Extramedullary hematopoiesis

Findings

There are at least three non-enhancing T1 mildly hypo intense, T2 hypo intense masses in the posterior epidural space of the mid thoracic spinal canal causing mass effect on the adjacent spinal cord. There is also abnormal T1 and T2 hypo intensity of the vertebral body marrow.

Differential diagnosis:
- Extramedullary hematopoiesis
- Epidural hematoma
- Epidural abscess
- Neurogenic tumor
- Lymphoma
- Metastases


Diagnosis: Extramedullary hematopoiesis


Key points

Extramedullary hematopoiesis (EH) is a compensatory response to deficient bone marrow blood cell production.
Either in response to continued RBC destruction (e.g. sickle cell disease, thalassemia, spherocytosis) or inability of normal RBC precursor to produce cells (e.g. iron deficiency, pernicious anemia, myelofibrosis, leukemia, lymphoma, diffuse osseous mets).
Liver and spleen most common sites followed by the spine. Other common sites include thymus, cardiac, adrenals, kidneys, lymph nodes, and GI tract.
Spinal involvement most common with thalassemia.
Epidural EH thought to arise from primitive rests in the dura mater or epidural space. Another theory attributes it to direct extension from vertebral bone marrow.
Typical imaging appearance is of a lobular multi-segmental mass in the mid thoracic posterior epidural space that is T1 isointense and T2 hypo intense to the cord with variable enhancement.
Cord and nerve root compression can occur.
Treatment: EH very radiosensitive with prompt response; surgery considered when severe symptoms or failed radiotherapy. Hydroxyurea and blood transfusions may also be used.