The magnetic resonance imaging (MRI) appearance of an "established" bone marrow infarct is well-known, consisting of an area of preserved bone marrow signal surrounded by a serpiginous line. We report the uncommon observation of the very early phases of appearance of a bone marrow infarct, showing its progressive de novo appearance on MR images paralleling clinical symptoms and high-dose systemic steroid administration in a young female patient, presenting with acute knee pain. The initial knee MR examination performed one week after pain onset showed no abnormality. One week later, a second examination showed subtle ill-defined dotted signal abnormalities of the bone marrow of uncertain significance, of high signal on PDFS sequences. A third MR study obtained again one week later showed more evident findings with confluence of the high signal "dots" into a serpiginous line with a geographical appearance of the lesion, corresponding to the typical MRI presentation of bone marrow infarcts. Follow-up MRI at seven weeks showed definitive stability of this bone marrow infarct. A whole-body MRI performed for whole skeleton screening revealed multiple bone marrow infarcts typical for systemic avascular necrosis. This case represents a novel observation of the "birth" of a bone marrow infarct, from early intriguing changes to its typical ring-shaped appearance on MR images. It also reminds of the key role of MRI for early diagnosis of bone marrow infarcts and illustrates the emerging role of whole-body MRI for the detection of multifocal, asymptomatic skeletal involvement by ischemic lesions in systemic osteonecrosis.
Keywords: Bone marrow; MRI; corticosteroids; infarcts; knee; magnetic resonance imaging.