The role of MRI and ultrasound imaging in Morton's neuroma and the effect of size of lesion on symptoms.

We investigated 29 cases, diagnosed clinically as having Morton's neuroma, who had undergone MRI and ultrasound before a neurectomy. The accuracy with which pre-operative clinical assessment, ultrasound and MRI had correctly diagnosed the presence of a neuroma were compared with one another based on the histology and the clinical outcome. Clinical assessment was the most sensitive and specific modality. The accuracy of the ultrasound and MRI was similar and dependent on size. Ultrasound was especially inaccurate for small lesions. There was no correlation between the size of the lesion and either the pre-operative pain score or the change in pain score following surgery. Reliance on single modality imaging would have led to inaccurate diagnosis in 18 cases and would have only benefited one patient. Even imaging with both modalities failed to meet the predictive values attained by clinical assessment. There is no requirement for ultrasound or MRI in patients who are thought to have a Morton's neuroma. Small lesions, < 6 mm in size, are equally able to cause symptoms as larger lesions. Neurectomy provides an excellent clinical outcome in most cases.