Bone Infarct
Medullary Bone Infarct, Osteonecrosis

General Considerations

• Usually found within the intramedullary cavity of the metaphysis or diaphysis of bone
• When osteonecrosis occurs in the epiphysis, it is called avascular necrosis
• In long bones, their calcification is similar to an intramedullary bone infarct
• Bone infarcts tend to have a well-circumscribed, sclerotic margin
• Due to interruption of the blood supply from numerous causes including:
• Sickle cell disease
• Polycythemia
• Arteritis, as in connective tissue diseases
• Trauma
• Idiopathic
• Excessive exogenous or endogenous steroids
• Alcoholism and pancreatitis

Imaging Findings

• Intramedullary calcification will be seen on conventional radiographs after months or years
• Frequently has a well-defined “membrane” or “shell” surrounding it (unlike enchondromas)
• There may be associated periostitis
• MRI is much more sensitive to ischemic changes and may show findings in 6-12 hours
• On MRI, the signal in the center of  a chronic bone infarct is similar to normal marrow; in acute infraction, the T1 signal is decreased
• “Double line sign” on T2-weighted MRI is due to hyperintense central ring of granulation tissue and hypointense peripheral ring that is sclerotic

Differential Diagnosis

• Enchondroma

Prognosis

• Very rarely may de-differentiate into a malignancy such as osteosarcoma or fibrosarcoma

Chronic Bone Infarct. There is a well-defined, intramedullary calcification in the meta-diaphysis of the distal tibia with a "shell-like" outer calcified membrane characteristic of an old bone infarct.

Densities in both proximal tibias an distal femurs represent areas of avascular necrosis in a patient with sickle cell disease.