What imaging modalities are recommended for diagnosing Morton's (Morton's Neuroma)?

Imaging for Morton's Neuroma

For diagnosing Morton's neuroma, ultrasound should be considered the first-line imaging modality due to its high sensitivity (90%), excellent specificity (88%), and cost-effectiveness compared to MRI. 1

Recommended Imaging Algorithm

First-Line Imaging

• Plain Radiographs:
  • Should be performed initially to exclude other causes of forefoot pain such as stress fractures, osteoarthritis, or Freiberg's infraction 2
  • Note: Radiographs are insensitive for directly visualizing Morton's neuroma but help rule out differential diagnoses

Second-Line Imaging

• Ultrasound (US):
  • High sensitivity (90%) and specificity (88%) 1
  • Advantages:
    • Cost-effective
    • No radiation
    • Allows dynamic examination and direct clinical correlation during assessment 2
    • Enables real-time guidance for therapeutic interventions 3, 4
    • Can distinguish between neuroma and intermetatarsal bursitis 2

Third-Line Imaging (if ultrasound is inconclusive)

• MRI without contrast:
  • High sensitivity (87%) and specificity (100%) 2
  • Particularly useful when:
    • Ultrasound results are equivocal
    • Multiple neuromas are suspected
    • Complex anatomical relationships need evaluation
    • Differential diagnoses remain unclear

Technical Considerations

Ultrasound Technique

• High-frequency linear transducer (>12 MHz)
• Examine in both longitudinal and transverse planes
• Dynamic testing during examination can elicit Mulder's click 4
• Power Doppler can identify increased blood flow in the affected area 2

MRI Protocol

• T1-weighted axial and coronal images
• Axial FSE T2-weighted sequence 5
• Patient positioning: prone with foot plantar flexed provides better visualization than supine position 6
• Contrast administration is not routinely necessary 2

Clinical Pearls and Pitfalls

Pearls

• Morton's neuroma most commonly affects the third intermetatarsal space 7
• Ultrasound allows for immediate correlation with the patient's symptoms during examination
• Imaging should be performed after clinical tests (thumb-index finger squeeze, Mulder's click) suggest Morton's neuroma 4

Pitfalls

• Ultrasound accuracy is operator-dependent and requires experience 7
• Small neuromas (<5mm) may be missed on imaging
• Asymptomatic neuromas can be incidental findings on MRI in up to 4% of asymptomatic individuals 2
• Intermetatarsal bursitis can mimic or coexist with Morton's neuroma and should be distinguished on imaging 2

Comparative Effectiveness

• Ultrasound offers comparable sensitivity to MRI (90% vs. 93%) but better specificity (88% vs. 68%) 1
• Ultrasound is more cost-effective and allows for immediate intervention if needed
• MRI provides better soft tissue contrast and overall anatomic detail but at higher cost

By following this imaging algorithm, clinicians can effectively diagnose Morton's neuroma while minimizing unnecessary testing and expediting appropriate treatment.