What would a CT (Computed Tomography) scan show in a case of muscle strain?

CT Findings in Muscle Strain

CT is not recommended as a first or second-line imaging modality for muscle strain as it is less sensitive than MRI for soft tissue injuries, but when performed, it can show muscle edema, hematoma formation, and disruption at the myotendinous junction. 1, 2

Appropriate Imaging Modalities for Muscle Strain

First-Line Imaging

• Radiographs (X-rays): Should be obtained first to rule out fractures or other bony abnormalities
  • Limited sensitivity (15-35%) for soft tissue injuries 1
  • Primary purpose is to exclude other conditions such as stress fractures or tumors

Second-Line Imaging (Preferred)

• MRI without contrast: Gold standard for muscle strain evaluation
  • Extremely sensitive for detecting muscle injuries 1
  • Can visualize:
    • Disruption at the myotendinous junction
    • Fluid collection at disruption site
    • Edema and inflammation in muscle tissue
    • Precise localization of strain to specific muscles 2
  • No radiation exposure

CT Findings in Muscle Strain

When CT is performed (though not typically recommended as first or second-line), findings may include:

1. Myotendinous junction disruption: Visible as discontinuity at the muscle-tendon interface 2
2. Fluid collection: Accumulation of fluid at the disruption site that may dissect along the epimysium and subcutis 2
3. Muscle edema: Appears as decreased attenuation (darker areas) within the affected muscle 2, 3
4. Hematoma formation: Visible as higher density areas within or adjacent to the injured muscle
5. Follow-up changes: In later stages, CT can demonstrate:
   • Muscle atrophy
   • Fibrosis
   • Calcium deposition 2

Limitations of CT for Muscle Strain

• Less sensitive than MRI or bone scintigraphy for soft tissue injuries 1
• Involves ionizing radiation exposure
• Limited soft tissue contrast compared to MRI
• Cannot adequately evaluate the inflammatory response in muscle tissue 1
• Mean muscle attenuation measurements can be affected by contrast administration and tube voltage settings 3

Clinical Pearls

• Commonly strained muscles that can be visualized on CT include adductor longus, rectus femoris, and medial head of gastrocnemius 2, 4
• Muscles crossing two joints and containing high percentages of fast-twitch fibers are most susceptible to strain 5, 4
• CT can help differentiate between strain and other conditions like stress fractures when MRI is equivocal 1
• For optimal imaging of muscle strain, MRI remains the modality of choice due to superior soft tissue contrast and ability to detect subtle edema 1, 5, 6

Common Pitfalls

• Mistaking normal anatomical variants for pathology
• Using CT as first-line imaging for suspected muscle strain
• Failing to correlate imaging findings with clinical presentation
• Not considering that contrast administration can slightly influence muscle measurements 3