Extramedullary Hematopoiesis

General Considerations

• Response to insufficient blood cell production by production of blood elements outside of the marrow cavity
• Most often due to hemolytic anemias such as sickle cell anemia, thalassemia and hereditary spherocytosis
• May also be seen in prolonged iron deficiency anemia, myelofibrosis and sclerosis, polycythemia, leukemia and lymphoma
• About a quarter of patients have no known hematologic disease
• Areas of extramedullary hematopoiesis include the spleen, paraspinal regions of the thorax, liver and sometimes adrenals, bowel, dura mater and breast
• Thalassemia is an inherited autosomal recessive blood dyscrasia resulting in underproduction of globins which may lead to severe anemia

Clinical Findings

• Most often microscopic and asymptomatic
• Chronic anemia

Imaging Findings

• Bilateral paraspinal masses with round,  lobulated margins
• Thoracic masses occur most often in patients with thalassemia or congenital hemolytic anemia
• Medullary expansion of the bony structures with widening of the ribs being the most pronounced bony finding
• Resorption of trabeculae produces coarsened appearance to bones
• Splenomegaly (or absent spleen)
• Masses to don’t calcify and do not usually cause bone erosion
• The lesions are usually of low-attenuation on non-contrast CT and may mildly enhance after contrast

Differential Diagnosis

• Neurofibromatosis

Treatment

• Blood transfusions
• Hydroxyurea reported to decrease the size of the masses

Complications

• Spinal cord compression
• Pleural effusions
• Hemothorax
• Respiratory failure  

Extramedullary Hematopoiesis in Thalassemia. There are large
paraspinal masses (white arrows) with smoothly marginated,
lobulated contours. All of the ribs (red arrow) are expanded
and the overall bone density is increased.
For this same photo without the arrows, click here

For more information, click on the link if you see this icon

Extramedullary Hematopoiesis: Breathtaking and Hair-Raising. N Engl J Med 1999; 341:1702-1704

Extramedullary hematopoiesis (EMH). Rita Agarwala, MD. Applied radiology, April, 2006.