Atypical Palmaris Profundus with Median Nerve Perforation Presenting Ultrasonically as an Intraneural Mass

An accessory palmaris profundus tendon might cause carpal tunnel like symptoms and in addition is a known potential reason for persistent symptoms following carpal tunnel release. In our case, a 34-year-old female patient presented with paresthesia of the third digit. Electromyography was without pathological findings. Diagnostic high-resolution ultrasound showed an intraneural mass within the median nerve in the region of the distal forearm. A tumorous lesion was suspected and a microsurgical resection was planned. Intraoperatively, a palmaris profundus tendon was found, perforating the median nerve and keeping an intraneural course, before leaving the median nerve within the carpal tunnel to migrate into the distal retinaculum fibers. The resection of the intraneural tendon of the palmaris profundus led to a recovery of the digital paresthesia's. We discuss the intraoperative findings and review the literature.