What are the findings of normal nerve on USG examination?
The normal nerve, in transverse section, reveals small hypoechoic areas separated by hyperechoic septae, giving a "honeycomb-like" appearance. The hypoechoic areas represent nerve fascicles while the echogenic septae represent interfascicular perineurium. The longitudinal sections also reveal the fascicular architecture, leading to a "bundle of straws" appearance. The nerve is more echogenic as compared to the muscle which shows hypoechoic muscle fiber bundles with intervening echogenic perimysium.
There is thickening of the median nerve with cross section area > 10mm2 at the proximal carpal tunnel (scaphoid-pisiform level) with loss of normal fascicular architecture.
On dynamic examination the median nerve is sliding superficially to the flexor digitorum superficalis tendon.