AJR 2002; 178:1389-1393
© American Roentgen Ray Society
Large Coalescent Parenchymal Nodules in Pulmonary Sarcoidosis: "Sarcoid Galaxy" Sign
Masashi Nakatsu1,2,
Hiroto Hatabu1,2,
Kenji Morikawa1,
Hidemasa Uematsu2,
Yoshiharu Ohno2,
Koichi Nishimura3,
Sonoko Nagai3,
Takateru Izumi3,
Junji Konishi1 and
Harumi Itoh4
1 Department of Radiology and Nuclear Medicine, Kyoto University Hospital, 54
Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan.
2 Present address: Department of Radiology, University of Pennsylvania Medical
Center, 3400 Spruce St., Philadelphia, PA 19104.
3 Chest Disease Research Institute, Kyoto University Hospital, Sakyo-ku, Kyoto
606-8507, Japan.
4 Department of Radiology, Fukui Medical University, 23 Shimoaizuki,
Matsuoka-cho, Yoshida-gun, Fukui 910-1193, Japan.
Received June 4, 2001;
accepted after revision December 6, 2001.
Address correspondence to H. Hatabu.
Abstract
OBJECTIVE. The purpose of this study was to evaluate the large
parenchymal nodules in pulmonary sarcoidosis and to describe a new CT sign
termed the "sarcoid galaxy."
CONCLUSION. The CT appearance of pulmonary sarcoidosis suggests that
the large nodules arise from a coalescence of small nodules. The large nodules
are surrounded by many tiny satellite nodules. These findings were considered
to simulate the appearance of a galaxy. This observation was supported by
radiologic—pathologic correlation. The sarcoid galaxy sign may be a
useful adjunct in the diagnosis of pulmonary sarcoidosis.
Introduction
Sarcoidosis is a systemic disorder of unknown cause characterized by the
presence of noncaseating granulomas
[1,
2]. The prevalence of
sarcoidosis in Japan involves two to three per 100,000 individuals, which is
less frequent than in the United States where 40-60 per 100,000 individuals
are affected. Although small parenchymal nodules along the bronchoarterial
bundles, interlobular septa, and major fissures and in the subpleural regions
are frequently observed in pulmonary sarcoidosis on CT
[3,4,5,6,7,8,9,10],
large nodules (
1 cm in diameter) are less common
[3]. To our knowledge, a
detailed description of large nodules in pulmonary sarcoidosis has not been
reported in previous research. The purpose of this study was to evaluate the
large parenchymal nodules in pulmonary sarcoidosis on CT and to describe a new
CT sign the "sarcoid galaxy" sign.
Materials and Methods
Patients
Fifty-nine patients (37 men and 22 women) ranging in age from 21 to 73
years (mean age, 42.7 years) with histologically confirmed pulmonary
sarcoidosis were included in this retrospective study. All CT scans showed
parenchymal abnormalities. Histologic proof was obtained by means of bronchial
biopsy (n = 28), mediastinal or peripheral nodal biopsy (n =
12), transbronchial lung biopsy (n = 11), open lung biopsy
(n = 5), and biopsy of other organs (n = 3).
CT Examination
CT studies were performed with a helical scanner (X-Vigor; Toshiba Medical,
Tokyo, Japan). After routine helical CT scans were obtained with a 10-mm
collimation, CT scans with a 3-mm collimation at 10-mm intersection spacing
(120 kVp, 200 mA, and 1.0-sec scanning time) were acquired. A
high-spatial-frequency algorithm (bone-detail algorithm) with a field of view
of 20 cm and a matrix of 512 x 512 was used. All scans were obtained
from the lung apices to the bases during suspended end-inspiration, and all
patients were in the supine position when examined. All images were observed
and photographed at window settings appropriate for pulmonary parenchyma
(level, -700 H; width, 900 H) and mediastinum (level, 30-50 H; width, 350-500
H).
Data Analysis
Large nodules in pulmonary sarcoidosis were defined as round areas of
soft-tissue attenuation greater than or equal to 1 cm in diameter
[3,
4]. The presence of large
nodules was assessed by three radiologists who were experienced in chest
radiography and CT and who were informed that all patients had pulmonary
sarcoidosis; however, the radiologists were unaware of other clinical
information. A conclusion was reached by consensus if there was disagreement.
The number, character, size, and extension of the large nodules and their
relation to other findings, including mediastinal and hilar lymphadenopathy
and ground-glass areas of attenuation, were examined. The large nodules were
classified according to diameter (1-2 cm, 2-3 cm, and >3 cm). The spatial
distribution was also assessed independently for the upper, middle or lingual,
and lower lobes of each lung. CT—pathologic correlation was performed in
five patients who underwent open lung biopsy.
Results
Of the 59 patients, 16 (27%; 14 men and two women; age range, 21-70 years;
mean age, 31.4 years) were found to have large nodules on CT. Multiple large
nodules were seen in 15 patients, whereas a solitary nodule was noted in only
one patient. The large parenchymal nodules consisted of numerous small nodules
and showed irregular margins (Figs.
1A,1B,1C,2A,2B,2C,3A,3B).
In the periphery of the large nodules, each constituent small nodule had a
relatively distinct margin. Small low-attenuation spots were seen in the large
nodules (Figs. 1B and
1C). This characteristic
appearance of large parenchymal nodules resembled a galaxy that is a vast
collection of millions and occasionally billions of stars
(Fig. 4). This sign was
recognized in all 16 patients.
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Fig. 1B. —23-year-old man with mild cough. CT scan of right upper lobe
shows "sarcoid galaxies" that are composed of numerous small
granulomas. Fine nodular opacities are seen around large nodules. Small
low-attenuation spots are noted in periphery of large nodules
(arrows).
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Fig. 1C. —23-year-old man with mild cough. CT scan of left lung shows
another sarcoid galaxy. Small low-attenuation spot is seen in periphery of
large nodule (arrow). Distortion of left major fissure is also seen
(arrowhead).
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Fig. 2A. —Asymptomatic 22-year-old man who was found to have radiologic
abnormalities by routine examination. Posteroanterior chest radiograph shows
mediastinal and hilar lymphadenopathy and large parenchymal nodules in both
upper lung fields (arrows).
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Fig. 2B. —Asymptomatic 22-year-old man who was found to have radiologic
abnormalities by routine examination. CT scan of right upper lobe shows large
nodule with partially smooth margin (arrows); however, "sarcoid
galaxy" appearance is also evident in remaining margin
(arrowhead).
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Fig. 3A. —Asymptomatic 23-year-old woman who was found to have
radiologic abnormalities by routine examination. Posteroanterior chest
radiograph shows mediastinal and hilar lymphadenopathy and large parenchymal
nodules in both lung fields. Cavitary nodule is observed in right upper
zone.
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Fig. 3B. —Asymptomatic 23-year-old woman who was found to have
radiologic abnormalities by routine examination. CT scan of right upper lobe
shows cavitary wall is round and smoothly marginated. "Sarcoid
galaxy" sign is also noted.
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Fig. 4. —Photograph shows globular cluster M92 (NGC 6341), class IV,
in Hercules cluster of galaxies. Globular clusters are distributed in
spherical halo around galactic center. Stars are more concentrated toward
galactic center than in periphery. (Courtesy of Takahashi H, Tokyo, Japan)
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Smooth boundaries in three of the large nodules caused investigators to
disagree about their classification as the sarcoid galaxy sign. However,
galaxy appearances were also evident in portions of these questionably large
nodules (Fig. 2B). After
reaching a consensus, we categorized these large nodules with partially smooth
boundaries as sarcoid galaxies. Fine nodular opacities and large nodules were
observed predominantly along the bronchoarterial bundles and, to a lesser
extent, in the subpleural lymphatics and along the interlobular septal
lymphatics.
A sarcoid galaxy sign with cavitation was noted in two patients
(Fig. 3B). Both cavities were
located in the center of the nodules, and the cavitary walls were round and
smoothly demarcated. The diameters of the cavities were 1.5 and 1.8 cm,
respectively. No fungus balls were observed. Ground-glass attenuations were
observed in nine (56.3%) of the 16 patients.
The sarcoid galaxy of the large nodule represents innumerable coalescent
granulomatous lesions. This finding was clearly revealed by the
CT—pathologic correlation (Fig.
5A,5B).
Toward the center of the sarcoid galaxy, granulomas were much more
concentrated than in its periphery. When granulomas were not so densely
assembled, it was possible to identify individual macroscopic granulomas.
Peripheral low-attenuation spots corresponded to the spaces between partially
coalescent small nodules (Fig.
5A,5B).
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Fig. 5B. —Pathologic specimens of pulmonary sarcoidosis.
Photomicrograph of histopathologic specimen shows large sarcoid nodule
produced by numerous small granulomas. Peripheral low-attenuation spots on CT
correspond to spaces between partially coalescent small nodules
(arrow). (H and E, x5)
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The number of sarcoid galaxies is shown in
Figure 6. The upper and middle
lobes revealed almost the same frequency of sarcoid galaxies, whereas the
lower lobes had a small number of sarcoid galaxies in both lungs. Most
(>50) sarcoid galaxies were 1-2 cm in diameter, seven were 2-3 cm, and one
was greater than 3 cm. Fifteen (93.8%) of the 16 patients were associated with
mediastinal and hilar lymphadenopathy that was also identified on helical CT
with 10-mm collimation.
Discussion
To our knowledge, this is the first report focusing on large sarcoid
nodules. CT showed the characteristic pattern of large parenchymal nodules in
pulmonary sarcoidosis resembling a galaxy, which corresponded to coalescent
granulomas. This observation was proven by the CT—pathologic
correlation. Some small nodules aggregated loosely and appeared to be in the
process of composing a large nodule. In addition, we found some large nodules
with partially smooth margins.
The sarcoid galaxy was found in 16 (27%) of 59 patients in our study. In
previous publications on pulmonary sarcoidosis, large parenchymal nodules or
spherical (alveolar) masslike areas of attenuation were observed in 25% (2/8),
15% (4/27), and 7.3% (3/41) of patients
[3,
6,
7]. The incidence of large
nodules in our study appears slightly high. First, patients with mediastinal
and hilar lymphadenopathy without parenchymal abnormalities on CT were not
included in our study. Second, patients with advanced pulmonary sarcoidosis
were referred to our institution from outside hospitals. These factors may
have resulted in the slightly higher incidence of large nodules.
Pathology studies show that sarcoid granulomas are present mostly along the
lymphatics in the peribronchoarterial sheath and, to a lesser extent, in the
subpleural and interlobular septal lymphatics
[5]. On CT, irregularly
thickened bronchoarterial bundles in the lung parenchyma correspond to
granulomas formed in the connective tissue sheath around the pulmonary vessels
and airways. Nodular densities represent noncaseating granulomas that are
distributed along the lymphatics, a distribution that is considered to be the
pathologic hallmark of sarcoidosis.
The appearance of a coalescence of numerous noncaseating granulomas is
different from spiculation of adenocarcinoma of the lung. However, when too
much contrast is shown, CT window settings could create spiculations that are
actually not present by the fusion of peripheral micronodules, resulting in a
more or less linear arrangement. Therefore, in some cases of large nodules of
sarcoidosis, different diagnoses, including lung carcinoma, might be
considered. Although the incidence of extensive mediastinal and hilar
lymphadenopathy is relatively small in peripheral non—small cell lung
carcinoma less than 3 cm in diameter
[11], extensive mediastinal
and hilar lymphadenopathy was observed in 15 (93.7%) of the 16 patients with
pulmonary sarcoidosis in this study.
Although sarcoidosis can sometimes have an appearance resembling
progressive massive fibrosis associated with coal worker's disease and
silicosis [12],
differentiation of large sarcoid nodules from other nodular lesions on CT is
not difficult in typical cases that show the sarcoid galaxy sign; as a result,
unnecessary intervention may be avoided. However, histologic confirmation is
needed in some cases, especially for a solitary or growing large nodule. In
such cases, CT may also be helpful in suggesting the best site to obtain a
tissue sample for diagnosis.
Although high-resolution CT is usually performed with a slice thickness of
1-2 mm, a 3-mm collimation was used for the evaluation of large sarcoid
nodules in this study. A 3-mm CT collimation may show more peripheral
micronodules and more bronchioles and their branches as three-dimensional
structures than will images obtained with a 1-mm collimation. However, future
studies could evaluate the sarcoid galaxy sign on 1-mm CT collimation.
In conclusion, we described a new CT sign for large sarcoid nodules.
Although the sensitivity, specificity, and accuracy of the sarcoid galaxy sign
should be tested in a future prospective study, this sign may be a useful
adjunct in the diagnosis of pulmonary sarcoidosis.
Acknowledgments
We thank Lorene M. Yoxtheimer and Justin Kung for their contributions to
the preparation of this manuscript.
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Abstract
Introduction
