Intrathyroid parathyroid carcinoma and its diagnostic challenges ‒ case report and systematic review

This study presents a case of asymptomatic Intrathyroidal Parathyroid Carcinoma (IPC) and a scoping review of the literature from the past 25-years, aiming to characterize the clinical and laboratory profiles and diagnostic difficulties of this rare condition. We present a 61-year-old male presented with a thyroid nodule incidentally detected during routine ultrasonography, with normal serum calcium and Parathyroid Hormone (PTH) levels. The patient underwent right hemithyroidectomy with level VI lymphadenectomy, and histopathological analysis confirmed intrathyroidal parathyroid carcinoma after extensive expert review. The patient remains under regular follow-up, with no evidence of recurrence or metastasis.

A systematic search was conducted in the PubMed database (2000-2025) using the descriptors "parathyroid carcinoma" and "intrathyroidal". Of 51 studies initially identified, 37 met the inclusion criteria, totaling 38 IPC cases when including the present report. Data extracted included patient demographics, symptoms, laboratory findings, tumor location, histopathological characteristics, and outcomes.

Results demonstrated a female predominance, with ages ranging from 14- to 77-years and a higher frequency of tumors located in the right thyroid lobe. Most patients (81.5%) presented with hypercalcemia and elevated PTH levels, whereas 7.9% were normocalcemic. Metastatic disease occurred in 23.6% of cases during follow-up. En bloc surgical resection, including ipsilateral thyroidectomy and level VI lymphadenectomy, remains the gold standard treatment and provides better local disease control. Definitive diagnosis, however, is usually achieved only after histopathological evaluation due to cytological overlap with thyroid neoplasms.

In conclusion, IPC represents a diagnostic and clinical challenge, often identified retrospectively, and early clinical suspicion is essential to improve prognosis and survival outcomes.