ULTRASOUND FOR THE DIAGNOSIS OF MORTON NEURINOMA

Abstract

Purpose of the study: Morton neurinoma is a well defined anatomic entity despite certain questions about the pathogenic mechanisms. Diagnosis of the metatarsalgia sometimes produced can be difficult due to the frequency of an associated static metatarsalgia. Magnetic resonance imaging has not met expectations. We have oriented our research towards ultrasonography which can provide high quality information with good reliability.

Material and methods: We reviewed the files of 11 patients with Morton neurinoma which led to 14 operations (bilateral cases or two localizations on the same foot). The series included three men and eight women, mean age 56 years. The operation was conducted under locoregional anesthesia and consisted in tumor resection via the plantar commissure, with removal of the entire neurinoma. Ultrasonography used a high-frequency probe (6–13 MHz linear scan). The compartments were studied via the plantar aspect and the dorsal aspect using static and stress positions. MRI had been performed in two patients before the ultrasound.

Results: Eight of the eleven patients had an associated syndrome (hallux valgus, disharmonious length with mid metatarsal weight bearing). Objective signs (Mudler’s sign, hyoesthesia), were noted in seven patients. The neurinoma was confirmed in all cases at surgery; in two cases, ultrasonography demonstrated a neurinoma where the MRI had been negative. The operative specimen was typical. Two compartments were explored because of the ultrasound results which were highly suggestive; two tumors were demonstrated at surgery. Clinical outcome at mean seven months was good in ten patients and fair in one.

Discussion: Ultrasonography should no longer be considered as «operator-dependent». It enables the detection of mid-sized neurinomas measuring about 2 cm. Magnetic resonance imaging has been less productive for diagnosis; many studies have been reported without surgical confirmation of MRI-negative cases. False negatives are frequent and patient follow-up is insufficient to determine whether the symptoms persist or resolve after surgery.

Conclusion: Ultrasonography is a simple examination devoid of iatrogenic risk. The use of stress images has greatly improved performance. This low cost examination may not however be necessary because the diagnosis of Morton is basically clinical.