IS Case 4: Extramedullary hematopoiesis.
Imaging Sciences URMC 2008.
Publication Date: 2009-05-18
Chest x-ray (Fig. 1) reveals bilateral sharply circumscribed paraspinal masses with smooth borders at the mid-thoracic level. CT scan (Figs. 2 & 3) shows large bilateral paravertebral soft tissue masses with minimal enhancement. The masses are smooth, lobulated, homogeneous and do not erode into the vertebral bodies. The vertebral bodies have a coarse, lacy appearance throughout the spine.
Extramedullary hematopoiesis is the production of blood elements outside the bone marrow cavity. It occurs in cases of severe chronic anemia, and can be seen in thalassemia, hereditary spherocytosis, B12 and folate deficiency, aplastic anemia, myeloproliferative disorders, leukemia, lymphoma and sickle cell disease. Extramedullary hematopoiesis primarily occurs in the liver, spleen, lymph nodes and as paraspinal masses (as pictured in this case). It has been reported to occur in virtually every organ of the body including the thyroid, prostate, pericardium, liver and lung. The growth pattern is unique, with rapid initial growth followed by slow or no growth.
The differential diagnosis for a paraspinal mass includes neurogenic tumors, lymphoma, metastasis, paravertebral abscesses, and lateral meningocele. Extramedullary hematopoiesis should also be included particularly if there is a history of chronic anemia.
Characteristic findings of extramedullary hematopoiesis include unilateral or bilateral smooth, sharply delineated, often lobular paraspinal masses. The masses rarely calcify and usually are caudal to T6. There is no erosion into the vertebral bodies or ribs. The bones may provide a hint to the diagnosis. In extramedullary hematopoiesis, there is resorption of trabeculae giving a coarse, lace-like appearance to the bones. Additionally, thinning of the cortices and widening of ribs may occur due to marrow expansion and reconversion. Associated paracostal, hepatic or splenic soft tissue masses and/or lymphadenopathy can also aid in the diagnosis.
There is no treatment necessary, unless it is complicated by spinal cord compression, bleeding or effusion. A technetium-99m sulfur colloid study may help to confirm the diagnosis by revealing extrahepatosplenic uptake of colloid. Otherwise a fine-needle biopsy can be obtained.
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