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Imaging Diagnosis

Skeletal System

The radiologist may be the first to suggest the correct diagnosis of sickle cell disease. If the underlying pathological changes are remembered, the radiological findings are not difficult to envision. The skeletal abnormalities are the result of two fundamental alterations in the bone marrow: hyperplasia and infarction.

The marrow hyperplasia seen in sickle cell anemia causes generalized osteoporosis, bone softening and resorption (Fig. 31.1). There is widening of the medullary canal of virtually all bones; the finer trabeculae disappear and the major trabeculae are thinned (but may actually appear more prominent on the radiograph because of the loss of the finer trabeculae and the appearance of reinforcement trabeculae). The cortex becomes thinned and attenuated as a result of resorption. The long and short bones of the extremities lose their normal biconcave contour and become squared off or rectangular in outline as a result of the marrow hyperplasia, medullary expansion, and cortical thinning. These changes occur in young children, particularly in the hands and feet. The foramina for the nutrient arteries become enlarged and appear unusually prominent. The digits tend to be short and thickened, especially in cases of superimposed infarction (see later). In the spine and weight-bearing bones of the lower extremities, especially the hips, there may be deformity because of softening of the bone, with or without associated fractures.

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Fig. 31.1 Sickle cell anemia. Changes in the hands of a young child (A) and young adult (B). There is generalized osteopenia with loss of the fine trabeculae and thinning of the major trabeculae which actually appear coarser (as in B) because of the loss of the finer trabeculae. In young children (such as in A) there is a widening of the medullary canals of the metacarpals and phalanges and thinning of the cortices caused by marrow hyperplasia. The long and short bones of the extremities may lose their usual biconcave contour and become squared off or rectangular in outline. Also note that in A there is a periosteal reaction surrounding the shaft of the fifth metacarpal due to infarction of this bone. There are also multiple translucent areas noted between the coarsened trabeculae in the first metacarpal. In the older child or young adult (B), the medullary expansion and cortical thinning of the long and short bones have virtually disappeared with the bones remodeling to a more normal configuration, reflecting the change in the site of marrow activity from the long bones to the spine and pelvis as the child grows towards adulthood. The osteopenia with coarse appearance of the remaining trabeculae still persists, giving a somewhat cystic appearance to the ends of the metacarpals and phalanges. In some adults the metacarpal index is increased and the tubular bones of the hands and feet are elongated (the "pseudo-Marfan's syndrome" sign of sickle cell anemia).

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