THE ACCURACY OF ULTRASOUND SCAN IN THE DIAGNOSIS OF INTERDIGITAL NEUROMA IN THE FOOT

Abstract

Eighty-two consecutive patients with forefoot pain and clinical signs strongly suggesting a neuroma all underwent ultrasound scan of both feet using a 10-5 MHz transducer where a well defined hypoechoic area defined a neuroma . All ultrasound positive feet had the lump excised surgically for histological studies. Plain x-rays were done on all symptomatic feet to exclude other pathology.

Sixty-four feet had an ultrasound positive diagnosis. Of these, there were 82.3% female and 17.1% male (ratio 4.8:1 , p< 0.001). Thirty-six percent had bilateral neuromata but with only one side being symptomatic.59.5% of the neuroma were located in the interspace between the third and fourth toes whilst 41.5% were found in the interspace between the second and third toes.

The size of the lesions varied from 3 to 11mm with a mean of 6.86mm. No lesion less than 5mm was symptomatic in our series.

One false positive was noted in the series giving the test a sensitivity of 97.9% but the specificity was low at 50% as the scan negative feet were not surgically explored for ethical reasons

All surgically explored patients had become asymptomatic at an average of 5.3 weeks (range 4–24 weeks) post surgery. Thirty-three ultrasound negative patients treated non-operatively were completely asymptomatic at an average of 30 weeks (range 6–50 weeks).

We conclude that an ultrasound scan is a cheap, non-invasive, time-efficient test useful in identifying interdigital neuroma as a cause of forefoot pain.