Ultrasonograhic Identification of the Entrapment of a Transligamentous Sensory Branch of the Ulnar Nerve

Anatomical variations of the ulnar nerve at the wrist are uncommon and may lead to diagnostic confusion or iatrogenic injury if unrecognized. We present an ultrasound-based identification of a rare transligamentous ulnar nerve sensory branch entrapment in an elderly male with chronic ulnar-sided hand paresthesia. High-resolution ultrasonography revealed an aberrant sensory branch deviating from the ulnar nerve, piercing the palmar carpal ligament, and coursing superficially rather than entering Guyon's canal. Further assessment demonstrated focal nerve flattening within the ligament with proximal enlargement, consistent with entrapment. This case highlights the value of ultrasound in detecting rare peripheral nerve variants and their entrapments. Therefore, it is also noteworthy to extend the sonographic evaluation beyond conventional entrapment sites at the wrist.