Surgery for Morton Neuroma Workup

Updated: May 28, 2019
  • Author: Lyle T Jackson, MD; Chief Editor: Vinod K Panchbhavi, MD, FACS  more...
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Workup

Imaging Studies

A large body of literature addresses the use of imaging modalities to aid in the diagnosis of Morton neuroma. [17] The condition is most commonly diagnosed strictly on the basis of the history and physical examination findings. In equivocal cases, ultrasonography (US), magnetic resonance imaging (MRI), or both may be helpful. [18, 19, 20, 21]

Standing radiographs are helpful for evaluation of overall osseous structure and joint abnormalities.

The skill of the technologists and physicians performing and interpreting MRI or US plays a key role in determining just how valuable these modalities can be in clinical practice.

On US, a Morton neuroma typically appears as a hypoechoic oblong mass oriented along the long axis of the foot. Prospective studies in symptomatic patients reveal that US can reliably detect these neuromas. [17, 22] Furthermore, it can help identify contributing pathologic lesions, such as lipomas or bursae. [23] Nonetheless, in a small series, 26 (54%) of 48 asymptomatic patients had greater than 5 mm enlargement of an interdigital nerve on US. [21] This finding emphasizes the importance of the history and clinical examination and the risk of false positives.

US may be used to determine the size of a Morton neuroma, but its reliability appears to depend, to a large degree, on observer experience. [24] It may also be used to identify posttreatment changes (eg, ill-defined borders, reduced or absent pain with the application of transducer pressure) after laser therapy for Morton neuroma. [25]

MRI technology and applications continue to evolve and can provide reliable information regarding the pathoanatomy of the forefoot. [26] Characteristically, a Morton neuroma shows low intensity on T1- and T2-weighted MRI sequences, because of its high degree of fibrous content. In contrast, an intermetatarsal bursa is associated with increased intensity on T2-weighted images, because of its fluid content. [27] MRI with gadolinium contrast enhancement and with fat suppression probably provides the most reliable images for diagnosis. [28]

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Other Tests

Electrodiagnostic testing has been described to aid in diagnosis, but its use is not common, and its utility has yet to be determined. [29, 30]

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Procedures

An injection of local anesthetic with sterile technique may be useful in the diagnostic evaluation of Morton neuroma. [7] The temporary resolution of pain, paresthesias, or both in response to the injection may confirm the location of the pathology. A positive response to the injection tends to be predictive of satisfactory postoperative outcomes.

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