Extramedullary Hematopoiesis and Osseous Metaplasia in Thyroid Gland in Association with Papillary Thyroid Carcinoma: A Report of two Cases

Bone marrow is known as the major site of hematopoiesis. It could occur in several other tissues both during fetal development and after birth. Extramedullary hematopoiesis (EH) is known to occur in the organs of reticuloendothelial system, mainly spleen and liver. It is very uncommonly seen and reported in thyroid normally in association with anemias and myeloid metaplasias. Papillary thyroid carcinoma (PTC) is the most common type of thyroid carcinoma and the most common endocrine malignancy. Herein, we reported two cases of PTC with osseous metaplasia and EH without any other underlying hematological disorders. Even though programmed EH is required to supplement the hematopoietic activity in the bone marrow, excessive and disease- associated EH can occur and mediate chronic inflammation. PTC with osseous metaplasia could be regarded as a unique subtype of thyroid carcinoma, which is more aggressive. Further studies are required in this regard so that PTC with osseous metaplasia could be considered as a prognostic marker.