ARRS 2022 Abstracts

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E1502. Gas in the Musculoskeletal System: The Good and the Bad
Authors
  1. Samuel Madson; San Antonio Military Medical Center
  2. Nathan Cecava; San Antonio Military Medical Center; Uniformed Services University Health Sciences
  3. Liem Mansfield; Shannon Clinic
Background
Gas in the musculoskeletal system is frequently encountered in clinical practice and can indicate either a benign or nefarious process. Anaerobic infection is capable of producing gas in musculoskeletal structures; however, non-aggressive processes accounting for gas are much more common. In some instances, gas is actually used to exclude a diagnosis of infection. Gas bubble formation may form with joint manipulation, in volume loss and degeneration, in traumatic dislocation/diastasis and open fractures, or iatrogenic formation. Infection should always be considered with scrutiny of clinical conditions, so treatment is not delayed. Therefore, it is important for the radiologist to recognize the presence of gas on imaging studies and have the expertise to appropriately raise clinical suspicion of infection or assign a typically benign cause to avoid unnecessary work-up and procedures.

Educational Goals / Teaching Points
Case examples from radiography, CT, sonography, and MRI of intra-articular, intraosseous, and soft tissue gas will be presented. Clinical presentation, location, and differentiating imaging features will be emphasized to aid in correct diagnosis. Examples of musculoskeletal gas imaging features that can be used in the exclusion or inclusion of infection will be highlighted. Additional examples of gas as a harbinger of more sinister pathology will be described. The fundamental goal of this activity is educating radiologists in the accurate evaluation of musculoskeletal gas when it presents in various locations in the body.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Location and clinical context are key to accurate diagnosis. Soft tissue gas should be treated differently than intra-articular or intraosseous gas. Radiography is generally the initial imaging modality performed and is essential for evaluation of bony pathology and identifying key features that may necessitate advanced imaging to exclude infection or other aggressive process. CT is often complimentary to radiographs and can provide information regarding osseous matrix, periostitis, cortical destruction, and limited soft tissue assessment. MRI provides excellent soft tissue contrast and enables evaluation of marrow processes; however, correlation with radiography or CT is needed to avoid confusing gas with calcific deposits or other mineralization.

Conclusion
Gas in the musculoskeletal system can have a variety of causes and does not always indicate infection. In certain situations, the presence of gas is beneficial to exclude infection. In other situations, musculoskeletal gas is pathognomonic for a benign etiology. In the appropriate clinical context and location, musculoskeletal gas can alert the radiologist and clinician to serious underlying pathology such as infection, open fracture, dislocation, or osteonecrosis. The astute radiologist should be familiar with the presentations and distinguishing features of musculoskeletal gas to ensure timely diagnosis, limit unnecessary diagnostic and therapeutic interventions, and improve patient outcomes.