EP1586 - ECE_3112 - Ectopic papillary thyroid carcinoma of the lateral neck: an unusual presentation

The presence of thyroid tissue outside its normal anatomical location, between the second and fifth tracheal rings, is defined as ectopic thyroid tissue. Approximately one to three percent of ectopic thyroid tissue is located in the lateral neck. Most cases are asymptomatic and considered benign.However, lateral neck ectopic thyroid tissue may also represent metastatic disease from an occult primary thyroid carcinoma, making accurate diagnosis challenging. A 36-year-old male presented for microwave ablation of a large right-lobe thyroid nodule after five years of ultrasound surveillance. Progressive growth had been documented, and surgery was recommended, but the patient opted for minimally invasive treatment. Repeated fine-needle aspiration of the right-lobe nodule showed benign cytology, thyroid function tests were normal, and no cervical lymphadenopathy was detected. Clinical examination revealed a palpable right thyroid mass causing compressive symptoms and cosmetic concerns. Ultrasound demonstrated a parenchymatous-colloid nodule measuring 3.1 × 4.1 × 2.5 cm in the right lobe, a 0.2 cm micronodule in the left lobe, and an enlarged left lateral cervical lymph node with microcalcifications, highly suspicious for malignancy. During microwave ablation in November 2024, fine-needle aspiration of the suspicious lymph node suggested papillary carcinoma, possibly arising from ectopic thyroid tissue. In February 2025, right lobectomy with excision of lateral neck tissue and lymph node dissection was performed. Histopathology confirmed a benign right-lobe nodule and papillary carcinoma of conventional and follicular variants originating from ectopic thyroid tissue, with microscopic lymphatic invasion and no vascular invasion.Postoperative evaluation revealed elevated serum thyroglobulin levels of 123.6 ng/mL. Computed tomography identified enlarged lateral cervical lymph nodes. Completion thyroidectomy and removal of metastatic lymph nodes were performed. Histology demonstrated a 0.2 cm papillary microcarcinoma in the left thyroid lobe and metastases in three of eleven lymph nodes, while remaining thyroid tissue showed nodular colloid goiter. Follow-up computed tomography and whole-body scintigraphy were normal. The patient received radioactive iodine therapy I-131 150 mCi. Ectopic thyroid carcinoma of the lateral neck is a rare but clinically important entity. Papillary microcarcinoma, despite its small size, may exhibit aggressive behavior and requires careful evaluation. Thermal ablation enabled early detection, appropriate surgical management, and adjuvant therapy, resulting in a favorable oncological outcome and long-term disease control. This case highlights the importance of multidisciplinary assessment, imaging, and histopathological correlation in complex thyroid disease presentations in clinical practice.