Diagnosis
Extramedullary hematopoiesis
Findings
Axial-enhanced computed tomography (CT) images
demonstrate heterogeneously enhancing soft tissue masses, right greater than
left, in the posterior mediastinum. Adjacent ribs are expanded with coarsened
trabeculae.
Discussion
The best diagnostic clue for extramedullary
hematopoiesis is multiple lobulated soft tissue masses in the posterior
mediastinum with adjacent bone marrow expansion and coarsened trabeculae, especially
in the clinical setting of chronic anemia. The mass may contain fat, but does
not have calcification or bony erosion due to its very slow growth. The
location is usually in the paraspinal region and usually caudal to the sixth
thoracic vertebra. The mass may be either unilateral or bilateral and symmetric
or asymmetric. Contrast enhancement is heterogeneous.
Extramedullary hematopoiesis is defined as benign marrow elements occurring outside the osseous medulla as a compensatory mechanism
for chronic anemia due to bone marrow dysfunction. It is most commonly associated
with thalassemia major, congenital spherocytosis, congenital hemolytic anemia,
and sickle cell anemia. Although extramedullary hematopoiesis usually occurs in
the liver, spleen, and lymph nodes, it may occur in the posterior mediastinum.
The underlying mechanism probably involves extrusion of bone marrow elements through
thinned cortex of neighboring ribs and vertebral bodies.
Extramedullary hematopoiesis is usually
asymptomatic and no treatment is needed. Most patients are diagnosed
incidentally on radiographic imaging. Rarely, extramedullary hematopoiesis
leads to spinal cord compression from paravertebral extension. Spontaneous hem
thorax very rarely occurs. Hemorrhage rarely occurs as a complication from
transthoracic needle biopsy.
- Koch CA, et al. Nonhepatosplenic extramedullary hematopoiesis: Associated
diseases, pathology, clinical course, and treatment. Mayo Clin Proc. 2003;78:1223-1233.
- Kwak HS, et al. CT findings of extramedullary hematopoiesis in the
thorax, liver and kidneys, in a patient with idiopathic myelofibrosis. J Korean Med Sci. 2000;15:460-462.
- Korsten J, et al. Extramedullary hematopoiesis in patients with
thalassemia anemia. Radiology. 1970;95:257-263.
- Parker MS, Rosado-de-Christenson ML, Abbott GF. Abnormalities and diseases of the
mediastinum-extramedullary hematopoiesis. Teaching Atlas of Chest Imaging
2006; Thieme, New York, 695-698.