8373 High suspicion for thyroid cancer in patient with thyroid Hemiagenesis

Abstract Disclosure: L. Aoun: None. S. Almardini: None. M. Anise: None. F. Haddadin: None. F. Saliba: None. J. Zaidan: None. Background: Thyroid Hemiagenesis (THA) is a rare condition characterized by congenital absence of one lobe of the thyroid gland. Notably, THA is more prevalent in females and the left lobe is more likely to be absent with or without the isthmus. Most patients are euthyroid, and diagnosis is usually incidental, so the true prevalence of THA is uncertain as there are certainly undiagnosed cases. Studies have shown a link between THA, thyroid cancer, and hyperparathyroidism. We present a case of THA and high suspicion for thyroid cancer. Case Presentation: 54-year-old female with history of Rheumatoid arthritis who presented for evaluation of incidental thyroid nodules, occasional palpitations, tremors, and mild change in her voice. She denied abnormal weight loss or diarrhea. No history of radiation to the neck and no family history of thyroid disease or thyroid cancer. The thyroid exam showed an enlarged left palpable nodule. Labs significant for TSH 1.6 mIU/L (normal: 0.4-4 mIU/L), FT4 0.8 ng/dl (normal 0.7-1.9 ng/dL) and T3 77ng/dL (normal: 60-180 ng/dL). Thyroid U/S showed left hemiagenesis and right sided nodules biggest is 1.1 cm solid, hypoechoic with coarse calcifications, FNA was recommended and showed follicular lesion of undetermined significance, molecular testing was done and Thyroseq came back intermediate to high risk RAS and EIF1AX positive reflecting a 70 % probability of cancer. Based on these results, surgery was recommended, and the patient underwent right thyroidectomy. Surgery was uncomplicated and despite reported higher risk of hyperparathyroidism patient’s calcium and PTH were normal, and no parathyroid adenomas were identified intraoperatively. The pathology from the thyroidectomy showed follicular adenoma of 1 cm and no malignancy. She was started on Synthroid 100mcg daily post op. Discussion: This case demonstrates a case of a benign thyroid nodule and preserved parathyroid levels in the setting of thyroid hemiagenesis. Usually in THA, the contralateral lobe is at an increased risk for pathology of compensatory hypertrophy or hyperplasia. According to available studies, cancer association with THA was more common in left hemiagenesis and parathyroid adenomas more common ipsilateral to hemiagenesis . Despite Our patient’s FNA revealed atypical findings, molecular testing revealed RAS and EIF1AX positive, marking intermediate to high cancer risk. However, the thyroidectomy pathology report unveiled no evidence of malignancy, contraindicating the anticipated high cancer risk in those with left THA. This case highlights the rarity of THA and different possible presentations and cancer risks. Presentation: 6/2/2024