What imaging modalities are used to diagnose Morton's neuroma?

From the Guidelines

Ultrasound is the recommended first-line imaging modality for suspected Morton's neuroma, offering high sensitivity and specificity while being cost-effective and readily available. According to the most recent study 1, high-resolution US can approach the sensitivity of MRI in detecting Morton’s neuromas, with pooled sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio of 90%, 88%, 2.77, and 0.16 for US. When performing ultrasound, the examination should include both longitudinal and transverse views of the intermetatarsal spaces, with special attention to the third intermetatarsal space where Morton's neuromas most commonly occur.

A typical Morton's neuroma appears as a hypoechoic, ovoid mass between the metatarsal heads, often measuring 5-7mm in diameter. Dynamic ultrasound with weight-bearing or toe compression can enhance visualization by displacing the neuroma plantarward. MRI is an excellent alternative when ultrasound results are inconclusive or when additional soft tissue pathology is suspected, as it has been shown to be a sensitive and reliable method to evaluate patients with metatarsalgia and Morton’s neuroma with a sensitivity of 87%, specificity of 100%, accuracy of 89%, PPV of 100%, and NPV of 60% in surgically treated patients 1.

Plain radiographs have limited value for direct visualization of neuromas but may help rule out other causes of forefoot pain such as stress fractures or arthritis, as they are insensitive to diagnose Morton’s neuroma but are useful to exclude other causes of webspace pain such as osteoarthritis, Freiberg’s infraction, and stress fractures 1. CT scans are rarely indicated unless bony pathology is the primary concern. The imaging findings should always be correlated with clinical symptoms, as asymptomatic neuromas are relatively common incidental findings. Key points to consider when imaging for Morton's neuroma include:

• Ultrasound as the first-line imaging modality
• MRI as an alternative for inconclusive ultrasound results or additional soft tissue pathology
• Plain radiographs to rule out other causes of forefoot pain
• CT scans rarely indicated unless bony pathology is the primary concern
• Correlation of imaging findings with clinical symptoms.

From the Research

Imaging Modalities for Morton's Neuroma

• Ultrasonography and magnetic resonance imaging (MRI) are commonly used for the diagnosis of Morton's neuroma 2, 3.
• A study found that ultrasonography has a slightly higher sensitivity in the diagnosis of Morton's neuroma, particularly for neuromas smaller than 5 mm, and should be the preferred imaging modality in suspected cases 2.
• MRI had a higher sensitivity than ultrasonography in another study, with a sensitivity of 82.9% compared to 56.5% for ultrasonography 3.

Diagnostic Accuracy and Correlation

• The diagnostic accuracy of ultrasonography and MRI in Morton's neuroma has been evaluated in several studies, with varying results 2, 3, 4.
• A study found that clinical assessment was the most sensitive and specific modality for diagnosing Morton's neuroma, and that reliance on single modality imaging would have led to inaccurate diagnosis in 18 cases 4.
• The correlation between ultrasonography and MRI in diagnosing Morton's neuroma was found to be poor in one study, with a kappa statistic of 0.31 3.

Role of Imaging in Diagnosis and Treatment

• Ultrasonography can aid in the accurate diagnosis of Morton's neuroma and guide treatment, including infiltration of the area with a corticosteroid and local anesthetic, chemical neurolysis with alcohol or radiofrequency thermal neurolysis 5, 6.
• Imaging may not be necessary for the diagnosis of Morton's neuroma, as clinical assessment is often sufficient 4.
• The size of the lesion does not appear to correlate with symptoms, and small lesions can cause significant symptoms 4.