Abstract
BACKGROUND: Atypical parathyroid tumor is an uncommon neoplasm of the parathyroid gland with unknown malignant potential. Differentiation may be necessary between it and the thyroid lesion in certain cases. However, there is a paucity of literature regarding the misdiagnosis of atypical parathyroid tumor as papillary thyroid carcinoma. CASE PRESENTATION: A 70-year-old Chinese Han male patient presented with a complaint of pain in the neck. Laboratory findings revealed elevated parathyroid hormone and hypercalcemia. Ultrasound and computed tomography showed a lesion in the lower pole of the thyroid gland and the paratracheal area. Cytological examination indicated papillary thyroid carcinoma. Unilateral thyroidectomy with central neck dissection was performed. The intraoperative frozen section indicated adenomatoid changes in the mass. Histopathological diagnosis was atypical parathyroid tumor. Postoperative parathyroid hormone and serum calcium decreased significantly and returned to normal 1 month after the operation. CONCLUSION: Cytology of large atypical parathyroid tumor can mimic papillary thyroid carcinoma. Therefore, a comprehensive approach that integrates clinical, radiological, and pathological evaluation is essential.