The ribs in thalassemia. II. The pathogenesis of the changes.

In 32 patients with thalassemia the spectrum of rib changes, including widening, osteoporosis, localized lucencies, cortical erosions, "rib-within-a-rib" appearance, subcortical lucency, and extramedullary hematopoiesis, is reviewed. This material is supplemented by the radiographic and computed tomographic findings in a specimen of spine, posterior ribs, and extramedullary hematopoietic masses. The relevant literature on thalassemia, including two cases of "costal osteoma," is reviewed. A mechanism is offered to explain the various rib changes based on (a) the relationship of the proliferating marrow to the medulla, cortex, and periosteum, (b) the patient's age at the onset of a transfusion regimen, and (c) the type of transfusion regimen used.