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Ann Thorac Surg 1995;60:27-30
© 1995 The Society of Thoracic Surgeons

Helical Computed Tomography for the Evaluation of Tracheal Stenosis

Section of Thoracic Surgery, Department of Surgery, and Department of Radiology, The University of Michigan Medical Center, Ann Arbor, Michigan

	Abstract

Top Footnotes Abstract Introduction Patients and Methods Results Comment References

 
Background. Helical computed tomography with multiplanar reconstruction (CT/MPR) was used to study proximal airway stenosis.

Methods. Twenty-eight helical CT/MPR studies were obtained in 25 patients with known or suspected stenosis of the trachea or main bronchi. Computed tomographic results were compared with planar tomograms and bronchoscopic evaluation of the airway.

Results. CT/MPR accurately demonstrated the site and degree of tracheal and main bronchial stenoses with a sensitivity of 93%, a specificity of 100%, and an accuracy of 94%. There was one false negative study in a patient with tracheomalacia. In a second patient, a tracheal web was only apparent on nonstandard viewing windows.

Conclusions. CT/MPR provides good anatomic detail and is an increasingly available technique. Potential drawbacks include the need for a longer breath-hold (15 to 45 seconds) and increased complexity of data compared with conventional tomograms. Helical CT/MPR is useful in the preoperative evaluation of these patients and, as experience accumulates, may replace the use of conventional tomograms.

	Introduction

Top Footnotes Abstract Introduction Patients and Methods Results Comment References

 
See also page 30.

The preoperative evaluation of patients with tracheal stenosis traditionally has involved planar tomograms (laminagrams) [1, 2]. Over the past decade, advances in computed tomography (CT) have resulted in decreasing need for planar tomograms; thus, the availability of equipment and the expertise and familiarity of those responsible for obtaining the images have declined. Axial CT scans, although producing excellent resolution in the horizontal plane, are not well suited to evaluating the tracheobronchial tree, which lies in a near-vertical plane. When sagittal reconstructions are obtained from conventional axial CT images, spatial resolution is compromised due to scan plane misregistration from variable degrees of breath-holding; the resulting image quality has been unacceptable. In contrast, helical CT scanning enables acquisition of a large number of thin sections during a single breath-hold. This technique, only briefly described previously [3, 4] in the setting of major airway stenosis, provides both high resolution and the ability to reconstruct images of good quality in multiple planes including the longitudinal axis of the trachea. This technique was used to evaluate 25 patients with known or suspected tracheal or main bronchial stenosis. The results were compared with standard tomograms and bronchoscopic findings when available.

	Patients and Methods

Top Footnotes Abstract Introduction Patients and Methods Results Comment References

 
Patients
Helical CTs with multiplanar reconstructions (MPR) were obtained in 25 patients with known or suspected stenosis of the trachea or either main bronchus. Of these patients, 11 had postintubation or posttracheostomy stenoses, 4 had Wegener's granulomatosis, 4 had prior airway reconstruction, 1 had neck irradiation, 2 had tracheal tumors, 1 had Williams-Campbell syndrome, and 2 had clinically suspected tracheal stenosis without an identifiable risk factor. One patient with Wegener's granulomatosis had two CTs separated by 5 months, and 2 patients had CTs performed both before and after airway reconstruction. As such, 28 CTs were available for study.

Seventeen of the patients included herein have been described previously [5].

Radiologic Methods
Computed tomographic examinations were performed on a General Electric HiSpeed scanner (Milwaukee, WI) in helical mode, using 3-mm collimation and 1:1 pitch (3 mm/s table speed) at approximately 280 mA and 120 kV. Images were reconstructed using the ``bone'' algorithm for cases of intrathoracic pathology and ``detail'' algorithm for extrathoracic pathology. No intravenous contrast was given. After removal of any indwelling tracheostomy tube, scans were obtained through the area of clinical interest under a single breath-hold. When the area of stenosis was not known, the entire trachea was imaged from the epiglottis to the origin of the left upper lobe bronchus. When a patient could not hold his or her breath for the entire examination, the acquisition was broken up into two or more breath-hold segments and the images subsequently were concatenated. All but one examination were performed during inspiration; 1 patient could not hold his breath, and the study was done under free breathing. One study was done in both inspiration and expiration.

The CT data were reconstructed in the axial plane at 1.5-mm intervals. These axial images then were used to create one-pixel-thick reconstructions angled along the long axis of the airway being examined.

Data Analysis
The CT/MPR images were interpreted by a consensus of three radiologists (L.E.Q., E.A.K., P.N.C.). The CT/MPR studies were analyzed for the presence of airway stenosis. The site and degree of airway stenosis (none, mild [<25% decrease in luminal diameter], moderate [25% to 50%], severe [>50%]) were recorded. The CT/MPR studies were compared with results of planar tomograms and bronchoscopic findings.

	Results

Top Footnotes Abstract Introduction Patients and Methods Results Comment References

 
The results of the twenty-eight CT/MPR studies are shown in Figure 1. One study was aborted, as the patient could not tolerate temporary airway decannulation, and one other study was uninterpretable, as the patient's tracheostomy tube had not been removed. Twenty-six studies therefore were suitable for additional analysis. Of these studies, 19 demonstrated tracheal or main bronchial stenoses: 6 mild, 8 moderate, and 5 severe. Seven studies demonstrated no stenosis. Of the 19 studies with identifiable stenoses, 13 were confirmed bronchoscopically, 5 were confirmed with planar tomograms, and 4 (3 of which were mild stenoses) were unconfirmed. Of the 7 patients without identifiable stenosis, 3 underwent bronchoscopy and 3 had no further evaluation.

View larger version (41K): [in this window] [in a new window]   Fig 1. . Results of helical computed tomography (CT) with multiplanar reconstructions (MPR) in 28 known or suspected cases of tracheal or main bronchial stenosis. (FN = false negatives; FP = false positives; TN = true negatives; TP = true positives.)

View larger version (131K): [in this window] [in a new window]   Fig 2. . Helical CT/MPR study of a patient with severe upper tracheal stenosis measuring approximately 3 to 4 cm long. The length of trachea above the lesion to the vocal cords and the distance below to the carina can be measured easily.

View larger version (99K): [in this window] [in a new window]   Fig 3. . (A) Helical CT/MPR of a tracheobronchial anastomotic stricture after carinal sleeve resection. The anastomosis of the left main bronchus to the trachea is narrowed by approximately 50%, a fact confirmed at later bronchoscopy. (B) Conventional planar tomogram of the same anastomotic stricture.

View larger version (89K): [in this window] [in a new window]   Fig 4. . Helical CT/MPR of a midtracheal squamous cell carcinoma. The tumor occludes approximately 75% of the lumen of the trachea. The lesion measures approximately 2 cm long and there is little apparent extratracheal disease.

	Comment

Top Footnotes Abstract Introduction Patients and Methods Results Comment References

 
The management of patients with tracheal or main bronchial stenosis is dependent on an accurate determination of the length, position, and severity of the stenosis. Multidirectional planar tomograms have been used in the past as they produce images of good spatial resolution and can include the entire trachea and main bronchial tree in one image. This technique also provides some, albeit rather limited, information regarding the soft tissues surrounding the trachea. Multidirectional tomographic equipment, previously commonplace, is now found in only a few centers. Biplanar tomography, generally used for renal imaging, although readily available, is less well suited to the evaluation of oblique-oriented structures such as the tracheobronchial tree. High-voltage radiography with added filtration can provide reasonably good imaging of the trachea but provides little information on the surrounding soft tissues [6]. Conventional (nonhelical) CT provides good anatomic detail in the axial plane [7], but nonaxial image reconstructions suffer from inadequate spatial resolution for the preoperative evaluation of the tracheobronchial tree.

In this study we have shown that helical CT with MPR provides accurate anatomic information that the surgeon may use in planning therapy. Helical CT/MPR provides reliable information regarding the presence, length, and severity of tracheal and main bronchial stenosis. Our data indicate that cases of intermittent stenosis, as one sees with tracheomalacia, may be missed with this technique. Although not demonstrated in this study, the addition of expiratory studies may improve the detection of tracheomalacia or bronchomalacia. The clinical significance of missing mild tracheal stenosis may be minimal. We believe the specificity of CT/MPR to be high, but the calculated value of 100% may be falsely elevated because all ``negative'' CTs were not corroborated by tomography or bronchoscopy.

Helical CT/MPR provides information regarding the soft tissues surrounding the tracheobronchial tree that is not available using conventional tomograms. This is particularly important in cases of tracheal neoplasms, where the condition of the surrounding soft tissues may determine resectability. Although we did not use intravenous contrast when obtaining these studies, we will use this modification in the future, particularly for the evaluation of tracheal neoplasms. The administration of intravenous contrast is not necessary for studies of inflammatory or postintubation stenoses, for which details of the extratracheal tissues are less important.

An additional advantage of this technique is the ability to obtain images in oblique planes. Conventional planar tomograms, nonmultidirectional, are obtained in the longitudinal axis of the body. Because the tracheobronchial tree is oriented in a slightly oblique plane, the ability to image it in its long axis may be advantageous. Finally, helical CT/MPR studies can be obtained rapidly and with increasingly available equipment.

One of the primary drawbacks of helical CT/MPR is the need for a prolonged breath-hold. Even at 3-mm/s table speed, it typically takes approximately 40 seconds to obtain a study extending from the vocal cords to the carina, a distance of 12 to 14 cm. Although it may be possible for a normal individual to hold his or her breath for this long period of time, patients with tracheal stenosis may have baseline pulmonary function that prohibits this. In such cases, it is necessary to obtain two or more acquisitions, each with a single breath-hold, and to later combine the data into a single image. One obvious problem with this is the potential for introducing misregistration artifact when the images are combined. This can be minimized, however, by studying the area of clinical interest in a single breath-hold.

The need for individualizing the study underscores the necessity for active participation on the part of a radiologist or experienced technologist in obtaining comprehensive studies. The radiologist must (1) direct the technologist to scan the region of interest, (2) assure breath-holding while scanning through this region, (3) confirm that the airway is decannulated, and (4) create multiplanar reconstructions from the helical CT data. As our data indicate, the tracheostomy tube was inadvertently left in place during scanning in 1 patient. Because the tube passed through the area of suspected tracheal stenosis, no useful data were obtained from this study. In another patient, even brief decannulation of the trachea was not tolerated, and the study had to be abandoned. Although this potential situation may apply equally to other methods of imaging the tracheobronchial tree (planar tomography, high kV radiography, and standard CT scanning), both of the above cases demonstrate the need for physician input at the time of performing the studies.

Other disadvantages of helical CT/MPR compared with conventional tomography include cost and radiation exposure. At our institution, the cost for planar tomograms of the airway is approximately $500. In contrast, the cost for a CT/MPR study is $1,300. Radiation exposure is slightly higher with CT than with conventional tomograms. Computed tomography with MPR exposes the patient to an average dose of 20 mGy, whereas planar tomograms provide an exposure of approximately 14 mGy. This difference is not clinically relevant.

In conclusion, this preliminary study demonstrates the feasibility of using CT/MPR techniques in the evaluation of patients with tracheal and main bronchial stenosis. The technique provides good anatomic detail but is more operator-dependent than conventional tomography. As additional experience accumulates, helical CT with MPR may replace conventional tomograms in the preoperative evaluation of patients with tracheal and bronchial stenosis.

	Footnotes

Top Footnotes Abstract Introduction Patients and Methods Results Comment References

 
Presented at the Thirty-first Annual Meeting of The Society of Thoracic Surgeons, Palm Springs, CA, Jan 30–Feb 1, 1995.

Address reprint requests to Dr Whyte, Section of Thoracic Surgery, The University of Michigan, 2120 Taubman, Box 0344, 1500 E Medical Center Dr, Ann Arbor, MI 48109.

	References

Top Footnotes Abstract Introduction Patients and Methods Results Comment References

 

1. Webber AL, ed. Symposium on the larynx and trachea. Radiol Clin N Am 1978;16(2).
2. Grillo HC. Benign and malignant diseases of the trachea. In: Shields TW, ed. General thoracic surgery, 3rd ed. Philadelphia: Lea & Febiger, 1989:667–79.
3. Newmark GM, Conces DJ, Kopecky KK. Spiral CT evaluation of the trachea and bronchi. J Comput Assist Tomogr 1994;18:522–4.
4. Schaefer CM, Prokop M, Zink C, Galanski M. Spiral CT of anastomotic complications after lung transplantation. Radiology 1993;189:263.
5. Quint LE, Whyte RI, Kazerooni EA, et al. Stenosis of the central airways: evaluation by helical CT with multiplanar reconstructions. Radiology 1995;194:871–7.[Abstract/Free Full Text]
6. Grillo HC. Primary reconstruction of airway after resection of subglottic laryngeal and upper tracheal stenosis. Ann Thorac Surg 1982;33:3–18.[Abstract]
7. Kwong JS, Adler BD, Padley SPG, Muller NL. Diagnosis of diseases of trachea and main bronchi: chest radiography vs CT. AJR 1993;161:519–22.[Abstract/Free Full Text]

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Richard I. Whyte Mark D. Iannettoni Mark B. Orringer Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Whyte, R. I. Articles by Orringer, M. B. Search for Related Content PubMed PubMed Citation Articles by Whyte, R. I. Articles by Orringer, M. B.