Magnetic Resonance Imaging–Measured Cross-Sectional Area of the Median Nerve

Abstract

The size of the median nerve may serve as a useful parameter to predict carpal tunnel syndrome (CTS) in a subset of patients. The purpose of this study was to evaluate magnetic resonance imagingebased measurements of median nerve cross-sectional area (CSA) to examine trends between patient subgroups and CSA that may assist in predicting the individuals who are most likely to develop CTS symptoms. Methods: A retrospective chart review of 1,273 wrist magnetic resonance images was performed, and the images were analyzed to evaluate the median nerve CSA at the level of the pisiform and the hook of hamate. The age, sex, height, weight, and body mass index (BMI) of the patients were collected from their medical records. Results: The median nerve size correlated with patient BMI. Additionally, patients with CTS had larger median nerves at the hook of hamate and pisiform than those without CTS. When subdividing patients on the basis of BMI, obese patients with CTS had larger median nerve CSA at the pisiform than those without CTS. Conclusions: This study demonstrated that increased BMI is associated with increased median nerve CSA at the hook of hamate and pisiform in patients with or without CTS. Additionally, patients with CTS had larger median nerve CSA than those without CTS. Measurements at these locations may help predict individuals who are likely to experience median nerve impingement. Type of study/level of evidence: Prognostic III.

Characteristics of Patients with Clinical Signs and Symptoms of Carpal Tunnel Syndrome but Negative Diagnostic Testing

“…Research has shown increasing BMI is correlated with increased median nerve cross-sectional area. 23 Our studies show patients with lower BMI are more likely to have signs and symptoms of carpal tunnel without increases in median nerve cross-sectional area reaching diagnostic thresholds. Therefore, patients with lower BMI may be more likely to have false-negative US studies despite positive CTS-6.…”

Potential Relationships between the Median Nerve Cross-Sectional Area and Physical Characteristics in Unilateral Symptomatic Carpal Tunnel Syndrome Patients

“…Regarding the relationships between physical characteristics and median nerve CSA, previous studies suggested a positive correlation between BMI and median nerve CSA [ 37 , 38 , 39 , 40 , 41 ]. Cartwright et al reported that mean age based on BMI was a major parameter for predicting median nerve CSA in healthy subjects [ 42 ]. Other studies demonstrated that BMI and diabetes were associated with larger median nerves at the CT [ 39 , 40 , 41 ].…”

“…Other studies demonstrated that BMI and diabetes were associated with larger median nerves at the CT [ 39 , 40 , 41 ]. An MRI-based median nerve CSA study also showed that CSA increased with BMI in non-CTS patients, and obese patients with CTS had larger CSA values at the CT inlet level [ 42 ]. The mechanism by which obesity/high BMI increases median nerve CSA is unknown.…”