OBJECTIVES: To provide a quantitative analysis of ultrasonographic measurements 
and possible pathophysiology of carpal tunnel syndrome by comparing 
cross-sectional areas of the median nerve, carpal tunnel, and nerve/tunnel index 
and the difference in ultrasonographic findings between affected and nonaffected 
hands and between sexes.
DESIGN: Blinded comparison study.
SETTING: Secondary referral and training hospital of institutional practice.
PARTICIPANTS: Patients (N=51; 42 women, 9 men) with suspected carpal tunnel 
syndrome who underwent sonography within 1 week after the electrodiagnostic 
study.
INTERVENTIONS: Not applicable.
MAIN OUTCOME MEASURES: Electrodiagnostic and ultrasonographic studies were 
conducted on both upper extremities. Cross-sectional areas of the median nerve 
and carpal tunnel were measured at 2 separate levels; proximal and distal 
cross-sectional areas of the carpal tunnel were each measured at the 
scaphoid-pisiform and trapezium-hamate levels, respectively.
RESULTS: Comparison between normative (n=24) and abnormal hands (n=78) revealed 
the following: the mean proximal cross-sectional areas of the median nerve, 
carpal tunnel, and nerve/tunnel index of electrodiagnostically normative hands 
were 10.941mm(2), 192.43mm(2), and 5.635%, respectively, whereas those of 
abnormal hands were 13.74mm(2), 208.87mm(2), and 6.693%, respectively, showing 
statistically significant differences for all (P<.05). Distal measurements of 
the cross-sectional area of the median nerve, carpal tunnel, and nerve/tunnel 
index were 10.088mm(2), 150.4mm(2), and 6.762%, respectively, in normative 
hands, and 11.178mm(2), 149.6mm(2), and 7.493%, respectively, in abnormal hands, 
showing no statistically significant differences (P>.05). In women, proximal 
cross-sectional areas of the median nerve and nerve/tunnel index of abnormal 
hands showed statistically significant differences, but no ultrasonographic 
measurement with a statistically significant difference was observed in men.
CONCLUSIONS: Compared with nonaffected hands, the proximal cross-sectional areas 
of the median nerve and carpal tunnel were greater, but the distal 
ultrasonographic measurements were not in affected hands. Ultrasonographic 
findings of carpal tunnel syndrome were different according to sex.