Original Article

Organizing pneumonia: chest HRCT findings*

Pneumonia em organização: achados da TCAR de tórax

Igor Murad Faria1, Gláucia Zanetti2, Miriam Menna Barreto3,

Rosana Souza Rodrigues4, Cesar Augusto Araujo-Neto5, Jorge Luiz Pereira e Silva5,
Dante Luiz Escuissato6, Arthur Soares Souza Jr7, Klaus Loureiro Irion8,
Alexandre Dias Mançano9, Luiz Felipe Nobre10, Bruno Hochhegger11, Edson Marchiori12

Abstract
Objective: To determine the frequency of HRCT findings and their distribution in the lung parenchyma of
patients with organizing pneumonia. Methods: This was a retrospective review of the HRCT scans of 36 adult
patients (26 females and 10 males) with biopsy-proven organizing pneumonia. The patients were between 19
and 82 years of age (mean age, 56.2 years). The HRCT images were evaluated by two independent observers,
discordant interpretations being resolved by consensus. Results: The most common HRCT finding was that
of ground-glass opacities, which were seen in 88.9% of the cases. The second most common finding was
consolidation (in 83.3% of cases), followed by peribronchovascular opacities (in 52.8%), reticulation (in 38.9%),
bronchiectasis (in 33.3%), interstitial nodules (in 27.8%), interlobular septal thickening (in 27.8%), perilobular
pattern (in 22.2%), the reversed halo sign (in 16.7%), airspace nodules (in 11.1%), and the halo sign (in 8.3%). The
lesions were predominantly bilateral, the middle and lower lung fields being the areas most commonly affected.
Conclusions: Ground-glass opacities and consolidation were the most common findings, with a predominantly
random distribution, although they were more common in the middle and lower thirds of the lungs.
Keywords: Cryptogenic organizing pneumonia; Respiratory tract diseases; Tomography, X-ray computed.

Introduction
Organizing pneumonia (OP) is a clinical observed in the respiratory bronchioles.(2,3) The
entity that is associated with nonspecific clinical term cryptogenic OP (COP) is more appropriate
findings, radiographic findings, and pulmonary than the term bronchiolitis obliterans OP, which
function test results.(1) It corresponds to a has been abandoned.(2) This is primarily due to
histological pattern characterized by granulation the fact that the hallmark of COP is OP rather
tissue polyps within alveolar ducts and alveoli, than bronchiolitis.(4)
with chronic inflammation of the adjacent When the cause is unknown, OP is classified as
lung parenchyma. Similar lesions can also be primary or cryptogenic; when a causal connection

1. Master’s Student in Radiology. Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
2. Professor. Graduate Program in Radiology, Federal University of Rio de Janeiro, Rio de Janeiro; and Professor of Clinical
Medicine. Petrópolis School of Medicine, Petrópolis, Brazil.
3. Physician. Department of Radiological Diagnosis, Clementino Fraga Filho University Hospital, Federal University of Rio de
Janeiro, Rio de Janeiro, Brazil.
4. Physician. Department of Radiological Diagnosis, Clementino Fraga Filho University Hospital, Federal University of Rio de
Janeiro; and Physician. D’Or Institute for Research and Education, Rio de Janeiro, Brazil.
5. Associate Professor. Department of Internal Medicine and Diagnostic Support, Universidade Federal da Bahia – UFBA, Federal
University of Bahia – Salvador, Brazil.
6. Adjunct Professor of Radiology. Department of Clinical Medicine, Universidade Federal do Paraná – UFPR, Federal University
of Paraná – Curitiba, Brazil.
7. Tenured Professor. São José do Rio Preto School of Medicine, São José do Rio Preto, Brazil.
8. Head. Department of Radiology, Royal Liverpool and Broadgreen University Hospital, Liverpool, United Kingdom.
9. Physician. Radiologia Anchieta, Hospital Anchieta, Taguatinga, Brazil.
10. Adjunct Professor of Radiology. Universidade Federal de Santa Catarina – UFSC, Federal University of Santa Catarina –
Florianópolis, Brazil.
11. Adjunct Professor of Diagnostic Imaging. Federal University of Health Sciences of Porto Alegre, Porto Alegre, Brazil.
12. Full Professor Emeritus. Fluminense Federal University, Niterói, Brazil.
*Study carried out at the Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Correspondence to: Edson Marchiori. Rua Thomaz Cameron, 438, Valparaíso, CEP 25685-120, Petrópolis, RJ, Brasil.
Tel. 55 24 2249-2777. Fax: 55 21 2629-9017. E-mail: edmarchiori@gmail.com
Financial support: None.
Submitted: 24 January 2015. Accepted, after review: 10 March 2015.

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232 Faria IM, Zanetti G, Menna-Barreto M, Rodrigues RS,
Araujo-Neto CA, Pereira-Silva JL, Escuissato DL, et al.

can be established, OP is classified as secondary. with the patients in the supine position and
The causes of OP are numerous and include without intravenous injection of iodinated contrast
infections, iatrogenic causes (a reaction to material, a high spatial resolution filter (bone
drugs and radiation therapy), illicit drug use, filter) being used for image reconstruction. The
and autoimmune diseases.(1,2,5,6) The distinction images were obtained and reconstructed with a
between primary and secondary OP is extremely 512 × 512 pixel matrix and were photographed
important because the treatment of patients with for evaluation of the lung fields with a window
secondary OP includes treatment for OP itself and opening of 1,200-2,000 HU and an opening
for the underlying disease or causative agent.(1) level of −300 to −700 HU. For mediastinal
The literature does not provide sufficient data evaluation, a window opening of 350-500 HU
to determine whether COP and secondary OP are and an opening level of 10-50 HU were used.
two distinct entities or the same entity, in which The images were independently evaluated by two
there is nonspecific lung injury and repair.(5) experienced observers. Discordant interpretations
Although the diagnosis of OP is established were resolved by consensus.
by biopsy and histology, the clinical findings and With regard to the HRCT findings, the following
imaging changes can suggest the diagnosis. In this definitions were used:
context, HRCT is the imaging method of choice • ground-glass opacity—slightly increased
for diagnosing OP. In addition, HRCT allows us to attenuation of the lung parenchyma,
evaluate the response to treatment and is useful unrelated to the obscuration of the vessels
for selecting the type of biopsy and the best site and adjacent airway walls
to perform it (when necessary). The objective of • consolidation—increased attenuation of the
the present study was to determine the frequency lung parenchyma, resulting in obscuration
of HRCT findings and their distribution in the of the vascular outlines and adjacent airway
lung parenchyma of patients with OP. walls
• peribronchovascular opacity—increased
Methods attenuation of the lung parenchyma adjacent
The present study was approved by the Research to the peribronchovascular interstitium
Ethics Committee of the Fluminense Federal • reticulation—innumerable small linear
University Antonio Pedro University Hospital, opacities that, by summation, produce
located in the city of Niterói, Brazil. Because this an appearance resembling a net
was a retrospective study examining existing clinical • bronchiectasis—bronchial diameter greater
data and involving no changes in the treatment than the diameter of the adjacent artery
or follow-up of patients, no written informed or absence of tapering of the bronchi and
consent was required. This was a retrospective identification of a bronchus 1 cm from the
descriptive observational study of the HRCT scans pleural surface
of 36 patients with histologically confirmed OP. • interlobular septal thickening—thin linear
Of those 36 patients, 20 had primary OP and opacities, which correspond to thickened
16 had secondary OP. The HRCT scans were interlobular septa
randomly collected by personally contacting • perilobular pattern—thick, irregular polygonal
pulmonologists and radiologists and by searching opacities in the periphery of the secondary
the image databases of 8 medical institutions pulmonary lobules
in 6 different Brazilian states in the 2005-2013 • reversed halo sign—round, focal ground-
period. Of the 36 patients, 26 (72.2%) were glass opacity surrounded by a ring-shaped
female and 10 (27.8%) were male. The patients peripheral consolidation
were between 19 and 82 years of age (mean • airspace nodules—ill-defined nodules smaller
age, 56.2 years). than 1 cm and tending to confluence
Given that multiple institutions were involved, • halo sign—ground-glass opacity surrounding
different CT scanners were used for image a nodule or mass
acquisition. All patients underwent HRCT scans, The criteria for the aforementioned findings
which were taken from the lung apices to the are defined in the Fleischner Society Glossary of
lung bases. Thin (1- or 2-mm) scans were taken Terms,(7) and the terms used are those found in
during inhalation, in increments of 5 or 10 mm, the Brazilian Thoracic Association Department

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Organizing pneumonia: chest HRCT findings 233

of Diagnostic Imaging consensus guidelines.(8,9)

The scans were also evaluated for the presence
of pleural effusion, lymph node enlargement,
and associated findings.
On the basis of their distribution in the lung
parenchyma, the findings were classified as follows:
• left-sided, right-sided, or bilateral findings
• findings in the upper third, middle third,
or lower third of the lungs
• central or peripheral findings
In the craniocaudal axis, the lung was divided
into upper third (from the lung apex to the level
of the aortic arch), middle third (from the aortic Figure 1 - Chest HRCT scan (lung window) at the
arch to 2 cm below the carina), and lower third level of the middle lung field of a 39-year-old male
(from 2 cm below the carina to the costophrenic patient, showing ground-glass opacities predominantly
sulci). Lesions located predominantly in the middle in the lung periphery.
third were defined as central lesions; those located
predominantly in the upper and lower thirds
were defined as peripheral lesions; and those
with a predominantly random distribution were
defined as random lesions.

Results
The most common HRCT findings (Table 1),
in descending order, were as follows: ground-
glass opacities (Figure 1); consolidation (Figure
2); peribronchovascular opacities (Figure 3);
reticulation (Figure 4); bronchiectasis; interstitial
nodules; interlobular septal thickening; perilobular
pattern (Figure 5); reversed halo sign; airspace
Figure 2 - Chest HRCT scan at the level of the lower
nodules; and halo sign. There were signs of
lung field of a 53-year-old male patient, showing
architectural distortion in 14 (38.9%) of the 36 areas of consolidation with air bronchograms and
patients studied. peripheral distribution in the anterior lung regions.
Of the 36 patients studied, 33 (91.7%) had
bilateral lung involvement. In 2 (5.6%), only
the right lung was affected, and, in 1 (2.8%),

Table 1 - Most common HRCT findings in 36 patients

with organizing pneumonia.a
HRCT findings Patients
Ground-glass opacities 32 (88.9)
Consolidation 30 (83.3)
Peribronchovascular opacities 19 (52.8)
Reticulation 14 (38.9)
Bronchiectasis 12 (33.3)
Interstitial nodules 10 (27.8)
Interlobular septal thickening 10 (27.8)
Perilobular pattern 8 (22.2)
Reversed halo sign 6 (17.1) Figure 3 - Chest HRCT scan (lung parenchymal window
Airspace nodules 4 (11.1) settings) of a 50-year-old male patient, showing bilateral
Halo sign 3 (8.3) consolidations with peribronchovascular distribution,
a
Values expressed as n (%). interspersed with bronchiectasis.

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234 Faria IM, Zanetti G, Menna-Barreto M, Rodrigues RS,
Araujo-Neto CA, Pereira-Silva JL, Escuissato DL, et al.

only the left lung was affected. With regard to and sixth decades of life.(11,12) Although OP is
the distribution of the lesions, the middle third rarely seen in children, there have been reports
of the lung was the most commonly affected of OP in such individuals. In the present study,
area—in 33 (91.7%) of the 36 patients studied— the patients were between 19 and 82 years of
followed by the lower third, in 28 (77.8%), and age (mean age, 56.2 years).
the upper third, in 21 (58.3%). In addition, the The initial symptoms of OP are nonspecific.
most common lesions were random lesions—in Fever, cough, asthenia, mild dyspnea, anorexia,
26 (72.2%) of the 36 patients studied—followed and weight loss are the most common findings,
by peripheral lesions, in 9 (25%), and central mimicking influenza.(13) Therefore, an initial
lesions, in 1 (2.8%). diagnosis of infectious disease is often made in
patients with such findings. In addition, patients
Discussion with such findings are often given empirical
antibiotic therapy, which is ineffective. Fever
Studies evaluating the distribution of patients
with COP and secondary OP by gender have can be absent in 50% of patients.(2) Therefore,
shown no significant difference between the two the diagnosis is often delayed, being generally
groups.(1,10,11) Of the 36 patients in the present suspected 4-10 weeks after the onset of symptoms.
study, 26 (72.2%) were female and 10 (27.8%) As the disease progresses, most of the initial
were male. With regard to age, studies have symptoms can disappear, the exception being
shown that OP is most common in the fifth dyspnea, which sometimes worsens and becomes
predominant. In some patients, the disease can
progress rapidly, leading to severe dyspnea and
even acute respiratory distress syndrome.(14) In
general, there is no difference between the clinical
manifestations of COP and those of secondary
OP.(1,5) However, some clinical manifestations
can provide important clues for the differential
diagnosis. Severe arthralgia, myalgia, or both are
more common in patients with OP associated with
connective tissue disease.(15) Patient history taking
is essential, given that it can aid in identifying a
cause for the OP. Patients with a history of lung
radiation therapy can present with symptoms and
Figure 4 - Chest HRCT scan (lung parenchymal window
imaging changes suggestive of OP in the lung
settings) at the level of the lung bases of a 75-year-old
male patient, showing bilateral reticular opacities in parenchyma several months after treatment.(16)
the posterior lung regions. In our sample, 20 patients (55.6%) had been
diagnosed with primary (idiopathic) OP and 16
(44.4%) had been diagnosed with secondary OP
on the basis of their clinical history and clinical
examination findings. In studies involving larger
samples of patients with OP, the proportion of
patients with COP ranged from 52% to 65%,(1,10 ‑ 12)
being similar to that found in the present study.
Of the 16 patients with secondary OP in the
present study, 5 (31.2%) had OP associated with
drugs (amiodarone, in 2, nitrofurantoin, in 1,
bleomycin, in 1, and busulfan, in 1), 3 (18.8%)
had OP associated with infections (influenza A
(H1N1) infection, in 2, and cryptococcosis, in 1),
Figure 5 - Chest HRCT scan (lung parenchymal
window settings) at the level of the upper lobes of 3 (18.8%) had OP associated with bone marrow
a 47-year-old female patient, showing a perilobular transplantation, 3 (18.8%) had OP associated
pattern predominantly on the right. Note faint nodular with collagen diseases (rheumatoid arthritis, in
opacities in the left lung. 2, and systemic lupus erythematosus, in 1), and

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Organizing pneumonia: chest HRCT findings 235

2 (12.5%) had OP associated with malignancy ground-glass opacities and consolidations, seen
(lymphoma, in 1, and colon cancer, in 1). The in 89% and 83%, respectively. Our findings are
causes of secondary OP vary widely across similar to those of larger studies.(1,20,21)
studies and include drugs, infections, solid or A solitary focal opacity is an uncommon
hematologic malignancies and their treatments presentation of OP that is known as focal OP
(chemotherapy, radiation therapy, and bone marrow and accounts for 10-15% of all cases.(5) The
transplantation), and collagen diseases.(1,10-12) diagnosis is usually made by biopsy of a nodule
The diagnosis of OP is made by biopsy or mass that was removed because of a suspicion
and histology. However, clinical and physical of bronchogenic carcinoma.(7) In the present
examination findings (including an investigation of study, only 1 patient (2.8%) had focal OP. In
possible causes), together with imaging changes, that patient, the HRCT finding was a nodule
can suggest the diagnosis.(2) Histopathological with the halo sign.
examination reveals irregular filling of the alveoli, It is known that OP can also present as
alveolar ducts, and respiratory bronchioles by overlapping interstitial and alveolar opacities.
granulation tissue plugs, which are known as In addition, OP can overlap with other types of
Masson bodies.(3) There is also a process of intra- interstitial pneumonia, particularly idiopathic
alveolar fibrosis resulting from the organization of pulmonary fibrosis and nonspecific interstitial
an inflammatory exudate. Unlike usual interstitial pneumonia.(22) This pattern is characterized by
pneumonia, OP is not related to a progressive and a relative lack of consolidation and ground-
irreversible fibrotic process.(17) After a diagnosis of glass opacities, with a predominance of reticular
OP is established, it is necessary to determine the opacities with architectural distortion.(23) In our
cause, which can be relatively evident or require sample, there were signs of architectural distortion
further investigation.(2) In our study, all cases in 14 patients (38.9%), a proportion that is higher
of OP were histopathologically confirmed after than that reported in the literature (i.e., 10-18%).
transbronchial biopsy, in 17 (47.2%); CT-guided (1,20)
It should be noted that none of our patients
transthoracic biopsy, in 5 (13.9%); video-assisted had previously been treated for OP.
thoracoscopic biopsy, in 8 (22.2%); and open lung Although the reversed halo sign was initially
biopsy, in 5 (13.9%). In 1 (2.8%), the diagnosis considered to be an OP-specific finding,(24) it was
was confirmed by autopsy. subsequently described in a number of other
Although some authors have reported using diseases.(25-27) Nevertheless, it is an important
surgical biopsies more frequently (in 88% of clue to the diagnosis of OP.(28,29) In our study, the
their patients),(12) transbronchial biopsy was used reversed halo sign was seen in 6 patients (17.1%).
in most of the studies involving large samples In a study by Kim et al., the reversed halo sign
of patients with OP (being used in 67-78% of was found in 19% of the cases.(24) However, it
the patients). (1,10) Although surgical biopsy (via was not found in other studies involving large
thoracoscopy or open thoracotomy) remains samples of patients.(1,12,20,21) It is known that OP
the gold standard for the diagnosis of OP, can present as centrilobular nodules of 3-5 mm
transbronchial biopsy can be conclusive in most and small (1- to 10-mm) nodular opacities that
cases if the findings are appropriately related to are typically ill-defined. The differential diagnosis
the clinical and CT findings.(1) with metastases is crucial, especially in patients
For evaluating OP, HRCT is the imaging method with a history of cancer, given that there is an
of choice. There are no differences between COP association between OP and cancer. (30) In our
and secondary OP regarding HRCT findings. (1) study, airspace nodules were seen in 4 patients
However, Vasu et al.(12) showed that pleural effusion (11.1%).
was more common in patients with secondary Another important aspect in the HRCT
OP than in those with COP. evaluation of OP is the distribution of opacities.
The most common finding in patients with OP Subpleural/peribronchovascular distribution and a
is that of consolidation and ground-glass opacities, perilobular pattern can be found in approximately
which are usually bilateral and peripheral. (16) 60% of cases.(20,21,31) In the present study,
However, such opacities are nonspecific, being peribronchovascular opacities were found in 19
often mistaken for infectious pneumonia.(18,19) patients (52.8%). However, a perilobular pattern
In our sample, the most common findings were was found in only 8 patients (22.2%). Bilateral

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236 Faria IM, Zanetti G, Menna-Barreto M, Rodrigues RS,
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