLUSION: Thyroid-associated paragangliomas are an important part of the differential diagnosis of a hypervascular thyroid nodule, especially in a patient with a fine-needle aspiration biopsy suggestive of medullary thyroid carcinoma, but with unremarkable serum calcitonin levels. Consideration of a thyroid-associated paraganglioma also has important operative and postoperative implications for determining the extent of thyroid resection as well as follow-up testing.