Age / Sex : 50 / F

Chief complaint: incidental finding during carpal tunnel syndrome evaluation

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Two weeks later, you can see the final diagnosis with a brief discussion of this case.

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Courtesy: Ik Yang, Kangnam Sacred Heart Hospital, Hallym University

Bifid median nerve with persistent median artery

Discussion

Findings:

Right wrist color Doppler US shows persistent median artery between bifid median nerve.

Differential Diagnosis:

Diagnosis:  

Bifid median nerve with persistent median artery

Discussion:

The median nerve may divide into two nerve bundles in the distal forearm and appear as a bifid median nerve in the carpal tunnel. It has an incidence of ~3%. 

The median nerve usually divides into two or three branches after exiting the distal edge of the transverse carpal ligament that covers the carpal tunnel. These subdivide into digital nerves that supply opposing sides of the digits.

A bifid median nerve may be accompanied by an accessory artery, the persistent median artery of the forearm, which lies in between the two nerve bundles. The artery and bifid nerve can be enclosed by a common epineurium. 

As the median artery can be easily detected on US, it is essential that this be mentioned in the radiologist's report to avoid inadvertent injury to the nerve and artery during surgical release of the transverse carpal ligament.

 The persistent median artery of the forearm is an accessory artery that arises from the ulnar artery in the proximal forearm and is a persistent embryological remnant that usually regresses by eight weeks gestation.

The persistent median artery of the forearm accompanies the median nerve as it passes through the forearm and carpal tunnel. 

It is unilateral ~67% of the time and is associated with anomalous median nerves ~70% (range 63-80%) of the time - most commonly bifid median nerves followed by high division of the median nerve. The persistent median artery is contained within the epineurium of the normal or bifid median nerve. 

The persistent median artery is located on the ulnar aspect of the normal median nerve but if the median nerve is bifid the persistent median artery is located between the two nerve bundles. 

References:

1.     Propeck T, Quinn TJ, Jacobson JA et-al. Sonography and MR imaging of bifid median nerve with anatomic and histologic correlation. AJR Am J Roentgenol. 2000;175 (6): 1721-5.

2.     Gassner EM, Schocke M, Peer S et-al. Persistent median artery in the carpal tunnel: color Doppler ultrasonographic findings. J Ultrasound Med. 2003;21 (4): 455-61.

3.     Bayrak IK, Bayrak AO, Kale M et-al. Bifid median nerve in patients with carpal tunnel syndrome. J Ultrasound Med. 2008;27 (8): 1129-36.