Value of power Doppler and gray-scale US in the diagnosis of carpal tunnel syndrome: contribution of cross-sectional area just before the tunnel inlet as compared with the cross-sectional area at the tunnel

Abstract

Objective: To determine the value of gray-scale and power Doppler ultrasonography in the evaluation of carpal tunnel syndrome (CTS).

Materials and methods: Median nerves at the carpal tunnel were evaluated by using gray-scale and power Doppler ultrasonography and by using accepted and new criteria in 42 patients with CTS (62 wrists) confirmed by electromyogram and 33 control subjects. We evaluated the cross-sectional area of the nerve just proximal to the tunnel inlet (CSAa), and at mid level (CSAb). We then calculated the percentage area increase of CSAb, and area difference (CSAb-CSAa). We measured two dimensions of the nerve at the distal level to calculate the flattening ratio. The power Doppler ultrasonography was used to assess the number of vessels, which proceeded to give a score according to the vessel number, and lastly evaluated the statistical significance by comparing the means of patients with control subjects by the Student t test for independent samples. Sensitivities and specificities were determined for sonographic characteristics mentioned above. We obtained the receiver operating characteristic (ROC) curve to assess the optimal cut-off values for the diagnosis of CTS.

Results: A statistically significant difference was found between patients and the control group for mean CSAb, area difference, percentage area increase, and flattening ratio (p < 0.001, p < 0.001, p < 0.001, p < 0.05, respectively). From the ROC curve we obtained optimal cut-off values of 11 mm(2) for CSAb, 3.65 for area difference, 50% for the percentage of area increase, and 2.6 for the flattening ratio. The mean number of vessels obtained by power Doppler ultrasonography from the median nerve was 1.2. We could not detect vessels from healthy volunteers. Mean CSAbs related to vascularity intensity scores were as follows: score 0: 12.3 ± 2.8 mm(2), score 1: 12.3 ± 3.1 mm(2), score 2: 14.95 ± 3.5 mm(2), score 3: 19.3 ± 3.8 mm(2). The mean PI value in vessels of the median nerve was 4.1 ± 1.

Conclusion: Gray-scale and power Doppler ultrasonography are useful in the evaluation of CTS.

Keywords: Carpal tunnel syndrome; Power Doppler; Ultrasonography.

Fig. 1

Ultrasonographic images of 48-year-old woman with history of pain in her wrists over last five years. A. Axial image reveals markedly enlarged median nerve with low level echo at pisifom bone level (CSAb) (figure in left). Cross-sectional area of median nerve just proximal to carpal tunnel inlet (CSAa) measured 10.8 mm² (figure on right). CSAb measures 21.9 mm² and percentage increase in area is 103% (figure in left) (median nerves are surrounded by dotted line). B. Median nerve is flattened at hamate bone level, with flattening ratio of 2.63 (median nerve is pointed with two lines perpendicular to each other).

Fig. 2

Ultrasonographic images related to 35-year-old women who was healthy volunteer. Median nerve shows speckled pattern which was echogenic throughout its length. A. CSAa (figure in right) and CSAb (figure in left) are 8.3 mm², 11 mm², respectively. Percent increase in area was 33% (median nerves are surrounded by dotted line). Power Doppler examination shows no vessel in median nerve (figure in left). B. Flattening ratio was found to be 1.67 (median nerve is pointed with two lines perpendicular to each other).

Fig. 3

Power Doppler images of patient median nerves. A. Longitudinal image shows increased vascularization which is orange to red in color. B. Pulsatility index is 2.63 in axial sonogram. C. Duplex Doppler ultrasonogram of another patient's pulsatility index was 6.1. Longitudinal image of median nerve shows swelling at carpal tunnel with abrupt increase in diameter and low level echogenicity.