(Radiology. 2000;214:237-246.)
© RSNA, 2000
Postcricoid Region and Cervical Esophagus: Normal Appearance at CT and MR Imaging1
Ilona M. Schmalfuss, MD,
Anthony A. Mancuso, MD and
Roger P. Tart, MD
1 From the Department of Radiology, University of Florida, 1600 SW Archer Rd, Gainesville, FL 32610. Received October 13, 1997; revision requested December 19; final revision received March 11, 1999; accepted July 1. Address reprint requests to I.M.S. (e-mail: schmalfussi@xray.ufl.edu).
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Abstract
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PURPOSE: To establish the normal variations of the postcricoid portion of the hypopharynx, esophageal verge, and cervical esophagus, as seen on computed tomographic (CT) and magnetic resonance (MR) images.
MATERIALS AND METHODS: One hundred twenty-one CT and 92 MR images were reviewed. Diameter and wall thickness were measured at multiple levels. Depiction of the layers of the musculature and adjacent fat planes was evaluated. The frequency and size of the tracheoesophageal lymph nodes were noted.
RESULTS: An esophageal anteroposterior diameter greater than 16 mm and lateral diameter greater than 24 mm were considered abnormal. The average wall thickness was 4.8 mm laterally and 3.8 mm posteriorly. Demonstration of the intramural fat planes of the postcricoid region decreased from the upper to the lower region of the cricoid cartilage. The ability to separate the esophageal wall from the trachea was highest at the esophageal verge and declined markedly more distally. The tracheoesophageal groove nodes were seen more often on the right (mean size [± SD], 4.5 mm ± 2.2).
CONCLUSION: Knowledge of the normal appearance and variations of the postcricoid region and cervical esophagus is essential in detecting abnormalities in these areas.
Index terms: Esophagus, 71.92 • Esophagus, CT, 71.12112 • Esophagus, MR, 71.121412, 71.12143 • Pharynx, 272.92 • Pharynx, CT, 272.12112 • Pharynx, MR, 272.121412, 272.12143
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Introduction
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In the past, the normal appearances of the postcricoid portion of the hypopharynx (also referred to as the postcricoid region) and of the cervical esophagus received limited attention in the radiology literature. To our knowledge, the normal appearance of only the thoracic portion of the esophagus has been described at cross-sectional imaging (1). With increasing use of computed tomography (CT) and/or magnetic resonance (MR) imaging of the head and neck region in the work-up of patients with swallowing difficulties, globus sensation, and other symptoms potentially related to the esophagus or adjacent anatomic structures, detailed knowledge of the normal postcricoid portion of the hypopharynx, esophageal verge, cervical esophagus, and the surrounding structures is required. Cross-sectional imaging is of particular importance in evaluating the inferior extent of hypopharyngeal cancers (Fig 1) or the superior extent of esophageal tumors (Fig 2) before surgery and in detecting submucosal lesions.
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Figure 1. Transverse CT image through the lower postcricoid region in a 62-year-old man with a fungating mass in the right piriform sinus demonstrates definite involvement of the lower postcricoid region by a tumor (T) on the right, which is seen as a thickening of the pharyngeal wall and obliteration of the intramural fat planes. These subtle findings are more obvious when they are compared with those of the normal pharyngeal wall and intramural fat planes (arrowheads) on the uninvolved left side. The inferior extension of the hypopharyngeal tumor is entirely submucosal in location and was nondetectable at endoscopy. (Reprinted, with permission, from reference 2.)
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Figure 2. Transverse contrast-enhanced CT image in a 68-year-old man with a large carcinoma of the upper cervical esophagus shows two- to threefold thickening of the anterior wall (arrowheads) of the postcricoid portion of the hypopharynx, which indicates superior extension of the esophageal tumor into the postcricoid region. This superior extension of the tumor is entirely covered by mucosa (dots) and was nondetectable at endoscopy.
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With fluoroscopy and/or endoscopy with biopsy, small or submucosal infiltrating tumors might be missed, and only CT and/or MR imaging might enable the diagnosis of such a mass while it is still at a curable stage. Percutaneous biopsy with CT guidance may be performed on a submucosal lesion detected on a cross-sectional study if endoscopic biopsy is not successful (2).
The purpose of this study was to define the normal appearance of the postcricoid region and the surrounding structures in the lower neck at CT and MR imaging.
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MATERIALS AND METHODS
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One hundred twenty-one consecutive CT scans of the neck of individual patients (53 [43.8%] female, 68 [56.2%] male; age range, 1–94 years; average age [± SD], 49 years ± 21) that were obtained at our institution in 1993 were analyzed. In addition, 92 consecutive MR imaging studies (in 45 [49%] female patients and 47 [51%] male patients; age range, 1–78 years; average age, 42 years ± 19) of the lower neck and/or distal cervical spine that were of adequate quality and demonstrated the postcricoid region and cervical esophagus in the transverse plane with various pulse sequences (T1 [repetition time msec/echo time msec, 500–900/10–17], T2 [5,000–9,000/110–120], gadopentetate dimeglumine–enhanced T1 [600–800/12–17], and other sequences when available) were chosen for assessment. All MR imaging examinations were performed at our institution between January 1993 and April 1994. Only the studies of patients who did not have complaints (eg, dysphagia, chest pain, regurgitation, globus sensation), clinical or imaging findings suggestive of esophageal abnormalities, or signs or a medical history of a head or neck malignancy were included for evaluation. Patients with a history of lymphoma were excluded from only the evaluation of lymph nodes in the tracheoesophageal groove.
For adequate visualization and analysis of the postcricoid region and cervical esophagus, image quality was graded on a scale of 1–5, where 5 represented excellent image quality and 1, a nondiagnostic study. Approximately 12% (nine of 130 CT scans and 18 of 110 MR images) of the images had a rating lower than 3 and thus were excluded from this study; this left 121 CT and 92 MR images for evaluation. The limitations in image quality were due predominantly to shoulder artifacts at CT and motion artifacts at MR imaging.
The CT examinations were performed by using a model 9800 scanner (GE Medical Systems, Milwaukee, Wis) with a maximum collimation of 3 mm and maximum intersection gap of 2 mm. All but four CT examinations were performed with intravenous administration of an ionic (iothalamate meglumine 60% [Conray 60]; Mallinckrodt, St Louis, Mo) or nonionic (iohexol [Omnipaque 300]; Nycomed Amersham, Princeton, NJ) contrast agent. The MR images were obtained by using 1.0-T Magneton (Siemens, Erlangen, Germany) and 1.5-T Signa (GE Medical Systems) units with a maximum section thickness of 5.0 mm and maximum intersection gap of 0.5 mm. Most of the MR examinations were performed with a section thickness of 3 mm at T1-weighted imaging and of 5 mm at T2-weighted imaging. Each sequence was evaluated separately.
To standardize the assessments, the postcricoid region and cervical esophagus were subdivided as follows: The postcricoid region was divided into the upper margin of the cricoid at the cricoarytenoid joint level (Fig 3a), middle portion of the cricoid cartilage (Fig 3b), and inferior margin of the cricoid cartilage (Fig 3c). The cervical esophagus was divided into the esophageal verge (or esophageal inlet) 3–5 mm caudal to the attachment of the inferior pharyngeal constrictor muscle to the inferior horn of the thyroid cartilage (Figs 3d, 4), the area 0.9–1.2 cm below the esophageal verge (Fig 3e), the area 1.8–2.1 cm below the esophageal verge, and the area 2.7–3.3 cm below the esophageal verge.
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Figure 3a. (a) Transverse contrast-enhanced CT images through the upper margin of the cricoid region (stars) at the cricoarytenoid joint (ca, arrowheads). The posterior wall (arrows) is well demonstrated, with faint enhancement of the mucosa (circles). (b) Transverse contrast-enhanced CT image through the middle portion of the cricoid cartilage (CB). At this level, the attachment of the postcricoid musculature (arrows) to the inferior horn of the thyroid cartilage (stars) is visible. The muscular wall of the pharynx in the postcricoid region consists of the posterior cricoarytenoid muscle (dots) and the inferior constrictor muscle (arrowheads). (c) Transverse contrast-enhanced CT image through the inferior margin of the cricoid cartilage (stars). Note the beginning change in shape of the muscular wall in the postcricoid region (arrows) and the complete lack of intramural fat planes at this level. (d) Transverse contrast-enhanced CT image through the esophageal verge or inlet, which corresponds to a level approximately 5 mm caudal to the attachment of the inferior pharyngeal constrictor muscle to the inferior horn of the thyroid cartilage. Note the narrower and ovoid appearance of the esophageal verge (star) compared with the appearance of the postcricoid region in a-c and with the appearance of the cervical esophagus in e. (e) Transverse contrast-enhanced CT image through the cervical esophagus, approximately 1 cm below the esophageal verge. At this level, the esophagus (stars) has a typical rounded appearance. Note the small contrast-enhanced vessel (arrowhead) in the tracheoesophageal groove on the left side.
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Figure 3b. (a) Transverse contrast-enhanced CT images through the upper margin of the cricoid region (stars) at the cricoarytenoid joint (ca, arrowheads). The posterior wall (arrows) is well demonstrated, with faint enhancement of the mucosa (circles). (b) Transverse contrast-enhanced CT image through the middle portion of the cricoid cartilage (CB). At this level, the attachment of the postcricoid musculature (arrows) to the inferior horn of the thyroid cartilage (stars) is visible. The muscular wall of the pharynx in the postcricoid region consists of the posterior cricoarytenoid muscle (dots) and the inferior constrictor muscle (arrowheads). (c) Transverse contrast-enhanced CT image through the inferior margin of the cricoid cartilage (stars). Note the beginning change in shape of the muscular wall in the postcricoid region (arrows) and the complete lack of intramural fat planes at this level. (d) Transverse contrast-enhanced CT image through the esophageal verge or inlet, which corresponds to a level approximately 5 mm caudal to the attachment of the inferior pharyngeal constrictor muscle to the inferior horn of the thyroid cartilage. Note the narrower and ovoid appearance of the esophageal verge (star) compared with the appearance of the postcricoid region in a-c and with the appearance of the cervical esophagus in e. (e) Transverse contrast-enhanced CT image through the cervical esophagus, approximately 1 cm below the esophageal verge. At this level, the esophagus (stars) has a typical rounded appearance. Note the small contrast-enhanced vessel (arrowhead) in the tracheoesophageal groove on the left side.
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Figure 3c. (a) Transverse contrast-enhanced CT images through the upper margin of the cricoid region (stars) at the cricoarytenoid joint (ca, arrowheads). The posterior wall (arrows) is well demonstrated, with faint enhancement of the mucosa (circles). (b) Transverse contrast-enhanced CT image through the middle portion of the cricoid cartilage (CB). At this level, the attachment of the postcricoid musculature (arrows) to the inferior horn of the thyroid cartilage (stars) is visible. The muscular wall of the pharynx in the postcricoid region consists of the posterior cricoarytenoid muscle (dots) and the inferior constrictor muscle (arrowheads). (c) Transverse contrast-enhanced CT image through the inferior margin of the cricoid cartilage (stars). Note the beginning change in shape of the muscular wall in the postcricoid region (arrows) and the complete lack of intramural fat planes at this level. (d) Transverse contrast-enhanced CT image through the esophageal verge or inlet, which corresponds to a level approximately 5 mm caudal to the attachment of the inferior pharyngeal constrictor muscle to the inferior horn of the thyroid cartilage. Note the narrower and ovoid appearance of the esophageal verge (star) compared with the appearance of the postcricoid region in a-c and with the appearance of the cervical esophagus in e. (e) Transverse contrast-enhanced CT image through the cervical esophagus, approximately 1 cm below the esophageal verge. At this level, the esophagus (stars) has a typical rounded appearance. Note the small contrast-enhanced vessel (arrowhead) in the tracheoesophageal groove on the left side.
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Figure 3d. (a) Transverse contrast-enhanced CT images through the upper margin of the cricoid region (stars) at the cricoarytenoid joint (ca, arrowheads). The posterior wall (arrows) is well demonstrated, with faint enhancement of the mucosa (circles). (b) Transverse contrast-enhanced CT image through the middle portion of the cricoid cartilage (CB). At this level, the attachment of the postcricoid musculature (arrows) to the inferior horn of the thyroid cartilage (stars) is visible. The muscular wall of the pharynx in the postcricoid region consists of the posterior cricoarytenoid muscle (dots) and the inferior constrictor muscle (arrowheads). (c) Transverse contrast-enhanced CT image through the inferior margin of the cricoid cartilage (stars). Note the beginning change in shape of the muscular wall in the postcricoid region (arrows) and the complete lack of intramural fat planes at this level. (d) Transverse contrast-enhanced CT image through the esophageal verge or inlet, which corresponds to a level approximately 5 mm caudal to the attachment of the inferior pharyngeal constrictor muscle to the inferior horn of the thyroid cartilage. Note the narrower and ovoid appearance of the esophageal verge (star) compared with the appearance of the postcricoid region in a-c and with the appearance of the cervical esophagus in e. (e) Transverse contrast-enhanced CT image through the cervical esophagus, approximately 1 cm below the esophageal verge. At this level, the esophagus (stars) has a typical rounded appearance. Note the small contrast-enhanced vessel (arrowhead) in the tracheoesophageal groove on the left side.
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Figure 3e. (a) Transverse contrast-enhanced CT images through the upper margin of the cricoid region (stars) at the cricoarytenoid joint (ca, arrowheads). The posterior wall (arrows) is well demonstrated, with faint enhancement of the mucosa (circles). (b) Transverse contrast-enhanced CT image through the middle portion of the cricoid cartilage (CB). At this level, the attachment of the postcricoid musculature (arrows) to the inferior horn of the thyroid cartilage (stars) is visible. The muscular wall of the pharynx in the postcricoid region consists of the posterior cricoarytenoid muscle (dots) and the inferior constrictor muscle (arrowheads). (c) Transverse contrast-enhanced CT image through the inferior margin of the cricoid cartilage (stars). Note the beginning change in shape of the muscular wall in the postcricoid region (arrows) and the complete lack of intramural fat planes at this level. (d) Transverse contrast-enhanced CT image through the esophageal verge or inlet, which corresponds to a level approximately 5 mm caudal to the attachment of the inferior pharyngeal constrictor muscle to the inferior horn of the thyroid cartilage. Note the narrower and ovoid appearance of the esophageal verge (star) compared with the appearance of the postcricoid region in a-c and with the appearance of the cervical esophagus in e. (e) Transverse contrast-enhanced CT image through the cervical esophagus, approximately 1 cm below the esophageal verge. At this level, the esophagus (stars) has a typical rounded appearance. Note the small contrast-enhanced vessel (arrowhead) in the tracheoesophageal groove on the left side.
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Figure 4. Histologic section at lower border of the cricoid cartilage in the transverse plane shows the esophageal verge or inlet (E). Note how the emerging muscular wall of the esophagus (arrowheads) merges with the lowermost fibers of the inferior constrictor muscle (arrows). (Reprinted, with permission, from reference 2.)
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The following parameters were evaluated at each of the levels defined above:
Location of Esophagus
The location of the esophagus was defined in relation to a line that bisects the trachea in an anteroposterior direction. The possible resultant positions of the esophagus are central, left, or right. The level at which the location of the esophagus changed (eg, from central to one side) was noted in centimeters below the esophageal verge.
Esophageal Margins
Subjective evaluation of the esophageal margins was performed by using the descriptive terms "well-defined" and "indistinct." If artifacts precluded assessment, then the images that were obtained adjacent to the level of interest were included in the evaluation, and the overall impression was noted.
Mural Thickness in the Postcricoid Region
The entire thickness of the muscular wall in the postcricoid region was measured at its fullest extent and divided into anterior (corresponding to the posterior cricoarytenoid muscles) and posterior (consisting of the inferior pharyngeal constrictor muscle) portions (Fig 5). In addition, the transverse diameter of the inferior constrictor muscle (Fig 5) between its attachments to the thyroid cartilage was noted. For the MR imaging studies, these measurements were obtained only on the T1-weighted images.
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Figure 5. Transverse contrast-enhanced CT image at the middle cricoid level demonstrates marked enhancement of the mucosa (circles) in the postcricoid region, which is surrounded by a thin intramural fat plane (small arrowheads). The mucosal enhancement makes measuring the thicknesses of the anterior (area between white arrow and interrupted line) and posterior (area between black arrow and interrupted line) mural walls of the postcricoid region easier. The transverse extent of the musculature is measured between the medial margins of the inferior horns of the thyroid cartilage (area between large arrowheads).
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Cervical Esophageal Musculature
Measurements of the outer anteroposterior and transverse diameters of the esophagus were obtained in all patients without subtracting the amount of air in the esophageal lumen; however, the maximum diameter of the esophageal air column was noted. In addition, the lateral and posterior wall thicknesses were recorded (Fig 6). For the MR examinations, these measurements were obtained only on the T1-weighted images.
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Figure 6. Transverse contrast-enhanced T1-weighted MR image (650/15, four signals acquired, 3-mm collimation) through the cervical esophagus shows marked enhancement of the esophageal mucosa (circles) compared with the appearance of the esophageal musculature. The thicknesses of the lateral and posterior walls of the esophagus are measured between the superficial margin of the mucosa and the outer margin of the esophageal musculature in a horizontal (area between circles and open arrow) or vertical (area between circles and solid arrow) direction, respectively.
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Visibility and Symmetry of Intramural Fat Planes in the Postcricoid Region
Subjective assessment of the intramural fat planes in the postcricoid region was performed at CT and MR imaging. The fat planes (Figs 7, 8) were described as visible, absent, or asymmetric. If the intramural fat distribution was asymmetric, then the side with the most prominent fat plane was evaluated. The intramural fat planes were assessed with each MR imaging sequence separately.
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Figure 7. Transverse contrast-enhanced CT image through the postcricoid region demonstrates prominent symmetric intramural fat planes (arrowheads) adjacent to the mucosa (circles) of the middle cricoid cartilage.
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Figure 8. Pathologic section at lower cricoid cartilage in the transverse plane shows the intramural fat planes (arrows) of the anterior and posterior walls of the postcricoid portion of the hypopharynx. (From North C, Schneiderman B, Plaisant C. The visible human project Web site. Available at http://www.cs.umd.edu/projects/hcil/Research/1995/vhe.html.
Accessed September 1998.)
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Visibility of Esophageal Layers
The visibility of the esophageal wall layers (mucosa, muscular layer, and tunica) was subjectively evaluated on the MR images and described as visible or nondiscernible with each sequence separately. There was no attempt to evaluate the individual layers of the esophagus at CT.
Mucosal Enhancement Visibility
The presence of mucosal enhancement in the postcricoid region and that in the cervical esophagus were recorded separately on contrast material–enhanced CT and MR imaging studies, when they were available.
Common (Party) Wall of the Trachea and Esophagus
The common wall of the trachea and esophagus was evaluated by using a grading system, with a 1–5 scale, based on whether the esophageal wall could be differentiated from the membranous tracheal wall; 5 indicated that the different layers could be differentiated to their full extent and 1 indicated that they were definitely indistinguishable. The common wall of the trachea and esophagus was assessed with each MR imaging sequence separately.
Adjacent Fat Planes
The fat planes adjacent to the postcricoid region and cervical esophagus were subdivided into posterior, right, and left portions. These fat planes were described as visible or absent in each location. The results with each MR imaging sequence were recorded separately.
Tracheoesophageal Groove Contents
The tracheoesophageal groove was evaluated for lymph nodes on each side, with the largest short-axis diameter recorded when a node was present. In patients with multiple lymph nodes, the total number of nodes also was noted. The results with each MR imaging sequence were recorded separately. In addition, the vessels in the tracheoesophageal groove were identified, and the diameter of the largest vessel was measured on each side separately.
All images were independently evaluated by two radiologists (I.M.S., R.P.T.) who are familiar with cross-sectional studies of the head and neck area. In cases of disagreement, the decision was made by consensus with the help of the most experienced head and neck radiologist (A.A.M.) at our institution. Statistical comparisons were made by using the nonparametric 
2 test and unpaired Student t test.
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RESULTS
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Esophagus Location
At the esophageal verge, the esophagus was located centrally in 117 (97%) of 121 cases at CT versus in 58 (63%) of 92 cases at MR imaging. Just below the esophageal verge, the esophagus typically coursed to the left side in all but three patients at both CT (three [3%] of 110) and MR (three [7%] of 46) imaging; in these six patients, it shifted to the right. On 24 (22%) of 110 CT studies, the entire length of the evaluated esophagus was in the central position. The shift of the esophagus from its usually central position at the esophageal verge to the side was found to occur, on average (± SD), 1.3 cm ± 0.8 and 0.5 cm ± 0.6 below the esophageal verge at CT and MR imaging, respectively. The esophageal margins were well defined in all patients with both imaging modalities.
Musculature of the Postcricoid Region and Cervical Esophagus
The anteroposterior diameter of the postcricoid region varied little through its cephalocaudal extent, whereas the transverse diameter of the same distance tended to taper about 1 cm. At the esophageal verge, there was an abrupt change: The anteroposterior diameter of the pharyngoesophageal junction widened to an average size of 10 mm, and the transverse diameter tapered to an average size of 16 mm (Table 1). The cervical esophagus then changed little in its anteroposterior and transverse diameters.
The anteroposterior diameter of the cervical esophagus increased with advancing age on both types of images: It was an average of 3.2 mm larger at CT and an average of 3.6 mm larger at MR imaging in the patients aged 70 years and older compared with those between the ages of 20 and 29 years (P value range, .001 - .032). There was no statistically significant difference in transverse diameter based on age when the patients younger than 20 years were excluded from analysis. The anteroposterior diameters in the female patients were slightly smaller than those in the male patients; however, the difference was only statistically significant in the cervical esophagus at CT (P value range, .005 to < .001 at the different levels). The anteroposterior diameter of the cervical esophagus was, on average, 1.7 mm smaller at CT in the female patients.
There was a statistically significant difference in the transverse diameter at all levels between the sexes with both imaging modalities. The transverse extension of the postcricoid musculature was an average of 4.4 and 4.8 mm smaller in the female patients at CT and MR imaging, respectively (P value range, .02 to < .001). The difference in the transverse diameter of the cervical esophagus was less pronounced: In the female patients, this measurement was 2.5 mm smaller at CT and 2 mm smaller at MR imaging (P value range, .09–.001).
The mean ratio (± SD) of the anteroposterior diameter of the esophagus to the anteroposterior diameter of the trachea at MR imaging was slightly higher (0.68 mm ± 0.19) than that at CT (0.62 mm ± 0.24) (P = .003). The mean ratio of the transverse diameter of the esophagus to the transverse diameter of the trachea also was slightly higher at MR imaging (1.12 mm ± 0.21) than that at CT (0.98 mm ± 0.18) (P < .001). There were no statistical differences based on age or sex.
The anterior and posterior wall thicknesses in the postcricoid region tended to increase minimally in the caudal direction. The posterior wall tended to be 1 mm thicker than the anterior wall (Table 2). There were no statistically significant differences related to sex or age.
The lateral and posterior walls of the cervical esophagus thickened minimally (approximately 1–2 mm) at the pharyngoesophageal junction and then remained essentially 3.5–4.5 mm thick throughout the cervical esophagus (Table 2). There were no statistically significant differences related to sex or age.
Air inside the esophageal lumen was depicted on 112 (92.6%) of 121 CT scans and on 30 (33%) of 92 MR images. The average maximum diameter (± SD) of the air column was 3.8 mm ± 2.9 at CT and 1.6 mm ± 2.5 at MR imaging (P < .001). The maximum diameter of the air column tended to increase with age. There was no statistical difference in this measurement between the female and male patients.
Intramural Fat Planes in the Postcricoid Region
The frequency of visible intramural fat in the postcricoid region diminished in the caudal direction, from visibility in 94 (84.7%) of 111 cases at the upper cricoid level to visibility in 38 (34.2%) cases at the lower level of the cricoid cartilage on CT images (Fig 7). The changes seen at MR imaging were similar but less pronounced: The intramural fat plane was depicted on at least one type of MR image in 63 (68%) of the 92 images of the upper cricoid region (Fig 9) and in 28 (30%) of the 92 images of the lower margin of the cricoarytenoid joint.
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Figure 9. Transverse nonenhanced T1-weighted MR image (500/17, three signals acquired, 3-mm section thickness) through the upper cricoid cartilage demonstrates thin intramural fat planes (arrowheads) of increased signal intensity.
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Asymmetric intramural fat planes were seen more often in the proximal postcricoid region at CT. At CT and MR imaging, asymmetry was present at the upper cricoid level in 10 (11%) of 93 and in 31 (34%) of 92 cases, respectively; at the middle portion of the cricoid cartilage, in eight (10%) of 78 and in 26 (31%) of 83 cases, respectively; and at the lower cricoid level, in one (3%) of 33 and in 12 (38%) of 32 cases, respectively. The intramural fat was more often or more prominently seen on the left side with both imaging modalities (in an average of 75% of the cases with asymmetry at both CT and MR imaging). There was no statistically significant difference in these findings based on sex or age.
In an analysis of the visibility of the intramural fat planes with the different MR imaging sequences (fat planes seen in 60%–67% of cases), there was no difference in visibility at the upper cricoid level (Fig 10): The fat planes were seen on T1-weighted images in 46 of 75 cases; on T2-weighted images, in 14 of 21 cases; and on T2-weighted gradient-echo images, in 33 of 54 cases. At the middle and lower cricoid levels, the intramural fat planes were identified on the T2-weighted gradient-echo images almost twice as often as they were identified on the T1- and T2-weighted images (approximately 40% versus 80%, respectively, in the middle cricoid region and approximately 12% versus 35%, respectively, in the lower cricoid region). In the middle cricoid region, the fat planes were seen on the T1-weighted images in 28 of 75 cases; on T2-weighted images, in 10 of 22 cases; and on T2-weighted gradient-echo images, in 43 of 55 cases. In the lower cricoid region, the fat planes were seen on the T1-weighted images in eight of 75 cases; on T2-weighted images, in three of 22 cases; and on T2-weighted gradient-echo images, in 20 of 55 cases.
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Figure 10a. Transverse nonenhanced (a) T1-weighted (650/17, three signals acquired, 3-mm section thickness) and (b) gradient-echo T2-weighted (550/11, 11° flip angle, three signals acquired, 3-mm section thickness) MR images at the level of the cricoarytenoid joint (stars in a). The delineation of the intramural fat planes (arrowheads) is demonstrated better on the gradient-echo T2-weighted image. Only small portions of the fat planes are depicted on the T1-weighted image.
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Figure 10b. Transverse nonenhanced (a) T1-weighted (650/17, three signals acquired, 3-mm section thickness) and (b) gradient-echo T2-weighted (550/11, 11° flip angle, three signals acquired, 3-mm section thickness) MR images at the level of the cricoarytenoid joint (stars in a). The delineation of the intramural fat planes (arrowheads) is demonstrated better on the gradient-echo T2-weighted image. Only small portions of the fat planes are depicted on the T1-weighted image.
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Esophageal Layers at MR Imaging
The mucosa of the cervical esophagus was identified with 133 (71.5%) of 186 MR imaging sequences. It was visible on all the T2-weighted and contrast-enhanced T1-weighted studies (additional results follow), on 45 (85%) of 53 T2-weighted gradient-echo images, and on 27 (38%) of 72 T1-weighted images. The difference in the rate of depiction with the different sequences was statistically significant (P < .001). There were no significant differences based on age or sex. The muscular layer was seen in all patients and with all the sequences. The tunica could not be differentiated from the muscular layer in any of the patients.
Mucosal Enhancement
Mucosal enhancement was present in the postcricoid region and in the cervical esophagus in 90 (86.5%) of 104 and in 91 (77.8%) of 117 patients, respectively, at CT and in all the patients at MR imaging. There were no significant differences based on age or sex.
Common (Party) Wall of the Trachea and Esophagus
The visibility of the different layers of the common wall of the trachea and esophagus (Fig 11) decreased distally with both imaging modalities. The distinction remained visible more often on the MR images than on the CT scans, especially in the lower portion of the cervical esophagus. The results are summarized in Table 3. The frequency of definite or probable differentiation of the layers of the tracheoesophageal wall was higher at all levels on the MR images compared with that on the CT scans (P value range, <.001 to .002). No significant differences based on age or sex were found.
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Figure 11. On this transverse contrast-enhanced CT image through the cervical esophagus, there is excellent visibility of the different components of the tracheoesophageal common wall, including the membranous tracheal wall (arrows), esophageal wall (E), and prominent fat plane (arrowheads) between the two walls.
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TABLE 3. Differentiation of the Membranous Tracheal Wall from the Esophageal Wall at Their Common Wall on CT and MR Images
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The frequency of definite or probable differentiation of the tracheal and esophageal wall layers was highest on the gadopentetate dimeglumine–enhanced T1-weighted images, followed by the non-enhanced T1-weighted and gradient-echo T2-weighted images (Fig 12). The results are summarized in Table 4. The difference between sequences was not statistically significant.
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Figure 12a. Transverse (a) T2-weighted gradient-echo (733/18, four signals acquired, 3-mm section thickness) and (b) nonenhanced T1-weighted (700/15, six signals acquired, 3-mm section thickness) images. The common wall of the trachea and esophagus is better demonstrated on the gradient-echo image. The fat plane (arrowheads) between the esophagus and the trachea is partly depicted on the T1-weighted image but can be delineated in its entire length on the gradient-echo T2-weighted image.
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Figure 12b. Transverse (a) T2-weighted gradient-echo (733/18, four signals acquired, 3-mm section thickness) and (b) nonenhanced T1-weighted (700/15, six signals acquired, 3-mm section thickness) images. The common wall of the trachea and esophagus is better demonstrated on the gradient-echo image. The fat plane (arrowheads) between the esophagus and the trachea is partly depicted on the T1-weighted image but can be delineated in its entire length on the gradient-echo T2-weighted image.
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TABLE 4. Differentiation of the Membranous Tracheal Wall from the Esophageal Wall at Their Common Wall with Various MR Imaging Sequences
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Fat Planes around the Postcricoid Region and Cervical Esophagus
The fat planes surrounding the postcricoid region were visible more often on the CT scans than on the MR images; however, the difference was not statistically significant. The results are summarized in Table 5. With both imaging modalities and at all levels, the posterior fat plane was seen least frequently, and the left-sided fat plane was seen most frequently. The difference in frequency between the sides was statistically significant at all levels (P value range, <.001 to .011 with both imaging modalities). The depiction of all fat planes improved in the caudal direction and was more pronounced at CT (P < .001). No significant differences among the different MR imaging sequences or based on age and sex were found.
The fat planes surrounding the cervical esophagus were seen at a similar frequency with both imaging modalities. The results are summarized in Table 5. Similar to the fat planes posterior to the postcricoid region, the fat planes surrounding the cervical esophagus posteriorly were least commonly demonstrated at all levels. No statistically significant differences among the different sequences were found (Table 6). No difference in the depiction of the lateral fat planes based on age or sex was noted.
Tracheoesophageal Groove Contents
The lymph nodes of the tracheoesophageal groove (Fig 13) were visible in 39 (33.3%) of 117 patients at CT and in 31 (34%) of 91 patients at MR imaging. On the 39 CT studies, only right-sided lymph nodes were identified in 25 (64%), only left-sided lymph nodes were identified in three (8%), and bilateral lymph nodes were identified in 11 (28%) patients. Similar results were found at MR imaging: Bilateral lymph nodes were identified in six (19%), only right-sided lymph nodes were identified in 21 (68%), and only left-sided lymph nodes were identified in four (13%) of 31 patients. The maximum number of lymph nodes seen in one patient was on an MR image, on which four lymph nodes (three on the right and one on the left) were identified. The more common depiction of lymph nodes on the right side was statistically significant at both CT (P < .001) and MR imaging (P = .024). There were no significant differences based on sex or age.
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Figure 13. Transverse nonenhanced T1-weighted (700/15 msec, six signals acquired, 3-mm section thickness) image shows normal- sized tracheoesophageal lymph nodes (arrows) bilaterally.
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The right-sided lymph nodes were detected with the different sequences at almost the same frequency, which ranged from 33% (16 of 48 cases) with T1-weighted sequences to 17% (eight of 48) with T2-weighted gradient-echo sequences. The differences were not statistically significant. Contrary to the trend on the right, the left-sided lymph nodes were more often identified on the T1-weighted images, on which they were depicted at a frequency of 56% (nine of 16 cases) compared with the other sequences, with which they were depicted at a frequency of 6% (one of 16 cases) to 19% (three of 16 cases) (P = .006).
The average diameter (± SD) of the lymph nodes was similar on both types of imaging studies: on the right side, 4.6 mm ± 2.3 at CT versus 4.7 mm ± 2.5 at MR imaging; on the left side, 4.5 mm ± 2.2 at CT versus 4.3 mm ± 1.6 at MR imaging. There were no significant differences based on age or sex. The mean diameter of the vessels within the tracheoesophageal groove was 2 mm, with no difference between the two sides. No significant differences based on age or sex were identified.
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DISCUSSION
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The esophagus is more commonly located on the left side. The difference in frequencies of the esophagus on the left side between CT and MR imaging and the level of the esophageal shift to the side could be due to the relative position of the neck during data acquisition. The neck is typically hyperextended for CT studies and is left less extended or in a neutral position for the MR imaging examination. To our knowledge, only Halber et al (3) have described the position of the esophagus in the thorax, including the thoracic inlet on cross-sectional imaging studies. Their group saw the esophagus first shift to the left at the level of the carina. The apparent difference in the results in our study is most likely due to the use of different anatomic landmarks as references for the location of the esophagus. Halber et al (3) described the position of the esophagus in relation to the vertebral bodies, but in our study, the middle line of the trachea was the reference.
At CT, air in the esophageal lumen was more frequently seen in our patient population than in populations in previously described studies: The frequency of depiction in our study was 92.6% (112 of 121 images) versus 15.0%–66.7% in previous studies. These differences are most likely due to thinner sections with improved spatial resolution and/or the faster scanning times of today's CT units (1,3,4). At MR imaging, only 30 (33%) of 92 patients demonstrated air in the esophageal lumen; this difference might have been due to the different position of the neck and/or the differences in data acquisition times. In any case, this is a common and, in our opinion, unimportant normal variation.
The average anteroposterior diameter of the cervical esophagus peaked with both imaging modalities 1 cm below the esophageal verge at approximately 11.0 mm (SD, 2.5 mm). An anteroposterior diameter of the cervical esophagus of greater than 16 mm should be considered to be abnormal (equal to 2 SD added to the average diameter). Because the difference in anteroposterior diameter between younger and older patients is most likely due to the slightly greater amount of air in the esophageal lumen that is seen in older patients, some adjustment of this measurement based on the amount of air present in individual cases may be necessary. The average transverse diameter of the cervical esophagus was, at a minimum, about 16 mm at the esophageal verge at CT and at 1.0 cm below the esophageal verge at MR imaging; it reached a maximum of approximately 17.6 mm at the esophageal verge at CT and at 3.0 cm below the esophageal verge at MR imaging. Therefore, with an SD of about 3.5 mm, a transverse diameter of the cervical esophagus of greater than 24 mm should be considered to be abnormal.
The dimensions of the postcricoid portion of the hypopharynx are relatively constant to the pharyngoesophageal junction. The only statistically significant differences seem to be based on sex and are most likely due to the different shapes and sizes of the thyroid cartilage, which influence the transverse extent of the inferior pharyngeal constrictor with its attachment to the inferior cornua. An anteroposterior diameter of the postcricoid region of the hypopharynx of more than 10 mm should be considered to be abnormal. The transverse diameter tapers from the upper to the lower margin of the cricoid cartilage to the extent that a substantial pathologic entity in this region can probably be better recognized by observing the lack of normal tapering or other morphologic features (eg, obscuration of the intramural or adjacent fat planes) rather than the overall change in size.
The average anteroposterior and lateral diameters of the esophagus in our study were slightly smaller than those measured by Quint et al (1), who evaluated only the thoracic esophagus. To our knowledge, no such normal values have been established for the postcricoid region and cervical esophagus at cross-sectional imaging.
The ratio of the anteroposterior or lateral diameter of the esophagus to that of the trachea allows easier evaluation of the esophagus and prevents measurements of these diameters at all levels of the cervical esophagus. A ratio greater than 1.1 with both imaging modalities for the anteroposterior diameter and a ratio greater than 1.3 at CT and greater than 1.5 at MR imaging for the lateral diameter should be considered to be abnormal (equal to 2 SDs added to the average ratio) and may be used as quick references if desired.
In the postcricoid region, the anterior muscular wall was slightly thinner than the posterior muscular wall; the average values were 2.5 and 3.5 mm, respectively (Fig 5). The lateral and posterior walls of the cervical esophagus tended to be about 1 mm thicker than the muscular walls of the postcricoid region. In previously published studies (1,3,5), a wall thickness of the entire esophagus of less than or equal to 3 mm was assumed to be normal and a wall thickness of greater than 5 mm was definitely abnormal; however, no standardized evaluation in a larger number of patients was obtained. The results of our study, which essentially agree with these findings, suggest that a lateral wall thickness of up to 5 mm and a posterior wall thickness of 4.5 mm are probably the upper limits of normal.
The normal values listed herein were measured at cross-sectional examinations of the neck that were performed in a plane parallel to the laryngeal ventricle. An artificial widening of the muscular walls of the postcricoid region might be misinterpreted as pathologic if the cross-sectional examination is performed in a more oblique plane.
Halber et al (3) found that the differentiation of the esophagus from the adjacent soft tissues was difficult secondary to the lack of adjacent fat planes in the region of the cervical esophagus. This finding is different from the results presented here, most likely because of advances in cross-sectional imaging that include improved spatial resolution and image quality. The left lateral fat plane in the postcricoid region and cervical esophagus was visible in the majority of patients, and the right lateral plane was visible in approximately two-thirds of the patients. The posterior fat plane was least commonly seen at all levels; it was most often seen at the esophageal verge, with a decreasing frequency of demonstration more proximally and distally.
As demonstrated previously by Quint et al (1) in their study of the thoracic esophagus, the T1-weighted and gradient-echo T2-weighted images best depicted the esophageal margins by emphasizing the differences in signal intensity between the muscular esophageal wall and the adjacent fat. The esophageal margins were well defined in all patients with both imaging modalities and all sequences.
Quint et al (1) also commented on the lack of differentiation between the trachea and the thoracic esophagus at CT in the majority of cases. In approximately two-thirds of the cases in our study, however, differentiation was possible at the level of the esophageal verge, with a gradual decrease in frequency more distally. The layers of the common wall could be better differentiated on MR images than on CT scans and better differentiated with the contrast-enhanced T1-weighted sequences than with the other sequences.
The intramural fat planes in the postcricoid region are of special importance, because obliteration of these fat planes might be the only sign of cancer infiltration in this area (Fig 1). The intramural fat planes were visible at the upper cricoid level in 85% of the cases at CT and in 69% at MR imaging, but they were seen at the lower cricoid level in only about 30% of the cases with both imaging modalities. Asymmetric intramural fat planes were seen more often on the MR images. With both imaging modalities, the left-sided fat planes were more obvious. Overall, the visibility of the intramural fat planes was better at CT than at MR imaging, and asymmetry was seen less commonly at CT. This may be explained by the fewer motion artifacts and higher spatial resolution on the CT studies.
The mucosa had marked enhancement with both imaging modalities in the majority of cases. With the T2-weighted and gradient-echo T2-weighted sequences, the mucosa could be well delineated as a separate layer in the majority of patients. The extent of mucosal enhancement might be affected by the rate of contrast material injection. In the CT examinations, the contrast material was administered with a power injector at a rate of 1 mL/sec for 45 seconds, followed by 0.5 mL/sec for the remainder of the bolus administration. The contrast-enhanced T1-weighted MR images were performed after manual injection of the gadopentetate dimeglumine bolus.
According to imaging criteria, tracheoesophageal groove lymph nodes smaller than 1 cm should be considered to be normal in size. This is slightly higher than the 7-mm upper limits of normal suggested by Picus et al (6); however, their results were based on the sizes of small metastatic foci that were found in the lymph nodes of patients with esophageal cancer; these foci were present in nodes 7–10 mm in size. Glazer et al (7) evaluated paratracheal lymph nodes in the mediastinum and found the same size limits as those in our study. As in our study, the lymph nodes on the right side were slightly larger than those on the left side (7).
One application of this largely descriptive, normative data was suggested by Saleh et al (2): The results of their work indicate that the inferior spread of hypopharyngeal carcinoma may be underestimated endoscopically because of the submucosal spread of the tumor. Furthermore, this submucosal component may remain undetected at fluoroscopic examination and even at endoscopic biopsy. This can lead to a positive margin of resection—that is, that which contains gross or microscopically apparent tumor—or a margin of resection that is very close to the tumor, which is associated with a high risk of recurrence. In this particular patient group, obliteration of the intramural fat planes and/or thickening of the muscular wall at cross-sectional examination might be the only sign of a submucosal extension of the hypopharyngeal tumor (Fig 1). Other applications of the normative data in this article include the determination of the superior extent of an upper esophageal cancer (Fig 2), the diagnosis of submucosal lesions in patients with dysphagia, and the detection of esophageal invasion by adjacent tumors such as thyroid cancer.
In conclusion, knowledge of the detailed anatomic features of the postcricoid region and cervical esophagus described herein is essential for detecting lesions in these areas and determining the extent of hypopharyngeal, esophageal, and thyroid gland tumors that might have subtle focal wall thickening or fat plane obliteration.
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Footnotes
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Author contributions: Guarantor of integrity of entire study, I.M.S.; study concepts, I.M.S., A.A.M.; study design, I.M.S., A.A.M., R.P.T.; definition of intellectual content, I.M.S., A.A.M.; literature research, I.M.S.; clinical studies, I.M.S., R.P.T.; data acquisition and analysis, I.M.S., R.P.T.; statistical analysis, I.M.S.; manuscript preparation and editing, I.M.S.; manuscript review, A.A.M.
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Halber MD, Daffner RH, Thompson WM. CT of the esophagus. I. Normal appearance. AJR 1979; 133:1047-1050.
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Goldwin RL, Heitzman ER, Proto AV. Computed tomography of the mediastinum. Radiology 1977; 124:235-241.[Abstract]
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Moss AA, Schnyder P, Thoeni RF, Margulis AR. Esophageal carcinoma: pretherapy staging by computed tomography. AJR 1981; 136:1051-1056.[Abstract/Free Full Text]
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TOP
Abstract
Introduction
