Abstract
MRI plays a critical role in the evaluation of osteomyelitis. However, MRI findings of osteomyelitis are not entirely specific and may mimic infiltrative tumors. We describe a case of extraosseous extruded medullary fat with a tiny transcortical tract caused by acute osteomyelitis, diagnosed by MRI and confirmed with intraoperative findings and pathology. Identification of extruded medullary fat is a specific MRI finding that aids in the differentiation of acute osteomyelitis from infiltrative tumor thereby preventing unnecessary biopsy and facilitating prompt diagnosis and initiation of appropriate treatment.
Highlights
Case presentation A 62-year-old male with a history of diabetes mellitus and rheumatoid arthritis, treated with leflunomide and rituximab, presented with bacteremia and acute onset right knee pain
The identification of a transcortical tract with expulsion of marrow fat to the extraosseous soft tissues, is considered a highly specific finding in acute osteomyelitis effectively narrowing the differential to a single diagnosis and preventing an unnecessary biopsy to exclude malignancy
Osteomyelitis has been previously described masquerading as Ewing sarcoma, chondrosarcoma, and other skeletal neoplasms.[1,2]
Summary
Case presentation A 62-year-old male with a history of diabetes mellitus and rheumatoid arthritis, treated with leflunomide and rituximab, presented with bacteremia and acute onset right knee pain. MRI with and without contrast of the right tibia and fibula, the site of greatest clinical suspicion, revealed diffuse heterogeneous marrow edema throughout the proximal tibial metadiaphysis with extensive periosteal edema compatible with an infiltrative process. Further evaluation on T1 imaging revealed small foci of extraosseous macroscopic fat tracking from a tiny cortical defect in the anterior tibial cortex (Figures 2–4).
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