AJR 2000; 174:1765-1768
© American Roentgen Ray Society
Usefulness of the Double-Wall Sign in Detecting Pneumothorax in Patients with Giant Bullous Emphysema
Gayle M. Waitches1,
Eric J. Stern and
Theodore J. Dubinsky
1
All authors: Department of Radiology, Harborview Medical Center, University of
Washington, Box 359728, 325 Ninth Ave., Seattle, WA 98104.
Received April 12, 1999;
accepted after revision November 19, 1999.
Address correspondence to G. M. Waitches.
Abstract
OBJECTIVE. We describe a new sign improving detection of
pneumothorax in patients with giant bullous emphysema: air surrounding both
sides of the bulla wall (the intrathoracic equivalent of the double-wall sign
of pneumoperitoneum). We report the radiographic and CT appearances of the
double-wall sign in seven patients with giant bullous emphysema, four of whom
had pneumothorax.
CONCLUSION. Recognizing the double-wall sign of pneumothorax should
aid in the triage of patients with giant bullous emphysema.
Introduction
Giant bullous emphysema, originally described by Burke
[1] in 1937, is an idiopathic,
distinct clinical syndrome of severe progressive dyspnea caused by extensive,
predominantly asymmetric upper lobe bullous emphysema, which may eventually
lead to respiratory failure. Giant bullous emphysema has also been called
vanishing lung syndrome [1]. It
typically occurs in young or middle-aged cigarette-smoking men, who often
present clinically with acute shortness of breath. In this setting,
difficulties arise in distinguishing pneumothorax from progression of the
underlying bullous emphysema. The clinical signs of pneumothorax in patients
with giant bullous emphysema are unreliable
[2,
3]. A complex and distorted
radiographic appearance of the lungs in these patients hinders detection of,
and may even falsely suggest, pneumothorax
[2,3,4,5,6].
The distinction between the pleural line of a pneumothorax and the bulla wall
can be difficult. The advantage of CT over conventional radiography in aiding
diagnosis and treatment of pneumothorax has been described, but air in the
pleural space may still be a challenge to diagnose with certainty in these
patients [2,
3,
6,7,8,9].
The purpose of this article is to describe the appearance and clinical
relevance of the double-wall sign of pneumothorax in the setting of giant
bullous emphysema.
Materials and Methods
All patients with giant bullous emphysema diagnosed in our hospital over a
3-year period who underwent both conventional chest radiography and chest CT
were included in this retrospective study. This patient group included seven
patients with chest radiographic, CT, and clinical evidence of giant bullous
emphysema. Four of the seven patients had acute pneumothorax. All seven
patients were men (age range, 33-82 years; mean, 54 years). Four were known
cigarette smokers (range, 20-120 packs per year; mean, 66 packs per year). The
medical records of all seven patients were retrospectively reviewed, followed
by retrospective evaluation of conventional radiographs and CT scans
(n = 7) for the presence of and extent of bullae and pneumothoraces,
with consensus by two experienced radiologists. Bullae were defined as sharply
demarcated areas of pulmonary emphysema measuring larger than 1 cm with a wall
thickness of less than 1 mm
[10]. The diagnosis of giant
bullous emphysema was made if radiographic features consisted of one or more
bullae occupying at least one third of a hemithorax. Chest CT was performed on
a HiSpeed Advantage system (General Electric Medical Systems, Milwaukee, WI)
using 7-mm contiguous collimation, 1:1 pitch, and 100 ml of nonionic IV
contrast material, reconstructed in bone algorithm. High-resolution CT was
performed with 1-mm noncontiguous collimation without contrast administration
and reconstructed in bone algorithm.
Chest CT with clinical and radiographic evidence of response to chest tube
drainage was considered the gold standard for diagnosis of pneumothorax.
Patients were considered to have pneumothorax when air in the pleural space
was detected external to the parenchymal bullae and when clinical and
radiographic improvement occurred after chest tube placement. Patients were
considered not to have pneumothorax on the basis of the imaging findings and
clinical stability. The double-wall sign was evaluated retrospectively in all
cases.
Results
Of the seven patients with giant bullous emphysema, pneumothorax and the
double-wall sign were seen in four patients. The double-wall sign was absent
in the three patients without evidence of pneumothorax.
Of those patients with pneumothorax, one presented with pneumonia and
incurred an iatrogenic pneumothorax, two presented with acute shortness of
breath and spontaneous pneumothorax, and the last sustained a posttraumatic
pneumothorax after a motor vehicle collision. In the first patient, chest
radiography revealed a large right upper lobe radiolucency, which was
initially misinterpreted as a large pneumothorax. Placement of a small
catheter with a one-way flutter valve produced no symptomatic relief or change
in the chest radiographic findings. Subsequent chest CT revealed an
intrabullous location of the small pleural catheter and a small
hydropneumothorax (Fig. 1). A
double-wall sign indicated air in the pleural space. In another patient, chest
CT findings confirmed the clinical suspicion of left pneumothorax, not
appreciated on initial conventional radiography (Figs.
2A,2B,2C).
Emergent decompression was obtained with chest tube placement. In another
patient, initial chest radiography revealed a large spontaneous right
pneumothorax. Clinical improvement occurred after chest tube placement. A
chest CT scan obtained to evaluate the extent of the bullous disease showed
adequate positioning of the tube, a small residual pneumothorax with
double-wall sign, and severe giant bullous emphysema
(Fig. 3). The final patient
with pneumothorax and giant bullous emphysema presented with a posttraumatic
left pneumothorax after a motor vehicle collision. The patient was treated
with chest tube decompression, but left the hospital against medical advice a
few days after chest tube removal. He returned 2 days later with symptoms of
pneumonia and an exudative left pleural effusion necessitating chest tube
drainage. Chest CT performed to evaluate extent of residual pleural fluid
showed a small effusion and the double-wall sign of a small left pneumothorax
(Fig. 4). All patients showed
clinical improvement with appropriate CT-guided drainage.
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Fig. 1. —76-year-old man with giant bullous emphysema. Chest CT scan shows
small drainage catheter entering anterior right chest wall. Catheter coursed
through several upper lobe bullae creating iatrogenic bronchopleural fistula
that required right upper lobectomy. Note small adjacent pneumothorax and
double-wall sign of air on both sides of bulla walls, parallel to chest wall
(arrow).
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Fig. 2A. —35-year-old man with giant bullous emphysema and left pneumothorax.
Chest CT scan through lower thorax shows large lucency in lower lobe. It is
difficult to determine whether this represents huge bulla or pneumothorax.
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Fig. 2B. —35-year-old man with giant bullous emphysema and left pneumothorax.
Chest CT scan more superior than A shows that this air is in large
bulla and that there is also double-wall sign of large pneumothorax
(arrow). This information is invaluable in indicating and directing
appropriate site for chest tube placement.
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Fig. 2C. —35-year-old man with giant bullous emphysema and left pneumothorax.
Chest CT scan through mid thorax shows pneumothorax surrounding very large
bulla, not evident in A. This emphasizes importance of visualization of
air external to bulla (double-wall sign) and of not confusing air within
adjacent large bulla as seen in Figure
5A,5B.
Bulla wall is seen parallel to parietal pleura.
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Fig. 3. —49-year-old man with giant bullous emphysema and spontaneous right
pneumothorax. Chest CT scan shows large asymmetric upper lobe bullae. Chest
tube is located peripherally in right pleural space. Note presence of air in
pleural space surrounding anterior bulla on right (arrow) and
parallel configuration of bulla wall with chest wall. This is double-wall sign
of pneumothorax. This case illustrates benefit of identifying this sign to
distinguish intraparenchymal air, as seen in huge bullae on left, from small
pneumothorax surrounding these large bullae on right.
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Fig. 4. —33-year-old-man with giant bullous emphysema and left pneumothorax.
Chest CT scan shows asymmetric upper lobe bullae. Double-wall sign on left
confirms presence of extrapleural air. Note comparison with right side where
air is contained only within walls of bullae. Recognition of this sign in
patients with giant bullae, shortness of breath, and suspicion of pneumothorax
is invaluable in accurately directing appropriate chest tube placement.
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Fig. 5B. —60-year-old man with giant bullous emphysema and no pneumothorax.
Chest CT scan through upper thorax shows apparent double-wall sign
(arrow) in absence of pneumothorax. However, CT scans at other levels
(not shown) revealed apparent sign to be opposing walls of two adjacent
bullae. Note absence of air external to these bullae and nonparallel
configuration of bulla wall with chest wall.
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Of the three patients with giant bullous emphysema and no pneumothorax, two
were evaluated for medical problems related to their underlying pulmonary
disease and one was seen for preoperative evaluation of anticipated hernia
repair. In one of these patients, who was admitted with shortness of breath
and back pain, chest radiography did not clearly indicate pneumothorax.
Because the patient was clinically stable, a chest CT scan was obtained to
confirm suspected pneumothorax before chest tube placement to avoid potential
inadvertent complications. CT showed giant bullous emphysema and a T8
compression fracture (Fig.
5A,5B),
but no pneumothorax and no double-wall sign. The patient's back pain was
attributed to his compression fracture, and his shortness of breath was
believed to be an exacerbation of emphysema. Clinical follow-up was consistent
with this diagnosis. The remaining two patients with giant bullous emphysema
underwent chest CT to evaluate the extent of the bullous disease. On chest CT,
these patients had no clinical signs of pneumothorax, no acute exacerbation of
dyspnea, and no double-wall sign.
The double-wall sign was retrospectively identified in all four patients
with clinical suspicion and response to treatment of pneumothorax and was
absent in the three patients without clinical evidence of pneumothorax.
Discussion
Giant bullous emphysema is a distinct clinical syndrome, characterized by
large bullae in the upper lobes, usually in young or middle-aged men
[1,
4,
5]. Most patients with bullous
emphysema are cigarette smokers. Giant bullous emphysema has been referred to
as the vanishing lung syndrome, type 1 bullous disease, bullous pneumopathy,
or primary bullous disease of the lung
[1,
4,
5].
The radiographic criteria for giant bullous emphysema, as defined by
Roberts et al. [4], include the
presence of giant bullae in one or both upper lobes, occupying at least one
third of the hemithorax and compressing surrounding normal lung parenchyma.
Stern et al. [5] described the
CT findings of giant bullous emphysema, which included multiple large bullae,
ranging from 1 to 20 cm in diameter, usually 2-8 cm, without a single dominant
giant bulla. All seven of our patients had bilateral asymmetric bullous
emphysema.
Patients with giant bullous emphysema are prone to spontaneous
pneumothorax, as seen in two of our patients. Clinical and conventional
radiographic detection of pneumothorax in patients with giant bullous
emphysema and shortness of breath can be extremely difficult. When the
diagnosis on chest radiography is uncertain, chest CT is recommended
[2,
3,
7]. Two of our patients had a
pneumothorax that was not detected until CT was performed. In our study
another patient without pneumothorax was inappropriately treated with chest
tube placement. Confirmatory CT would have avoided the eventual complications
of bronchopleural fistula and right upper lobectomy. Review of the literature
found a report of treating patients with severe bullous emphysema with
intentional intrabullous catheter placement, but use of this procedure is not
routine [11].
The following signs have been used to detect pneumothorax in patients with
giant bullous emphysema: compressed or consolidated lung, nonanatomic
hyperlucency, and immediate symptomatic relief and lung expansion at chest
tube placement [9]. We describe
in this report another valuable sign to distinguish pneumothorax from adjacent
giant bullae: the double-wall sign. This sign occurs when one sees air
outlining both sides of the bulla wall parallel to the chest wall (Figs.
2A,2B,2C,
3,
4B, and
4C). Absence of this sign
provides further evidence and increased confidence against the diagnosis of
pneumothorax, which can prevent unnecessary chest tube placement. The
double-wall sign may not be evident on all CT slices, particularly with
compression of adjacent bullae, but careful observation of multiple images
will reveal this sign when a pneumothorax is present
(Fig. 4). One potential pitfall
in the appreciation of the double-wall sign of pneumothorax occurs when two
large bullae are adjacent to one another. This situation can produce an
apparent double-wall sign, mimicking pneumothorax. However, careful scrutiny
of multiple images will show the absence of air in the pleural space and that
the bulla wall is not parallel to the chest wall or parietal pleura (Fig.
5A,5B).
The double-wall sign was seen in all patients with pneumothorax and was
absent in those without, but our study was limited by a small population. An
additional prospective study with a larger group of patients would define the
overall accuracy of this sign in detecting pneumothorax.
Another limitation of this study results from using chest CT as the gold
standard for detecting pneumothorax while testing its diagnostic capabilities.
Although CT findings were used to determine the presence or absence of
pneumothorax, clinical stability was also evaluated in each patient to ensure
that clinical diagnosis remained consistent with the imaging findings.
Moreover, the only reasonable avenues currently available to render the
diagnosis of pneumothorax are chest CT, conventional radiography, and clinical
examination; therefore, we must rely on these diagnostic tools. False-negative
or false-positive cases of pneumothorax may have occurred in this study, but
the consistent correlation of imaging findings and clinical presentation in
each patient argues against this possibility. Ultimately, the double-wall sign
should be validated prospectively.
Last, another potential pitfall in using the double-wall sign to detect
pneumothorax in patients with giant bullous emphysema occurs in the setting of
chronic pneumothorax. Those patients with long-standing pneumothorax may
develop pleural septations or adhesions that could simulate a double-wall
sign. However, this situation is quite rare, and was not seen in our study
over a 3-year period.
In summary, understanding and recognizing the double-wall sign should aid
in the triage of patients with giant bullous emphysema and acute shortness of
breath. We advocate chest CT in any patient with known or suspected giant
bullous emphysema who becomes acutely breathless and in whom consideration of
chest tube placement is based on equivocal clinical and conventional
radiographic findings [2,
3,
6,
7].
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Abstract
Introduction
