Spine, extradural space - extramedullary haematopoiesis (EMH).
Postoperative course: The patient's neurological state improved markedly following the removal of the tumor and he was soon able to walk unassisted. Sensation also gradually improved. In light of the histological findings the patient received a bone marrow biopsy which showed a myeloproliferative disease and polycythemia vera. The patient was subsequently lost to follow-up.
Discussion: Extramedullary hematopoiesis (EMH) is a compensatory phenomenon that occurs when normal function of the bone marrow is disturbed. The organs that are most frequently involved include the spleen, liver and lymph nodes. However, other organs may also be involved but less frequently.
EMH in the spinal epidural space is a rare but treatable cause of progressive paraparesis in patients with a variety of hematological disorders. Since 1956 there have been more than 50 reported cases, most of which occurred in association with thalassaemia (1, 2). In spinal cord compression secondary to EMH, the lesions are commonly localized to the mid-lower thoracic region (1-6).
Theories concerning the pathogenesis of this lesion include the hematopoietic capacity of the dura (in the fetus), primitive rests, embolization of hematopoietic stem cells to the dura, and extrusion of vertebral bone marrow consequent to bony erosions or fractures.
Contributed by G Stuart Rutherfoord, Deon Lamprecht and Richard H Hewlett