6645 Paraganglioma or Benign Ectopic Thyroid Tissue?

Abstract Disclosure: J.A. Dower: None. R. MacLeod: None. B. Cardoso: None. C. Matouk: None. S. Mehra: None. G. Riccio: None. L. Williams: None. S.K. Majumdar: None. Introduction: During gestation, cells destined to form the thyroid descend through the thyroglossal duct; ectopic thyroid tissue may deposit anywhere along this route from tongue base to mediastinum (1). Less commonly, thyroid tissue can be found lateral to the duct, either alone or in association with a lymph node (2). We present a case of lateral ectopic thyroid tissue mimicking paraganglioma. Clinical Case: A healthy 32-year-old woman presented to ENT with cervical adenopathy persisting for several months after a flulike illness. FNA showed no evidence of malignancy. A neck CT with contrast ordered for further evaluation revealed a 3.2 x 2.3 x 1.5 cm enhancing mass within the right carotid space, splaying the external and internal carotid artery branches, most concerning for paraganglioma. A second, smaller lesion was noted inferiorly. Neck MRI confirmed these findings and revealed a subcentimeter T2 lesion within the right thyroid lobe. The patient was referred to endocrine for further workup. She had no symptoms of sympathetic hyperactivity and no family history suggestive of pheochromocytoma or paraganglioma. Biochemical workup was largely within normal limits: plasma metanephrines 53 pg/mL (57), normetanephrines 94 pg/mL (148), calcitonin <2 pg/mL, TSH 1.210 uIU/mL (0.27-4.2), FT4 1.52 ng/dL (0.8-1.7). Follow-up 24-h urine studies were also unremarkable: metanephrines 166 mcg (36-190), normetanephrines 159 mcg (35-482). Brain MRI, chest CT, and abdomen/pelvis MRI were negative for additional masses. DOTATATE PET/CT was completed to determine if the thyroid lesion was another potential paraganglioma requiring resection versus a nodule amenable to biopsy; uptake was confined to the carotid space lesions, so FNA of the thyroid nodule was considered safe. Thyroid FNA revealed FLUS with genetic testing indicating low likelihood of malignancy. The patient underwent tumor embolization followed by neck dissection with successful removal of both the larger and smaller masses identified on imaging. Frozen and permanent tissue section revealed that both masses consisted of benign thyroid tissue without associated lymphoid tissue. The patient experienced jaw pain with eating after surgery and is under consideration for Botox injection. Conclusion: Benign thyroid tissue can deposit in unexpected places, mimicking malignancy and paraganglioma, alike. Even a very thorough workup can mistake the identity of a mysterious mass; only the tissue itself can make the diagnosis. References: 1. Cooper, David S., and Paul W. Ladenson. “The Thyroid Gland.” Greenspan’s Basic & Clinical Endocrinology, McGraw-Hill Medical, New York, NY, 2011, pp. 163-226. 2. LiVolsi, Virginia A. “Developmental Biology and Anatomy of the Thyroid.” Surgical Pathology of the Thyroid, Saunders, Philadelphia, PA, 1990, pp. 3-23. Presentation: 6/3/2024