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Emphysematous osteomyelitis: Novel use of PET-MRI and a review of characteristic imaging findings.

INTRODUCTION
Emphysematous osteomyelitis (EO) is an extremely rare bone infection by gas-forming bacteria with few documented cases in the literature. Our study aims to highlight characteristic imaging features, including the novel use of positron emission tomography-magnetic resonance imaging (PET-MRI) in the diagnosis of this potentially fatal entity.


CASE
Radiography and computed tomography (CT) of the pelvis were performed due to complaints of persistent back pain in a 36 year old male with history of recent abdominal aorta surgery. Sacroiliac joint aspiration was performed and a follow-up PET-MRI was subsequently performed.


RESULTS
Radiography and CT demonstrated bilateral sacroiliitis, osteonecrosis and EO in the bony pelvis. Left sacroiliac joint aspiration identified Staphylococcus aureus as the causative organism. PET-MRI revealed EO with left iliopsoas abscess and abdominal aortic graft infection. The patient's symptoms resolved following antibiotic therapy and image-guided abscess drainage.


CONCLUSION
EO is a lethal variant of osteomyelitis with a dearth of published cases. Pertinent imaging characteristics of EO on radiography, CT and PET-MRI are discussed here, along with a review of the literature surrounding this rare condition.