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Department of Radiology, Clínica de Diagnóstico por Imagem (CDPI)/DASA, Avenida das Américas, 4666, 302A, 303, 307, 325, 326, Barra da Tijuca, Rio de Janeiro, RJ, 2640-102, Brazil
Department of Radiology, Hospital Universitário Clementino Fraga Filho, Federal University of Rio de Janeiro, Rua Rodolpho Paulo Rocco, 255, Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ, 21941-913, Brazil
entitled “Imaging update on musculoskeletal infections”, in which the authors reviewed the imaging features of musculoskeletal infection, including osteomyelitis, on radiograph, ultrasound, computed tomography, and magnetic resonance imaging (MRI). Although the authors have made an extensive list of characteristic MRI findings, we would like to add a discussion about an important imaging sign, that despite not being pathognomonic for the diagnosis of osteomyelitis, it is quite specific, and has a fundamental importance in the differential diagnosis between osteomyelitis and primary bone tumors.
In some cases, osteomyelitis may be confounded radiographically, and even on MRI, with a variety of benign and malignant bone tumors, especially in children. Then, MRI features that can help to differentiate infection from tumor are of utmost value.
The extramedullary and/or intramedullary fat globules sign, seen as extraosseous or intramedullary fat, characterized by hyperintensity on T1-weighted imaging and conversely hypointensity on sequences with fat suppression, in the region of marrow signal abnormality, as well as in the adjacent soft tissue (Fig. 1), can improve the MRI specificity for the diagnosis of acute osteomyelitis.
Its pathophysiology is related with the increase in the intramedullary bone pressure, due to bone edema, secondary to the medullary bacterial proliferation, acute suppurative response, exudate formation and hyperemia, which lead to obliteration of the fat marrow MRI signal, as well as to septic necrosis, with lipocyte death and release of free fat globules. The increasing intramedullary pressure leads to a rupture of the osseous cortex and expulsion of medullary fat into the adjacent soft tissues.
actually, it can also be seen in medullary infarction, trauma, bone sarcomas after treatment with chemotherapy and/or radiotherapy, and Gaucher disease. However, in the correct clinical context it can play an important role in diagnosis of acute osteomyelitis and in the differential diagnosis with bone tumors.
Therefore, the visualization of the intramedullary and/or extramedullary fat globules sign on MRI is an important feature of acute osteomyelitis, which can be used in the differentiation from other bone diseases.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.