[Thoracic extramedullary hematopoiesis. Apropos of a case]

Extramedullary haematopoiesis is a compensatory response of bone marrow to abnormal haematopoietic tissue formation: the commonest etiology is thalassemia (generally intermedia). The thorax is a rare site and the posterior mediastinum is usually involved. CT scan completes standard chest radiology and allows fine needle aspiration to provide adequate cytologic material for the diagnosis of extramedullary haematopoiesis, especially when an intercurrent pathology is present and could involve paravertebral areas. Thoracotomy may be necessary in rare cases of complications.