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The computed tomography mucous bronchogram sign
CT: THE JOURNAL
OF COMPUTED
TOMOGRAPHY
1988;
12:165-168
165
THE COMPUTED TOMOGRAPHY MUCOUS BRONCHOGRAM SIGN JOHN H. WOODRING,
MD
Mucous secretions filling the bronchial tree may be identified on computed tomography (CT) as Jowdensity, treelike branching structures within consolidated or collapsed lungs similar to air bronchoThese mucous bronchograms may occur grams. from mucoid impaction of the bronchi distal lo an obstructing lesion of the bronchus, most notably bronchogenic carcinoma, and from conditions that cause impaired mucociliary transport. In most cases, thin-section CT (5 mm) will demonstrate the presence or absence of an obstructing tumor involving the bronchus and will allow a correct assessment as to the cause of the mucous bronchograms; however, on occasion mucus within the central bronchi may result in a false-positive CT diagnosis of obslrucfing tumor. The demonstration of mucous bronchograms within a thoracic mass indicates that the mass is consolidated or collapsed pulmonary tissue and allows distinction from pleural disease. KEY WORDS:
Mucoid impaction of bronchi; Mucous plugging of bronchi; Computed tomography, lung and bronchus
Air bronchograms are a well-known sign of airspace disease that may be imaged by plain films, computed tomography (CT) studies, and ultrasonogof noncontrast related raphy (1, 2). Other types are less well known. Dorne (3) “bronchograms” demonstrated “fluid bronchograms” within consol-
From the Department of Diagnostic Radiology, University of Kentucky Medical Center, Lexington, Kentucky. Address reprint requests to: John H. Woodring, MD, Department of Diagnostic Radiology, University of Kentucky Medical Center, 800 Rose Street, Lexington, Kentucky 40536-0084. Received October 1987. 0 1988 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Avenue, New York, NY 10017 0149-936X/88/$3.50
idated lung by ultrasonography, and McAlister et al. (4) reported similar findings in bronchial atresia. Mucoid impaction of bronchi refers to an abnormally dilated segment of the bronchial tree that retains its normal connection to the distal tree (5, 6). This condition develops when mucus trapped in a bronchus leads to progressive bronchial dilatation. If the surrounding lung remains aerated by collateral ventilation, the impacted bronchi may be visualized by plain films or CT as branching V- or Yshaped opacities directed toward the hilum (5, 6). Mucoid impaction of bronchi has been reported to occur from a variety of causes of bronchial obstruction, most notably bronchial atresia and obstructing tumor, and from a variety of conditions without bronchial obstruction (5, 6). If the involved portion of lung is not aerated by collateral ventilation, pulmonary atelectasis ensues, obliterating the shadow of the impacted bronchi. This is by far the most common situation (6). Mucous plugging of the bronchi may also occur within normal caliber bronchi from a variety of common conditions that result in impaired mucociliary transport within the tracheobronchial tree (7). These conditions often result in pulmonary atelectasis; occasionally, visible mucous plugs within the bronchi may also be demonstrated radiographitally (8, 9). The CT demonstration of mucous material filling bronchi within a consolidated or collapsed lung has received little attention. It is the purpose of this paper to demonstrate the CT mucous bronchogram sign, to discuss its common causes, and to illustrate the clinical usefulness of this observation.
MATERIALS
AND
METHODS
The study group consisted of 50 consecutive patients with pulmonary collapse or consolidation evaluated by CT studies performed on commer-
166
WOODRING
CT: THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 12, NO. 2
cially available fourth-generation scanners. A lomm slice thickness was routinely employed; g-mm slice thickness was selectively used when there was a question of bronchial obstruction. A variety of window widths (300to 2000 HU) and window levels (-30 to -800 HU) were employed. The CT
scans were analyzed for the presence or absence of mucous bronchograms within the consolidated or collapsed lung, and the bronchi were evaluated for the presence or absence of an obstructing lesion as the cause. Ultimately the patients’ medical records were reviewed to ascertain the true cause of pulmonary abnormality. RESULT
Mucous bronchograms were visible as low-density, tubular branching structures radiating outward from the hilum in 12 cases (24%).When imaged along their long axis, mucous bronchograms were seen as linear branching structures. When imaged 90” to their long axis, mucous bronchograms were seen as clustered low-density circular structures within the consolidated or collapsed lung. In nine cases CT showed central bronchial narrowing or occlusion associated with a hilar mass (Figure 1A and B). In all nine obstructing tumor was confirmed by bronchoscopy or thoracotomy (bronchogenic carcinoma in eight and lymphoma in one). In three cases CT showed that the central bronchi were patent and that there was no hilar mass (Figure 2).Mucous
FIGURE 1. Mucous bronchograms distal to obstructing tumor. (A) Contrast-enhanced CT scan of left lower lobe collapse from non-Hodgkin’s lymphoma shows numerous low-density, linear, branching mucous bronchograms imaged along their long axis (arrowheads). Bubbles of air are also present within a few bronchi.
bronchograms in these three cases were caused by postoperative and posttraumatic impairment of mucociliary transport in one case each and bacterial pneumonia in one case.
In several cases (Figure 3A through C) demonstration of mucous bronchograms was helpful in confirming the pulmonary origin of the thoracic abnormality and in excluding a pleural or mediastinal lesion. DISCUSSION In this study the main causes of mucous bronchograms were retained mucus distal to an obstructing tumor and mucous plugs from abnormal mucociliary transport mechanisms. Naidich et al. (9) reported that mucous plugs usually could be distinguished from obstructing tumor within the bronchus on CT by the low-density nature of mucous plugs and by the fact that mucous material does not obliterate the image of the bronchial wall. In addi-
tion, a simple posttussive
view may show the tran-
FIGURE 1. (B) At the hilar level, a large, inhomogenous mass surrounds the left pulmonary artery and extends into the subcarinal area with complete occlusion of the distal left mainstem bronchus.
APRIL
1988
CT MUCOUS BRONCHOGRAMS
167
FIGURE 2. Mucous bronchograms from altered mucociliary transport mechanisms. Contrast-enhanced CT scan of left lower lobe collapse from blunt chest trauma shows that the left lower lobe bronchus is patent (arrow). Mucous bronchograms imaged 90” to their long axis are seen as a cluster of low-density circular structures within the contrast-enhanced parenchyma.
FIGURE 3. (B) Image obtained 1 cm higher shows more numerous mucous bronchograms; the bifurcation of one bronchus is noted [arrow).
FIGURE 3. Evaluation of an unexplained “left chest mass” found on routine chest radiograph. (A) Contrastenhanced CT scan shows a sharply circumscribed mass in a left paraspinal location. Mucous bronchograms imaged 90” to their long axis are identified as low-density circular structures within the “mass,” indicating that it is lung parenchyma.
FIGURE 3. (C) CT at the hilar level shows a central mass occluding the left lower lobe bronchus [arrow) resulting in lobar collapse. Bronchoscopy with a biopsy revealed squamous cell carcinoma.
168
CT: THE JOURNAL OF COMPUTED
WOODRING
sient nature of a mucous plug within the bronchus, effectively excluding an endobronchial tumor (8). However, false-positive diagnoses of obstructing tumor because of simple mucous plugs do occur (9). When mucous bronchograms are identified on CT, bronchial obstruction from tumor should be excluded by careful scrutiny of the central bronchi, frequently with 5-mm slice thickness. If central bronchial patency is documented and there is no evidence of a hilar mass, the presence of an obstructing tumor can be effectively excluded, suggesting benign conditions as the cause. If central bronchial narrowing, occlusion, or hilar mass is identified by CT, an obstructing tumor would be most likely, and bronchoscopy for tissue diagnosis should be performed. Bressler et al. (10) recently demonstrated that bolus contrast enhancement can opacify pulmonary vessels within intrathoracic abnormalities, confirming the pulmonary localization of the abnormality, and thus excluding pleural disease. It is apparent that the identification of mucous bronchograms within an intrathoracic abnormality may also serve to identify the abnormality correctly as a parenchyma1 disease process, thus excluding pleural or mediastinal disease (Figure 3).
CONTINUING MEDICAL EDUCATION QUESTIONS
Which of the following are causes of mucoid impaction of bronchi? a. Bronchial atresia. b. Obstructing bronchial tumors. c. Both of the above. Which of the following statements concerning the plain film appearance of mucoid impaction of bronchi are correct? a. If the surrounding lung remains aerated, mucoid impaction may be visualized as branching V- or Yshaped opacities. b. When the lung becomes consolidated or collapsed, mucoid impaction of bronchi is no longer visible. C. Mucoid impaction of bronchi usually is visible within collapsed lung parenchyma on chest radiographs. d. The exclusion of obstructing tumors as the cause of mucoid impaction is easily accomplished by the chest radiograph. e. a and b above. 3.
Which of the following statements concerning mucous bronchograms identified bv CT are correct? a. Mu&us bronchograms- may be visualized within collapsed or consolidated lung parenchyma by CT. of mucous bronchograms within b. The identification an intrathoracic abnormality indicates that the abnormality is collapsed or consolidated lung parenchyma. C. When imaged along their long axis, mucous bronchograms are seen as low-density, linear, branching structures. d. When imaged 90” to their long axis, mucous bronchograms are seen as clustered, low-density, circular structures. e. All of the above.
4.
Which of the following statements concerning intrabronchial mucus are correct? a. CT may be very useful in demonstrating an obstructing tumor as the cause. b. CT demonstration of patent central bronchi and absence of a central mass effectively excludes an obstructing tumor as the cause. C. Mucous plugs from impaired mucociliary transport mechanisms may occasionally produce false-positive diagnoses of endobronchial tumor. d. A posttussive view may show the transient nature of a mucous plug, thereby demonstrating its true nature. e. All of the above.
1. Osborne DR. The lung: Segmental
anatomy and non-neoplastic diseases. In: Godwin JD, ed. Computed tomography of the chest. Philadelphia: Lippincott, 1984:160-86.
2. Weinberg B, Diakoumakis EE, Kass EG, Seife B, Zvi ZB. The air bronchogram: Sonographic demonstration. Am J Roentgenol 1986;147:593-5. 3. Dorne HL. Differentiation of pulmonary parenchymal consolidation from pleural disease using the sonographic fluid bronchogram. Radiology 1986;158:41-2.
5. Woodring JH, Bernardy MO, Loh FK. Mucoid impaction bronchi. Australas Radio1 1985;29:234-9. 6. Felson B. Mucoid impaction mental bronchial obstruction.
of
(inspissated secretions) in segRadiology 1979;133:9-16.
7. Gamsu G, Singer MM, Vincent HH, Berry S, Nadel JA. Postoperative impairment of mucous transport in the lung. Am Rev Respir Dis 1976;114:673-9. 8. Karasick D, Karasick S, Lally JF. Mucoid pseudotumors of the tracheobronchial tree in two cases. Am J Roentgen01 1979;132:459-60. 9. Naidich DP, McCauley DI, Khouri NF, et al. Computed tomography of lobar collapse: 1. Endobronchial obstruction. J Comput Assist Tomogr 1983:7:745-57. 10. Bressler EL, Francis IR, Glazer GM, Gross BH. BoIus contrast
VOL. 12, NO. 2
medium enhancement for distinguishing pleural from parenchymal lung disease: CT features. J Comput Assist Tomogr 1987;11:436-40.
REFERENCES
4. McAlister WH, Wright JR Jr, Crane JP. Main-stem bronchial atresia: Intrauterine sonographic diagnosis. Am J Roentgen01 1987;148:364-6.
TOMOGRAPHY
OF COMPUTED
TOMOGRAPHY
1988;
12:165-168
165
THE COMPUTED TOMOGRAPHY MUCOUS BRONCHOGRAM SIGN JOHN H. WOODRING,
MD
Mucous secretions filling the bronchial tree may be identified on computed tomography (CT) as Jowdensity, treelike branching structures within consolidated or collapsed lungs similar to air bronchoThese mucous bronchograms may occur grams. from mucoid impaction of the bronchi distal lo an obstructing lesion of the bronchus, most notably bronchogenic carcinoma, and from conditions that cause impaired mucociliary transport. In most cases, thin-section CT (5 mm) will demonstrate the presence or absence of an obstructing tumor involving the bronchus and will allow a correct assessment as to the cause of the mucous bronchograms; however, on occasion mucus within the central bronchi may result in a false-positive CT diagnosis of obslrucfing tumor. The demonstration of mucous bronchograms within a thoracic mass indicates that the mass is consolidated or collapsed pulmonary tissue and allows distinction from pleural disease. KEY WORDS:
Mucoid impaction of bronchi; Mucous plugging of bronchi; Computed tomography, lung and bronchus
Air bronchograms are a well-known sign of airspace disease that may be imaged by plain films, computed tomography (CT) studies, and ultrasonogof noncontrast related raphy (1, 2). Other types are less well known. Dorne (3) “bronchograms” demonstrated “fluid bronchograms” within consol-
From the Department of Diagnostic Radiology, University of Kentucky Medical Center, Lexington, Kentucky. Address reprint requests to: John H. Woodring, MD, Department of Diagnostic Radiology, University of Kentucky Medical Center, 800 Rose Street, Lexington, Kentucky 40536-0084. Received October 1987. 0 1988 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Avenue, New York, NY 10017 0149-936X/88/$3.50
idated lung by ultrasonography, and McAlister et al. (4) reported similar findings in bronchial atresia. Mucoid impaction of bronchi refers to an abnormally dilated segment of the bronchial tree that retains its normal connection to the distal tree (5, 6). This condition develops when mucus trapped in a bronchus leads to progressive bronchial dilatation. If the surrounding lung remains aerated by collateral ventilation, the impacted bronchi may be visualized by plain films or CT as branching V- or Yshaped opacities directed toward the hilum (5, 6). Mucoid impaction of bronchi has been reported to occur from a variety of causes of bronchial obstruction, most notably bronchial atresia and obstructing tumor, and from a variety of conditions without bronchial obstruction (5, 6). If the involved portion of lung is not aerated by collateral ventilation, pulmonary atelectasis ensues, obliterating the shadow of the impacted bronchi. This is by far the most common situation (6). Mucous plugging of the bronchi may also occur within normal caliber bronchi from a variety of common conditions that result in impaired mucociliary transport within the tracheobronchial tree (7). These conditions often result in pulmonary atelectasis; occasionally, visible mucous plugs within the bronchi may also be demonstrated radiographitally (8, 9). The CT demonstration of mucous material filling bronchi within a consolidated or collapsed lung has received little attention. It is the purpose of this paper to demonstrate the CT mucous bronchogram sign, to discuss its common causes, and to illustrate the clinical usefulness of this observation.
MATERIALS
AND
METHODS
The study group consisted of 50 consecutive patients with pulmonary collapse or consolidation evaluated by CT studies performed on commer-
166
WOODRING
CT: THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 12, NO. 2
cially available fourth-generation scanners. A lomm slice thickness was routinely employed; g-mm slice thickness was selectively used when there was a question of bronchial obstruction. A variety of window widths (300to 2000 HU) and window levels (-30 to -800 HU) were employed. The CT
scans were analyzed for the presence or absence of mucous bronchograms within the consolidated or collapsed lung, and the bronchi were evaluated for the presence or absence of an obstructing lesion as the cause. Ultimately the patients’ medical records were reviewed to ascertain the true cause of pulmonary abnormality. RESULT
Mucous bronchograms were visible as low-density, tubular branching structures radiating outward from the hilum in 12 cases (24%).When imaged along their long axis, mucous bronchograms were seen as linear branching structures. When imaged 90” to their long axis, mucous bronchograms were seen as clustered low-density circular structures within the consolidated or collapsed lung. In nine cases CT showed central bronchial narrowing or occlusion associated with a hilar mass (Figure 1A and B). In all nine obstructing tumor was confirmed by bronchoscopy or thoracotomy (bronchogenic carcinoma in eight and lymphoma in one). In three cases CT showed that the central bronchi were patent and that there was no hilar mass (Figure 2).Mucous
FIGURE 1. Mucous bronchograms distal to obstructing tumor. (A) Contrast-enhanced CT scan of left lower lobe collapse from non-Hodgkin’s lymphoma shows numerous low-density, linear, branching mucous bronchograms imaged along their long axis (arrowheads). Bubbles of air are also present within a few bronchi.
bronchograms in these three cases were caused by postoperative and posttraumatic impairment of mucociliary transport in one case each and bacterial pneumonia in one case.
In several cases (Figure 3A through C) demonstration of mucous bronchograms was helpful in confirming the pulmonary origin of the thoracic abnormality and in excluding a pleural or mediastinal lesion. DISCUSSION In this study the main causes of mucous bronchograms were retained mucus distal to an obstructing tumor and mucous plugs from abnormal mucociliary transport mechanisms. Naidich et al. (9) reported that mucous plugs usually could be distinguished from obstructing tumor within the bronchus on CT by the low-density nature of mucous plugs and by the fact that mucous material does not obliterate the image of the bronchial wall. In addi-
tion, a simple posttussive
view may show the tran-
FIGURE 1. (B) At the hilar level, a large, inhomogenous mass surrounds the left pulmonary artery and extends into the subcarinal area with complete occlusion of the distal left mainstem bronchus.
APRIL
1988
CT MUCOUS BRONCHOGRAMS
167
FIGURE 2. Mucous bronchograms from altered mucociliary transport mechanisms. Contrast-enhanced CT scan of left lower lobe collapse from blunt chest trauma shows that the left lower lobe bronchus is patent (arrow). Mucous bronchograms imaged 90” to their long axis are seen as a cluster of low-density circular structures within the contrast-enhanced parenchyma.
FIGURE 3. (B) Image obtained 1 cm higher shows more numerous mucous bronchograms; the bifurcation of one bronchus is noted [arrow).
FIGURE 3. Evaluation of an unexplained “left chest mass” found on routine chest radiograph. (A) Contrastenhanced CT scan shows a sharply circumscribed mass in a left paraspinal location. Mucous bronchograms imaged 90” to their long axis are identified as low-density circular structures within the “mass,” indicating that it is lung parenchyma.
FIGURE 3. (C) CT at the hilar level shows a central mass occluding the left lower lobe bronchus [arrow) resulting in lobar collapse. Bronchoscopy with a biopsy revealed squamous cell carcinoma.
168
CT: THE JOURNAL OF COMPUTED
WOODRING
sient nature of a mucous plug within the bronchus, effectively excluding an endobronchial tumor (8). However, false-positive diagnoses of obstructing tumor because of simple mucous plugs do occur (9). When mucous bronchograms are identified on CT, bronchial obstruction from tumor should be excluded by careful scrutiny of the central bronchi, frequently with 5-mm slice thickness. If central bronchial patency is documented and there is no evidence of a hilar mass, the presence of an obstructing tumor can be effectively excluded, suggesting benign conditions as the cause. If central bronchial narrowing, occlusion, or hilar mass is identified by CT, an obstructing tumor would be most likely, and bronchoscopy for tissue diagnosis should be performed. Bressler et al. (10) recently demonstrated that bolus contrast enhancement can opacify pulmonary vessels within intrathoracic abnormalities, confirming the pulmonary localization of the abnormality, and thus excluding pleural disease. It is apparent that the identification of mucous bronchograms within an intrathoracic abnormality may also serve to identify the abnormality correctly as a parenchyma1 disease process, thus excluding pleural or mediastinal disease (Figure 3).
CONTINUING MEDICAL EDUCATION QUESTIONS
Which of the following are causes of mucoid impaction of bronchi? a. Bronchial atresia. b. Obstructing bronchial tumors. c. Both of the above. Which of the following statements concerning the plain film appearance of mucoid impaction of bronchi are correct? a. If the surrounding lung remains aerated, mucoid impaction may be visualized as branching V- or Yshaped opacities. b. When the lung becomes consolidated or collapsed, mucoid impaction of bronchi is no longer visible. C. Mucoid impaction of bronchi usually is visible within collapsed lung parenchyma on chest radiographs. d. The exclusion of obstructing tumors as the cause of mucoid impaction is easily accomplished by the chest radiograph. e. a and b above. 3.
Which of the following statements concerning mucous bronchograms identified bv CT are correct? a. Mu&us bronchograms- may be visualized within collapsed or consolidated lung parenchyma by CT. of mucous bronchograms within b. The identification an intrathoracic abnormality indicates that the abnormality is collapsed or consolidated lung parenchyma. C. When imaged along their long axis, mucous bronchograms are seen as low-density, linear, branching structures. d. When imaged 90” to their long axis, mucous bronchograms are seen as clustered, low-density, circular structures. e. All of the above.
4.
Which of the following statements concerning intrabronchial mucus are correct? a. CT may be very useful in demonstrating an obstructing tumor as the cause. b. CT demonstration of patent central bronchi and absence of a central mass effectively excludes an obstructing tumor as the cause. C. Mucous plugs from impaired mucociliary transport mechanisms may occasionally produce false-positive diagnoses of endobronchial tumor. d. A posttussive view may show the transient nature of a mucous plug, thereby demonstrating its true nature. e. All of the above.
1. Osborne DR. The lung: Segmental
anatomy and non-neoplastic diseases. In: Godwin JD, ed. Computed tomography of the chest. Philadelphia: Lippincott, 1984:160-86.
2. Weinberg B, Diakoumakis EE, Kass EG, Seife B, Zvi ZB. The air bronchogram: Sonographic demonstration. Am J Roentgenol 1986;147:593-5. 3. Dorne HL. Differentiation of pulmonary parenchymal consolidation from pleural disease using the sonographic fluid bronchogram. Radiology 1986;158:41-2.
5. Woodring JH, Bernardy MO, Loh FK. Mucoid impaction bronchi. Australas Radio1 1985;29:234-9. 6. Felson B. Mucoid impaction mental bronchial obstruction.
of
(inspissated secretions) in segRadiology 1979;133:9-16.
7. Gamsu G, Singer MM, Vincent HH, Berry S, Nadel JA. Postoperative impairment of mucous transport in the lung. Am Rev Respir Dis 1976;114:673-9. 8. Karasick D, Karasick S, Lally JF. Mucoid pseudotumors of the tracheobronchial tree in two cases. Am J Roentgen01 1979;132:459-60. 9. Naidich DP, McCauley DI, Khouri NF, et al. Computed tomography of lobar collapse: 1. Endobronchial obstruction. J Comput Assist Tomogr 1983:7:745-57. 10. Bressler EL, Francis IR, Glazer GM, Gross BH. BoIus contrast
VOL. 12, NO. 2
medium enhancement for distinguishing pleural from parenchymal lung disease: CT features. J Comput Assist Tomogr 1987;11:436-40.
REFERENCES
4. McAlister WH, Wright JR Jr, Crane JP. Main-stem bronchial atresia: Intrauterine sonographic diagnosis. Am J Roentgen01 1987;148:364-6.
TOMOGRAPHY