Musculoskeletal Imaging

Infarction

necrosis of cells or tissues resulting from ischaemia or obstruction of blood supply. For a general description, see infarction.

Bone infarct usually refers to a necrotic focus in the metaphyseal or diaphyseal regions (Fig.1), whereas osteonecrosis indicates the presence of ischaemic cellular death of bone and bone marrow, and ischaemic necrosis generally applies to areas of epiphyseal or subarticular involvement. Bone infarcts can be subdivided into four zones:

  • a central zone of cell death,

  • a zone of ischaemic injury,

  • a zone of active hyperaemia, and

  • normal tissue.

    Infarcts occurring within an epiphysis or small, round bone almost always have one surface covered by compact subchondral bone and articular cartilage.

    In sickle cell anaemia, diaphyseal infarction of larger tubular bones, especially in the proximal aspect of the femur, is common. Radiographically, bone infarction appears initially as a linear radiodense shadow adjacent to the cortex, which may extend along the entire shaft. Subsequently, the cortex becomes thickened. A bone within bone appearance, which is diagnostic of osteonecrosis, is seen beneath the cortical bone. Other bones that may be infarcted include those of the pelvis, spine and thorax. Increased radiodensity of bone and a coarsened trabecular pattern are typical. In addition, epiphyseal infarcts in sickle cell anaemia may involve the capital femoral epiphysis, leading to an appearance simulating that of Legg Calv Perthes disease. Focal lucency and sclerosis, subchondral linear or curvilinear radiolucent shadows, collapse, and fragmentation are evident in involved epiphyses. In the proximal part of the humerus, alternating areas of lucency and sclerosis produce a snow-capped appearance.

    Skeletal muscle infarction attributable to atherosclerosis obliterans may occur in diabetes mellitus. Patients experience excruciating pain, and a mass or swelling may develop in the involved muscle. In patients with coma-induced compression of the musculature, myonecrosis or rhabdomyolysis may develop. On MR imaging, infarcted muscles usually reveal little change in signal intensity or are of low signal intensity in T1-weighted images and of high signal intensity in T2-weighted and short tau inversion recovery (STIR) images.

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    Fig.1

    Coronal proton-density-weighted MR image demonstrates bone infarcts involving both femora and tibiae. The infarcts have sharply defined serpentine borders of low signal intensity. (Courtesy of Tor Mattsson, MD, Riyadh, Saudi Arabia)
    Infarction, Fig.1