Extramedullary Hematopoiesis of the Liver and Spleen

Abstract

Hematopoiesis is the formation of blood cellular components and, consequently, immune cells. In a more complete definition, this process refers to the formation, growth, maturation, and specialization of blood cells, from the hematopoietic stem cell, through the hematopoietic progenitor cells, to the s pecialized blood cells. This process is tightly regulated by several elements of the bone marrow microenvironment, such as growth factors, transcription factors, and cytokines. During embryonic and fetal development, hematopoiesis takes place in different organs: the yolk sac, the aorta–gonad mesonephros region, the lymph nodes, and not lastly, the fetal liver and the spleen. In the current review, we describe extramedullary hematopoiesis of the spleen and liver, with an emphasis on myeloproliferative conditions.

Tipping the balance between erythroid cell differentiation and induction of anemia in response to the inflammatory pathology associated with chronic trypanosome infections

“…As anemia results in tissue hypoxia, a compensatory stress-induced erythropoiesis can be triggered. When occurring in the spleen or even liver, this process is referred to as extramedullary erythropoiesis ( 35 ). At the level of the spleen, it is initiated by either the migration of bone marrow erythroid progenitors into spleen or by the expansion of splenic resident erythroid progenitors ( 36 , 37 ).…”

Marked Hyperbilirubinemia Associated with Primary Myelofibrosis Responsive to Ruxolitinib

“…In addition, extramedullary hematopoiesis (EMH) is a well-known phenomenon that occurs in PMF. EMH, a process in which hematopoietic tissue and blood cells develop outside of the blood marrow, develops as a compensatory response to the bone marrow fibrosis seen in PMF, and the liver and spleen are well-known sites of EMH [ 5 ]. Given its predilection for liver involvement, EMH has been suggested to be a rare etiology of obstructive jaundice.…”

Extramedullary Hematopoiesis Adjacent to Vertebral Fracture in a Patient with Pernicious Anemia

“…The patient was advised to have a bone marrow biopsy of her posterior iliac crest, but refused the procedure. A bone marrow biopsy was indicated to evaluate for marrow replacement processes, which may have resulted in the development of EMH, as it does for the liver and spleen 2 . There was no change in the size of the paraspinal soft-tissue mass on serial CT scans 1 year after biopsy.…”

“…Sites of pathological EMH may be due to the activation and migration of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) outside of bone marrow origins because of pathological stress and/or injury 1 . Underlying conditions, such as various myeloproliferative disorders or congenital hemolytic anemia, can stimulate HSC/HPC release from the bone marrow to induce the growth of erythroblastic islands, leading to extramedullary hematopoietic tumor formation [1][2][3][4] . This report describes, to our knowledge, the first case of paravertebral EMH spatially related to a lumbosacral compression fracture, possibly representing mechanical extrusion of marrow contents in a patient predisposed to EMH because of underlying pernicious anemia.…”