A rare coexistence of intrathyroidal heterotopic bone formation with extramedullary hematopoiesis and oncocytic papillary thyroid carcinoma: a case report and literature review

Background Papillary thyroid carcinoma (PTC) is the most frequently encountered thyroid malignancy, yet its coexistence with intrathyroidal heterotopic bone formation (HBF) and extramedullary hematopoiesis (EMH) is exceedingly rare. This report describes, to our knowledge, the first published case of oncocytic PTC occurring alongside EMH and HBF. A literature review of previously documented cases of intrathyroidal HBF and EMH, along with a discussion on their pathophysiology, was conducted. Case presentation A 49-year-old woman was presented with a calcified mass in the right thyroid lobe and an enlarged cervical lymph node. Preoperative fine-needle aspiration cytology of the lymph node suggested metastatic papillary thyroid carcinoma. The patient underwent total thyroidectomy with central neck lymph node dissection. Histopathological examination revealed multifocal PTCs on both thyroid lobes, including an oncocytic subtype adjacent to the area of mature lamellar bone with intertrabecular trilineage hematopoiesis, and multiple lymph node metastasis. Extensive lymphocytic infiltration consistent with Hashimoto thyroiditis was also observed. Conclusions Our case illustrates a unique combination of pathologic findings: intrathyroidal HBF, EMH, and oncocytic PTC. It highlights the diagnostic challenges posed by these rare entities and emphasizes the importance of thorough histopathological evaluation when encountering calcified thyroid nodule on imaging study. Additionally, this report contributes to the limited literature on this phenomenon and discusses the current understanding of its pathogenesis.