MRI findings of extramedullary haemopoiesis.

Extramedullary haemopoiesis (EH) is a compensatory process associated with chronic haemolytic anaemia. It is rare, however, for such an abnormality to cause spinal cord compression. We present two patients with known beta-thalassaemia intermedia who developed spinal cord compression due to masses of extramedullary haematopoietic tissue in the epidural space of the thoracic spine. The EH masses were diagnosed by MRI as an isointense epidural lesion on both T1- and T2-weighted images, compressing severely the spinal cord. After administration of a paramagnetic agent, an intermediate enhancement of the masses was evident. All the vertebral bodies had low to intermediate signal intensity as a result of displacement of fatty marrow by haematopoietic marrow. Expansion of thoracic ribs with bilateral paravertebral masses were characteristic. A small dose of radiotherapy was given and marked improvement in neurological symptoms was evident. An MRI examination established shrinkage of the mass and decompression of spinal cord. The role of MRI in diagnosis of EH masses is essential and radiation therapy is a very effective treatment for this rare complication.