Diagnostic pitfalls in a cystic ectopic intrathyroidal parathyroid adenoma mimicking a nodular goiter: A care-compliant case report

RATIONALE: Cystic parathyroid adenomas are rare and seldom arise in ectopically located glands which may be found within the carotid sheath, mediastinum, thymus, or thyroid grand. They cannot be detected consistently by any imaging methods. Unusual symptoms may bring about certain pitfalls and difficulties for the diagnosis of primary hyperparathyroidism (PHPT) caused by cystic parathyroid adenomas. Until now, there are no specific guidelines on the management of cystic ectopic intrathyroidal parathyroid adenoma (ETPA). PATIENT CONCERNS: An 82-year-old male musician presented abrupt thyroid enlargement, hoarseness, and trachea compression when he was playing the clarinet. Thyroid and renal function tests were normal. Serum-free calcium and parathyroid hormone (PTH) were in high concentration. Thyroid ultrasonography (US) detected a giant and cystic nodule within right thyroid lobe, which is the very image of cystic nodular goiter. Parathyroid US was negative. The cystic nodule had a decreasing radioactive uptake of Technetium-99m-methoxyisobutylisonitrile ((99m)Tc-MIBI). At patient's request, the invasive fine-needle aspiration (FNA) was not conducted. DIAGNOSES: The patient was initially diagnosed as cystic nodular goiter and inconclusive PHPT. INTERVENTIONS: Enucleation of solitary cystic intrathyroidal nodule was conducted. OUTCOMES: The cystic nodule strongly resembled a nodular goiter grossly, but it was proved cystic ETPA by histopathology. Postoperative follow-ups found that serum-free calcium and PTH decreased sharply into normal range, and hoarseness and trachea displacement were obviously improved. LESSONS: The diagnosis of cystic ETPA is easily overlooked for its rarity. Diagnostic pitfalls, including atypical symptoms, inconclusive imaging manifestation, and unidentified gross specimen, are highlighted. They make the diagnosis of PHPT caused by cystic ETPA challenging. Patients would rather choose surgical excision directly than invasive FNA. Acute hemorrhage of the preexisting ETPA may account for the cystic degeneration.