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Median Nerve Variation: A Complete Spin before
Terminal Branching
Amgad S. Hanna1Zhikui Wei2Barbara A. Hanna3
1Department of Neurological Surgery, University of Wisconsin School
of Medicine and Public Health, Madison, Wisconsin, United States
2Department of Neurology, Vanderbilt University, Nashville,
Tennessee, United States
3College of Letter and Science (Premed), Undergraduate Student,
University of Wisconsin, Madison, Wisconsin, United States
J Brachial Plex Peripher Nerve Inj 2020;15:e1–e4.
Address for correspondence Amgad S. Hanna, MD, Department of
Neurological Surgery, University of Wisconsin School of Medicine and
Public Health, 600 Highland Avenue, MC 8660, Room K4/830, CSC,
Madison, WI 53792, United States (e-mail: ah2904@yahoo.com).
Introduction
Median nerve anatomy and variations have fascinated both
clinicians and researchers. Classically, the median nerve is
described to be derived from both the lateral and medial
cords of the brachial plexus. It runs down the upper arm
without any branches, and enters forearm between the two
heads of pronator teres. In the forearm, the median nerve
travels between flexor digitorum superficialis (FDS) and
flexor digitorum profundus. It then gives out the anterior
interosseous nerve from the dorsolateral aspect. In the wrist
and hand, median nerve travels deep to the flexor retinacu-
lum (transverse carpal ligament) and gives out its terminal
branches, including the recurrent motor branch on the
lateral side, and the palmar digital branches medially.
While textbook descri ptions provide an excellent baseline
for understanding the anatomy of this nerve, it does not
represent the whole reality of median nerve anatomy, as
seen by surgeons and researchers. Median nerve anatomical
variations have been frequently reported in the literature.
We report a rare median nerve anatomical variant that was
encountered during a cadaveric dissection. The median nerve
was deep to FDS in the carpal tunnel and showed a 360-degree
spin before dividing into its terminal branches. To our knowl-
edge, this has never been described before. Recognition is a key
since this anomaly may put the median nerve at risk of injury
during surgery for carpal tunnel release.
Case Presentation
This is a cadaveric dissection of an 82-year-old female’sleft
upper limb. There were no signs of trauma or previous surgery.
Once the flexor retinaculum was opened, only tendons of FDS
were seen (►Fig. 1). Normally the median nerve is located
betweenthe flexor retinaculum and the FDS. Furtherdissection
revealed thatthe median nerve madea 180-degree spinaround
the lateral border of the FDS tendon to the index finger toward
the distal end of the carpal tunnel (►Figs. 1 and 2). The median
nerve and its branches then travelled medially superficial to
FDS, along with the superficial palmar arch (►Figs. 1 and 2).
Keywords
►anatomy
►carpal tunnel
►flexor digitorum
superficialis
►median nerve
►variants
Abstract Median nerve anatomy is of great interest to clinicians and scientists given the
importance of this nerve and its association with diseases. A rare anatomical variant
of the median nerve in the distal forearm and wrist was discovered during a cadaveric
dissection. The median nerve was deep to the flexor digitorum superficialis (FDS) in the
carpal tunnel. It underwent a 360-degree spin before emerging at the lateral edge of
FDS. The recurrent motor branch moved from medial to lateral on the deep surface of
the median nerve, as it approached the distal carpal tunnel. This variant doesn’tfallinto
any of Lanz’s four groups of median nerve anomalies. We propose a fifth group that
involves variations in the course of the median nerve. This report underscores the
importance of recognizing variants of the median nerve anatomy in the forearm and
wrist during surgical interventions, such as for carpal tunnel syndrome.
received
June 3, 2019
accepted after revision
August 28, 2019
DOI https://doi.org/
10.1055/s-0039-3402734.
ISSN 1749-7221.
© 2020 Georg Thieme Verlag KG
Stuttgart · New York
THIEME
Case Report e1
Published online: 12.02.2020
When the FDS tendons were separated, the median nerve was
found to have another 180-degree spin around itself proximal
to the carpal tunnel deep to FDS, thus completing a 360-degree
spin (►Fig. 2A). An interfascicular dissection was then per-
formed to separate the palmar recurrent branch. This was
found to be on the medial aspect of the median nerve in the
proximal carpal tunnel, and then it travels on the deep surface
of the median nerve to head laterally toward the thenar
muscles in the distal carpal tunnel (►Fig. 2B). We completed
the dissection byexposing the mediannerve in the cubitalfossa
and the upper forearm (►Fig. 3).
Discussion
Carpal tunnel syndrome is one of the most common forms
of entrapment neuropathy, often requiring surgical release
of the transverse carpal ligament. Common causes of
carpal tunnel syndrome include changes that led to the
increased tissue turgor, hypertrophy of connective tissue,
or deposition of metabolic products in the tissue. These
changes could be the downstream effects of traumatic,
hormonal, metabolic, vascular, inflammatory, neoplastic,
or aging processes.
Fig. 1 (A) Dissection of the palmar aspect of the left hand and forearm. Only tendons of flexor digitorum superficialis (FDS; 1) were visible once
the flexor retinaculum (transverse carpal ligament) was opened. The median ner ve, while not visible in the carpal tunnel, its branches (2)
appeared distally toward the radial aspect of FDS and crossed medially superficial to FDS along with the superficial palm ar arch (3). (4) represents
flexor carpi radialis and (5) i s the flexor carpi ulnaris. H, hypothenar muscles; T, thenar muscles; arrow, cut end of the transverse carpal ligament.
(B)Magnified view of A.
Journal of Brachial Plexus and Peripheral Nerve Injury Vol. 15 No. 1/2020
Variation of Median Nerve Hanna et al.e2
Stancićet alstudied 100 hands and found that less than 50%
of them aligned with the median nerve anatomy described in
textbooks.1Thus, they proposed that knowledge of these
variations should be applied preoperatively to minimize chan-
ces of incomplete decompression of the nerve during surgery.
Henry et al proposed that variations in median nerve location
and branching in the carpal tunnel are not onlyexisting but are
common, and carpal tunnel release should be approached
from the ulnar side to minimize further injury in surgery.2
Vinding et al identified a rare anatomical variant of the thenar
branch that originates from ulnar side and runs supraligmen-
tously close to the top of the transverse ligament which carries
great risk of injury during endoscopic release for carpal tunnel
syndrome.3Hanna classified the motor branch of the median
nerve into types I-IV based on location on the median nerve,
and A-D based on the angle it takes.4Spagnoli et al reported a
high division of the median nerve proximal to the carpal
tunnel, also known as a bifid median nerve, and itsassociation
with carpal tunnel syndrome and with persistent median
vessels.5Lis et al reported a variation of the median nerve
that passed through the head of the flexor digitorum super-
ficialis.6Atoni and Oyinbo identified a splitting of the median
nerve into medial and lateral divisions in the proximal one-
third of the forearm to accommodate an anomalous muscle
which could be a source of median nerve compression.7
Papathanassiou found a variation of the median nerve that
gave a motor branch more proximally than expected, thus
passing through the flexor retinaculum.8
Lanz supported the ulnar approach in surgery, reporting
29 variations in 246 hands. He classified the variations of
median nerve in the wrist into four groups. Group I includes
variations of the thenar branch. Group II includes variations
that involve accessory branches of the median nerve at the
distal end of carpal tunnel. Group III includes median nerve
with high divisions, and group IV includes variations that
involve accessory branches proximal to the carpal tunnel.9
Among group I, four variations are identified and these
include subligamentous, transligamentous, ulnarwards,
and supraligamentous courses of thenar branch, in addition
to the standard anatomy, extraligamenous thenar branch.9
Interestingly, our case identified an anatomical basis for the
ulnarward origin of the thenar branch which is due to a
proximal rotation of median nerve deep to FDS rather than
actual variations of the terminal branches of median nerve
itself. This warrants adding a separate group, may be group V
that includes variation in the course of the median nerve.
Fig. 2 (A) When the flexor tendons were retracted, the medianner ve(M) was observed making a 360-degree spiralturn deep to the FDS tendonsto emerge
lateral to then superficial to FDS. (B) Interfascicular dissection showing the palmar recurrent branch (yellow vessel loops) moving from medial to lateral on
the deep surface of the median nerve toward its destination to the thenar muscles. FDS, flexor digitorum superficialis; T, thenar muscles.
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This case highlights the importance of recognizing varia-
tions of the median nerve anatomy in the forearm and wrist
region, and their significance with regard to the diagnosis
and treatment of conditions, such as the carpal tunnel
syndrome. It is crucial to gather as much information as
possible regarding the anatomy prior to surgery, as well as be
able to recognize the variations when encountered intra-
operatively, to minimize the possibility of iatrogenic events.
Conflict of Interest
None declared.
References
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Fig. 3 The entire course of the median nerve is observed from the cubital
fossa, under the flexormuscles, and then distally making a 360-degree turn
until it branches distal to the transverse carpal ligament. 1, common flexor
tendon originating from the medial epicondyle of the humerus; 2, flexor
carpi radialis; BR, brachioradialis; FDS, flexor digitorum superficialis; M,
median nerve; T, thenar muscles.
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