Evaluating the cross-sectional area (CSA) of the median
nerve by use of ultrasound in carpal tunnel syndrome (CTS)
Poster No.:
C-0080
Congress:
ECR 2011
Type:
Scientific Exhibit
Authors:
B. Wanitwattanarumlug , V. Varavithya , W. Aramrussameekul ;
1
1
2
2
2
Nakhon Nayok, 26120/TH, Nakhon Nayok/TH
Keywords:
Musculoskeletal system, Neuroradiology peripheral nerve,
Ultrasound, Diagnostic procedure, Inflammation
DOI:
10.1594/ecr2011/C-0080
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Purpose
The current method for diagnosis of carpal tunnel syndrome (CTS) is based on clinical
symptom and is confirmed by using nerve conductive study (NCS). Recently, magnetic
resonance imaging (MRI) and ultrasound (US) have also been used to confirm the
clinically suspected diagnosis of CTS. US is potentially advantages as it is widely
available, comfortable, with a relatively lower cost and have shorter examination time.
The aim of this study is to evaluate the diagnostic value of US of the median nerve in
carpal tunnel syndrome in Thai patients.
Methods and Materials
All CTS patients and control subjects were examined with ultrasound of the median nerve
and NCS. A linear array transducer was used to scan all wrist for median nerve crosssectional area. The CSA of median nerve was measured by two different methods. The
first method was direct measurement by using tracing method (TM), in which the margin
of median nerve was measured with electronic caliper. This measurement was performed
from the inner border of perineural echogenic rim surrounding hypoechoic median nerve
as shown in figure 1a and figure 2a. The second method was indirect measurement, using
the ellipsoid formula (EF), calculating the transverse and anteroposterior dimensions. In
this measurement, the formula of ellipsoid area was used D1xD2x3.14/4 as shown in
figure 1b and figure 2b. This data was compared to NCS results.
Images for this section:
Fig. 1: Fig.1 Sonography of the median nerve at the wrist in a 53-year-old woman. (a)
The median nerve appears as a oval shape, hypoechoic structure. The cross-sectional
area, by using tracing method,was 8 mm2. (b) The transverse diameter, AP diameter and
Page 2 of 6
cross-sectional area were 58 mm, 17 mm and 7.7 mm2, respectively using the ellipsoid
formula. Nerve conduction study of the median nerve in this patient was normal.
Fig. 2: Fig. 2 Sonogram of the median nerve at the wrist in a 56-year-old man whose
nerve conduction study of the median nerve was positive for carpal tunnel syndrome.
(a) The cross-sectional area was 11 mm2 by the tracing method. (b) The transverse
diameter, AP diameter and cross-sectional area were 60 mm, 25 mm and 11.8 mm2,
respectively by the ellipsoid formula.
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Results
Twenty-three carpal tunnel syndrome patients, in whom 34 wrists were diagnosed as
CTS with NCS, and 60 wrists in 30 asymptomatic control subjects were examined
with ultrasound and NCS. The mean cross-sectional area (CSA) measurements were
2
2
found as 10.29 + 2.02 mm by tracing method (TM) and 10.09 + 2.08 mm by ellipsoid
2
2
formula (EF) in the study group, and 6.87 + 0.93 mm by TM and 6.80 + 0.99 mm
by EF in the control group. CSA calculated by the TM and EF methods were found
to be significantly lower in the study group than in the control group (p<0.001). Thus,
quantitative assessment of the median nerve provides an accurate diagnostic test (TM;
sensitivity 85.29% and specificity 90.28%, EF; sensitivity of 70.59%, specificity 87.50%),
2
with an area larger than 9 mm being highly predictive of carpal tunnel syndrome.
Conclusion
We confirmed that US has high sensitivity and specificity for the diagnosis of CTS by
using both TM and EF quantitative methods.
We found no difference in the US cut-off value of the median nerve between the Thai
population and other countries.
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Personal Information
Boontaree Wanitwattanarumlug, M.D.
Office: Department of Radiology, Princess Maha chakri Sirindhorn Medical center,
Faculty of Medicine, Srinakarinwirot University, 62 Moo 7, Rangsit-Nakhonnayok Road,
Ongkarak, Nakhon Nayok, Thailand
Telephone: +66-3-739-5085, +66-86-535-0543
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Fax: +66-3-739-5085 ext. 10232
Email: [email protected]
Home: 51, Soi Ladprao 102, Ladprao Road, Wangthonglang, Wangthonglang Bangkok
10310, Thailand
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