The most common etiology of carpal tunnel syndrome (CTS) is idiopathic. However, 
secondary causes of CTS should be considered when symptoms are unilateral, or 
electrodiagnostic studies are discrepant with the clinical presentation. Imaging 
of the carpal tunnel should be performed when secondary causes of CTS are 
suspected. An ultrasound evaluation of the carpal tunnel can assess for 
pathologic changes of the median nerve, detect secondary causes of CTS, and aid 
in surgical planning.