Silent intrathyroid parathyroid carcinoma

SUMMARY: A 59-year-old male presented with an accidental thyroid mass in 2022. Ultrasound and CT scan showed a nodule 5.2 × 4.9 × 2.8 cm (EU-TIRADS 4) in the right lobe of the thyroid gland. Taking into account the results of the fine needle aspiration biopsy (Bethesda V), intrathyroid localization, and absence of clinical symptoms, a malignant tumor of the thyroid gland was suspected. The patient underwent total thyroidectomy using fluorescence angiography with indocyanine green, and two pairs of intact parathyroid glands were visualized in typical localization. Unexpected histological and immunohistochemistry examinations revealed parathyroid carcinoma. Due to the asymptomatic course of the disease and atypical localization of parathyroid tumor, primary hyperparathyroidism was not suspected before the surgery. The diagnosis of asymptomatic intrathyroid parathyroid cancer is a serious diagnostic challenge for a wide range of specialists. LEARNING POINTS: Parathyroid cancer is a rare disease that may be asymptomatic. Intrathyroidal localization of parathyroid carcinoma is casuistic and challenging for diagnosis, and the treatment strategy is not well defined. Preoperative parathyroid hormone and serum calcium testing are recommended for patients with solid thyroid nodules (Bethesda IV–V).