A hypoechoic (ultrasound) or low-signal (MRI) spindle-shaped mass in the intermetatarsal space, most often the third, at or just distal to the metatarsal heads, reproducing pain on compression.
Orient first
- Perineural fibrosis of the common plantar digital nerve, not a true neuroma.
- Intermetatarsal bursitis often coexists and lies dorsal to it.
- Size over 5 mm is more often symptomatic (verify your surgeons' threshold).
Acquire the study
- High-frequency linear probe on the plantar and dorsal aspects of the web spaces, with dorsal digital pressure (sonographic Mulder manoeuvre).
The manoeuvre
- Plantar approach, longitudinal and transverse: hypoechoic ovoid mass in the web space; size in mm.
- Continuity with the digital nerve.
- Sonographic Mulder click with pain on compression.
- Bursal fluid dorsal to the mass; plantar plate integrity.
What confirms it
- A web-space mass at the typical level reproducing the patient's pain.
What licenses you to exclude it
- No web space mass on a dynamic study makes Morton neuroma unlikely; look for plantar plate tears and stress fractures.
The classic misread
- Calling intermetatarsal bursal fluid a neuroma.
- Missing a plantar plate tear or stress fracture that causes the same pain.