Musculoskeletal ImagingSickle cell anaemia
a disorder involving reduction in the blood's capacity to transport oxygen (
anaemia), resulting from the presence of an abnormal haemoglobin termed haemoglobin S (Hb S). Sickle cell disease is used to describe all conditions in which Hb S is present: sickle cell anaemia (Hb S-S),
sickle cell trait (Hb A-S), and diseases in which Hb S is combined with another abnormal haemoglobin (
sickle cell haemoglobin C disease,
sickle cell thalassaemia disease). Patients have painful crises affecting the bones and joints of the
extremities with fever, icterus, nausea, vomiting,
abdominal pain and prostration. Sickle crises apparently occur when red blood cells become deformed, which produces vaso-occlusion and tissue death. Bone and joint pain and tenderness are frequently related to
infarction of bone marrow.
On radiographs, characteristic findings include marrow hyperplasia, sickle cell dactylitis,bone infarction, growth disturbances, fractures, osteomyelitis, septic arthritis and fish vertebrae due to compression by the adjacent intervertebral discs (Fig.1). Osteonecrosis is a well-recognized complication of sickle cell anaemia.
Children between the ages of 6 months and 2 years often have osteonecrosis of the small tubular bones of the hands and feet (sickle cell dactylitis or hand foot syndrome). The diaphyses (and epiphyses) of long tubular bones are also common sites of infarction in patients of all ages. A bone within bone appearance, which is diagnostic of osteonecrosis, is evident. Tibiotalar deformity, characterized by slanting of the articular surfaces of the distal portion of the tibia and the talus, is a nonspecific sign in sickle cell anaemia. In addition, central depression of the vertebral bodies, leading to squared-off endplate depressions (H vertebra) is a frequent finding. Hyperuricaemia and gout also occur in some patients with sickle cell anaemia.
Scintigraphy reveals focal areas of decreased uptake of bone-seeking radionuclides. Scanning with both bone- and bone marrow-seeking radionuclide agents allows differentiation between osteomyelitis and osteonecrosis in some patients with sickle cell anaemia.
On MR imaging, osteonecrosis and osteomyelitis are evident. In osteomyelitis, the affected region demonstrates decreased signal intensity on T1-weighted spin-echo MR images and increased signal intensity on T2-weighted spin-echo MR images. Differentiation of osteomyelitis and acute marrow ischaemia and infarction using MR imaging may not be possible, however.
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