SUN-334 Thyroglossal Cyst Unveiling Metastatic Hurthle Cell Carcinoma In Hashimoto Thyroiditis

Abstract Disclosure: H.A. Ballout: None. M.A. Karaki: None. R. Ibrahim: None. A. El Nemer: None. Thyroid disorders like Hashimoto's thyroiditis (HT) can complicate the diagnosis and management of concurrent thyroid cancers, including Hürthle cell carcinoma (HCC) and follicular variant papillary carcinoma (FVPTC). Case Presentation: This case describes a 53-year-old female with hypothyroidism, managed on thyroxine therapy, who presented with a recurrent neck mass. Despite normal TSH levels and multiple fine-needle aspirations showing no pathological findings, the mass continued to recur. Ultrasound imaging suggested a thyroglossal duct cyst, leading to surgical excision. Unexpectedly, the pathological examination of the excised cyst revealed metastatic clear cell carcinoma, prompting the patient to undergo a total thyroidectomy. The thyroid tissue analysis identified a bifocal follicular variant of papillary thyroid carcinoma (FVPTC) with no evidence of capsule invasion. Additionally, Hashimoto’s thyroiditis was noted, characterized by lymphocytic infiltration and fibrosis. Post-surgery, the patient was treated with radioactive iodine ablation therapy and thyroid suppression therapy with thyroxine. Discussion: This case illustrates the diagnostic challenges of distinguishing between benign and malignant thyroid conditions in the context of HT. HCC, known for its aggressive nature, and FVPTC, a common variant of papillary thyroid carcinoma, complicate diagnosis and treatment. Conclusion: Effective management of HT with concurrent thyroid cancers requires detailed histopathological assessment and tailored therapeutic strategies. Presentation: Sunday, July 13, 2025