Background: The diagnosis of carpal tunnel syndrome (CTS) is usually based on clinical combining with nerve conductive study (NCS). Recently, ultrasound (US) is the choice for investigation of median nerve morphology and size. The advantages of US are non-invasive in nature and no discomfort or pain. Data on median nerve cross sectional area (CSA) in healthy Thai subjects are still limited.
Objective: To know the mean value of normal CSA in healthy Thai population. Is it different from the other countries?
Material and Method: Thai populations, without clinical sign or symptom of CTS, were included in the present study. A linear array transducer was used to scan and measure median nerve cross sectional area and the maximum transverse and anteroposterior diameter were recorded.
Results: Eighty-eight wrists of 44 asymptomatic of CTS and healthy Thai volunteer were examined with US. The mean CSA measurement were found as 6.83 + 0.98 mm2 by tracing method (TM) and 6.81 + 1.12 mm2 by ellipsoid formula (EF) method. No significant differentiation was observed between CSA calculated using TM and EF of median nerve. There was no significant difference in CSA between right and left hand or dominate and non-dominate hand. CSA calculated by the TM and EF method were found to be significantly larger in male than in female. There was no correlation between CSA and age or BMI.
Conclusion: Although body habitus of people was different among countries, the mean CSA of median nerve in healthy people are not significantly difference.

Keywords: Ultrasound, Mean cross-sectional area (CSA), Median nerve