FRI367 An Unusual Presentation Of A Thyroid Nodule: A Thyroid Paraganglioma

Disclosure: M. Owrangi: None. F. Hasan: None. Introduction: Thyroid paraganglioma (PGL) is a rare thyroid tumor that originates from inferior laryngeal paraganglia. We present a case of a patient initially believed to have a thyroid nodule which turned out to be a PGL. Case Presentation: A 49 year-old white female with history of GERD and mild dysphagia who was found to have a left parathyroid adenoma vs. a left exophytic thyroid nodule. Previous ultrasounds had all showed slow but progressive enlargement of the lesion. Her labs had showed iPTH, Ca, TSH, and free T4 all within reference range and she was clinically euthyroid. She had 2 fine needle aspirations (FNA) which were both non diagnostic. She ultimately underwent surgical excision of the mass. The pathological examination showed cells that were positive for synaptophysin, chromogranin, GATA-3, S100, and neuron-specific enolase. They were negative for Ki-67, PTH, thyroglobulin, TTF-1, CK AE1/AE3, and CD 138. The overall findings were consistent with thyroid PGL. Discussion: In this case Thyroid PGL was diagnosed after pathological examination, including immunohistochemistry, was performed on a surgically excised sample, after 2 FNAs were non-diagnostic. Thyroid PGLs are elusive tumors. One study suggested that since they were first described in 1964, until 2015, there have only been 54 reported cases of thyroid PGLs, with a strong female predominance (88.9%). They often present as asymptomatic thyroid nodules and their diagnosis can be difficult by FNA alone as they can morphologically mimic medullary thyroid carcinoma, intrathyroidal parathyroid proliferation, metastatic neuroendocrine tumor, or calcitonin-negative neuroendocrine tumor of the thyroid gland (CNNETT). Thyroid PGLs are often benign, slow growing tumors and account for only 0.012% of all head and neck tumors with a malignancy rate of 4-16%. They usually present as single nodules averaging 3.5 cm and are often diagnosed with routine ultrasound assessment of the neck. Since they are associated with the parasympathetic nervous system, signs and symptoms including tachycardia, palpitations, and weight loss due to hormonal activity are classically absent from thyroid PGLs. In about 30% of cases, thyroid PGLs have a genetic predisposition and are more than one and associate with other tumors such as pheochromocytoma. Major hereditary disorders associated with paraganglioma include von Hippel-Lindau disease, multiple endocrine neoplasia, familial paraganglioma syndromes 1 to 4, and neurofibromatosis. Therefore, it is highly recommended that patients with a diagnosis of thyroid PGL undergo additional investigations with imaging, hormonal activity assessment, and genetic testing. Given the difference in management of thyroid PGLs compared to its cytology mimics, and their association with some familial cancer syndromes, use of immunohistochemical staining is crucial in making the correct diagnosis. Presentation: Friday, June 16, 2023