Rethinking Morton's neuroma: a sonographic study of bilateral prevalence and symmetry.

Abstract

Background: Morton neuroma (MN) is commonly regarded as a focal, unilateral condition. Whether sonographically detectable lesions also occur contralaterally to the symptomatic side has not been defined systematically. We aimed to determine the bilateral sonographic prevalence, anatomic distribution, symmetry, and size characteristics of lesions consistent with MN in patients referred with clinical suspicion of MN.

Methods: In this cross-sectional study, we included all consecutive patients referred between January 2023 and December 2024 for suspected MN. All underwent standardized bilateral high-resolution forefoot ultrasound irrespective of symptom laterality, with lesions defined as hypoechoic nodular enlargements measuring ≥ 3 mm. Prevalence was estimated using exact binomial 95% confidence intervals (CI), and size associations were assessed with linear mixed-effects models including random patient intercepts and fixed effects for intermetatarsal space, side, sex, age, morphology, and symptom status.

Results: A total of 226 patients (167 women; mean age, 55 ± 12 years) were included, and 568 lesions consistent with interdigital nerve enlargements were confirmed (mean, 2.5 ± 1.0 per patient). Lesions were most common in the third intermetatarsal space (62.3%) and second space (36.4%). Bilateral involvement was present in 183/226 patients (81.0%; 95% CI, 75.2-85.9%). Among those with strictly unilateral symptoms, contralateral lesions were found in 123/161 (76.4%; 95% CI, 69.1-82.7%). Bilateral disease was mirror-symmetric in 133/183 (72.7%). Intermetatarsal space and morphology were associated with size, whereas size was not independently associated with symptomatic status.

Conclusion: Sonographically detected interdigital nerve enlargements are frequently bilateral and often symmetric, including in patients with unilateral symptoms. The high prevalence of subclinical contralateral enlargements challenges the traditional view of MN as a focal, unilateral entity. Routine bilateral ultrasound may be useful at baseline to characterize overall lesion burden and support counseling. However, management must remain strictly symptom-based, as incidentally detected, asymptomatic enlargements do not justify intervention.