Explanation: Chronic haemolytic anaemia increases the demand on the bone marrow, causing expansion of the medullary cavity. If the haemopoeitic stimulus is marked and prolonged, sites of haemopoeitic tissue may appear outside the marrow.

Sites include:
• paraspinal, often T8 to T12
• spleen, liver and lymph nodes
• adrenal glands
• mediastinum, heart and thymus
• lung
In this case of a patient with thalassaemia major the radiological findings are:
• paravertebral soft-tissue density masses
• coarsening of trabeculae of vertebral body
• rib expansion
• pacemaker lead – the patient had cardiomyopathy due to iron overload

Reference: Dahnert W. Radiology Review Manual 3rd ed. 1996
Credit: Dr Laughlin Dawes