Keywords anatomical variations - median nerve - ulnar artery - ulnar collateral arteries -
common interosseous artery - cadaver
Introduction
The median nerve is formed by the fusion of the lateral and medial roots coming from
the lateral and medial cords of the brachial plexus, respectively.[1 ] After this fusion, the median nerve descends anterior to the axillary artery and
the upper third of the brachial artery. In the middle of arm, the median nerve crosses
from the lateral to the medial side of the brachial artery.[2 ]
[3 ] Anatomical variations of the median nerve have been described by many authors.[4 ]
[5 ] Budhiraja et al (2011) reported the existence of an additional root in the formation
of the median nerve in 26.4% of upper limbs, unusual low formation of the median nerve
in the arm in front of the brachial artery in 18.4% of upper limbs, and median nerve
formation medial to the axillary artery in 10.3% of upper limbs.[6 ] Mat Tiab et al (2017) studied the distribution of variations of the median nerve.
According to their study, normal formation of the median nerve from two roots represented
63.6% (14) and 72.7% (16) for the left and right upper limbs, respectively.[7 ] Three other variations of median nerve formation that have been observed are: one
root, three roots, and four roots. Three roots forming the median nerve were found
in ∼ 36.4% (8) in the left upper limb, and 18.2% (4) in the right one. More variations
were observed in the right upper limb. Median nerves formed from one root and four
roots were observed in 4.5% of upper limbs, each. A normal course of the median nerve
in relation to the axillary artery had the same distribution on the left and right
sides, 81.8% (18). In 13.6% (3) of the samples, the median nerve was running posterior
to the axillary artery, and in 4.5% (1) of the cases, it ran medial to the axillary
artery in the left upper limb. Beheiry[8 ] also reported anatomical variations of the median nerve distributions and communication
in the arm region. According to Beheiry's report, in 1.7% of the cases, the median
nerve gave off muscular branches to the brachialis muscle. Variations in the vascular
pattern of the upper limb have been also frequently observed. According to the Compendium
of Human Anatomic Variation, major variations are present in the brachial artery of
∼ 25% of the subjects studied. The variations in the form of high proximal division
into terminal branches occur in the radial artery (15%), ulnar artery (2%), and common
interosseous artery (very rarely).[9 ] According to the studies, at least four major types of variation of the brachial
artery have been described, with trifurcation of the brachial artery, double profunda
brachial artery (DPBA), high division of brachial artery (HDBA) and high origin of
radial artery (HORA) being the most commonly observed variations.[10 ] The variations described in the following case are quite different and rare in terms
of bilateral neurovascular variations. We observed a bilateral variant configuration
of the median nerve accompanied by variation of brachial artery branching in the arm
region and superficial ulnar artery in a male cadaver. Multiple neurovascular variations
in the upper extremities are of potential clinical implications, as this is a frequent
site of injury that is also involved in many surgical and invasive procedures. Therefore,
knowledge of such multiple variations could help to avoid malpractice.
Case Report
During a routine educational dissection, a bilateral variation of the brachial artery
was observed in a 45-year-old male cadaver. We found a bilateral, unusual and variant
course of the median nerve in the arm region. The right median nerve, after its formation,
descended from the medial to the brachial artery, crossed the brachial artery anteriorly
from medial to lateral, then inferiorly and lied medially to the distal third of the
brachial artery ([Fig. 1 ]). The left median nerve showed a different course to the brachial artery. It ran
medial to the brachial artery, passing anteriorly from medial to lateral, and, at
the distal end of the arm, it buried itself in the brachialis muscle ([Figs. 2 ], [3 ]). Additionally, a small anomalous branch was observed arising from the lateral aspect
of the left median nerve passed inferiorly into the left cubital fossa ([Fig. 2 ]). Further inspection revealed that the right superior and inferior ulnar collateral
arteries were replaced by two arteries arising from the lateral side of the brachial
artery. The right superior one ran deep into brachialis muscle as a muscular branch,
while the right lower (inferior) one descended between the biceps and brachialis muscles
([Fig. 4 ]). The left superior and inferior ulnar collateral arteries were also replaced by
one muscular branch aroused from the lateral side of the left brachial artery. Further
examination in the cubital region revealed that the right and left common interosseus
arteries aroused from the radial and ulnar arteries were superficial to the flexor
carpi radialis (both sides), and the ulnar recurrent arteries were absent bilaterally.
([Figs. 5 ], [6 ])
Fig. 1 Right arm. The right median nerve, after formation in the medial side of the brachial
artery, crosses it anteriorly and then runs inferior to the brachial artery and lies
medial to it.
Fig. 2 The left median nerve with a thin, small anomalous branch (blue arrowhead) formed
on the medial side of the brachial artery (red arrowhead) descending from its medial
to lateral side.
Fig. 3 Photograph shows the distal third of the left median nerve buried into the brachialis
(blue arrowheads).
Fig. 4 Right arm and right brachial artery (yellow arrowhead). Right superior and inferior
ulnar collateral arteries are replaced by two arteries arising from the lateral side
of the brachial artery
Fig. 5 Left cubital region. Common interosseous artery arising from the radial artery. A
single recurrent branch (radial recurrent artery [rad rec art]) stems from the radial
artery.
Fig. 6 The ulnar artery passing superficially to the flexor carpi radialis (Flex Carp Rad).
Discussion
According to the standard anatomy text books, the median nerve is formed by a fusion
of two roots, and, after joining, it crosses the brachial artery from the lateral
to the medial side. However, variations of the median nerve, including abnormal communication
with other nerves, splitting of the median nerve, and formation of the median nerve
by more than two roots, have been reported.[11 ]
[12 ]
[13 ] In the present case, a bilateral unusual course of the median nerve in the arm region
accompanied with brachial artery branching pattern variations was found. Unusual course
of the median nerve has been reported earlier by a few authors. Singh et al reported
that the median nerve was formed medial to the brachial artery and crossed it anteriorly
from the medial to the lateral side.1 There are also reports in which the median nerve was formed medial to the axillar
artery.[14 ]
[15 ]
[16 ] In another study, median nerve formation medial to the axillar artery was reported
in 6.12% of upper limbs.[6 ] Another study reported median nerve descending medial to the brachial artery in
6% of cases.[17 ] Chitra also reported median nerve coursing medial to the brachial artery.[14 ] In the present case, we observed a rare bilateral variation of the median nerve
course in the arm region. On the right side, the median nerve double crossed the brachial
artery. Precisely, the right median nerve descended medial to the brachial artery
in the upper third of the arm; then, it crossed the brachial artery anteriorly from
medial to lateral; in the middle third of the arm, it hooked the brachial artery,
and, in the distal third, it crossed from lateral to medial inferiorly. The left medial
nerve descended medial to the brachial artery in the upper half of the arm, crossing
the artery anteriorly at the junction of the upper and lower halves of the arm. In
the distal third of the arm, the left median nerve ran lateral to the brachial artery,
where it buried itself deeply into the brachial muscle. There are comprehensive studies
have dealt with the variations of the median nerve. For instance, Buhiraja et al[6 ] have studied 174 upper limbs and reported the variations of median nerve formation
in terms of roots and course in relation to the brachial artery. To the best of our
knowledge, the variation presented here of median nerve variation has not been reported.
Helical relation of the right median nerve to the brachial artery, and the deeply
buried left median nerve with a different course to the right median nerve may lead
to neurologic signs in the upper limbs, which would not be diagnosed by routine physical
examination. Peripheral nerve injury in the upper extremity is common, and certain
peripheral nerves are at an increased risk of injury because of their anatomic location.
Risk factors include a superficial position, a long course through an area at high
risk of trauma, and a narrow path through a bony canal. The most common nerve entrapment
injury is carpal tunnel syndrome, which has an estimated prevalence of 3% in the general
population, and 5 to 15% in the industrial setting.[18 ] Spinner et al[19 ] escribed entrapment of the median nerve caused by compression in the distal arm
because of an accessory. It was characterized by the paresis or paralysis of muscles
innervated by the anterior interosseous branch of the median nerve—the flexor pollicis
longus, the flexor digitorum profundus, and the pronator quadratus—as well as other
more proximal median nerve-innervated muscles, namely, the pronator teres and flexor
carpi radialis. The case we presented here raised another possible cause of median
nerve entrapment in vivid anatomy, which has not been noticed in clinical literatures.
Another set of findings were bilateral variations of brachial artery branching pattern.
We observed bilateral vascular variations that have not been reported before. For
instance, the right superior and inferior ulnar collateral arteries were absent; instead,
two branches aroused from the lateral side of the brachial artery with muscular distribution.
The left superior and inferior ulnar collateral arteries were replaced with a single
branch arising from the lateral side of the brachial artery. In the cubital region,
the ulnar artery in both sides ran superficially, while the common interosseus artery
aroused from the radial artery. To date, numerous anatomical variations in the brachial
artery and its branching pattern have been reported. The most commonly reported variation
in upper limb arteries is the higher division of brachial artery into the radial and
ulnar arteries above the cubital fossa. For instance, Kaur et al[20 ] studied 40 upper limbs and observed a higher division of the brachial artery into
radial and ulnar arteries above the elbow joint in 4 cases, trifurcated ulnar artery
at the lower border of pronator teres in 3 cases, and inferior ulnar collateral artery
absence in 4 cases. In another study, Chakravarthi et al[21 ] evaluated 140 upper limb specimens and reported accessory brachial artery as the
main arterial variation limb. Superficial ulnar artery is an uncommon variation in
which the ulnar artery is having its course superficial to the flexors of the forearm
and may arise directly from the axillary or brachial arteries. The presence of a superficial
ulnar artery seems to be a rare variation, with an incidence of 0.7 to 7% and has
unilateral preponderance.[22 ] Senanayake et al[23 ] reported superficial ulnar artery aroused from the upper one third of the brachial
artery. Quadros et al[22 ] also reported a unilateral superficial ulnar artery and a common interosseous stemming
from the radial artery. The most frequently reported finding pertinent to the present
case is the variation described by Quadros, but we found bilateral superficial ulnar
artery and common interosseous as the principle branch of the ulnar artery, stemming
from the radial artery. Bilateral multiple neuroarterial variations in the upper extremities
are considered challenging in surgical procedures. The case presented here showed
a series of neurovascular variations, including bilateral unusual course of the median
nerve and absent superior and inferior ulnar collateral arteries. The observed variations
in the arterial pattern of the brachial artery and the median nerve assume significance
during clinical examinations of neurologic symptoms, vascular surgeries and local
anesthesia procedures. Unusual course of the peripheral nerves may lead to nerve entrapments
and subsequent muscles paresis. Additionally, absence of major arterial branches—namely
ulnar collaterals around the elbow joint—could potentially trigger neurologic symptoms.
Therefore, the importance of such multiple variations goes beyond the merely anatomical
variation reports and need to be considered and emphasized in clinical practice. Some
of the most frequent types of arterial variations, such as superficial ulnar artery,
can be mistaken as veins during venipuncture.
Conclusion
Regarding the complex variations presently described, we believe that knowledge of
such compound unusual anatomical relations and patterns is not only of great importance
in orthopedic and vascular surgeries, but it should also be considered in common practices.
