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1
Department of Radiology, University Center Hospital Calmette, Blvd. Jules
Leclerc, 59037 Lille Cedex, France.
2
Medical Research Group "Equipe d'Accueil 2682," Blvd. Jules
Leclerc, 59037 Lille Cedex, France.
3
Department of Medical Statistics, University of Lille-1, Place de Verdun,
59045 Lille Cedex, France.
Received July 7, 1999;
accepted after revision November 10, 1999.
Address correspondence to M. Remy-Jardin.
Abstract
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SUBJECTS AND METHODS. Seventy-nine symptomatic patients (61 female patients [group 1]; 18 male patients [group 2]; mean age, 38 years) underwent helical CT angiography of the thoracic apexes in the neutral position and after a postural maneuver, enabling the evaluation of the functional anatomy of the musculoskeletal and arterial structures of the ipsilateral thoracic outlet.
RESULTS. A statistically significant difference was found between the distribution of the distances (maximum and costosubclavian) measured in the neutral position and after postural maneuver in groups 1 and 2. The median value of these distances was smaller after postural maneuver in groups 1 and 2. A statistically significant difference was found between the distribution of the distances (maximum and costosubclavian) measured in patients of group 1 with arterial stenosis and in patients of group 1 without arterial stenosis. A slight indentation of the anterior wall of the subclavian artery when it arches around the anterior scalene muscle was observed in 39 patients (64%) in group 1 and in 11 patients (61%) in group 2 in the neutral position, in 19 patients (31%) in group 1 and in six patients (33%) in group 2 after the postural maneuver. The predominant positional changes of the vascular structures were the posteroanterior displacement of the subclavian vessels observed in groups 1 and 2, the arch made by the subclavian artery above the first rib in 40 patients (66%) in group 1 and nine patients (50%) in group 2, and the posterior displacement of the axillary artery observed in 36 patients (59%) in group 1 and in 12 patients (67%) in group 2.
CONCLUSION. Helical CT shows significant narrowing of the costoclavicular space after postural maneuver in symptomatic patients.
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Until now, not a single objective method to assess neurovascular compression in the thoracic outlet has been defined, precluding an accurate recognition of the component of the neurovascular bundle that is compressed and the exact site of its compression. In an attempt to provide clinicians with pathophysiologic information, interest has been shown in the helical CT evaluation of this region. As seen in numerous skeletal disorders, this technique allows not only a multiplanar and three-dimensional evaluation but also the visualization of positional changes of the osseous, soft-tissue, and vascular structures of this region. A preliminary study has recently reported the anatomic characteristics of the thoracic outlet before and after dynamically induced modifications in a population of normal subjects [5]. On the basis of a similar study design using helical CT angiography, we sought to analyze the functional anatomy of this region in a population of symptomatic patients.
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Owing to the close anatomic relationships between the nerve tracts of the brachial plexus and the subclavian and axillary arteries, helical CT angiography of these vessels was performed to search for compression of the neurovascular structures. Seventy-four patients with unilateral symptoms underwent a unilateral CT examination, and five patients with bilateral symptomatology underwent a bilateral CT examination, leading to a total of 63 CT examinations in the group of female patients (group 1) and 21 CT examinations in the group of male patients (group 2). Forty-eight examinations evaluated the right upper extremity, and 36 examinations evaluated the left upper extremity. The diagnosis of thoracic outlet syndrome was made by the clinicians who referred the patients to the radiology department. This diagnosis was mainly based on the presence of clinical symptoms highly suggestive of thoracic outlet compression together with physical examination testing reproducing the patient's symptomatology. Additional investigations included helical CT angiography and color Doppler sonography aimed at providing complementary information. Because of the differences in the postural maneuvers obtained during the clinical examination and the CT study, negative findings on CT angiography did not exclude the diagnosis of thoracic outlet syndrome, which remained based on clinical data.
Helical CT Examination
Data acquisition.—A standard CT angiographic examination of
the thoracic outlet consisted of two helical CT angiograms, obtained at the
same session, using a protocol similar to that described by Remy-Jardin et al.
[5]. Applied to the analysis of
63 thoracic outlets in the female group and 21 thoracic outlets in the male
group, this protocol led to a total of 168 helical CT angiograms. Both
examinations were obtained at full inspiration on a Somatom Plus 4A scanner
(Siemens, Erlangen, Germany) while the patient was lying in the supine
position. A first acquisition was obtained with both arms alongside the body
and the head medially located (the neutral position). A second acquisition was
obtained with the patient's symptomatic arm elevated above the head
(approximately 130° of hyperabduction with external rotation) and
ipsilateral rotation of the head, which remained extended while the
contralateral arm was lying alongside the body (the postural maneuver). This
postural maneuver combined the positional characteristics of two maneuvers
currently obtained in the clinical evaluation of thoracic outlet
syndrome—namely, the Adson's and the Wright's maneuvers
[6].
For each acquisition, the surveyed volume extended from the seventh cervical vertebra to the lower extremity of the first rib (mean z-axis coverage, 78 mm; range, 57-114 mm). To include the bony structures of interest in the scanned subvolume, the latter was selected from a scout image systematically obtained before each acquisition. In the absence of guidelines in the radiology literature, the acquisition and injection protocols underwent minor modifications during the time of this study, resulting from the authors' progressive experience in CT angiography of the thoracic outlet. For each data acquisition, the scanning parameters consisted of 140 kVp, 206 mA with a 0.75-sec scanning time, and 2-mm collimation with a pitch of 1.5 (n = 44) or 3-mm collimation with a pitch of 1 (n = 124). The injection protocol included the administration of a 24% (n = 70) or 30% (n = 98) contrast agent at a rate of 3 ml/sec (n = 32) or 4 ml/sec (n = 136). In every patient, care was taken to administer the contrast material via venous access from the asymptomatic arm to obtain an exclusive opacification of the subclavian and axillary arteries without venous artifacts. These CT examinations were obtained during a period of evaluation of a dose reduction system based on on-line tube current control (i.e., Siemens care dose system) installed on our scanner as a work-in-progress option (WIP Dose Adaption, version 0.1; Siemens Mediziniche Technik), enabling a 30-40% reduction in dose [7].
Image reconstruction at the level of the symptomatic side.—Transverse CT scans of the thoracic outlet in the neutral position and after the postural maneuver were reconstructed at 1-mm intervals using a 180° linear interpolation algorithm and a standard kernel (370-mm field of view) and photographed at mediastinal window settings (window width, 350 H; window level, 50 H).
A second set of transverse CT scans (intervals of reconstruction, 1 mm; 180° linear interpolation algorithm; standard kernel; field of view, 220 mm) was systematically reconstructed from each data set to generate multiplanar and three-dimensional reformations. Two series of sagittal reformations were obtained from the medial portion of the lower cervical vertebrae to the head of the humerus, one from the data set acquired in the neutral position and one from the data set acquired after the postural maneuver. Each series was composed of 17 successive sagittal images spaced 8-10 mm apart. These images were photographed at mediastinal window settings (window width, 350 H; window level, 50 H).
Three series of fused images were generated to analyze the postural displacement of the clavicle. First, two craniocaudal maximum intensity projections were generated from the data set acquired in the neutral position and after the postural maneuver; these images were superimposed with the first rib as the fixed structure to allow further measurement of the angle of retraction of the clavicle. Second, two anteroposterior maximum-intensity-projection images were similarly fused to calculate the angle of upward displacement of the clavicle. Third, two reformations obtained perpendicular to the lateral extremity of the clavicle in both positions were fused to calculate the angle of rotation of the clavicle. For planning adequate planes of reformation, three-dimensional shaded-surface displays of the bony structures in the neutral position and after the postural maneuver were systematically reconstructed (threshold value, 150 H); these images also provided an overall view of the bony and vascular structures of each thoracic outlet.
Volume-rendered images of the thoracic outlet before and after the postural maneuver were systematically created to provide a simultaneous analysis of the bones and arteries on a superoinferior image. The parameter selection for the reconstruction of the bony structures included a trapezoid width between 550 and 1400 H, a trapezoid center of 600-1200 H, 10% opacity, and the use of the unshaded reconstruction algorithm. For reconstruction of the arterial structures, the following parameters were selected: trapezoid width, 120-440 H; trapezoid center, 135-370 H; 90% opacity; unshaded algorithm. All of these reconstructions were created on a console (Magic View 1000, version VA30A; Siemens) using commercially available standard scanner software. The reformations were generated by technicians during their daily activity, and the measurements were obtained at the console after each CT examination by the same radiologist.
Evaluated parameters: functional anatomy of the musculoskeletal structures.—The musculoskeletal structures of the three anatomic compartments of the thoracic outlet were evaluated as further described. The first group of parameters evaluated the interscalene triangle. The anatomic situation of the first rib was assessed in the neutral position and after the postural maneuver by measuring the angle between the axis of the middle portion of the first rib (i.e., the costal shaft) [8] and the horizontal. This measurement was obtained on the sagittal reformation that depicted the longest portion of the first rib shaft. The angle between the anterior scalene muscle and the first rib was measured on the sagittal reformation, enabling the identification of the tubercle for the anterior scalene muscle before and after the postural maneuver. The anteroposterior and transverse diameters of the distal portion of the anterior scalene muscle in the neutral position were measured on the transverse CT scan depicting the subclavian artery arching around the anterior scalene muscle.
The second group of parameters evaluated the costoclavicular space. On the sagittal reformations that enabled the concurrent identification of the clavicle and first rib (i.e., two to three reformations per patient), the following parameters were recorded in the neutral position and after the postural maneuver: the minimum distance between the inferior border of the clavicle and the superior margin of the first rib, measured on the reformation that depicted the lower portion of the anterior scalene muscle; the maximum distance between the inferior border of the clavicle and the superior margin of the first rib; and the distance between the inferior border of the subclavius muscle and the superior margin of the first rib. Any change larger than 2 mm in the superoinferior distances, measured in both positions, was considered to reflect a postural modification in the costoclavicular space; a difference smaller than 2 mm was considered to be within the range of technically induced errors at manual positioning of the cursor between the two bone structures on the console screen.
The postural changes of the clavicle were analyzed as follows. The angle of retraction was measured on the fused craniocaudal maximum intensity projections; the main axis of the clavicle in each position was defined by the line joining the medial and lateral ends of the clavicle. On the fused anteroposterior maximum intensity projections, the main axis of the clavicle in each position enabled the calculation of the angle of upward displacement of the clavicle. The angle of rotation of the clavicle was measured on the fused reformations obtained perpendicular to the lateral extremity of the clavicle; the main axis of the clavicle in each position was used to calculate the angle value.
The third series of parameters evaluated the subcoracoid tunnel. Because of the potential neurovascular compression at this level after the postural maneuver, the width of the subcoracoid tunnel was obtained exclusively in this position. On the sagittal reformation that depicted the anterior end of the coracoid process and the smaller pectoral muscle, the distance between the posterior border of the smaller pectoral muscle and the anterosuperior chest wall was measured at the level of the axillary neurovascular bundle between the axillary vein and artery. The location of the neurovascular bundle relative to the anterior end of the coracoid process was systematically recorded.
Care was taken to analyze the diameters of the subclavian artery on CT angiograms that did not depict arterial stenosis at the corresponding anatomic levels. The arterial stenoses were assessed on the basis of a simultaneous interpretation of the four categories of reformations generated from each data set. Resulting from a consensus interpretation between the two observers, this analysis represented the standard of reference for the identification of arterial stenosis.
Evaluated parameters: functional anatomy of the arterial structures.—According to the usual anatomic criteria [9], the subclavian artery was defined by the arterial portion extending from its origin to the outer border of the first rib. From this point to the lower border of the tendon of the teres major muscle, the subclavian artery is known as the axillary artery. Three series of anatomic data were recorded. The first series concerned the evaluation of the diameter of the subclavian artery at two anatomic levels: (1) the anteroposterior diameter of the artery when it lies behind the anterior scalene muscle was visually assessed on the vertical volume-rendered image to detect the presence of an anteroposterior indentation caused by the presence of the lower portion of the anterior scalene muscle; a reduction of less than 30% of the anteroposterior diameter was considered normal, whereas a reduction of greater than 30% was considered an arterial stenosis; (2) the anteroposterior diameter of the subclavian artery when it runs above the first rib was measured on the sagittal reformation that enabled their concurrent depiction.
The second series of parameters evaluated the curvatures of the subclavian artery at the level of its first and second parts [9]. The first part of the subclavian artery ascends to the root of the neck and then arches laterally. The angle between the ascending and descending portions of the subclavian artery, further referred to as the angle of the frontal arch, was measured on the anteroposterior volume-rendered images obtained in the neutral position and after the postural maneuver. The second part of the subclavian artery passes around the anterior scalene muscle before reaching the lateral border of the first rib. The angle of the subclavian artery curvature in its course from the medial to the lateral border of the anterior scalene muscle, further referred to as the angle of the transverse arch, was measured on the vertical volume-rendered images obtained in the neutral position and after the postural maneuver.
The third series of parameters evaluated the postural displacement of the vascular structures. On the sagittal reformations that enabled the concurrent identification of the clavicle and first rib (i.e., two to three reformations per patient), the location of the subclavian vessels relative to the narrowest and largest portions of the costoclavicular space and to the costosubclavian space were recorded in the neutral position and after the postural maneuver. A posterior displacement of the subclavian or axillary artery or a modification in the arterial course were systematically recorded by comparing the arterial pathways on the vertical volume-rendered images obtained in the neutral position and after the postural maneuver.
Study Design
Several weeks after completion of this study, the anatomic characteristics
of the thoracic outlet of the entire study group were analyzed by two
radiologists who used a consensus analysis of the locations of the bone and
vascular and muscular structures. All comparisons were performed using
Wilcoxon's rank sum test.
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At the level of the costoclavicular space (Table 2), a statistically significant difference was observed in the distribution of the distances (maximum and minimum in group 1; maximum, minimum, and costosubclavian in group 2) measured in the neutral position and after the postural maneuver (Fig. 1A,1B,1C,1D). After the postural maneuver, the following changes were observed. The minimum costoclavicular distance was unchanged in 12 patients (20%) in group 1 and in one patient (6%) in group 2, increased in 42 patients (69%) in group 1 and in 15 patients (83%) in group 2, and decreased in seven patients (11%) in group 1 and in three patients (17%) in group 2. The maximum costoclavicular distance was unchanged in four patients (7%) in group 1 and in three patients (17%) in group 2, increased in two patients (3%) in group 1 and in four patients (22%) in group 2, and decreased in 56 patients (92%) in group 1 and in 12 patients (67%) in group 2. The costosubclavian distance was unchanged in eight patients (13%) in group 1 and in four patients (22%) in group 2, increased in 11 patients (18%) in group 1 and in four patients (22%) in group 2, and decreased in 38 patients (62%) in group 1 and in 12 patients (67%) in group 2. The median values of the angles of rotation, retraction, and upward displacement of the clavicle are summarized in Table 3.
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After the postural maneuver at the level of the subcoracoid tunnel, the median distance between the posterior border of the smaller pectoral muscle and the anterosuperior chest wall was 18 mm (range, 9-44 mm) in group 1 and 16 mm (range, 8-40 mm) in group 2. The median value of the distance between the neurovascular bundle and the anterior extremity of the coracoid process was 23 mm (range, 10-42 mm) in group 1 and 27 mm (range, 13-45 mm) in group 2.
Functional Anatomy of the Musculoskeletal Structures According to the
Presence of Arterial Stenosis
Group 1 (63 CT examinations) and group 2 (21 CT examinations) were divided
into two subgroups according to the absence (group 1A [n = 28] and
group 2A [n = 12]) or presence (group 1B [n = 35] and group
2B [n = 9]) of arterial stenosis on CT scans. The site of arterial
stenosis was the interscalene triangle in 24 patients (group 1, 19; group 2,
five) and the costoclavicular space in 21 patients (group 1, 17; group 2,
four). The 45 arterial stenoses were detected on the basis of the simultaneous
interpretation of the four categories of reformations generated from each data
set. Resulting from a consensus interpretation between the two observers, this
analysis represented the standard of reference for the identification of
arterial stenosis.
At the level of the interscalene triangle, no statistically significant difference was found in the distribution of the angle values between the first rib and the horizontal measured in patients with and without arterial stenosis in groups 1 and 2. In group 2, a statistically significant difference was found in the distribution of the angle values between the anterior scalene muscle and the first rib measured in patients with arterial stenosis and in patients without arterial stenosis (p<0.05).
At the level of the costoclavicular space, the results can be summarized as follows. In group 1, a statistically significant difference was found in the distribution of the distances (minimum, maximum, and costosubclavian) measured in the neutral position in patients with (group 1B) and in patients without (group 1A) arterial stenosis and in the distribution of the distances (maximum and costosubclavian) measured after the postural maneuver in patients with (group 1B) and in patients without (group 1B) arterial stenosis (p<0.05). In group 2, no statistically significant difference was found in the distribution of the minimum, maximum, and costosubclavian distances measured in groups 2A and 2B before and after the postural maneuver. No statistically significant difference was found in the distribution of the clavicular angle values measured in groups 1A and 1B and in groups 2A and 2B in the neutral position and after the postural maneuver.
After the postural maneuver in the subcoracoid tunnel, no statistically significant difference was found in the distribution of the distances between the posterior border of the smaller pectoral muscle and the anteroposterior chest wall, or in the distribution of distances between the axillary artery and the extremity of the coracoid process, measured in groups 1A, 1B, 2A, and 2B. The median values of the distance between the posterior border of the smaller pectoral muscle and the anteroposterior chest wall were 17.5 mm (range, 11-44 mm) in group 1A, 18 mm (range, 9-44 mm) in group 1B, 16 mm (range, 9-40 mm) in group 2A, and 15 mm (range, 8-40 mm) in group 2B. The median values of the distances between the axillary artery and the extremity of the coracoid process were 22.5 mm (range, 12-40 mm) in group 1A, 23 mm (range, 10-42 mm) in group 1B, 27 mm (range, 14-45 mm) in group 2A, and 28 mm (range, 13-44 mm) in group 2B.
Functional Anatomy of the Subclavian and Axillary Arteries
The anteroposterior diameter of the subclavian artery when it lies behind
the anterior scalene muscle was analyzed on the helical CT angiograms devoid
of arterial stenosis at this level. Nineteen CT angiograms in group 1 and five
CT angiograms in group 2 showed an arterial stenosis at the level of the
interscalene triangle. In group 1, 12 stenoses were depicted in the neutral
position and seven stenoses were found after the postural maneuver. In group
2, three stenoses were depicted in the neutral position and two stenoses were
found after the postural maneuver. Consequently, the anteroposterior diameter
of the subclavian artery in the interscalene triangle was analyzed in 51 CT
angiograms in group 1 and in 12 CT angiograms in group 2 in the neutral
position and in 56 CT angiograms in group 1 and in 19 CT angiograms in group 2
after the postural maneuver. A reduction of less than 30% of the
anteroposterior diameter of the subclavian artery was observed in 39 patients
(76%) in group 1 and in 11 patients (61%) in group 2 in the neutral position
(Fig.
2A,2B,2C,2D,2E,2F)
and in 19 patients (34%) in group 1 and in six patients (32%) in group 2 after
the postural maneuver. The mean diameter of the subclavian artery at the level
of the outer border of the first rib was 8 mm in both groups of patients.
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No statistically significant difference was found in the distribution of the angle values of the transverse arch measured in the neutral position and after the postural maneuver in group 1 and in group 2. The median value of the frontal arch of the subclavian artery was 109° (range, 90-130°) in group 1 and 114° in group 2 (range, 100-140°) in the neutral position and 113° (range, 90-130°) in group 1 and 116° (range, 100-140°) in group 2 after the postural maneuver (Fig. 3A,3B,3C,3D). A statistically significant difference was found in the distribution of the angle values of the transverse arch measured in the neutral position and after the postural maneuver in group 1 but not in group 2. The median angle value of the transverse arch of the subclavian artery was 141° (range, 110-170°) in the neutral position and 152° (range, 115-180°) after the postural maneuver in group 1, and was 147° (range, 110-170°) in the neutral position and 152° (range, 140-180°) after the postural maneuver in group 2. A statistically significant difference was observed in the distribution of the angle values measured in the neutral position and after the postural maneuver in groups 1A and 1B (p<0.005).
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Table 4 summarizes the positional changes of the subclavian vessels in the costoclavicular space. The subclavian vascular bundle was located posterior to the narrowest portion of the costoclavicular space in all patients in groups 1 and 2. At the level of the largest distance between the inferior border of the clavicle and the superior margin of the first rib, the following vessels were identified in the costoclavicular space. The subclavian artery was present in 29 patients (48%) in group 1 and in 10 patients (56%) in group 2. The subclavian vein was present in five patients (8%) in group 1 and in one patient (6%) in group 2 (Fig. 1A,1B,1C,1D). The vessels identified between the inferior border of the subclavius muscle and the superior margin of the first rib were the subclavian artery (group 1, 27 patients [44%]; group 2, 10 patients [56%]) or the subclavian vein (group 1, 25 patients [41%]; group 2, nine patients [50%]) or both. After the postural maneuver, the following changes were observed. The location of the second part of the subclavian artery when it lies behind the anterior scalene muscle was unmodified in 51 patients (84%) in group 1 and in 17 patients (94%) in group 2. The subclavian artery arched over the first rib in 40 patients (66%) in group 1 and in nine patients (50%) in group 2. A posterior displacement of the axillary artery was observed in 36 patients (59%) in group 1 and in 12 patients (67%) in group 2.
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Using the four series of reconstructions generated from each data set, it was possible to provide an objective evaluation of the anatomic characteristics of the arterial structures of the thoracic outlet. In addition to confirming an average diameter of 8 mm for the arterial section in the costoclavicular space, this study showed a reduction of less than 30% of the subclavian artery diameter when it courses behind the anterior scalene muscle, observed in 76% of females and 61% of males when the arm was positioned by the patient's side. Confirming previous anatomic descriptions that considered it a physiologic feature [11,12,13], this finding can be interpreted as the CT visualization of the continuous state of contraction of the scalene muscles, even at rest, because these muscles are known not only to participate in the positioning of the head but also to be active during inspiration. In addition to the active muscular contraction, the diameter of the lower portion of the scalene anterior muscle can also explain the arterial indentation, varying from 5 x 5 mm to 20 x 20 mm when measured on transverse CT scans. Our results are in agreement with the wide range in measurements reported in anatomic studies, the width of the insertion of the anterior scalene muscle varying from 4 to 25 mm [10, 14]. These variations have been related mainly to a great variability in the shape of insertion of the anterior scalene muscle but have also been related to the presence of accessory scalene muscles [10, 11, 13]. A relationship between the length of the shaft of the first rib and the width of the scalene muscles has also been reported by Baumann et al. [15]. The subclavian artery indentation was less frequently depicted after the postural maneuver, identified in 34% of females and in 32% of males.
The last objective of our study was the evaluation of the course of the subclavian and axillary arteries before and after the postural maneuver, easily achieved on three-dimensional images. In its first part extending from its origin to the medial border of the anterior scalene muscle, the subclavian artery arches over the cervical part of the pleura and the apex of the lung, whereas the second part of the artery lies behind the anterior scalene muscle [9]. These successive curvatures were analyzed on frontal and vertical volume-rendered images, respectively. Although the patient's position was not found to influence the distribution of the angle values of the arterial arches in group 2, a statistically significant difference was observed between the distribution of the angle values of the frontal and transverse arches before and after the postural maneuver in group 1. The greatest postural variations were observed in the median values of the transverse arch; the median values of the frontal arch did not considerably differ between the two positions. These findings are in agreement with those of Brunet et al. [13], who reported the results of dissections carried out at the level of 120 thoracic outlets. We observed that the median value of the angle of the transverse arch was significantly larger in females with arterial stenosis seen on CT angiograms than in those without arterial stenosis. Three-dimensional images enabled us to show a trend toward a posterior displacement of the axillary artery after the postural maneuver, observed in 58% of females and 57% of males, and to confirm the lack of postural modification at the level of the subclavian artery, suggested by the lack of arterial displacement observed in 81% of patients in both groups after the postural maneuver. These results are in agreement with the results of anatomic studies that emphasized the cirsoid course of the axillary artery, designed to allow free movements of the shoulder in all directions without causing undue tension on the artery [10, 11, 13].
Although it provides objective information on the functional anatomy of the thoracic outlet in symptomatic patients, our study has a few limitations. Patients were examined in the supine position on helical CT angiography, whereas they are clinically examined in the erect position. Two additional differences exist: namely, the lack of strict standardization of the positional maneuver, and the analysis of dynamically induced changes after a single postural maneuver (whereas clinically several maneuvers are usually performed).
Despite these limitations, this study provides the first in vivo evaluation of the functional anatomy of the thoracic outlet in a population of symptomatic patients. Our study suggests that CT angiography is a suitable method to analyze both vascular and musculoskeletal structures of this anatomic region. Nevertheless, our study is a preliminary investigation, and larger series are needed to confirm the findings observed in our population.
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