General points:
Thomas Mortan (1876)
Most common between 3 and 4th metatarsal heads, next common site is between 2-3rd heads
More common in women (high heeled shoes)
Fusiform enlargement of plantar digital nerve at bifurcation with thickened epineural fascicles, perineural fibrosis and loss of the myelinated fibers
Clinical features:
Exercise provoked pain, relieved on rest
Compression in the intermetatarsal space may induce pain
Usually not paplable unless associated with synovial cysts
Usually asymptomatic
Ultrasound:
Round/ oval, well-defined, hypoechoic mass just proximal to metatarsal heads in intermetatarsal space. Less than 5mm lesion difficult to see
Intermetatarsal bursa is on the dorsal aspect
Lateral compression will move the neuroma to the plantar side
Best seen on sagittal axis as a round disc
MRI:
Most evident on coronal T1, best seen on FS Gd T1
Less conspicuous on T2 and difficult to differentiate it from surrounding muscle and fat.
Fat FS T2 useful
Seen centered in neurovascular bundle within intermetatarsal space on plantar side of transverse metatarsal ligament as a well defined (beware of partial volume artifact from adjacent joint capsule) mass with signal similar to skeletal muscle on T1 and less than fat on T2
Intermetatarsal bursal fluid may be seen proximal to Morton neuroma in majority (66%)
Often enhance on Gd
Accuracy of 90%
Treatment:
Modification of footwear, neurolysis, steroid injection, ultrasound therapy
Ultrasound guided steroid/LA injection, alcohol injection
Surgical dempression by releasing transverse metatarsal ligament
Surgical resection of neuroma and involved nerve segment
References:
Murphey MD et al. Imaging of Musculoskeletal Neurogenic Tumors: Radiologic-Pathologic Correlation . Radiographics. 1999;19:1253-1280
JOURNAL WATCH:
Alcohol injection under ultrasound guidance is highly effective in Mortan's neuroma
AJR 2007; 188:1535-1539
Hughes et al, in their paper 'Treatment of Morton's Neuroma with Alcohol Injection Under Sonographic Guidance: Follow-Up of 101 Cases', report the technical success of 100%, partial or total symptom improvement in 94%, totally pain free in 84%. Transient increase in pain occurred in 17%. There were no major complications. The decrease in size was by 30%.
Conclusion: Alcohol injection has high success rate, well tolerated and comparable to surgical results.
