Sonographic Detection of a Bifid Median Nerve and Persistent Median Artery
Among Patients with a Clinical Diagnosis of Carpal Tunnel Syndrome
Francis Luk, Carolyn R. O’Connor, Humaira Hussain, Vincent J Zarro and Angel Checa
Drexel University College of Medicine, Philadelphia, PA
Background
Rheumatologists often manage patients with carpal tunnel
syndrome (CTS) by corticosteroid injections with or without
ultrasound guidance. Although new imaging techniques that
permit the identification of the bifid median nerve (BMN) and
persistent median artery (PMA) are being used more frequently,
the prevalence of these variants continues to be unclear. Both PMA
and BMN, if present, are potential sources of complications due to
laceration during interventional procedures such as carpal tunnel
release or steroid injection.
Purpose
Methods
A total of 129 wrists of 77 consecutive patients (9 males, 68
females) with a clinical diagnosis of CTS assessed by ultrasound in a
rheumatology office were studied from January 2010 to June 2011.
These patients had symptoms of pain, paresthesia, and/or
weakness. Longitudinal and transverse scans of the volar aspect of
the wrist were performed with a GE Logiq e machine equipped
with a broadband linear transducer from 8 to 13 MHz. The crosssectional area of the median nerve was calculated with the ellipse
at the scaphoid-pisiform level. In those cases with BMN, both
branches were measured separately. The functional status of the
median artery was evaluated by the presence or absence of a
Doppler signal.
ma
mn
A
ua
cb
B
l
m
C
Figure 1. (A) Diagram showing the transverse orientation of the transducer. (B)
Transverse sonographic view of the volar aspect of the wrist. This view shows a bifid
median nerve and the nerve structures, carpal bones, and ulnar artery. (C) Magnified
image of the two branches of a bifid nerve, medial and lateral, accompanied by the
median artery. cb, carpal bones; l, lateral; m, medial; ma, median artery; mn, bifid
median nerve; ua, ulnar artery
m
mn
A
mn
l
B
m
l
Short axis
C
b
b
B
mn
m
l
Long axis
D
Long axis
Figure 2. (A) Bifid median nerve without the median artery.
(B) Diagrammatic representation of a longitudinal
sonographic scan and examination of the medial and lateral
branches emerging from a common trunk. (C) Medial
branch of the bifid nerve in longitudinal view. (D) Lateral
branch of the bifid nerve in longitudinal view. l, lateral; m,
medial; mn, bifid median nerve
Wrists with PMA
10
1
3
3
pma
Left
Right
BMN
UA
A
C
pma
B
To determine the prevalence and sonographic characteristics of
BMN and PMA in patients with carpal tunnel syndrome
Wrists with BMN
D
Lateral > Medial
Medial > Lateral
Same size
8
1
2
E
Results
Of 77 patients (129 wrists), 13 (14 wrists) had BMN or PMA. The
mean age of those with BMN or PMA was 52.5 (31-81) years; the
prevalence of BMN and PMA was 8.5% and 4.6%, respectively.
BMN was more common in the left hand, and a greater lateral
branch was the most characteristic sonographic pattern, observed
in 70%. The average cross-sectional area for BMN was 11.4 (range
6-18) mm2. The PMA was associated with a BMN in three wrists,
and it appeared as an isolated variant in 3 other wrists. The
average diameter of a PMA was 1.4 (range 0.8-3.1) mm. In three
of them, the Doppler signal showed a functional artery. A
Doppler signal was absent in two PMAs; in one artery, the
Doppler signal was not explored. In those patients with PMA but
no Doppler signal, a nonfunctional, cord-like remnant may be
present.
Number of Patients
(%)
10 (13)
Number of
Wrists (%)
11 (8.5)
Persistent median artery
5 (6.5)
6 (4.6)
Both BMN and PMA
3 (3.9)
3 (2.3)
BMN only
PMA only
7(9.1)
2 (2.6)
8 (6.2)
3 (2.3)
77
129
Total scanned
Number of Wrists with BMN
Mean Cross-sectional
Range of CrossArea of BMN (mm2) sectional Areas of BMN
(mm2)
Figure 3. Panels A and B show power Doppler scan in short- and long-axis views,
respectively. (C) Cross-sectional measurement of lateral medial branch of a
BMN. (D) Power Doppler scan of a patient with a persistent median artery. (E)
B
Transverse view of the same patient shown in (D), illustrating sonographicguided injection in the opposite side of the PMA (arrow). BMN, bifid median
A pma, permanent median artery; ua, ulnar artery
nerve;
Bifid median nerve
Cross -sectional Area
Medial branch
3.2
1-9
Lateral branch
7.9
6 - 11
Number of
Wrists with PMA
Diameter of
PMA (mm)
PMA only
3
Mean
1.4
PMA associated
with BMN
Doppler signal
Present
3
Range
0.8 – 3.1
3
Conclusions
Although studies of large populations are needed, the
increased observation of BMN and PMA by ultrasound in
patients with CTS should be considered more than a medical
curiosity. This study demonstrates that BMN were observed
in 8.5% of wrists referred for evaluation of hand pain. The
PMA was seen in 4.6% of wrists. We suggest that
ultrasound evaluation of the carpal tunnel should be routine
procedure in the rheumatology office prior to corticosteroid
injection and surgical release.
References
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tunnel syndrome. J Rheumatol 2011;38:1694-1696.
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