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Computed tomographic characteristics of pleural empyema
JOURNAL OF COMPUTED
TOMOGRAPHY
1983;7:179-182
COMPUTED TOMOGRAPHIC CHARACTERISTICtil OF PLEURAL EMPYEMA MYUNG
S. SHIN
AND KANG-JEY
HO
The computed tomographic characteristics of the pleural empyema were illustrated in three patients. A typical empyema is characterized by lower thorax location, oblong or round contour in crosssection, homogeneous content with or without air spaces or air-fluid levels, regularly thin wall opposing the chest wall [a rim sign), irregularly thick wall opposing the lung parenchyma, and smooth inner and outer margins. By application of such computed tomographic criteria, a pleural empyema can lung abhe readily distinguished from a peripheral
can delay the diagnostic and therapeutic thoracocentesis for empyema from 1 to 12 days (6) Since the introduction of the computed tomography (CT), we have found it extremely useful in the diagnosis of pleural empyema. We have seliected the following three rather classical cases of pleural empyema to illustrate its computed tomographic characteristics. CASE REPORTS
scess.
Case 1
KEY WORDS:
A &?-year-old liver cirrhosis
Computed
tomography;
Empyema;
Pleura; pus; Abscess
Pleural empyema or a collection of purulent fluid in the pleural space should be distinguished from lung abscess because the treatment of choice for an empyema is evacuation of its purulent contents by closed or open drainage, and the treatment for a lung abscess is antibiotic therapy with postural drainage (l-4). The differential diagnosis of these two lesions by conventional radiography or ultrasonography is difficult, if not impossible, particularly when an abscess is located close to the chest walls (5-10). It has been shown that such difficulty
From the Departments of Diagnostic Radiology and Pathology, School of Medicine, University of Alabama in Birmingham; and Veterans Administration Hospital, Birmingham, Alabama. Address reprint requests to: M. S. Shin, MD, Department of Diagnostic Radiology, University of Alabama Hospitals, Birmingham, Alabama 35233. Accepted July 1982 0 1983by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., New York, NY 10017 0149-936x1831020179-04$3.00
male chronic alcoholic with known developed intermitltent fever for 3 to 4 weeks. Dullness to percussion and increased breath sound were noted on the right lower thorax. The chest roentgenogram revealed a homogeneous opacity in the right lower lobe with small pleural effusion, suggestive of a pneumonic process (Figure 1A). Initial thoracocentesis obtained only minimal fluid. A CT scan was done, discljosing a large empyema in the posterior lower aspects of the right thorax and an area of pneumonic consolidation in the right middle lobe (Figure l$). This empyema had a round contour on CT crosasection. The portion of the wall of empyema cavity made up by the parietal pleura formed a thin rim: of uniform thickness (a rim sign], whereas the pdrtion made up by the visceral pleura was much thicker. Apparently, atelectasis of the lung due to compression by the expanding empyema contributed to this thickened portion of the wall because air bronchogram could be seen leading to this area (Figure 1B). The inner margin of the cavity was rather smooth and its content quite homogeneous with a CT number of 0 to 15 Hounsfield units (HU). The empyema was proved by subsequent thoracocentesis, followed by chest tube drainage. The culture df the content grew Escherichia coli.
180
SHIN
AND
HO
THE JOURNAL
OF COMPUTED
TOMOGRAPHY
VOL.
7 NO.
2
FIGURE 1. Case 1. A. Chest roentgenogram revealing a homogeneous opacity in the right lower lobe with small pleural effusion suggestive of a pneumonic process. B. Computed tomography scan showing a large round empyema in the right lower posterior thorax.
pleura (Figure 2B). The content of the empyema cavity was homogeneous in density with a CT number of 0 to 20 HU. Multiloculated air spaces of various sizes and shapes with air-fluid levels were present in the cavity. Thoracotomy revealed a partially organized, multiloculated empyema which was resected and drained. Culture of the content grew group A, (3-hemolytic streptococcus.
Case
Case
2
A 15-year-old boy developed left lower lobe pneumonia after incidental aspiration of a piece of sea oat. Despite antibiotic therapy he continued to have intermittent fever for 4 weeks. Chest roentgenogram revealed a multiloculated lesion with air-fluid levels suggestive of lung abscesses (Figure 2A). Bronchoscopy, however, showed neither purulent material nor bronchial obstruction. A CT scan was then done. A large empyema was found extending from the superior segment of the left lower lobe to the diaphragm. The CT cross-section of lesion showed a round contour with a rim of uniformly thickened parietal pleura against the chest wall and the spine (a rim sign) and a thicker wall along the visceral
3
A 31-year-old woman developed right lower lobe pneumonia manifested by chest pain, fever, chillness, and shortness of breath. Throat culture grew group A, (3-hemolytic streptococcus and the antistreptolysin-0 titer was 1200 Todd units. Chest roentgenogram revealed an inhomogeneous opacity in the middle and lower lobe of the right lung, compatible with pneumonia (Figure 3A). Despite antibiotic therapy for 10 days she continued to have fever and the lung lesions did not dissolve. A CT scan showed a large empyema in the posterior lower right thorax (Figure 3B). The empyema was made up by two parts, one large oval cavity in the lateroposterior chest and one smaller triangular portion opposing the spine. The cavity wall was rather thin in the area made up of the parietal pleura and irregularly thickened in the area composed of visceral
MAY
1983
CT IN PLEURAL
EMPYEMA
181
derlying lung. The pneumonia was brought under control in cases 1 and 2, but the empyema did not dissolve by antibiotic therapy alone. Empyema requires external drainage for successful treatment (2-4). It is therefore important to recognize an empyema early and to distinguish it from a lung abscess. In this aspect CT is much superior to the conventional roentgenography, as demonstrated in the present three cases.
FIGURE 3. Case 3. A. Chest roentgenogram revealing an inhomogeneous opacity in the right middle and lower lobes, compatable with a pneumonic process. B. Computed tomography scan showing an early empyema conforming to the shape of the pleural space in the right lower posterior thorax.
FIGURE 2. Case 2. A. Chest roentgenogram revealing a multloculated lesion with air-fluid levels suggestive of lung abscesses. B. Computed tomography scan showing a round pleural empyema in the left lower posterior thorax with air-fluid level. pleura and atelectatic lung. The inner margin was smooth and the content homogeneous. The CT number was 0 to 10 HU. About 200 ml of purulent exudate was drained during a CT-guided thoracocentesis. DISCUSSION As in the great majority of cases, the primary condition for developing the pleural empyema in our three patients was a pneumonic process in the un-
182
SHIN AND HO
The general characteristics of the CT image of a pleural empyema are summarized as follows:
1. A pleural
empyema in its early stage of development usually has an oblong and flattened contour (case 3), roughly confirming to the shape of the pleural space. In a later stage when the pressure in the cavity has built up, it attains a more or less round contour in the CT cross-section (cases 1 and 2). 2. An empyema is most commonly located in the lower thorax, directly against the chest wall. 3. The content of the empyema cavity is radiographically homogeneous with a narrow attenuation range. The CT number ranges from 0 to 20 HU. 4. Air or air-fluid levels may be present in an empyema cavity. Multiloculated air spaces with or without fluid levels can be seen in an empyema undergoing organization (case 2). 5. The inner margin of the cavity is almost invariably smooth. 6. The parietal pleura that forms part of the wall of an empyema cavity may be slightly and uniformly thickened. Such a thin rim of uniform thickness opposing the chest wall, a rim sign, is quite characteristic for an empyema. 7. The portion of the empyema wall opposing the lung parenchyma is, on the other hand, much thicker, and often irregularly thickened. This portion includes not only the visceral pleura but also the compressed atelectatic lung parenchyma. is usually 8. The outer margin of an empyema sharply demarcated unless the pneumonic process remains active in the adjacent lung tissue. The differentiation between pleural empyemas and peripheral pulmonary abscesses by CT has been evaluated by Baber et al (11). They emphasized in their illustration that the cavity shape can be changed with a change of patient position in empyema but not in lung abscess. Our own experience indicates that the conventional CT scan is sufficient to distinguish an empyema from a peripheral lung abscess. As a rule, a lung abscess is characterized by its irregular shape and nonuniformly thickened wall with undulated, rough inner margin and ill-
THE JOURNAL OF COMPUTED TOMOGRAPHY
VOL. 7 NO. 2
defined outer margin. By application of the above characteristics and criteria, a pleural empyema can be readily distinguished from a lung abscess by CT scan, assuring adequate treatment and early recovery.
REFERENCES 1. Schweppe
HI, Knowles JH, Kane L: Lung abscess. N Engl J Med 243:1039-1043, 1961
2. Clagett OT: Changing
of pleural empyema.
aspects of the etiology and treatment Surg Clin North Am 58:863-866, 1973
3. Weese WC, Shindler
ER, Smith IM, et al: Empyema of the thorax then and now. Arch Intern Med 131:516-520, 1973
4. Alexander
JC Jr, Wolfe WG: Lung abscess and empyema the thorax. Surg Clin North Am 60:835-849, 1980
5. Friedman
chopleural
PJ, Hellekant GAG: Radiologic recognition fistula. Radiology 124:289-295, 1977
of
of bron-
6. Schachter
EN, Kreisman H, Putman C: Diagnostic problems in suppurative lung disease. Arch Intern Med 136:167-171, 1976
7. Landay MJ, Conrad
on ultrasonography.
MR: Lung abscess mimicking empyema Am J Roentgen01 133:731-734, 1979
8. Laing FC, Filly RA: Problems
nography 1978
for the pleural
in the application of ultrasoopacities. Radiology 126:211-214,
9. Hirsch
HJ. Carter SJ, Chikos PM, Colacurcio C: Ultrasonic evaluation of radiographic opacities of the chest. Am J Roentgen01 130:1153-1156, 1978
10. Shin
MS, Grey PW Jr: Pittfalls in ultrasonic detection pleural fluid. J Clin Ultrasound 6:421-423, 1978
of
11. Baber CE, Hedlund
LW, Oddson TA, et al: Differentiating empyemas and peripheral plumonary abscesses: The value of computed tomography. Radiology 135:755-758, 1980
CONTINUING MEDICAL EDUCATION QUESTIONS (CT FINDINGS OF PLEURAL FMPYEMA)
True or False
Distinction between the lung abscess and pleural empyema is relatively easy by conventional chest roentgenogram and ultrasonographic study, and CT is indicated only in difficult patients. CT findings of pleural empyema are oblong shape, smooth inner margin of the cavity with or without air fluid level, and attenuation numbers O-20 HU, directly against the chest wall. The parietal pleura which forms part of the wall of empyema cavity is usually undulated and very thick in appearance, whereas the empyema wall opposing the lung parenchyma is usually smooth in appearance.
TOMOGRAPHY
1983;7:179-182
COMPUTED TOMOGRAPHIC CHARACTERISTICtil OF PLEURAL EMPYEMA MYUNG
S. SHIN
AND KANG-JEY
HO
The computed tomographic characteristics of the pleural empyema were illustrated in three patients. A typical empyema is characterized by lower thorax location, oblong or round contour in crosssection, homogeneous content with or without air spaces or air-fluid levels, regularly thin wall opposing the chest wall [a rim sign), irregularly thick wall opposing the lung parenchyma, and smooth inner and outer margins. By application of such computed tomographic criteria, a pleural empyema can lung abhe readily distinguished from a peripheral
can delay the diagnostic and therapeutic thoracocentesis for empyema from 1 to 12 days (6) Since the introduction of the computed tomography (CT), we have found it extremely useful in the diagnosis of pleural empyema. We have seliected the following three rather classical cases of pleural empyema to illustrate its computed tomographic characteristics. CASE REPORTS
scess.
Case 1
KEY WORDS:
A &?-year-old liver cirrhosis
Computed
tomography;
Empyema;
Pleura; pus; Abscess
Pleural empyema or a collection of purulent fluid in the pleural space should be distinguished from lung abscess because the treatment of choice for an empyema is evacuation of its purulent contents by closed or open drainage, and the treatment for a lung abscess is antibiotic therapy with postural drainage (l-4). The differential diagnosis of these two lesions by conventional radiography or ultrasonography is difficult, if not impossible, particularly when an abscess is located close to the chest walls (5-10). It has been shown that such difficulty
From the Departments of Diagnostic Radiology and Pathology, School of Medicine, University of Alabama in Birmingham; and Veterans Administration Hospital, Birmingham, Alabama. Address reprint requests to: M. S. Shin, MD, Department of Diagnostic Radiology, University of Alabama Hospitals, Birmingham, Alabama 35233. Accepted July 1982 0 1983by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., New York, NY 10017 0149-936x1831020179-04$3.00
male chronic alcoholic with known developed intermitltent fever for 3 to 4 weeks. Dullness to percussion and increased breath sound were noted on the right lower thorax. The chest roentgenogram revealed a homogeneous opacity in the right lower lobe with small pleural effusion, suggestive of a pneumonic process (Figure 1A). Initial thoracocentesis obtained only minimal fluid. A CT scan was done, discljosing a large empyema in the posterior lower aspects of the right thorax and an area of pneumonic consolidation in the right middle lobe (Figure l$). This empyema had a round contour on CT crosasection. The portion of the wall of empyema cavity made up by the parietal pleura formed a thin rim: of uniform thickness (a rim sign], whereas the pdrtion made up by the visceral pleura was much thicker. Apparently, atelectasis of the lung due to compression by the expanding empyema contributed to this thickened portion of the wall because air bronchogram could be seen leading to this area (Figure 1B). The inner margin of the cavity was rather smooth and its content quite homogeneous with a CT number of 0 to 15 Hounsfield units (HU). The empyema was proved by subsequent thoracocentesis, followed by chest tube drainage. The culture df the content grew Escherichia coli.
180
SHIN
AND
HO
THE JOURNAL
OF COMPUTED
TOMOGRAPHY
VOL.
7 NO.
2
FIGURE 1. Case 1. A. Chest roentgenogram revealing a homogeneous opacity in the right lower lobe with small pleural effusion suggestive of a pneumonic process. B. Computed tomography scan showing a large round empyema in the right lower posterior thorax.
pleura (Figure 2B). The content of the empyema cavity was homogeneous in density with a CT number of 0 to 20 HU. Multiloculated air spaces of various sizes and shapes with air-fluid levels were present in the cavity. Thoracotomy revealed a partially organized, multiloculated empyema which was resected and drained. Culture of the content grew group A, (3-hemolytic streptococcus.
Case
Case
2
A 15-year-old boy developed left lower lobe pneumonia after incidental aspiration of a piece of sea oat. Despite antibiotic therapy he continued to have intermittent fever for 4 weeks. Chest roentgenogram revealed a multiloculated lesion with air-fluid levels suggestive of lung abscesses (Figure 2A). Bronchoscopy, however, showed neither purulent material nor bronchial obstruction. A CT scan was then done. A large empyema was found extending from the superior segment of the left lower lobe to the diaphragm. The CT cross-section of lesion showed a round contour with a rim of uniformly thickened parietal pleura against the chest wall and the spine (a rim sign) and a thicker wall along the visceral
3
A 31-year-old woman developed right lower lobe pneumonia manifested by chest pain, fever, chillness, and shortness of breath. Throat culture grew group A, (3-hemolytic streptococcus and the antistreptolysin-0 titer was 1200 Todd units. Chest roentgenogram revealed an inhomogeneous opacity in the middle and lower lobe of the right lung, compatible with pneumonia (Figure 3A). Despite antibiotic therapy for 10 days she continued to have fever and the lung lesions did not dissolve. A CT scan showed a large empyema in the posterior lower right thorax (Figure 3B). The empyema was made up by two parts, one large oval cavity in the lateroposterior chest and one smaller triangular portion opposing the spine. The cavity wall was rather thin in the area made up of the parietal pleura and irregularly thickened in the area composed of visceral
MAY
1983
CT IN PLEURAL
EMPYEMA
181
derlying lung. The pneumonia was brought under control in cases 1 and 2, but the empyema did not dissolve by antibiotic therapy alone. Empyema requires external drainage for successful treatment (2-4). It is therefore important to recognize an empyema early and to distinguish it from a lung abscess. In this aspect CT is much superior to the conventional roentgenography, as demonstrated in the present three cases.
FIGURE 3. Case 3. A. Chest roentgenogram revealing an inhomogeneous opacity in the right middle and lower lobes, compatable with a pneumonic process. B. Computed tomography scan showing an early empyema conforming to the shape of the pleural space in the right lower posterior thorax.
FIGURE 2. Case 2. A. Chest roentgenogram revealing a multloculated lesion with air-fluid levels suggestive of lung abscesses. B. Computed tomography scan showing a round pleural empyema in the left lower posterior thorax with air-fluid level. pleura and atelectatic lung. The inner margin was smooth and the content homogeneous. The CT number was 0 to 10 HU. About 200 ml of purulent exudate was drained during a CT-guided thoracocentesis. DISCUSSION As in the great majority of cases, the primary condition for developing the pleural empyema in our three patients was a pneumonic process in the un-
182
SHIN AND HO
The general characteristics of the CT image of a pleural empyema are summarized as follows:
1. A pleural
empyema in its early stage of development usually has an oblong and flattened contour (case 3), roughly confirming to the shape of the pleural space. In a later stage when the pressure in the cavity has built up, it attains a more or less round contour in the CT cross-section (cases 1 and 2). 2. An empyema is most commonly located in the lower thorax, directly against the chest wall. 3. The content of the empyema cavity is radiographically homogeneous with a narrow attenuation range. The CT number ranges from 0 to 20 HU. 4. Air or air-fluid levels may be present in an empyema cavity. Multiloculated air spaces with or without fluid levels can be seen in an empyema undergoing organization (case 2). 5. The inner margin of the cavity is almost invariably smooth. 6. The parietal pleura that forms part of the wall of an empyema cavity may be slightly and uniformly thickened. Such a thin rim of uniform thickness opposing the chest wall, a rim sign, is quite characteristic for an empyema. 7. The portion of the empyema wall opposing the lung parenchyma is, on the other hand, much thicker, and often irregularly thickened. This portion includes not only the visceral pleura but also the compressed atelectatic lung parenchyma. is usually 8. The outer margin of an empyema sharply demarcated unless the pneumonic process remains active in the adjacent lung tissue. The differentiation between pleural empyemas and peripheral pulmonary abscesses by CT has been evaluated by Baber et al (11). They emphasized in their illustration that the cavity shape can be changed with a change of patient position in empyema but not in lung abscess. Our own experience indicates that the conventional CT scan is sufficient to distinguish an empyema from a peripheral lung abscess. As a rule, a lung abscess is characterized by its irregular shape and nonuniformly thickened wall with undulated, rough inner margin and ill-
THE JOURNAL OF COMPUTED TOMOGRAPHY
VOL. 7 NO. 2
defined outer margin. By application of the above characteristics and criteria, a pleural empyema can be readily distinguished from a lung abscess by CT scan, assuring adequate treatment and early recovery.
REFERENCES 1. Schweppe
HI, Knowles JH, Kane L: Lung abscess. N Engl J Med 243:1039-1043, 1961
2. Clagett OT: Changing
of pleural empyema.
aspects of the etiology and treatment Surg Clin North Am 58:863-866, 1973
3. Weese WC, Shindler
ER, Smith IM, et al: Empyema of the thorax then and now. Arch Intern Med 131:516-520, 1973
4. Alexander
JC Jr, Wolfe WG: Lung abscess and empyema the thorax. Surg Clin North Am 60:835-849, 1980
5. Friedman
chopleural
PJ, Hellekant GAG: Radiologic recognition fistula. Radiology 124:289-295, 1977
of
of bron-
6. Schachter
EN, Kreisman H, Putman C: Diagnostic problems in suppurative lung disease. Arch Intern Med 136:167-171, 1976
7. Landay MJ, Conrad
on ultrasonography.
MR: Lung abscess mimicking empyema Am J Roentgen01 133:731-734, 1979
8. Laing FC, Filly RA: Problems
nography 1978
for the pleural
in the application of ultrasoopacities. Radiology 126:211-214,
9. Hirsch
HJ. Carter SJ, Chikos PM, Colacurcio C: Ultrasonic evaluation of radiographic opacities of the chest. Am J Roentgen01 130:1153-1156, 1978
10. Shin
MS, Grey PW Jr: Pittfalls in ultrasonic detection pleural fluid. J Clin Ultrasound 6:421-423, 1978
of
11. Baber CE, Hedlund
LW, Oddson TA, et al: Differentiating empyemas and peripheral plumonary abscesses: The value of computed tomography. Radiology 135:755-758, 1980
CONTINUING MEDICAL EDUCATION QUESTIONS (CT FINDINGS OF PLEURAL FMPYEMA)
True or False
Distinction between the lung abscess and pleural empyema is relatively easy by conventional chest roentgenogram and ultrasonographic study, and CT is indicated only in difficult patients. CT findings of pleural empyema are oblong shape, smooth inner margin of the cavity with or without air fluid level, and attenuation numbers O-20 HU, directly against the chest wall. The parietal pleura which forms part of the wall of empyema cavity is usually undulated and very thick in appearance, whereas the empyema wall opposing the lung parenchyma is usually smooth in appearance.