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Radiographic characterization of prevertebral soft tissue shadow in the cervicothoracic region of normal adults
j o u r n a l o f s u r g i c a l r e s e a r c h 1 8 0 ( 2 0 1 3 ) 7 3 e7 9
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Radiographic characterization of prevertebral soft tissue shadow in the cervicothoracic region of normal adults Timothy I. Mullin, MD, Mei Wang, PhD,* and Raj D. Rao, MD Department of Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, Wisconsin
article info
abstract
Article history:
Background: Many studies have found measurement of prevertebral soft tissue shadow
Received 24 September 2012
(PVSTS) on a lateral cervical radiograph to be a useful indicator of cervical spine injury. The
Received in revised form
purpose of this study is to define, measure, and establish a normative set of values for
24 September 2012
radiographic width of the PVSTS in the cervicothoracic region of the spine (C7eT4), using
Accepted 11 October 2012
swimmer’s view in subjects with no trauma to the region.
Available online 27 October 2012
Materials and methods: Radiographic PVSTS widths were measured at each vertebral level from C7 to T4 on 131 patients who had “normal” radiographic examination (mean age 31.5
Keywords:
y, range 18e58 y). Intra-observer repeatability was assessed on a random subset of 24
Cervicothoracic spine
subjects. The range, mean, and standard error of these measurements were calculated and
Prevertebral soft tissue shadow
documented. Stepwise forward regression analysis was conducted on PVSTS data and
Radiograph
those normalized with respect to the C7 vertebral body width (rPVSTS) to study the
Swimmer’s view
influences of age, sex, disk level, and tracheal curve shape.
Anatomy
Results: Regression analysis showed that, in order of influence, the vertebral level, sex, and age were three significant factors that affected PVSTS, whereas tracheal curve shape was not significant. Similar results were obtained using normalized rPVSTS data, with the exception that the influence of sex was not significant in this instance. Conclusions: This study provides a reliable normative database of PVSTS in the North American population, and shows that measurement of prevertebral soft tissue shadow on a swimmer’s view radiograph can be used as a valuable screening tool in the evaluation of cervicothoracic spine injury. ª 2013 Elsevier Inc. All rights reserved.
1.
Introduction
Clearance of the cervical spine following traumatic injury is an area of significant controversy. When patients present with neck pain in the absence of obvious fracture, assessment of the radiographic prevertebral soft tissue shadow (PVSTS) measured on lateral radiographs of the cervical spine has been used as an indicator of occult cervical spine trauma between C1 and C7. Radiographic PVSTS has also been used to identify other nonbony conditions that may result in increased hematoma or edema in the prevertebral soft tissues of the
cervical spine, such as epiglottitis [1], retropharyngeal abscess [2], retropharyngeal tendinitis [3], retroesophageal abscess [4], and carcinoma of the cervical esophagus [4]. Increase in the PVSTS of the cervical region represents hemorrhage, edema, inflammation, or cellular hyperplasia within the soft tissues anterior to the vertebral column and posterior to the larynx and trachea. The cervicothoracic region of the spinal column (from the superior aspect of the C7 vertebral body to the disk space between T4 and T5) is a region of transitional morphology and function between the mobile and lordotic cervical spine and
* Corresponding author. Department of Orthopaedic Surgery, Medical College of Wisconsin, 9200 W. Wisconsin Ave, Milwaukee, WI 53226. Tel.: þ1 414 288 0699; fax: þ1 414 288 4471. E-mail address: [email protected] (M. Wang). 0022-4804/$ e see front matter ª 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jss.2012.10.015
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the stiff and kyphotic thoracic spine. The abrupt transition results in a region biomechanically susceptible to injury and degeneration [5,6]. Miller et al. [7], in a review of 399 cervical spine injuries, reported 18% at the C7 level. The C7eT1 segment accounts for 9% of all spine injuries in some series [8]. Despite the cervicothoracic spine being a region with unique pathology, biomechanical characteristics, and treatment requirements, routine radiographs do not allow good visualization of the cervicothoracic spine, making it more difficult to diagnose disorders of the region [9]. Normative data on radiographic PVSTS anterior to the cervicothoracic vertebral column on a swimmer’s view radiograph are not available. Radiographic determination of anterior displacement of the trachea from the cervicothoracic spinal column is subjective and potentially overlooked when subtle. Radiographic screening of C7 to T4 vertebral and superior mediastinal pathology on swimmer’s view radiographs can be facilitated by establishing objective standards for measurement of the PVSTS in this region, with an increased radiographic PVSTS serving as an indicator of occult pathology that requires further evaluation or intervention. The purpose of our study is to define, measure, and establish a normative set of values for radiographic width of the PVSTS in the cervicothoracic region of the spine (C7eT4), using swimmer’s view radiographs in subjects with no trauma to the region.
2.
Materials and methods
2.1.
Subject selection
Approval for the study was obtained from the authors’ institutional review board. Four hundred seventy-five consecutive swimmer’s view radiographs, performed during a 5-mo period, were reviewed for the study. All radiographs were obtained in subjects who presented through the Emergency Department of the authors’ institution. Subjects presented with complaints of neck pain, neck stiffness, headache, and shoulder pain most commonly resulting from motor vehicle and motorcycle collisions, falls, or assaults. Radiographs performed on subjects with fracture (n ¼ 24), dislocation (n ¼ 1), subluxation (n ¼ 6), spondylosis (n ¼ 136), congenital anomalies (n ¼ 3), metastatic disease (n ¼ 1), vertebral radiolucency of undetermined significance (n ¼ 2), mediastinal free air (n ¼ 1), and increased width of the PVSTS as seen on standard lateral cervical spine radiographs (n ¼ 9) were excluded from the study. Three radiographs were eliminated because of improper patient positioning, leading to rotational or sagittal malalignment. An additional 29 studies could not be included because of technical inadequacy from under-penetration or poor aiming of the tube or positioning of the cassette, yielding unusable radiographs. In eight cases, the vertebral levels could not be determined with confidence and thus were excluded. All radiographs selected for measurement were determined to be normal by a musculoskeletal radiologist. Patient charts were subsequently reviewed for history of cervical, thoracic, cardiopulmonary, or gastroesophageal pathology or prior surgical intervention that might compromise the integrity of our data, and three radiographs were excluded on this basis. Subjects who previously underwent
endotracheal intubation (n ¼ 35), nasogastric tube placement (n ¼ 4), or tracheostomy (n ¼ 1) or patients with radiographic evidence of prior surgery (n ¼ 78) were similarly excluded. Consistent with previously published studies of PVSTS measurements in the cervical spine [10], “normal” radiographs were deemed to be those without evidence of trauma or pathology, regardless of patient symptoms.
2.2.
Radiographic technique
All radiographs were obtained using a digital radiographic system. Subjects were positioned supine on the examining table with their right arm extended and abducted 180 . The beam was projected in a cross-table lateral fashion with a tube-film distance of 40 in. The radiographic cassette was positioned directly against the subject’s left shoulder.
2.3.
Measurements
The width of the prevertebral soft tissue shadow at each level from C7 to T4 was measured from the midpoint of the anterior cortex of each vertebral body within this region to the posterior aspect of the tracheaeidentified as the most posterior edge of the radiolucent vertical stripe anterior to the vertebral bodies in a plane perpendicular to the vertebral body (Fig. 1, line B). In each subject, the vertebral body width of C7 was
Fig. 1 e Measurement of parameters on swimmer’s view radiograph. (A) Vertebral body width at C7. (B) Prevertebral soft tissue width measured at T1. (Color version of figure is available online.)
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measured from the midpoint of the posterior cortex to the midpoint of the anterior cortex (Fig. 1, line A). All measurements were carried out to the nearest 0.1 mm, using the automated measurement function on a digital workstation. The relative difference in surrounding soft tissue density between the cervical spine and the chest cage surrounding the thoracic spine occasionally results in an image that is over- or under-penetrated. The use of a digital workstation that allowed adjustment of contrast and brightness settings, when required on a level-by-level basis, allowed improved delineation of soft tissue planes to increase accuracy of each measurement in our study.
2.4.
Data analysis
Radiographic PVSTS widths were recorded for each vertebral level from C7 to T4 by a single orthopedic surgeon (T.M.), and the range, mean, and standard error of these measurements were calculated and documented. Intra-observer repeatability was assessed on a random subset of 24 subjects, with the repeat measurements performed near the end of the study and following the same protocol. Repeatability was assessed using intra-class correlation coefficient (ICC) and coefficient of variance (CV). To study the influences of age, sex, disk level, and tracheal curve shape (anterior concavity or double curvature, anterior convexity at C7 transitioning to anterior concavity) on PVSTS width, stepwise forward regression analysis was carried out on all data. Post hoc Tukey HSD (Honestly Significant Difference) comparisons on the least squares means were subsequently performed on the statistically significant factors. To minimize the potential variation in radiographic measurements attributable to magnification and patient anthropometric factors, PVSTS data were normalized with respect to the C7 vertebral body width, termed rPVSTS, and the same regression analysis was repeated.
3.
Results
Radiographs from 131 subjects (mean age 31.5 y, range 18e58 y) were included in our study. Total numbers of radiographic measurements possible decreased progressively from C7 to T4 (Table 1), as superimposition of overlying chest cage bone and soft tissue or improper positioning of radiographic cassette led to inadequate visualization of caudal levels (Table 2).
3.1.
Intra-observer reliability
High degrees of reliability were found at all levels in the repeatability assessment where the mean CV was 4.4% and ICC was 0.95 (Table 3).
Factor
Number of vertebral level
Bone/soft tissues obscuring radiographs Vertebrae/trachea off radiograph Other
3.2.
45 14 2
Regression analysis
Results from regression analysis showed that, in order of influence, the vertebral level, sex, and age were three significant factors that affected PVSTS, whereas tracheal curve shape did not significantly affect PVSTS. Similar results were obtained using normalized rPVSTS data, with the exception that the influence of sex was not significant in this instance.
3.2.1.
Influence of sex
Mean PVSTS for female subjects was smaller than for male subjects at the C7 and T1 levels (19.8% smaller, P < 0.0001 and 19.1% smaller, P < 0.0002, respectively); however, female subjects also had smaller C7 vertebral body width. Radiographic PVSTS normalized to C7 body width (rPVSTS) followed a similar gradually decreasing value from C7 to T2 but remained relatively constant from T2 through T4 (Table 4).
3.2.2.
Influence of vertebral level
The mean width of the radiographic PVSTS anterior to the vertebral bodies of C7 to T4 was 16.1 mm, 12.2 mm, 10.1 mm, 10.0 mm, and 11.1 mm, respectively (Table 4). A progressive decrease in the average width of the PVSTS was noted at each successive caudal level, with the exception of T4. Post hoc Tukey HSD tests showed that both PVSTS and rPVSTS at C7 had the highest values (least squares mean of 16.8 mm or 75.1%) and was significantly higher than the other four vertebral levels. The PVSTS and rPVSTS width at the T1 came in second at 12.8 mm and 57.8% and was significantly higher than at T2 and T3. Finally, PVSTS and rPVSTS from T2 through T4 had no significant difference, and the combined least squares mean PVSTS and rPVSTS value of the three levels was 11.1 mm and 50.0%, respectively.
3.2.3.
Influence of age
To study the effect of aging on PVSTS values, the patient population was initially grouped into seven age groups: one group for subjects 20 y and younger, five groups for subjects from 21e45 y at 5-y intervals, and one group for subjects 46 y
Table 3 e Results of repeatability assessment using coefficient of variation and intra-class correlation coefficient.
Table 1 e Summary of total measurements by level.
All Male Female
Table 2 e Summary of factors resulting in unmeasureable PVSTS levels.
C7
T1
T2
T3
T4
125 58 67
120 57 64
117 54 63
104 47 57
85 34 51
CV ICC Subject count
C7
T1
T2
T3
T4
Mean
2.9% 0.976 24
4.4% 0.954 24
2.2% 0.934 22
4.5% 0.980 15
8.2% 0.908 10
4.4% 0.950
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Table 4 e Mean (standard error) values of the PVSTS (mm) and rPVSTS (%) for the male and female groups and all subjects.
PVSTS Male Female All rPVSTS Male Female All
C7
T1
T2
T3
T4
18.1 (0.50) 14.5 (0.36) 16.1 (0.34)
13.6 (0.52) 11.0 (0.44) 12.2 (0.36)
10.8 (0.65) 9.6 (0.56) 10.1 (0.43)
10.2 (0.72) 10.0 (0.66) 10.0 (0.48)
10.8 (0.88) 11.3 (0.66) 11.1 (0.53)
77.4 (2.3) 72.2 (1.8) 74.6 (1.4)
60.0 (2.4) 54.8 (2.3) 57.2 (1.7)
47.5 (2.9) 47.2 (2.8) 47.3 (2.0)
45.1 (3.3) 50.3 (3.3) 48.0 (2.4)
47.6 (4.1) 55.8 (3.6) 52.8 (2.8)
and older. Comparison of the group mean PVSTS revealed a marked increase in the two groups that included patients 41 y and older. Further Tukey HSD tests were conducted to compare the mean rPVSTS from those 40 y and younger (n ¼ 102) with those 41 y and older (n ¼ 29), at the level of C7, T1, and combined levels of T2eT3eT4 (Tables 5 and 6). The PVSTS and rPVSTS data from T2, T3, and T4 were combined as there was no significant difference between these values. The results of these tests revealed a consistently larger mean PVSTS and rPVSTS for the older patient group compared with the younger patient group, with the difference reaching level of significance at the T1 level, and combined levels of T2eT3eT4.
4.
Discussion
The lateral cervical spine radiograph has traditionally been the standard screening modality of cervical spine imaging as part of the initial evaluation of the trauma patient [11]. In cases where obvious fracture or dislocation is not present, assessment of prevertebral soft tissue shadow is carried out as an indicator of occult injury to the cervical spine. The soft tissue thickness between the bony cervical vertebral column and the air space of the pharynx and trachea is constituted by the anterior longitudinal ligament, the longus capitis and longus coli musculature, and the prevertebral and alar fascia. The retropharyngeal space between these fascial layers contains loose areolar tissue, which allows the pharynx to move up and down relative to the vertebral column [12]. Further anterior lies the buccopharyngeal fascia, esophagus,
Table 5 e Mean (standard error) values of PVSTS (mm) for the male and female groups and all subjects within two age groups.
40 y & younger All Male Female 41 y & older All Male Female
C7
T1
T2eT3eT4
16.0 0.4 17.8 0.6 14.4 0.4
11.8 0.4 13.1 0.6 10.7 0.5
9.7 0.3 9.9 0.4 9.6 0.4
16.8 0.7 18.9 0.7 14.8 0.9
13.6 0.9 15.2 1.2 12.2 1.2
12.8 0.6 13.3 1.1 12.4 0.7
and trachealis muscle. Injury to the cervical spinal column is generally accompanied by an increase in the soft tissue width, from hematoma tracking into the retropharyngeal space from injury to the spinal column and also from concurrent injury and edema within the soft tissues themselves. Increased PVSTS width has also been found in nontraumatic pathologic conditions of the cervical spinal column [1e4]. Many published reports have found measurement of PVSTS on a lateral cervical radiograph to be a useful indicator of cervical spine injury [12e15]. Dai [16] retrospectively reviewed 107 consecutive patients with suspected cervical spine injury, identifying 47 patients with swelling of the prevertebral soft tissues. Thirty-eight of the 47 patients (80.9%) with swelling had a bony injury, a statistically significant relationship. Some authors report poor reliability of radiographic PVSTS [17,18]. DeBehnke and Havel, in a retrospective series of 74 cervical trauma patients and 93 control patients [18], reported that a 22 mm measurement at C6 had a sensitivity of 5% and specificity of 95%. Similarly, Herr et al., in a study of 211 patients with cervical spine fracture [17], reported the mean PVSTS at C3 to be 6.2 mm G 3.3 mm (1e22 mm) and found that PVSTS width at C3 had poor sensitivity for detecting injury. Radiographic measurement of PVSTS in the cervical spine may be more sensitive at detecting injury and pathology that involves the anterior column of the spine, and should be used in conjunction with the history and clinical examination in any given patient. Adequate visualization of the cervicothoracic region is difficult on standard lateral imaging of the cervical spine, because of the overlying osseous and soft tissue structures of the shoulder and upper chest [19]. In a retrospective review of trauma patients who underwent plain film imaging in lateral and anterior/posterior views, Gale et al. [20] reported that the cervicothoracic junction could be visualized in only 27.8% of patients (178/640). The swimmer’s view radiograph is an alternative to the standard lateral cervical radiograph that
Table 6 e Mean (standard error) values of rPVSTS (%) between two age groups.
40 y & younger 41 y & older P value
C7
T1
T2-T3-T4
73.6 (1.7)% 77.6 (3.0)% 0.23
55.3 (1.9)% 63.4 (3.4)% 0.039
45.6 (1.5)% 60.1 (2.7)% <0.001
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provides improved visualization of the cervicothoracic region. Gisbert et al. [21], in a retrospective review of 22 injuries at C7eT1, reported a missed diagnosis on standard lateral cervical films in 19 patients. An accurate diagnosis was made on seven of the eight patients who underwent a swimmer’s view radiograph. To our knowledge, normative data on the prevertebral soft tissue shadow anterior to the cervicothoracic spine has not been previously reported in the North American population. The range of normal values we found in the cervicothoracic region is comparable to previously reported ranges of thickness of anterior soft tissue shadow on radiographs of the cervical spine in normal subjects. Penning reported a range of 8e20 mm (mean 14.9 mm) anterior to C5, 11e20 mm (mean 15.1 mm) anterior to C6, and 9e20 mm (mean 13.9 mm) anterior to C7 [12]. Wholey et al. [22] and Haug et al. [23] reported a range of normal values anterior to C6 of 9e22 mm (mean 14.0 mm) and 5.0e18.0 mm (mean 12.1 mm), respectively; Chen and Bohrer [10] reported a range of 11e26 mm (mean 15.5 mm) anterior to C5; and Oon [24] reported a range of 8e17 mm (mean 12.4 mm) in the retrotracheal width, below the inferior horn of the thyroid cartilage. Prior studies have not provided an explanation for this range in the PVSTS width, but we believe the variances can be explained on the basis of individual anthropometrics, muscle hypertrophy, and thickness of soft tissue layers in any individual patient. Regression analysis reveals that vertebral level, sex, and age had significant influences on PVSTS width. Variation in soft tissue thickness between C7 and T4 would be anticipated based on anatomic differences in the soft tissues present anterior to the spinal column at the different levels. To our knowledge, this association between age and increasing PVSTS width has not previously been reported. We assume that the increased width of the soft tissues anterior to the spinal column in older subjects may be related to loss in disk and vertebral body height and increase in local kyphosis with age, which result in infolding of the soft tissues anterior to the spinal column. We found significant difference in PVSTS between male and female subjects at the levels of C7 and T1 (P < 0.0001 and P < 0.0002). To assess the role of anthropometric differences between male and female subjects, we assessed normalized measurements with respect to the C7 vertebral body width. The normalized PVSTS (or rPVSTS) showed that whereas male subjects still had higher PVSTS than female subjects, the difference was not significant (least squares means are 60.5% and 61.5% female and male, respectively, P ¼ 0.64). The difference in PVSTS values between male and female subjects is largely explained by the larger body habitus in males and the effect of magnification from the greater distance between the spinal column and radiographic cassette, and not by an intrinsic difference in prevertebral soft tissue thickness between the sexes. From our series of 85 subjects with measureable T4 levels, only seven (8.2%) have an rPVSTS ratio over 1.0 and only four (4.7%) have a ratio over 1.1. The maximum rPVSTS in the lower portion (T2eT4) of the cervicothoracic spine is 1.2 in our series. At C7, the mean rPVSTS ratio is 0.746, with 11 of 125 subjects (8.8%) having an rPVSTS ratio over 1.0 and four (3.2%) having a ratio over 1.1, the maximum being 1.3. In addition to
77
measurements of absolute values for radiographic PVSTS, we propose that an rPVSTS ratio of 1.0 be set as a screening reference defining the upper limit of normal in the cervicothoracic spine on swimmer’s view radiographs. This value presents an appropriate level of sensitivity and is consistent with previously set standards for the cervical spine on lateral imaging [10]. An example of this screening application is presented in Figure 2. A limitation of our data is the increasing use of computerized tomographic (CT) scanning of the cervicothoracic region as a screening modality for underlying vertebral and soft tissue pathology. In a meta-analysis comparing CT scans with plain radiographs of the cervical spine for detecting cervical spine injuries, Holmes and Akkinepalli [25] reported the sensitivity of CT imaging to be 98% compared with 52% for plain radiographs. CT imaging has also been shown by some authors to be cost-effective as a screening modality for patients at moderate or high risk for cervical spine injury [26] and for trauma patients in whom C7eT1 was inadequately visualized with conventional radiography [27]. The increase in diagnostic accuracy for the limited number of patients with injury to the cervicothoracic region needs to be weighed against the substantial increase in individual and population radiation exposure that the use of CT scanning as a screening modality entails. Rybicki et al. [28], in a comparison of radiation exposure to the thyroid in patients undergoing cervical spine imaging with CT or plain radiography, reported a greater than 14-fold difference in thyroid radiation dose between the groups. Using historical data to estimate the risk of excess thyroid cancer mortality from CT as compared with plain radiography, Shu et al. [29] reported, for a 25-y-old male subject, a reduction from 96.7 estimated excess deaths per 100,000 for standard-dose CT imaging to 6.7 estimated excess deaths per 100,000 for plain-film cervical spine examination. In addition, while CT scans are frequent at major academic hospitals, community hospitals continue to use plain radiographs as an initial screening modality for spinal pathology. Our study also highlights the radiographic contour of the trachea in the cervicothoracic region. The trachea in the upper thoracic region follows the kyphotic curvature of the spine, and thus is concave anteriorly. This anterior concavity from C7 to T4 was observed on 108 of 131 radiographs. On the remaining 23 radiographs, a double curve was present with a flattening or convexity anterior to C7 transitioning to a concave contour from T1 to T4. Reversal of the anterior concavity of the trachea and anterior displacement of the trachea in the cervicothoracic region has previously been described by Jain et al. in patients with tuberculosis of the cervicothoracic spine [30]. These findings corrected to near normal in patients who underwent successful treatment. We conclude that measurement of prevertebral soft tissue shadow on a swimmer’s view radiograph provides a valuable screening tool in the evaluation of cervicothoracic spine injury and pathology. Our measurements provide a reliable normative database in the North American population. Variations in these measurements should be anticipated in normal patients without injury, between male and female sex, and with age. Abnormalities in this measurement should
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Fig. 2 e (A) Swimmer’s view radiograph in a 58-y-old male subject (below abnormalities precluded this patient from being included in this study) with a 1-mo history of upper back pain who presented with acute, progressive weakness in the right lower extremity of 2 d duration. (B) Measurement technique. rPVSTS ratio was calculated to be 1.18 at C7, 0.86 at T1, 1.11 at T3, and 1.61 at T4. (C) Sagittal and (D) axial magnetic resonance imaging scans were subsequently obtained, revealing a grade 3 chondrosarcoma of the mediastinum, displacing the trachea anteriorly and laterally. (Color version of figure is available online.)
serve as an indicator for further evaluation with either computed tomography or magnetic resonance imaging.
references
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[7] Miller MD, Gehweiler JA, Martinez S, et al. Significant new observations on cervical spine trauma. Am J Roentgenol 1978;130:659. [8] Nichols CG, Young DH, Schiller WR. Evaluation of cervicothoracic junction injury. Ann Emerg Med 1987; 16:640. [9] Rao RD, Fischgrund JS. Disorders of the cervicothoracic junction. In: . In: Frymoyer JW, Wiesel SW, editors. The adult and pediatric spine. 3rd ed., vol 2. Lippincott Williams & Wilkins, Philadelphia; 2004. p. 731. [10] Chen MY, Bohrer SP. Radiographic measurement of prevertebral soft tissue thickness on lateral radiographs of the neck. Skeletal Radiol 1999;28:444. [11] Bachulis BL, Long WB, Hynes GD, et al. Clinical indications for cervical spine radiographs in the traumatized patient. Am J Surg 1987;153:473. [12] Penning L. Prevertebral hematoma in cervical spine injury: incidence and etiologic significance. Am J Roentgenol 1981; 136:553. [13] Shmueli G, Herold ZH. Prevertebral shadow in cervical trauma. J Med Sci 1980;16:698.
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Available online at www.sciencedirect.com
journal homepage: www.JournalofSurgicalResearch.com
Radiographic characterization of prevertebral soft tissue shadow in the cervicothoracic region of normal adults Timothy I. Mullin, MD, Mei Wang, PhD,* and Raj D. Rao, MD Department of Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, Wisconsin
article info
abstract
Article history:
Background: Many studies have found measurement of prevertebral soft tissue shadow
Received 24 September 2012
(PVSTS) on a lateral cervical radiograph to be a useful indicator of cervical spine injury. The
Received in revised form
purpose of this study is to define, measure, and establish a normative set of values for
24 September 2012
radiographic width of the PVSTS in the cervicothoracic region of the spine (C7eT4), using
Accepted 11 October 2012
swimmer’s view in subjects with no trauma to the region.
Available online 27 October 2012
Materials and methods: Radiographic PVSTS widths were measured at each vertebral level from C7 to T4 on 131 patients who had “normal” radiographic examination (mean age 31.5
Keywords:
y, range 18e58 y). Intra-observer repeatability was assessed on a random subset of 24
Cervicothoracic spine
subjects. The range, mean, and standard error of these measurements were calculated and
Prevertebral soft tissue shadow
documented. Stepwise forward regression analysis was conducted on PVSTS data and
Radiograph
those normalized with respect to the C7 vertebral body width (rPVSTS) to study the
Swimmer’s view
influences of age, sex, disk level, and tracheal curve shape.
Anatomy
Results: Regression analysis showed that, in order of influence, the vertebral level, sex, and age were three significant factors that affected PVSTS, whereas tracheal curve shape was not significant. Similar results were obtained using normalized rPVSTS data, with the exception that the influence of sex was not significant in this instance. Conclusions: This study provides a reliable normative database of PVSTS in the North American population, and shows that measurement of prevertebral soft tissue shadow on a swimmer’s view radiograph can be used as a valuable screening tool in the evaluation of cervicothoracic spine injury. ª 2013 Elsevier Inc. All rights reserved.
1.
Introduction
Clearance of the cervical spine following traumatic injury is an area of significant controversy. When patients present with neck pain in the absence of obvious fracture, assessment of the radiographic prevertebral soft tissue shadow (PVSTS) measured on lateral radiographs of the cervical spine has been used as an indicator of occult cervical spine trauma between C1 and C7. Radiographic PVSTS has also been used to identify other nonbony conditions that may result in increased hematoma or edema in the prevertebral soft tissues of the
cervical spine, such as epiglottitis [1], retropharyngeal abscess [2], retropharyngeal tendinitis [3], retroesophageal abscess [4], and carcinoma of the cervical esophagus [4]. Increase in the PVSTS of the cervical region represents hemorrhage, edema, inflammation, or cellular hyperplasia within the soft tissues anterior to the vertebral column and posterior to the larynx and trachea. The cervicothoracic region of the spinal column (from the superior aspect of the C7 vertebral body to the disk space between T4 and T5) is a region of transitional morphology and function between the mobile and lordotic cervical spine and
* Corresponding author. Department of Orthopaedic Surgery, Medical College of Wisconsin, 9200 W. Wisconsin Ave, Milwaukee, WI 53226. Tel.: þ1 414 288 0699; fax: þ1 414 288 4471. E-mail address: [email protected] (M. Wang). 0022-4804/$ e see front matter ª 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jss.2012.10.015
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the stiff and kyphotic thoracic spine. The abrupt transition results in a region biomechanically susceptible to injury and degeneration [5,6]. Miller et al. [7], in a review of 399 cervical spine injuries, reported 18% at the C7 level. The C7eT1 segment accounts for 9% of all spine injuries in some series [8]. Despite the cervicothoracic spine being a region with unique pathology, biomechanical characteristics, and treatment requirements, routine radiographs do not allow good visualization of the cervicothoracic spine, making it more difficult to diagnose disorders of the region [9]. Normative data on radiographic PVSTS anterior to the cervicothoracic vertebral column on a swimmer’s view radiograph are not available. Radiographic determination of anterior displacement of the trachea from the cervicothoracic spinal column is subjective and potentially overlooked when subtle. Radiographic screening of C7 to T4 vertebral and superior mediastinal pathology on swimmer’s view radiographs can be facilitated by establishing objective standards for measurement of the PVSTS in this region, with an increased radiographic PVSTS serving as an indicator of occult pathology that requires further evaluation or intervention. The purpose of our study is to define, measure, and establish a normative set of values for radiographic width of the PVSTS in the cervicothoracic region of the spine (C7eT4), using swimmer’s view radiographs in subjects with no trauma to the region.
2.
Materials and methods
2.1.
Subject selection
Approval for the study was obtained from the authors’ institutional review board. Four hundred seventy-five consecutive swimmer’s view radiographs, performed during a 5-mo period, were reviewed for the study. All radiographs were obtained in subjects who presented through the Emergency Department of the authors’ institution. Subjects presented with complaints of neck pain, neck stiffness, headache, and shoulder pain most commonly resulting from motor vehicle and motorcycle collisions, falls, or assaults. Radiographs performed on subjects with fracture (n ¼ 24), dislocation (n ¼ 1), subluxation (n ¼ 6), spondylosis (n ¼ 136), congenital anomalies (n ¼ 3), metastatic disease (n ¼ 1), vertebral radiolucency of undetermined significance (n ¼ 2), mediastinal free air (n ¼ 1), and increased width of the PVSTS as seen on standard lateral cervical spine radiographs (n ¼ 9) were excluded from the study. Three radiographs were eliminated because of improper patient positioning, leading to rotational or sagittal malalignment. An additional 29 studies could not be included because of technical inadequacy from under-penetration or poor aiming of the tube or positioning of the cassette, yielding unusable radiographs. In eight cases, the vertebral levels could not be determined with confidence and thus were excluded. All radiographs selected for measurement were determined to be normal by a musculoskeletal radiologist. Patient charts were subsequently reviewed for history of cervical, thoracic, cardiopulmonary, or gastroesophageal pathology or prior surgical intervention that might compromise the integrity of our data, and three radiographs were excluded on this basis. Subjects who previously underwent
endotracheal intubation (n ¼ 35), nasogastric tube placement (n ¼ 4), or tracheostomy (n ¼ 1) or patients with radiographic evidence of prior surgery (n ¼ 78) were similarly excluded. Consistent with previously published studies of PVSTS measurements in the cervical spine [10], “normal” radiographs were deemed to be those without evidence of trauma or pathology, regardless of patient symptoms.
2.2.
Radiographic technique
All radiographs were obtained using a digital radiographic system. Subjects were positioned supine on the examining table with their right arm extended and abducted 180 . The beam was projected in a cross-table lateral fashion with a tube-film distance of 40 in. The radiographic cassette was positioned directly against the subject’s left shoulder.
2.3.
Measurements
The width of the prevertebral soft tissue shadow at each level from C7 to T4 was measured from the midpoint of the anterior cortex of each vertebral body within this region to the posterior aspect of the tracheaeidentified as the most posterior edge of the radiolucent vertical stripe anterior to the vertebral bodies in a plane perpendicular to the vertebral body (Fig. 1, line B). In each subject, the vertebral body width of C7 was
Fig. 1 e Measurement of parameters on swimmer’s view radiograph. (A) Vertebral body width at C7. (B) Prevertebral soft tissue width measured at T1. (Color version of figure is available online.)
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measured from the midpoint of the posterior cortex to the midpoint of the anterior cortex (Fig. 1, line A). All measurements were carried out to the nearest 0.1 mm, using the automated measurement function on a digital workstation. The relative difference in surrounding soft tissue density between the cervical spine and the chest cage surrounding the thoracic spine occasionally results in an image that is over- or under-penetrated. The use of a digital workstation that allowed adjustment of contrast and brightness settings, when required on a level-by-level basis, allowed improved delineation of soft tissue planes to increase accuracy of each measurement in our study.
2.4.
Data analysis
Radiographic PVSTS widths were recorded for each vertebral level from C7 to T4 by a single orthopedic surgeon (T.M.), and the range, mean, and standard error of these measurements were calculated and documented. Intra-observer repeatability was assessed on a random subset of 24 subjects, with the repeat measurements performed near the end of the study and following the same protocol. Repeatability was assessed using intra-class correlation coefficient (ICC) and coefficient of variance (CV). To study the influences of age, sex, disk level, and tracheal curve shape (anterior concavity or double curvature, anterior convexity at C7 transitioning to anterior concavity) on PVSTS width, stepwise forward regression analysis was carried out on all data. Post hoc Tukey HSD (Honestly Significant Difference) comparisons on the least squares means were subsequently performed on the statistically significant factors. To minimize the potential variation in radiographic measurements attributable to magnification and patient anthropometric factors, PVSTS data were normalized with respect to the C7 vertebral body width, termed rPVSTS, and the same regression analysis was repeated.
3.
Results
Radiographs from 131 subjects (mean age 31.5 y, range 18e58 y) were included in our study. Total numbers of radiographic measurements possible decreased progressively from C7 to T4 (Table 1), as superimposition of overlying chest cage bone and soft tissue or improper positioning of radiographic cassette led to inadequate visualization of caudal levels (Table 2).
3.1.
Intra-observer reliability
High degrees of reliability were found at all levels in the repeatability assessment where the mean CV was 4.4% and ICC was 0.95 (Table 3).
Factor
Number of vertebral level
Bone/soft tissues obscuring radiographs Vertebrae/trachea off radiograph Other
3.2.
45 14 2
Regression analysis
Results from regression analysis showed that, in order of influence, the vertebral level, sex, and age were three significant factors that affected PVSTS, whereas tracheal curve shape did not significantly affect PVSTS. Similar results were obtained using normalized rPVSTS data, with the exception that the influence of sex was not significant in this instance.
3.2.1.
Influence of sex
Mean PVSTS for female subjects was smaller than for male subjects at the C7 and T1 levels (19.8% smaller, P < 0.0001 and 19.1% smaller, P < 0.0002, respectively); however, female subjects also had smaller C7 vertebral body width. Radiographic PVSTS normalized to C7 body width (rPVSTS) followed a similar gradually decreasing value from C7 to T2 but remained relatively constant from T2 through T4 (Table 4).
3.2.2.
Influence of vertebral level
The mean width of the radiographic PVSTS anterior to the vertebral bodies of C7 to T4 was 16.1 mm, 12.2 mm, 10.1 mm, 10.0 mm, and 11.1 mm, respectively (Table 4). A progressive decrease in the average width of the PVSTS was noted at each successive caudal level, with the exception of T4. Post hoc Tukey HSD tests showed that both PVSTS and rPVSTS at C7 had the highest values (least squares mean of 16.8 mm or 75.1%) and was significantly higher than the other four vertebral levels. The PVSTS and rPVSTS width at the T1 came in second at 12.8 mm and 57.8% and was significantly higher than at T2 and T3. Finally, PVSTS and rPVSTS from T2 through T4 had no significant difference, and the combined least squares mean PVSTS and rPVSTS value of the three levels was 11.1 mm and 50.0%, respectively.
3.2.3.
Influence of age
To study the effect of aging on PVSTS values, the patient population was initially grouped into seven age groups: one group for subjects 20 y and younger, five groups for subjects from 21e45 y at 5-y intervals, and one group for subjects 46 y
Table 3 e Results of repeatability assessment using coefficient of variation and intra-class correlation coefficient.
Table 1 e Summary of total measurements by level.
All Male Female
Table 2 e Summary of factors resulting in unmeasureable PVSTS levels.
C7
T1
T2
T3
T4
125 58 67
120 57 64
117 54 63
104 47 57
85 34 51
CV ICC Subject count
C7
T1
T2
T3
T4
Mean
2.9% 0.976 24
4.4% 0.954 24
2.2% 0.934 22
4.5% 0.980 15
8.2% 0.908 10
4.4% 0.950
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Table 4 e Mean (standard error) values of the PVSTS (mm) and rPVSTS (%) for the male and female groups and all subjects.
PVSTS Male Female All rPVSTS Male Female All
C7
T1
T2
T3
T4
18.1 (0.50) 14.5 (0.36) 16.1 (0.34)
13.6 (0.52) 11.0 (0.44) 12.2 (0.36)
10.8 (0.65) 9.6 (0.56) 10.1 (0.43)
10.2 (0.72) 10.0 (0.66) 10.0 (0.48)
10.8 (0.88) 11.3 (0.66) 11.1 (0.53)
77.4 (2.3) 72.2 (1.8) 74.6 (1.4)
60.0 (2.4) 54.8 (2.3) 57.2 (1.7)
47.5 (2.9) 47.2 (2.8) 47.3 (2.0)
45.1 (3.3) 50.3 (3.3) 48.0 (2.4)
47.6 (4.1) 55.8 (3.6) 52.8 (2.8)
and older. Comparison of the group mean PVSTS revealed a marked increase in the two groups that included patients 41 y and older. Further Tukey HSD tests were conducted to compare the mean rPVSTS from those 40 y and younger (n ¼ 102) with those 41 y and older (n ¼ 29), at the level of C7, T1, and combined levels of T2eT3eT4 (Tables 5 and 6). The PVSTS and rPVSTS data from T2, T3, and T4 were combined as there was no significant difference between these values. The results of these tests revealed a consistently larger mean PVSTS and rPVSTS for the older patient group compared with the younger patient group, with the difference reaching level of significance at the T1 level, and combined levels of T2eT3eT4.
4.
Discussion
The lateral cervical spine radiograph has traditionally been the standard screening modality of cervical spine imaging as part of the initial evaluation of the trauma patient [11]. In cases where obvious fracture or dislocation is not present, assessment of prevertebral soft tissue shadow is carried out as an indicator of occult injury to the cervical spine. The soft tissue thickness between the bony cervical vertebral column and the air space of the pharynx and trachea is constituted by the anterior longitudinal ligament, the longus capitis and longus coli musculature, and the prevertebral and alar fascia. The retropharyngeal space between these fascial layers contains loose areolar tissue, which allows the pharynx to move up and down relative to the vertebral column [12]. Further anterior lies the buccopharyngeal fascia, esophagus,
Table 5 e Mean (standard error) values of PVSTS (mm) for the male and female groups and all subjects within two age groups.
40 y & younger All Male Female 41 y & older All Male Female
C7
T1
T2eT3eT4
16.0 0.4 17.8 0.6 14.4 0.4
11.8 0.4 13.1 0.6 10.7 0.5
9.7 0.3 9.9 0.4 9.6 0.4
16.8 0.7 18.9 0.7 14.8 0.9
13.6 0.9 15.2 1.2 12.2 1.2
12.8 0.6 13.3 1.1 12.4 0.7
and trachealis muscle. Injury to the cervical spinal column is generally accompanied by an increase in the soft tissue width, from hematoma tracking into the retropharyngeal space from injury to the spinal column and also from concurrent injury and edema within the soft tissues themselves. Increased PVSTS width has also been found in nontraumatic pathologic conditions of the cervical spinal column [1e4]. Many published reports have found measurement of PVSTS on a lateral cervical radiograph to be a useful indicator of cervical spine injury [12e15]. Dai [16] retrospectively reviewed 107 consecutive patients with suspected cervical spine injury, identifying 47 patients with swelling of the prevertebral soft tissues. Thirty-eight of the 47 patients (80.9%) with swelling had a bony injury, a statistically significant relationship. Some authors report poor reliability of radiographic PVSTS [17,18]. DeBehnke and Havel, in a retrospective series of 74 cervical trauma patients and 93 control patients [18], reported that a 22 mm measurement at C6 had a sensitivity of 5% and specificity of 95%. Similarly, Herr et al., in a study of 211 patients with cervical spine fracture [17], reported the mean PVSTS at C3 to be 6.2 mm G 3.3 mm (1e22 mm) and found that PVSTS width at C3 had poor sensitivity for detecting injury. Radiographic measurement of PVSTS in the cervical spine may be more sensitive at detecting injury and pathology that involves the anterior column of the spine, and should be used in conjunction with the history and clinical examination in any given patient. Adequate visualization of the cervicothoracic region is difficult on standard lateral imaging of the cervical spine, because of the overlying osseous and soft tissue structures of the shoulder and upper chest [19]. In a retrospective review of trauma patients who underwent plain film imaging in lateral and anterior/posterior views, Gale et al. [20] reported that the cervicothoracic junction could be visualized in only 27.8% of patients (178/640). The swimmer’s view radiograph is an alternative to the standard lateral cervical radiograph that
Table 6 e Mean (standard error) values of rPVSTS (%) between two age groups.
40 y & younger 41 y & older P value
C7
T1
T2-T3-T4
73.6 (1.7)% 77.6 (3.0)% 0.23
55.3 (1.9)% 63.4 (3.4)% 0.039
45.6 (1.5)% 60.1 (2.7)% <0.001
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provides improved visualization of the cervicothoracic region. Gisbert et al. [21], in a retrospective review of 22 injuries at C7eT1, reported a missed diagnosis on standard lateral cervical films in 19 patients. An accurate diagnosis was made on seven of the eight patients who underwent a swimmer’s view radiograph. To our knowledge, normative data on the prevertebral soft tissue shadow anterior to the cervicothoracic spine has not been previously reported in the North American population. The range of normal values we found in the cervicothoracic region is comparable to previously reported ranges of thickness of anterior soft tissue shadow on radiographs of the cervical spine in normal subjects. Penning reported a range of 8e20 mm (mean 14.9 mm) anterior to C5, 11e20 mm (mean 15.1 mm) anterior to C6, and 9e20 mm (mean 13.9 mm) anterior to C7 [12]. Wholey et al. [22] and Haug et al. [23] reported a range of normal values anterior to C6 of 9e22 mm (mean 14.0 mm) and 5.0e18.0 mm (mean 12.1 mm), respectively; Chen and Bohrer [10] reported a range of 11e26 mm (mean 15.5 mm) anterior to C5; and Oon [24] reported a range of 8e17 mm (mean 12.4 mm) in the retrotracheal width, below the inferior horn of the thyroid cartilage. Prior studies have not provided an explanation for this range in the PVSTS width, but we believe the variances can be explained on the basis of individual anthropometrics, muscle hypertrophy, and thickness of soft tissue layers in any individual patient. Regression analysis reveals that vertebral level, sex, and age had significant influences on PVSTS width. Variation in soft tissue thickness between C7 and T4 would be anticipated based on anatomic differences in the soft tissues present anterior to the spinal column at the different levels. To our knowledge, this association between age and increasing PVSTS width has not previously been reported. We assume that the increased width of the soft tissues anterior to the spinal column in older subjects may be related to loss in disk and vertebral body height and increase in local kyphosis with age, which result in infolding of the soft tissues anterior to the spinal column. We found significant difference in PVSTS between male and female subjects at the levels of C7 and T1 (P < 0.0001 and P < 0.0002). To assess the role of anthropometric differences between male and female subjects, we assessed normalized measurements with respect to the C7 vertebral body width. The normalized PVSTS (or rPVSTS) showed that whereas male subjects still had higher PVSTS than female subjects, the difference was not significant (least squares means are 60.5% and 61.5% female and male, respectively, P ¼ 0.64). The difference in PVSTS values between male and female subjects is largely explained by the larger body habitus in males and the effect of magnification from the greater distance between the spinal column and radiographic cassette, and not by an intrinsic difference in prevertebral soft tissue thickness between the sexes. From our series of 85 subjects with measureable T4 levels, only seven (8.2%) have an rPVSTS ratio over 1.0 and only four (4.7%) have a ratio over 1.1. The maximum rPVSTS in the lower portion (T2eT4) of the cervicothoracic spine is 1.2 in our series. At C7, the mean rPVSTS ratio is 0.746, with 11 of 125 subjects (8.8%) having an rPVSTS ratio over 1.0 and four (3.2%) having a ratio over 1.1, the maximum being 1.3. In addition to
77
measurements of absolute values for radiographic PVSTS, we propose that an rPVSTS ratio of 1.0 be set as a screening reference defining the upper limit of normal in the cervicothoracic spine on swimmer’s view radiographs. This value presents an appropriate level of sensitivity and is consistent with previously set standards for the cervical spine on lateral imaging [10]. An example of this screening application is presented in Figure 2. A limitation of our data is the increasing use of computerized tomographic (CT) scanning of the cervicothoracic region as a screening modality for underlying vertebral and soft tissue pathology. In a meta-analysis comparing CT scans with plain radiographs of the cervical spine for detecting cervical spine injuries, Holmes and Akkinepalli [25] reported the sensitivity of CT imaging to be 98% compared with 52% for plain radiographs. CT imaging has also been shown by some authors to be cost-effective as a screening modality for patients at moderate or high risk for cervical spine injury [26] and for trauma patients in whom C7eT1 was inadequately visualized with conventional radiography [27]. The increase in diagnostic accuracy for the limited number of patients with injury to the cervicothoracic region needs to be weighed against the substantial increase in individual and population radiation exposure that the use of CT scanning as a screening modality entails. Rybicki et al. [28], in a comparison of radiation exposure to the thyroid in patients undergoing cervical spine imaging with CT or plain radiography, reported a greater than 14-fold difference in thyroid radiation dose between the groups. Using historical data to estimate the risk of excess thyroid cancer mortality from CT as compared with plain radiography, Shu et al. [29] reported, for a 25-y-old male subject, a reduction from 96.7 estimated excess deaths per 100,000 for standard-dose CT imaging to 6.7 estimated excess deaths per 100,000 for plain-film cervical spine examination. In addition, while CT scans are frequent at major academic hospitals, community hospitals continue to use plain radiographs as an initial screening modality for spinal pathology. Our study also highlights the radiographic contour of the trachea in the cervicothoracic region. The trachea in the upper thoracic region follows the kyphotic curvature of the spine, and thus is concave anteriorly. This anterior concavity from C7 to T4 was observed on 108 of 131 radiographs. On the remaining 23 radiographs, a double curve was present with a flattening or convexity anterior to C7 transitioning to a concave contour from T1 to T4. Reversal of the anterior concavity of the trachea and anterior displacement of the trachea in the cervicothoracic region has previously been described by Jain et al. in patients with tuberculosis of the cervicothoracic spine [30]. These findings corrected to near normal in patients who underwent successful treatment. We conclude that measurement of prevertebral soft tissue shadow on a swimmer’s view radiograph provides a valuable screening tool in the evaluation of cervicothoracic spine injury and pathology. Our measurements provide a reliable normative database in the North American population. Variations in these measurements should be anticipated in normal patients without injury, between male and female sex, and with age. Abnormalities in this measurement should
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Fig. 2 e (A) Swimmer’s view radiograph in a 58-y-old male subject (below abnormalities precluded this patient from being included in this study) with a 1-mo history of upper back pain who presented with acute, progressive weakness in the right lower extremity of 2 d duration. (B) Measurement technique. rPVSTS ratio was calculated to be 1.18 at C7, 0.86 at T1, 1.11 at T3, and 1.61 at T4. (C) Sagittal and (D) axial magnetic resonance imaging scans were subsequently obtained, revealing a grade 3 chondrosarcoma of the mediastinum, displacing the trachea anteriorly and laterally. (Color version of figure is available online.)
serve as an indicator for further evaluation with either computed tomography or magnetic resonance imaging.
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