Background: Carpal tunnel syndrome (CTS) is the most common form of peripheral entrapment neuropathy. The use of sonography for investigation and diagnosis of musculoskeletal conditions has been rapidly increasing over the past few decades. Recent studies have demonstrated advantages of sonographic techniques in the diagnosis of carpal tunnel syndrome (CTS).
Objective: Assessing the utility of ultrasonography in the diagnosis of carpal tunnel syndrome (CTS) and grading its severity.
Patients and Methods : Sixty hands in 46 patients with clinically and electro-physiologically confirmed carpal tunnel syndrome,  and sixty asymptomatic hands in 34 healthy individuals as control group were included in the study and underwent high-resolution ultrasonography of the wrists. In ultrasonographic assessment the cross-sectional area (CSA) of the median nerve at the distal crease of the wrist and flattening ratio (FR) of the median nerve in the carpal tunnel as well as palmar bowing (PB) of the flexor retinaculum were measured. Ultrasonographic Data from the patients group and control group were compared to determine the statistical significance. The accuracy of the ultrasonographic diagnostic criteria for carpal tunnel syndrome was evaluated using receiver-operating characteristic (ROC) curve analysis. Sensitivity and specificity of ultrasonographic measurements were evaluated. Ultrasonographic measurements were correlated with severity of CTS according to nerve conduction studies (NCS).   
Results: The CSA of the median nerve and PB of the flexor retinaculum were significantly larger in the CTS hands compared to the normal control hands. However, FR of the median nerve showed no significant difference between both groups. Increased cross-sectional area of the median nerve was the most predictive measurement of carpal tunnel syndrome. Using the ROC curve, a CSA cut-off value of 10 mm² provided a diagnostic sensitivity of 93.3 % and specificity of 98.3 % and PB cut-off value of 3.3 mm provided a diagnostic sensitivity of 90 % and specificity of 85 %. No significant differences in CSA and PB were found among patients with mild, moderate and severe carpal tunnel syndrome so that CSA and PB did not reflect the severity of the condition.
Conclusion: Ultrasonography is a useful non-invasive method for the diagnosis of carpal tunnel syndrome but not assessing its severity.