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Extramedullary haematopoiesis

Dr Alexandra Stanislavsky and Radswiki et al.

Extramedullary haematopoiesis (EMH) is a response to erythropoiesis failure in bone marrow. EMH occurs in haemoglobinopathies, myeloproliferative disorders, or bone marrow infiltration. EMH occurs most often in the spleen and liver and occasionally in the lymph nodes. Less common organs include the pleura, lungs, gastrointestinal tract, breast, skin, brain, kidneys, and adrenal glands.

Pathology

Causes

Radiographic features

Where EMH involves an organ, there is usually radiographic evidence of its enlargement, e.g. hepatomegaly, splenomegaly visualised by ultrasound, CT or MRI. However, in the less common situation where EMH involves other tissues within the thorax, they can be seen as a posterior mediastinal mass. These are paraspinal masses that may be unilateral or bilateral and have smooth, sharply delineated, often lobulated margins.