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Diagnostic Features of Emphysematous Osteomyelitis.

Emphysematous osteomyelitis (EO) is a rare, aggressive, and potentially fatal variant of osteomyelitis related to gas-forming organisms. Imaging plays a vital role in diagnosis. The purpose of this study was to describe a novel and distinct imaging sign of EO, by analysis of the imaging characteristics of 3 newly identified cases of EO as well as all reported cases in the literature. Literature review and retrospective study in 2 tertiary care medical centers was conducted. During the course of clinical care over the last year, we have observed 2 cases of EO. An Institutional Review Board approved 1-year systematic retrospective review of our institutional radiology information system identified 1 additional case of EO. We conducted a MEDLINE literature search to identify all published EO case reports using key phrases. The imaging in all published cases was reviewed. To address the specificity of imaging characteristics, we identified cases demonstrating variants of intraosseous gas that were not caused by EO. We found 31 individual case reports of EO via MEDLINE search. Of the published cases, 25 of the 31 cases contained images of sufficient extent and quality for image analysis. Including our 3 cases, a total of 34 cases were identified. Of the 34 cases, 28 had images of sufficient quality and extent to determine the presence or absence of the "pumice stone" pattern. The "pumice stone" sign was identified in 27 of 28 cases (96%). The most commonly affected sites of infection include the pelvic bones (38%; 13 of 34), vertebral bodies (32%; 11 of 34), and femurs (24%; 8 of 34). Adjacent soft tissue inflammation and emphysema was evident in 23 of 29 cases (79%). Cortical destruction, a key diagnostic feature of traditional osteomyelitis, was absent in 79% of cases of EO. We describe the "pumice stone sign" as a radiological sign to identify EO. We found it present in 96% of all currently known cases of EO. EO commonly involves the pelvic bones (38%), vertebral bodies (32%), and femur (24%). Key features also include adjacent soft tissue emphysema (79%) and absence of cortical destruction (79%).