summary Bone Infarcts are medullary bony lesions that are in the same spectrum of disease as osteonecrosis. Patients typically present with an asymptomatic lesion in the metaphysis or diaphysis of long bones, discovered incidentally on radiographs. Diagnosis is made radiographically with the presence of a medullary lesion of sheet-like central lucency surrounded by sclerosis with a serpiginous border, commonly referred to as a "smoke up the chimney" lesion. Treatment is observation as lesions are generally asymptomatic. Epidemiology Risk factors similar risk factors as those seen in osteonecrosis trauma, sickle cell disease, thalassemia, connective tissue disorders, Gaucher's disease, steroid use Etiology Mechanism interruption of blood supply by intrinsic or extrinsic factors Presentation Symptoms usually asymptomatic often found when imaging the extremities for other reasons Imaging Radiographs medullary lesion of sheet-like central lucency surrounded by sclerosis with a serpiginous border "smoke up the chimney" MRI key feature is that central signal remains of normal marrow T1 weighted images peripheral low signal due to grannulation tissue and to lesser extent sclerosis periphery may enhance post gadolinium T2 weighted images acute infarct may show ill-defined non-specific area of high signal intense inner ring of granulation tissue and a hypointense outer ring of sclerosis Bone Scan cold in early phases hot in late resorptive and revascularisation phase Treatment Nonoperative observation indications usually asymptomatic and do not require treatment