What is the best imaging modality for assessing soft tissue infections of the chest?

Imaging for Soft Tissue Infections of the Chest

MRI with contrast is the best imaging modality for assessing soft tissue infections of the chest due to its superior tissue characterization, high sensitivity (82-100%), and specificity (75-96%) for detecting soft tissue infections. 1

Diagnostic Imaging Algorithm

Initial Imaging

1. Plain Radiographs
   • Should be obtained first to evaluate for:
     • Bone erosions
     • Periosteal reaction
     • Soft tissue swelling
     • Gas in tissues
     • Radiopaque foreign bodies 2, 1
   • Limitations: May only show mild soft tissue swelling in early infections and lacks specificity 2

Secondary Imaging (if radiographs are normal or equivocal)

1. MRI with contrast

   • Gold standard for soft tissue infections of the chest due to:
     • Highest sensitivity (93%) for detecting fluid and inflammation 1
     • Excellent characterization of soft tissues 1
     • Superior ability to define anatomic extent of infection 1
     • Can distinguish between abscesses, cellulitis, myositis, and necrotizing fasciitis 2, 1
     • Nearly 100% negative predictive value for osteomyelitis 1
   • Particularly useful for:
     • Deep-seated infections
     • Evaluation of complex intramuscular fluid collections
     • Detecting early signs of infection before severe clinical manifestations 1

2. Ultrasound

   • Useful for:
     • Detecting fluid collections in superficial soft tissues
     • Guiding aspiration or drainage procedures 2, 1
     • Differentiating solid from cystic lesions 2
   • Limitations:
     • Less reliable for deep masses in large anatomic areas 2
     • Limited in evaluation of deep chest wall infections

3. CT with IV contrast

   • Consider when:
     • MRI is contraindicated
     • Necrotizing soft tissue infection is suspected (sensitivity 100%, specificity 98%) 3
     • Need to detect gas in tissues (most sensitive modality) 2, 1
     • Evaluating bone destruction 1
   • Limitations:
     • Inferior soft tissue contrast compared to MRI 4
     • Radiation exposure 5, 4
     • Lower sensitivity than MRI for early soft tissue changes 1

Special Considerations

Suspected Necrotizing Soft Tissue Infection

• If necrotizing fasciitis is suspected, CT with IV contrast can be performed urgently
• CT findings suggestive of necrotizing infection include:
  • Gas in soft tissues
  • Multiple fluid collections
  • Absence or heterogeneity of tissue enhancement
  • Significant inflammatory changes under the fascia 3
• Urgent surgical consultation if imaging shows:
  • Fascial fluid or edema
  • Lack of fascial enhancement after IV contrast
  • Soft tissue gas
  • Involvement of multiple compartments 1

Image-Guided Procedures

• Consider image-guided aspiration for:
  • Diagnosis and culture of abscesses
  • Guiding appropriate antibiotic therapy 1
• MRI or ultrasound can help plan for safe aspiration 2

Pitfalls and Caveats

• Increasing use of CT for soft tissue infections has led to unnecessary radiation exposure without proven benefit 5
• Early osteomyelitis may not show radiographic changes for 2-3 weeks 1
• Biopsy remains the gold standard for definitive diagnosis of soft tissue infections 1
• MRI may be limited by motion artifacts in the chest, though newer sequences with respiratory gating have improved image quality 6

In conclusion, while radiographs should be obtained initially, MRI with contrast provides the most comprehensive evaluation of soft tissue infections of the chest and should be the preferred advanced imaging modality when available and not contraindicated.