Hematopoiesis and Extramedullary Hematopoiesis

Extramedullary Hematopoiesis: Definition and Pathophysiological Mechanisms

Extramedullary hematopoiesis (EMH) is the process by which blood cell formation occurs outside of the bone marrow, usually as a response to hematopoietic stress or disease conditions.

Physiological and Pathological Hematopoiesis

Normal hematopoiesis occurs primarily within the bone marrow. However, under certain pathological conditions, hematopoiesis may shift to extramedullary sites such as the liver, spleen, and lymph nodes.

Causes of Extramedullary Hematopoiesis

• Bone marrow failure (e.g., aplastic anemia)
• Myeloproliferative disorders
• Severe chronic hemolytic anemia
• Genetic mutations affecting hematopoiesis

Clinical Implications

EMH can lead to organ enlargement, particularly in the spleen and liver, causing complications such as hypersplenism and portal hypertension.

Diagnosis and Management

Diagnosis typically involves imaging studies like MRI or CT scans, along with biopsies to confirm extramedullary hematopoietic activity. Management often depends on treating the underlying cause of hematopoietic stress.