Soft Tissue, Extramedullary hematopoiesis

Extramedullary hematopoiesis (EMH) is a physiologic condition in the fetal state and can occur in adults as a compensatory phenomenon secondary to failure of the bone marrow to produce adequate blood elements. While liver, spleen, and lymph nodes are common sites, the CNS and its surrounding structures are rarely involved by EMH. Microscopically, there is trilineage hematopoiesis with an infiltrate of erythroid and myeloid elements and megakaryocytes. The most common underlying hematologic conditions associated with CNS EMH are beta-thalassemia and myelofibrosis.