Secondary carpal tunnel syndrome (CTS) can be caused by vascular anomalies usually involving persistent median artery, variations of the median nerve, and space-occupying lesions in the wrist and palm. High division of the median nerve proximal to the carpal tunnel (known as a bifid median nerve) is a median nerve anomaly with a reported incidence of 2.8% per wrist. The bifid median nerve is often associated with various abnormalities such as persistent median artery and aberrant muscles, causing clinical features of CTS. Most reported cases of bifid median nerves are associated with CTS due to its higher cross-sectional area compared to a non-bifid median nerve. We report a rare case in which an anomalous tendinous course of the flexor digitorum superficialis muscle is associated with bifid median nerve proximal to the flexor retinaculum at the distal wrist. Surgeons should consider the possibility of median nerve variation in patients with unilateral severe CTS and be aware of this anomaly during elective carpal tunnel release.
Carpal tunnel syndrome (CTS) is a common neuropathy caused by entrapment of the median nerve by a thickened flexor retinaculum in the wrist
A 55-year-old right-handed female patient presented with a 3-year history of progressively worsening paresthesias, numbness, and tingling in the lateral three digits and radial palm in her right hand. There was a constant aching pain in the radial palm. There was no neck pain or radicular symptom in her arms. Her medical history was unremarkable. Physical examination showed thenar muscle atrophy and muscle weakness of the abductor pollicis brevis in the right hand. Tendon reflexes were normal and symmetric. Decreased sensation to light touch and pinprick was evident in the lateral three digits of the right hand. Tinel sign was not elicited. However, a positive Phalen test was present on the right wrist. Pain and paresthesia in the right hand initially responded to repeated local steroid injection and medications. The symptoms of the patient progressively worsened over time, eventually showed no response to conservative treatment 6 months prior to admission.
Electrodiagnostic findings were compatible with median entrapment neuropathy around the right wrist and clinical carpal tunnel syndrome with severe degree by American Association of Electrodiagnostic Medicine (AAEM) classification
After incision of the skin and superficial fascia of the distal forearm and the palm, the underlying flexor retinaculum was identified and transected. The forearm fascia was then carefully dissected. The underlying median nerve just proximal to the flexor retinaculum in distal forearm was found to be duplicated. A tendon of the flexor digitorum superficialis (FDS) muscle traversed between the radial and ulnar division of the bifid median nerve (
Severe pain in radial palm and paresthesia disappeared immediately after the operation. Hand weakness improved gradually over 2 weeks. However, hypesthesia in the distal portion of the radial three digits remained until 12-month follow-up at an outpatient clinic.
High bifurcation of the median nerve, the so-called bifid median nerve, is an well-known but rare anomaly of the median nerve. Variations of the median nerve were first classified by Lanz
The two branches of the nerve which run parallel inside the tunnel are sometimes separated by a persistent median artery or an accessory muscle
The occurrence of a bifid median nerve has been reported to be frequently associated with persistent median artery
Aberrant muscles associated with bifid median nerve have been sporadically reported to cause carpal tunnel syndrome
It is difficult to suspect an anomaly of median nerve in every case of carpal tunnel syndrome preoperatively. However, considering the incidence of variations of the median nerve, surgeons should keep in mind potential surgical hazards and recurrence of symptoms with insufficient surgical decompression. It has been suggested that MRI and ultrasound examinations can be performed to show bifid median nerves so that surgeons can avoid potential surgical risks
Although we do not routinely use MRI or other imaging modalities for the diagnosis of carpal tunnel syndrome, we always perform ultrasound examination and high-resolution MRI in every suspicious case of secondary carpal tunnel syndrome. It has been suggested that imaging studies should be obtained for patients in whom secondary carpal tunnel syndrome is suspected with severe unilateral symptoms, young age (<40 years), and male sex
When this anatomical variation is present, it is important to have carpal tunnel release because of the increased risk of nerve injury. In addition, the two branches of the nerve might be constricted separately. Separate decompression might be required for each branch
We report a rare case of carpal tunnel syndrome with bifid median nerve in association with aberrant flexor digitorum superficialis muscle. It was not associated with persistent median artery. The present case highlights the importance of clear visualization of the median nerve and surrounding structures during surgical treatment of carpal tunnel release and knowledge of anatomical variation of the median nerve. Inadvertent injury to the median nerve during carpal tunnel surgery can be minimized if these variations are recognized prior to operation.
No potential conflict of interest relevant to this article was reported.
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