(Chest. 2001;120:725-729.)
© 2001
American College of Chest Physicians
CT Assessment of Subtypes of Pulmonary Emphysema in Smokers*
Katashi Satoh, MD;
Takuya Kobayashi, MD
;
Takahiko Misao, MD;
Yoshimi Hitani, MD;
Yuka Yamamoto, MD;
Yoshihiro Nishiyama, MD and
Motoomi Ohkawa, MD
*
From the Department of Radiology (Drs. Satoh, Kobayashi, Yamamoto, Nishiyama, and Ohkawa), Kagawa Medical University, Kagawa, Japan; the Department of Respiratory Disease (Dr. Misao), Kagawa Prefectural Cancer Detecting Center, Kagawa, Japan; and the Department of Surgery (Dr. Hitani), Numakuma Hospital, Hiroshima, Japan.
Presently at the Department of Radiology, KKR Takamatsu Hospital,
Kagawa, Japan.
Correspondence to: Katashi Satoh, MD, 1750–1 Ikenobe, Miki-cho, Kita-gun, Kagawa 761-0793, Japan; e-mail: satoh{at}kms.ac.jp
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Abstract
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Objective: To determine the incidence of subtypes of
pulmonary emphysema (PE) identified by CT imaging in male patients who
have a significant smoking history.
Patients and
setting: We reviewed 945 subjects (619 men and 326 women) who had
undergone CT scanning. However, only the data for male subjects were
analyzed due to there being too few female subjects. The male subjects
were divided into the following two age groups: group A (age, 
50
years) and group B (> 50 years). There were two subtypes of PE found:
centrilobular emphysema (CLE) and paraseptal emphysema (PSE). Based on
these subtypes, PE was divided into the following three categories: I
(CLE or CLE-predominant); II (CLE and PSE of equal extent); and III
(PSE or PSE-predominant).
Results: PE was found in 270
of 516 male smokers (10 of 38 female smokers had PE). Among male
subjects, in age group A there were 53 subjects with some degree of PE
(category I, 12 subjects [22.6%]; category II, 7 subjects
[13.2%]; and category III, 34 subjects [64.2%]). Among men in age
group B, there were 217 subjects with some degree of PE (category I,
109 subjects [50.2%]; category II, 23 subjects [10.6%]; and
category III, 85 subjects [39.2%]).
Conclusion: In
age group A, men < 50 years of age who were in category III (PSE or
PSE-predominant PE) predominated (34 of 53 subjects; 64.2%). In age
group B, men > 50 years of age who were in category I (CLE or
CLE-predominant PE) predominated (109 of 217 subjects;
50.2%).
Key Words: cigarette smoking • CT • emphysema • pulmonary
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Introduction
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Pulmonary
emphysema (PE) is defined pathologically as a group of diseases that
demonstrate "an anatomic alteration of lung characterized by
enlargement of airspaces distal to the terminal bronchiole, accompanied
by destructive changes of alveolar walls."1
PE is
one of the most important diseases related to cigarette smoking, and a
large proportion of cases of PE is caused by smoking. PE has been
observed in more than half of Japanese male smokers.2
In
the present study, subtypes of PE were identified by CT scanning
according to the age of the subjects.
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Materials and Methods
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Materials
We reviewed 945 subjects (619 men and 326 women, ranging in age
from 21 to 91 years) from the Kagawa Prefectural Cancer Detecting
Center and Numakuma Hospital, who had undergone CT scanning between
December 1997 and June 1999 because of suspected lung disease seen on
chest radiographs or because of respiratory complaints. Because there
were too few female smokers, only the data for male smokers were
analyzed. PE was diagnosed by the presence of low-attenuation areas
(LAAs) on CT scans and not by pulmonary function test results. Subjects
were divided into the following two age groups: group A ( 50 years);
and group B (> 50 years).
PE is usually classified into the following three main subtypes:
centrilobular emphysema (CLE); panlobular emphysema; and paraseptal
emphysema (PSE).3
In the present study, there were no
subjects with PLE, so PE was classified into the following three
categories based on the presence of CLE and PSE: I (CLE or
CLE-predominant); II (CLE and PSE of equal extent); and III (PSE or
PSE-predominant). Ex-smokers were included with current smokers. The
data on cigarette consumption in number of pack-years for male subjects
according to age group are shown in Table 1
. Patients with conditions such as silicosis were excluded because of
focal lung destruction that was found adjacent to progressive massive
fibrosis or postinflammatory scars. The level of serum
1-antitrypsin was not checked because its
deficiency is very rare in Japan.
CT Scans
Two CT machines (model 700S; Toshiba; Tokyo, Japan [used at 120
kV and 110 mA]; and Lemage SX/E; Yokogawa; Tokyo, Japan [used at 120
kV and 100 mA]) were used. In all cases, contiguous 1-cm sections
encompassed the entire thorax without using high-resolution
reconstruction. Hard-copy images were photographed at a 400-Hounslow
unit (HU) window width and a -200-HU window level (Toshiba 700S) and
at a 1,500-HU window level and a -620 window level (Yokogawa Lemage
SX/E).
According to the extent of LAAs in the peripheral lung fields, the CT
findings were classified into the following five grades: grade 0, no
LAAs; grade 1, sparse, scattered small LAAs up to 5 mm in diameter;
grade 2, adjacent LAAs up to 10 mm in diameter; grade 3, LAAs > 10 mm
that were adjacent to or indistinguishable from each other; and
grade 4, absence of normal lung parenchyma.4
The CT scans
were reviewed independently by two radiologists (K.S. and T.K.). When
there was a conflict in evaluation, they discussed the problem together
to reach a conclusion. As judged by the two radiologists, the image
quality in the present study was not different between the two CT
machines with respect to the presence or absence of LAAs in CT scans
with 1-cm collimation without high-resolution reconstruction.
Statistical Analysis
For comparison of the number of pack-years smoked according to
CT grade within each group, the Student’s t test was used.
The prevalence of PEs according to different categories between
different age groups was analyzed by 
2 test.
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Results
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Of 945 total subjects in the present study, there were only 41
(4.3%) with pulmonary disease other than PE (lung cancer, 10 subjects;
interstitial pneumonia, 8 subjects; pneumoconiosis, 8 subjects;
inflammatory change including tuberculosis, 9 subjects; and
bronchiectasis, 6 subjects). PE was found in 270 of 516 male smokers
(10 of 38 female smokers had PE). In male smokers, there were no
statistically significant differences in cigarette consumption in
number of pack-years according to CT grade within each age group
(Student’s t test) (Table 1)
. For the 53 subjects in age
group A and the 217 subjects in age group B, grade and category of
subtype of PE are shown in Figure 1
. The prevalence of PE by grade with all grades combined in the two age
groups was as follows: group A: category I, 22.6% (12 of 53 subjects);
category II, 13.2% (7 of 53 subjects); and category III, 64.2% (34 of
53 subjects); group B: category I, 50.2% (109 of 217
subjects); category II, 10.6% (23 of 217 subjects); and
category III, 39.2% (85 of 217 subjects). Among subjects with grade 1
PE, there were 27 subjects in group A (category I, 5 subjects; category
II, 5 subjects; and category III, 17 subjects) and 82 subjects in group
B (category I, 35 subjects; category II, 9 subjects; and category III,
38 subjects). Among subjects with grade 2 PE, there were 7
subjects in group A (category I, 1 subject; category II, 1 subject; and
category III, 5 subjects) and 59 subjects in group B (category I, 28
subjects; category II, 7 subjects; and category III, 24 subjects).
Among subjects with grade 3 PE, there were 9 subjects in group A
(category I, 5 subjects; category II, 1 subject; and category III, 3
subjects) and 40 subjects in group B (category I, 30 subjects; category
II, 2 subjects; and category III, 8 subjects). Among
subjects with grade 4 PE, there were 10 subjects in group A (category
I, 1 subject; and category III, 9 subjects) and 36 subjects in group B
(category I, 16 subjects; category II, 5 subjects; and category III, 15
subjects).
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Figure 1.. The prevalence of grade and category
subtypes of PE in male subjects according to age groups. Asterisks
indicate significance in the prevalence of categories I and II combined
and of category III between the respective age groups as indicated by
connecting lines. * = p = 0.005. ** = p < 0.0001.
*** = p < 0.0005 (2 test).
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The prevalence of PE in men according to age is shown in Figure 1 . The
prevalence of CLE was greater in older men. Thus, category I or II
(ie, CLE-predominant or CLE equal to PSE) was found in 4 of
14 subjects (28.6%) who were < 40 years, in 15 of 39 subjects
(38.5%) who were in their 40s, in 31 of 64 subjects (48.4%) who were
in their 50s, in 50 of 91 subjects (54.9%) who in their 60s, and
in 51 of 62 subjects (72.9%) who were > 70 years of age (these
figures combine all grades > 0). Especially with respect to the
prevalence of subjects in categories I and II combined and category III
in each age group including nonsmokers, there were the following
statistically significant differences: subjects < 40 years vs
subjects in their 60s (p = 0.005) and vs subjects > 70 years of age
(p < 0.0001); subjects in their 40s vs subjects > 70 years of age
(p < 0.0001); subjects in their 50s vs subjects > 70 years of age
(p < 0.0001); and subjects in their 60s vs subjects > 70 years of
age (p < 0.005 [2 test]).
CT scans of three typical subjects with grades 2, 3, and 4 PE are
shown in Figures 2
, 3
, and 4
, respectively.
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Figure 2.. CT scan of subject with grade 2, category III PE
(a 39-year-old man, smoking 50 pack-years of cigarettes). LAAs (arrows)
adjacent to the chest wall are seen from the apex to the upper lobes.
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Discussion
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CLE is by far the most common form of emphysema and has a proven
association with cigarette smoking.1
5
PSE can occur as an
isolated phenomenon in young adults.5
Bullae can develop
in association with any type of PE but are most common with PSE or CLE.
A bulla, by definition, is a sharply demarcated area of PE measuring
1 cm in diameter and possessing a wall < 1 mm in
thickness.6
PSE can occur in older patients with
CLE.5
At least some degree of PE is recognized in more than half of Japanese
male smokers.2
In male smokers < 50 years of age, PE is
found in 43.8%.2
Even in subjects < 40 years of age, PE
is found in 35.0%. The prevalence of CLE rises as age increases from
< 40 years to > 70 years. CLE-predominant subtypes were found in 4
of 14 subjects (28.6%) who were < 40 years of age and in 15 of 39
subjects (38.5%) who were in their 40s.
Category III (PSE-predominant) PE in the present study was found not
only in younger subjects but also in older subjects. In subjects 50
years of age, category III showed a high incidence, while in subjects
who were in their 50s and 60s, the prevalence in category III was the
same as in category I (CLE-predominant). In subjects > 70 years of
age , category I exceeded category III.
Although in the present study female smokers were too few to allow
study of the subtypes of PE, Chen et al7
showed that
cigarette smoking may be more detrimental in its effects on lung
function in women than in men. The problem of smoking in young women
has been noted in Japan, Southeast Asia, and Eastern Europe, and it is
feared that in 20 years PE, like lung cancer, will be a major problem.
CT scanning is undoubtedly the most sensitive method to diagnose
PE.8
Previous studies concerned with PE detection included
mostly older subjects and may not reflect the true incidence of PE in
the general population. The present study, which included younger
subjects, was based on data from a mass screening for lung cancer using
helical CT scanning.9
The patients in the study had a wide
age range (21 to 91 years) and almost all of them (95.7%) had normal
findings on CT scans. CT-pathologic correlation in PE is high even with
10-mm collimation, and it is higher still with 1.5-mm
collimation.10
No significant differences between the
high-resolution CT scores and pathology scores were found in patients
with mild-to-moderate PE.11
Although there is a good
correlation between the CT visual scores and pathologic scores of PE
extent, mild PE can be missed on high-resolution CT
scans.10
11
12
Objective or quantitative assessment of PE
has been described.13
14
15
The ability to diagnose PE,
however, is influenced by factors such as scanner type, collimation,
window setting, and interobserver variability and intraobserver
variability. Measurements of attenuation can vary to scanner type,
calibration, kilovoltage, reconstruction algorithm, volume averaging,
patient size, location, environment, and size of the area being
assessed.16
In the present study, the method of evaluation
and classification of PE that was used was a subjective one based on
visual judgment. This method is simple and is available in any hospital
because all CT scanners are not able to quantitatively measure CT
values.
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Conclusion
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CLE (or CLE mixed with PSE) can be found in young subjects
(ie, those 50 years of age), and even in those < 40
years of age. In older subjects (ie, those > 50 years of
age), CLE predominates. Although PSE can occur in nonsmokers, both CLE
and PSE are strongly related to smoking. Both types progress with age
and the cumulative cigarette smoking dose. PE was found in more than
half of male smokers. A high incidence of PE was found even in younger
subjects.
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Figure 3.. CT scan of subject with grade 3, category II PE (a
36-year-old man, smoking 17 pack-years of cigarettes). Both types of
LAAs of PE are seen (CLE, arrow heads; and PSE, arrows),.
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Figure 4.. CT scan of subject with grade 4, category II PE (a
51-year-old man, smoking 45.5 pack-years of cigarettes). Both types of
PE are seen (PSE, large arrows; and CLE, small arrows). In CLE, LAAs
> 10 mm in diameter fuse with each other in the whole of the upper
and middle lung fields.
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Footnotes
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Abbreviations:
CLE = centrilobular emphysema; HU = Hounslow unit;
LAA = low-attenuation area; PE = pulmonary emphysema;
PSE = paraseptal emphysema
Received for publication March 29, 2000.
Accepted for publication April 20, 2001.
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Abstract
Introduction
