Micrograph showing nucleated red blood cells (bottom left of image), one of the elements necessary to call<unk> , in an endometrial polyp. H&E stain.<unk>  <unk>  or sometimes<unk>  refers to<unk>  occurring outside of the medulla of the bone (bone marrow). It can be physiologic or pathologic. Physiologic<unk>  occurs during embryonic and fetal development; during this time the main site of fetal<unk>  are liver and the spleen. Pathologic<unk>  can occur during adulthood when physiologic<unk>  can't work properly in the bone marrow and the hematopoietic stem cells (HSC) have to migrate to other tissues in order to continue with the formation of blood cellular components. Pathologic<unk>  can be caused by myelofibrosis, thalassemias or disorders caused in the hematopoietic system.
Extramedullary hematopoiesis
Clonal hematopoiesis
Atypical localization of immature precursors
Splenogonadal fusion
Lymphoid neoplasms with plasmablastic differentiation
Dentin dysplasia
Progressive transformation of germinal centres
Progressive osseous heteroplasia