What imaging studies are recommended for a cat bite?

Imaging Recommendations for Cat Bite Wounds

For cat bite wounds, plain radiographs should be performed first to assess for foreign bodies or bone involvement, followed by CT scan if there is suspicion of deep tissue infection, abscess formation, or osteomyelitis. 1

Initial Imaging Approach

Plain Radiographs

• First-line imaging for all cat bite wounds 1
• Useful for detecting:
  • Radiopaque foreign bodies (metal, stone, glass, some ceramic materials)
  • Early signs of osteomyelitis
  • Gas in soft tissues
  • Fractures or bone involvement
• Limitations:
  • Cannot detect radiolucent foreign bodies (wood, plastic, rubber)
  • Low sensitivity (up to 47% false-negative rate) 1
  • May miss early soft tissue infections

When to Escalate to Advanced Imaging

Advanced Imaging Options

Computed Tomography (CT)

• Indicated when:
  • Suspicion of deep tissue infection or abscess formation
  • Negative radiographs but clinical suspicion of retained foreign body
  • Signs of systemic infection
  • Pain disproportionate to visible injury
  • Wounds near joints or bones with concern for osteomyelitis
• Benefits:
  • 5-15 times more sensitive than radiography for foreign body detection 1
  • Can visualize soft tissue gas, cellulitis, abscess formation
  • Can detect both radiodense and some radiolucent foreign bodies
  • Sensitivity of 90-100% for bone fragments 1
• Technique:
  • Use thin slices (1mm) to avoid missing small foreign bodies 1

Magnetic Resonance Imaging (MRI)

• Best for:
  • Evaluation of confirmed osteomyelitis
  • Assessment of soft tissue involvement including tendon or vascular injury
  • Evaluation of joint involvement
• MRI with contrast is the modality of choice when osteomyelitis is suspected 1
• Limitations:
  • Lower sensitivity for foreign body detection compared to CT or ultrasound
  • Metallic foreign bodies contraindicated or cause artifacts
  • Less readily available in emergency settings

Ultrasound

• Useful for:
  • Localizing non-radiopaque foreign bodies
  • Evaluating superficial soft tissue infections
  • Guiding abscess drainage procedures
  • Joint aspiration when septic arthritis is suspected

Clinical Considerations Affecting Imaging Choice

Cat bites have a high infection rate (30-50%) 1 with Pasteurella multocida present in 75% of cases, which can cause rapid infection onset (within 3-12 hours) 2. This rapid progression increases the importance of prompt and appropriate imaging.

High-Risk Features Requiring Advanced Imaging

• Bites over joints, tendons, or neurovascular structures
• Hand wounds (higher risk of complicated infection)
• Immunocompromised patients
• Signs of systemic infection
• Wounds >8 hours old
• Deep puncture wounds (typical of cat bites)

Pitfalls to Avoid

• Relying solely on plain radiographs when deep infection is suspected
• Failing to use thin-slice CT technique when searching for small foreign bodies
• Delaying imaging in rapidly progressing infections
• Not considering the possibility of osteomyelitis or septic arthritis with cat bites near bones or joints
• Using contrast studies (barium/gastrografin), which are not recommended and may delay appropriate intervention 1

Remember that cat bites can lead to serious complications including septic arthritis, osteomyelitis, abscess formation, tendonitis, and rarely bacteremia 1. Imaging plays a crucial role in early detection of these complications and guiding appropriate management.