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Carpal Tunnel Syndrome Assessment with US: Value of Additional Cross-sectional Area Measurements of the Median Nerve in Patients versus Healthy Volunteers¹

¹ From the Departments of Diagnostic Radiology (A.S.K., T.D.Z., G.M.F.), Neurology (W.N.L.), Internal Medicine (J.G.), and Trauma Surgery and Sports Medicine (R.A.), Medical University Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria; Departments of Radiology and Urology, Jefferson Prostate Diagnostic Center and Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pa (E.J.H.); and Cattedra "R" di Radiologia-DICMI, Università di Genova, Genoa, Italy (C.M.). From the 2008 RSNA Annual Meeting. Received February 29, 2008; revision requested April 26; revision received June 26; accepted July 8; final version accepted July 23. Address correspondence to T.D.Z. (e-mail: Tobias.De-Zordo{at}i-med.ac.at).

Purpose: To improve accuracy in the diagnosis of carpal tunnel syndrome (CTS) by comparing cross-sectional area (CSA) measurements of the median nerve obtained at the level of the carpal tunnel (CSAc) with those obtained more proximally (CSAp), at the level of the pronator quadratus muscle.

Materials and Methods: The study protocol was approved by the institutional review board, and all subjects gave written informed consent. One hundred wrists of 68 consecutive patients with CTS (16 men, 52 women; mean age, 57.9 years; range, 25–85 years) and 93 wrists of 58 healthy volunteers (16 male, 42 female; mean age, 55.1 years; range, 17–85 years) were examined with ultrasonography (US). Electrodiagnostic test results confirmed the diagnosis of CTS in all 68 patients. The US examiner was blinded to these test results. The CSA of the median nerve was measured at the carpal tunnel and proximal levels, and the difference between CSAc and CSAp (CSA) was calculated for each wrist.

Results: The mean CSAc in healthy volunteers (9.0 mm²) was smaller than that in patients (16.8 mm², P < .01). The mean CSA was smaller in asymptomatic wrists (0.25 mm²) than in CTS-affected wrists (7.4 mm², P < .01). Receiver operating characteristic analysis revealed a diagnostic advantage to using the CSA rather than the CSAc (P = .036). Use of a CSA threshold of 2 mm² yielded the greatest sensitivity (99%) and specificity (100%) for the diagnosis of CTS.

Conclusion: Receiver operating characteristic analysis revealed improved accuracy in the diagnosis of CTS determined with the CSA compared with the accuracy of the diagnosis determined with the CSAc.

© RSNA, 2008