Cervical Lymph Node Metastasis of Papillary Thyroid Carcinoma without Identifiable Primary Tumor on Examination: A Case Report

Background: Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer, with cervical lymph node metastases occurring in 20% to 50% of patients, often presenting as a neck mass. Incidental detection of PTC in cervical lymph nodes, without an identifiable primary tumor in the thyroid gland, is rare and can be easily overlooked. Case Report: The author reported the case of a 25-year-old woman who presented with a left neck mass but no palpable thyroid nodule. Fine needle aspiration revealed atypical cells. Ultrasound showed enlarged lymph nodes with partial necrosis or cystic changes on the left side of the neck, while the thyroid gland appeared normal. A computed tomography (CT) scan confirmed multiple enlarged left cervical nodes, some with necrosis, and normal thyroid glands. A biopsy of the lymph nodes confirmed the diagnosis of thyroid carcinoma. Hematoxylin and eosin staining demonstrated the nuclear features characteristic of PTC, and immunostaining was positive for thyroglobulin and thyroid transcription factor-1. The patient underwent total thyroidectomy and left modified radical neck dissection. Pathological examination revealed a 1.5×0.7×0.5 cm papillary carcinoma in the left lower pole. The surgery and postoperative radioactive iodine treatment were uneventful. After three years, a post-ablation whole-body scan was negative, and anti-thyroglobulin antibodies and thyroglobulin levels were also negative. Conclusion: The absence of malignant findings in the thyroid during examination complicates the diagnosis of PTC, presenting a significant challenge for clinicians. This case underscores the importance of thorough investigations to prevent missed diagnoses and delays in treatment.