Background and purpose: Carpal tunnel syndrome (CTS) is a common neuropathy resulting from compression of the median nerve at the carpal tunnel. Sonographic diagnosis of this condition relies on enlargement, flattening and/or demonstration of impaired mobility of the median nerve, as well as bowing or thickening of the flexor retinaculum. In most patients the cross-section of the median nerve at the level of the carpal tunnel has an oval or elliptical shape. We have noticed, however, that in a number of cases the cross-section of the median nerve at the inlet of the carpal canal was deformed, assuming a triangular shape. The purpose of this study was to assess the diagnostic value of the triangular median nerve cross-section sign.
Material and methods: One hundred and thirty-nine sonographic examinations in 76 patients with clinical signs of CTS, and 25 examinations in 14 healthy volunteers were performed. Standard electrodiagnostic studies were performed in all symptomatic patients.
Results: Triangular shape of the median nerve cross-section in the carpal canal was observed in 13/118 (11.0%) median nerves with abnormal result of the electrodiagnostic study, and in 2/21 (9.5%) cases with a normal electrodiagnostic examination result. No such deformation was seen in the control group.
Conclusions: The triangular cross-section sign has high specificity (0.90) and positive predictive value (0.87) in dia-gnosis of CTS.