DOI:10.2214/AJR.07.2824
AJR 2007; 189:1387-1396
© American Roentgen Ray Society
Advanced Visualization of Airways with 64-MDCT: 3D Mapping and Virtual Bronchoscopy
Karen M. Horton1,
Maureen R. Horton2 and
Elliot K. Fishman1
1 Department of Radiology, Johns Hopkins Medical Institutions, 601 N Caroline
St., JHOC 3253, Baltimore MD, 21287.
2 Department of Medicine, Division of Pulmonary and Critical Care Medicine,
Johns Hopkins Medical Institutions, Baltimore, MD.
Received July 5, 2007;
accepted after revision July 23, 2007.
Address correspondence to K. M. Horton.
Abstract
OBJECTIVE. The purpose of this pictorial essay is to review the
current role of virtual bronchoscopy and 3D imaging of the airways in clinical
practice.
CONCLUSIONS. Virtual bronchoscopy produces high-resolution images of
the tracheobronchial tree and endobronchial views that simulate the findings
at conventional bronchoscopy. Interest in virtual bronchoscopy is increasing
as a result of improvements in computer hardware and software and advances in
MDCT that allow acquisition of isotropic data.
Keywords: airways • CT • virtual bronchoscopy
Introduction
Virtual bronchoscopy (VB) is a computer-generated 3D CT post-processing
technique that produces high-resolution images of the tracheobronchial tree
and endobronchial views that simulate the findings at conventional
bronchoscopy. Although the technique was described in the mid 1990s, it is
generating new interest as a result of improvements in computer hardware and
software and advances in MDCT scanner technology that allow acquisition of
isotropic data. This essay reviews the current role of VB and 3D MDCT imaging
of the airways in clinical practice.
Technique
High-quality images of the lungs and airways require careful attention to
scanning protocols and reconstruction techniques.
CT Protocol
IV contrast medium may or may not be needed, depending on the clinical
indication. For example, for imaging of suspected tracheal stenosis and
evaluation of stent patency, no IV contrast medium is needed. If, however, the
indication is evaluation of airway involvement by malignant disease or
suspected cases of a vascular ring or sling, IV contrast medium is essential.
In addition, if CT is being performed to guide transbronchial biopsy,
identifying the course of the mediastinal vessels can be useful. If IV
contrast medium is needed, we typically inject 100–120 mL of nonionic
contrast medium at a rate of 3 mL/s through a peripheral angiocatheter. The
scan timing can be tailored to highlight the arteries (25 seconds after
injection) or veins (40 seconds after injection), depending on the clinical
scenario. In this setting, CT of the airway can be combined with CT
angiography to show the relations between the vessels and the trachea.
When dedicated airway imaging is needed, we use a 64-MDCT scanner at 0.6-mm
collimation setting to generate 0.75-mm slices reconstructed every 0.5 mm for
3D review. The other settings are 200 effective mAs at 120 kVp with a rotation
time of 0.5 seconds. Scanning takes only a few seconds and therefore even
infants usually can undergo imaging without sedation. It is often useful to
reconstruct the data with both a high-resolution edge-enhancing kernel and a
standard soft-tissue kernel. In some cases, it may be helpful to reconstruct
the data in 3- to 5-mm slices to evaluate other intrathoracic anatomic
structures.
Reduced radiation dose is possible because of the high natural contrast
between the airways and soft tissue. The dose can be reduced in children and
in adults when dedicated airway imaging is the goal. In a study by Kosucu et
al. [1] involving 23 children
with suspected foreign body aspiration, MDCT of the chest was performed at 25-
to 50-mA tube current. MDCT VB had excellent image quality in 39% of the
cases, good in 52%, and poor in 9%.
CT of the airways usually is performed during inspiration. In certain
clinical applications, however, such as tracheobronchomalacia, both
inspiration and expiration acquisitions should be performed to detect airway
narrowing and collapse. Similarly, expiratory phase imaging can be valuable
for detecting airway stent failure.
3D Imaging
Once a CT study is completed, the data are transferred to a real-time
interactive 3D workstation (Leonardo, Siemens Medical Solutions). The data are
reviewed with a combination of volume rendering, maximum intensity projection,
and multiplanar reformation (MPR). Volume rendering is especially helpful
because the degree of transparency can be controlled and, when slab clip plane
editing is used, can display the airways in great detail. Color assignments
can be used to highlight stents. Volume visualization of the lungs can be
performed with varying degrees of transparency to highlight differences in
lung aeration. A series of preset views can be used to expedite the review
process.
Sorantin et al. [2] found
that the precision and accuracy of radiologic findings can be improved when
axial images, MPRs, and endoluminal views are viewed simultaneously on a
workstation. This display method is similar to that used for virtual
colonoscopy. When the axial images, MPRs, and endoluminal views can be
evaluated at the same time, intraluminal and extraluminal anatomic structures
can be evaluated efficiently.
In the performance of surface or volume rendering of the airway, it is
essential to select appropriate thresholds because the threshold affects the
diameter of the airways [3]
(Fig. 1A,
1B). Inappropriate thresholds
also can cause artifacts. It is often necessary to use different threshold
values when visualizing the central airway and the distal airway. De Wever et
al. [4] found that a threshold
value of –400 to –600 H was optimal for visualization of the
central bronchial tree, whereas a threshold of –750 H was better for
evaluation of the distal airway branches.
Normal Anatomic Features
3D CT of the lungs and airway can be used to display the normal anatomic
features of the tracheobronchial tree and to identify normal variants. 3D CT
can depict the airway down to the sixth- and seventh-order subdivisions
[5] (Fig.
2A,
2B,
2C,
2D,
2E). This 3D map can be used to
guide bronchoscopy or to direct transbronchial needle biopsy. It is important
for the radiologist to be familiar with the normal bronchial anatomic
features.
The lung consists of a series of airways and parenchyma. The airways are a
series of bronchi (tubes) that branch into progressively numerous shorter and
narrower tubes penetrating deep into the lung parenchyma. The conducting zone,
composed of the trachea, which branches approximately 16 times to the terminal
bronchioles, functions to lead inspired air to the respiratory zone, where gas
exchange occurs. The conducting airways represent an anatomic dead space of
approximately 150 mL. Distal to the terminal bronchioles is the respiratory
zone, which consists of approximately seven divisions, including the
respiratory bronchioles, alveolar ducts, and alveolar sacs. Approximately 300
million alveoli (with approximately the surface area of a tennis court)
account for a volume of approximately 4.0 L. In the respiratory zone, gas
exchange occurs in the capillary-covered alveoli.
Trachea
The trachea is usually 9–15 cm long in an adult and begins at
approximately the sixth cervical vertebra, at the inferior border of the
cricoid cartilage. The diameter of the trachea is typically 2–2.5 cm.
The trachea has two sections. The cervical portion is superior to the thoracic
inlet. The intrathoracic portion extends from the thoracic inlet to the
bifurcation (carina). The trachea is supported anteriorly by 16–20
C-shaped rings of cartilage. In the posterior aspect, the trachea
consists of the pars membranacea. This membrane is flexible, allowing the
trachea to change in configuration during inspiration and expiration. The
membrane normally bulges during expiration and coughing.
Carina
At level of sternal angle (T4–T5), the trachea divides at the carina,
a ridge formed by the downward and backward projection of the last tracheal
ring, into the right and left mainstem bronchi.
Mainstem Bronchi
The mainstem bronchi pass inferolaterally from the carina into the lungs
and are supported by cartilaginous rings. Both mainstem bronchi are
accompanied into the hila by the main pulmonary arteries. In the hila, the
mainstem bronchi branch to form the bronchial tree. The right and left
mainstem bronchi branch into secondary lobar bronchi, three on the right and
two on the left, which further branch into tertiary segmental bronchi, each
bronchus supplied by a segmental artery. Each segmental bronchus–artery
unit makes up a bronchopulmonary segment, a commonly used anatomic,
functional, and surgical subdivision. The segmental bronchi continue to branch
until reaching the terminal bronchioles, the smallest airway without
alveoli.
Right Bronchi
The right mainstem bronchus is wider and shorter than the left mainstem
bronchus and in line with the trachea. Because of this configuration, more
foreign bodies are aspirated into the right rather than the left bronchus. The
right mainstem bronchus divides into three secondary lobar bronchi: right
upper lobe, right middle lobe, and right lower lobe. The right upper lobe
bronchus branches immediately beyond the carina along the lateral wall. It
divides into three tertiary bronchi: posterior, anterior, and apical segmental
bronchi.
Distal to the takeoff of the right upper lobe bronchus, the right mainstem
bronchus is called the bronchus intermedius. It has three orifices: the right
middle lobe bronchial orifice in the anterior aspect, the right lower lobe
bronchial orifice directly in the center, and the superior segment of the
right lower lobe orifice in the posterior aspect, across from the right middle
lobe. The right middle lobe bronchus divides into the medial and lateral
segmental bronchi. The orifice of the right middle lobe bronchus occasionally
is oblong or fish mouthed, causing retention of secretions, bronchiectasis,
and infections. The right lower lobe bronchus branches further into four
segmental bronchi: the medial basal segment along the medial side and the
posterior, anterior, and lateral segmental bronchi.
Left Bronchi
The left mainstem bronchus is more angulated and longer then the right.
Pulsations from the heart often can be appreciated in the inferior medial
portion of the bronchus. It branches into two secondary lobar bronchi: left
upper lobe and left lower lobe. The left upper lobe bronchus divides
immediately into two orifices: left upper lobe and lingular. The left upper
lobe orifice leads into three segmental bronchi: apical, posterior, and
anterior. Often there are only two branches: apical–posterior and
anterior. The lingular orifice leads to the superior and inferior segmental
bronchi. The left lower lobe bronchus opens into two orifices opening to the
superior segmental bronchus posteriorly and four basal segments inferiorly:
medial basal, anterior basal, posterior basal, and lateral basal.
Tracheobronchial Stenosis
VB is being increasingly used to detect and grade benign and malignant
airway stenosis (Figs. 3A,
3B,
3C,
4A,
4B,
4C,
4D,
5A,
5B,
5C). VB has been shown
accurate in assessment of the stenotic width and length of fixed airway
lesions. In a study by Burke et al.
[6], correlation of stenotic
shape and contour between VB and conventional bronchoscopy was excellent. The
stenosis-to-lumen ratios determined with VB and conventional bronchoscopy were
found to be within 10% of each other.
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Fig. 4A —4-year-old boy with history of aortopexy performed to release
congenital vascular compression of left mainstem bronchus. Patient had
persistent stridor after surgery. CT scans show persistent narrowing of left
mainstem bronchus (arrow), which is pinched between descending aorta
and left pulmonary artery. Coronal multiplanar reformation.
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Fig. 4B —4-year-old boy with history of aortopexy performed to release
congenital vascular compression of left mainstem bronchus. Patient had
persistent stridor after surgery. CT scans show persistent narrowing of left
mainstem bronchus (arrow), which is pinched between descending aorta
and left pulmonary artery. Volume-rendered image.
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Fig. 4C —4-year-old boy with history of aortopexy performed to release
congenital vascular compression of left mainstem bronchus. Patient had
persistent stridor after surgery. CT scans show persistent narrowing of left
mainstem bronchus (arrow), which is pinched between descending aorta
and left pulmonary artery. Endoluminal image.
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Fig. 4D —4-year-old boy with history of aortopexy performed to release
congenital vascular compression of left mainstem bronchus. Patient had
persistent stridor after surgery. CT scans show persistent narrowing of left
mainstem bronchus (arrow), which is pinched between descending aorta
and left pulmonary artery. Axial image.
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Fig. 5A —77-year-old woman with Wegener's granulomatosis. CT scans
show irregular thickening and narrowing of left mainstem bronchus
(arrow) with partial left upper lobe atelectasis. Axial image with
soft-tissue window.
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Fig. 5B —77-year-old woman with Wegener's granulomatosis. CT scans
show irregular thickening and narrowing of left mainstem bronchus
(arrow) with partial left upper lobe atelectasis. Axial image with
lung window.
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Fig. 5C —77-year-old woman with Wegener's granulomatosis. CT scans
show irregular thickening and narrowing of left mainstem bronchus
(arrow) with partial left upper lobe atelectasis. Endoluminal
image.
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In 2002, Hoppe et al. [7]
used 4-MDCT at 2-mm collimation to examine 200 bronchial segments obtained
from 20 patients. In that study, CT was highly accurate in revealing airway
stenosis (accuracy of VB, 98%; axial images, 96%; coronal MPR, 96%; sagittal
MPR, 96.5%). The VB images correlated closely with the findings at flexible
bronchoscopy (r = 0.91) for grading of stenosis. In that study, the
VB images were better than the other CT display methods for semiquantitative
assessment of stenosis. In a more recent study, Hoppe et al.
[8] used 4-MDCT at 1-mm
collimation with flexible bronchoscopy as the reference standard and found
that VB had an accuracy of 95.5% in detection of central airway stenosis
(trachea, main bronchi, lobar bronchi). VB also had an accuracy of 95.5% in
the detection of stenosis in the segmental airways. The authors, however,
mentioned that VB had a higher number of false-positive findings in the
segmental arteries than in the central airways. The positive predictive value
for VB was 40.9% for the segmental airways versus 84.4% for the central
airways.
VB can be especially valuable for evaluation of suspected tracheobronchial
stenosis in children. CT is less invasive and safer than fiberoptic
bronchoscopy. CT also has the advantage of depicting the adjacent structures,
such as vascular rings, which can be a cause of stridor in children. Honnef et
al. [9] used 16-MDCT and VB to
examine 12 children with stridor and stenosis detected at conventional
bronchoscopy. The CT findings correlated with those at fiberoptic bronchoscopy
in all 12 patients and with the surgical findings in eight of the 12 patients.
CT showed tracheal stenosis in 11 of 12 patients. The causes of compression
included vascular compression by the brachiocephalic trunk (n =6),
double aortic arch (n = 2), aberrant right subclavian artery
(n = 1), and vascular compression of the left main bronchus
(n =2). The one child in whom no stenosis was detected on CT but was
found at fiberoptic bronchoscopy did not undergo surgery. CT showed crossing
vessels, which may have caused the tracheal pulsation seen at conventional
bronchoscopy, but no stenosis.
CT and VB can be helpful in the evaluation of airway abnormalities in
patients who have undergone lung transplantation. McAdams et al.
[10], in a study involving 17
lung transplant recipients, concluded that CT bronchography was slightly more
accurate than axial CT in the diagnosis of anastomotic stenoses.
There are limitations to using VB for evaluation of airway stenosis. First,
retained mucus or blood can cause false-positive findings. Second, the mucosa
cannot be visualized with CT, as is possible at conventional bronchoscopy
[11]. Third, the diameter of
the airway on CT depends on the respiratory cycle. Stenosis can be
underestimated on inspiration; therefore, VB for this indication is typically
performed during expiration or, in some cases (e.g., tracheomalacia), during
both inspiration and expiration. Obtaining images in both stages of
respiration can be difficult in examinations of infants and children. Fourth,
it can be difficult or impossible to identify some dynamic airway lesions,
such as immobile vocal cords, with VB
[6]. Fifth, the diameter of
air-filled structures is partially dependent on the threshold and rendering
parameters. When the settings are exaggerated, the apparent diameter of the
structure changes [3].
Bronchogenic Carcinoma
CT is the primary imaging technique for the detection, staging, and
follow-up of primary malignant tumors of the lung. Radiologists typically rely
solely on axial images of this patient population. However, investigators have
begun to study the potential value of VB for this clinical application (Figs.
6A,
6B,
6C and
7A,
7B,
7C). Finkelstein et al.
[11] studied 32 consecutively
examined patients with malignant thoracic tumors and suspected
tracheobronchial lesions. VB and the results of conventional bronchoscopy were
compared for 20 of the 32 patients. VB depicted all 13 of the obstructive
lesions and five of the six endobronchial lesions but none of three mucosal
lesions. In that study, the sensitivity of VB for all abnormalities was 82%,
and the specificity was 100%. In a subsequent study, Finkelstein et al.
[12] found CT with VB had a
sensitivity of 100% for obstructive lesions, 16% for mucosal lesions, and 90%
for endoluminal lesions. The overall sensitivity was 83% in patients with
malignant tumors, and the specificity was 100%. In a similar study, Liewald
and coworkers [13] used VB and
fiberoptic bronchoscopy to examine 30 patients with lung cancer. All 13
obstructive lesions were well seen on VB, but no mucosal lesions were
identified on VB.
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Fig. 6A —75-year-old man with recurrent pneumonia. Lobular mass
(arrows, B and C) arises from bronchus intermedius
causing partial obstruction and atelectasis. Biopsy revealed atypical
carcinoid. Axial CT scan.
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Fig. 6B —75-year-old man with recurrent pneumonia. Lobular mass
(arrows, B and C) arises from bronchus intermedius
causing partial obstruction and atelectasis. Biopsy revealed atypical
carcinoid. Coronal multiplanar reformation CT scan.
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Fig. 6C —75-year-old man with recurrent pneumonia. Lobular mass
(arrows, B and C) arises from bronchus intermedius
causing partial obstruction and atelectasis. Biopsy revealed atypical
carcinoid. Endoluminal image.
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Fig. 7A —50-year-old man with bronchogenic carcinoma. CT scans show
extensive tumor involvement of mediastinum and pleura. Focal metastatic lesion
(arrow) is present along right wall of trachea. Coronal multiplanar
reformation.
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Fig. 7B —50-year-old man with bronchogenic carcinoma. CT scans show
extensive tumor involvement of mediastinum and pleura. Focal metastatic lesion
(arrow) is present along right wall of trachea. Volume-rendered
image.
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Fig. 7C —50-year-old man with bronchogenic carcinoma. CT scans show
extensive tumor involvement of mediastinum and pleura. Focal metastatic lesion
(arrow) is present along right wall of trachea. Endoluminal
image.
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An advantage of VB over fiberoptic bronchoscopy is the ability to image
beyond the site of obstruction and to visualize the smaller airways, which are
not accessible with fiberoptic bronchoscopy. For example, in the study by
Finkelstein et al. [11], in
five patients, VB depicted peripheral obstructive lesions that were beyond the
size limitation of the endoscope.
Endoluminal Lesions
Because it produces both a global view of the airways and endoluminal
images, VB can be used to identify endoluminal lesions
[14,
15] (Figs.
8A,
8B,
8C and
9A,
9B). The literature varies
regarding the usefulness of VB for this indication. For example, in a study by
LaCasse et al. [15] involving
163 patients (63 with endobronchial lesions), the sensitivity and specificity
of VB in the detection of endobronchial lesions were 68% and 90%. In that
study, in which 3-mm slices were reconstructed every 1.5 mm, only 26 of 34
lobar lesions and 11 of 23 segmental lesions were detected on CT. In a smaller
study, however, Finkelstein et al.
[11] used 1.25-mm slices and
detected five of six endoluminal lesions. It is likely that the ability to
perform submillimeter collimation will improve spatial resolution even more
and may improve the ability to visualize endoluminal lesions. It is unlikely,
however, that CT will completely replace conventional bronchoscopy in the
evaluation of suspected malignant tumors, because CT does not depict the
mucosa directly.
Anatomic Variants
VB can be easily used for identification of anatomic variants such as
tracheal and bronchial diverticula (Fig.
10A,
10B,
10C). A tracheal diverticulum
is characterized as an outpouching of the tracheal wall. Diverticula can be
single or multiple and are identified during 1% of autopsies
[16,
17]. Diverticula are usually
asymptomatic but can trap secretions and can become infected. Patients present
with cough, dyspnea, or repeated episodes of tracheobronchitis
[18,
19].
Tracheal diverticula can be congenital or acquired. Congenital diverticulum
is thought to represent a vestigial supernumerary lung or aborted abnormally
high division of the primary lung bud
[20]. The congenital variety
usually arise 4–5 cm below the true vocal cords or just above the carina
[20] and are almost always on
the right side. Congenital tracheal diverticula are true diverticula because
they contain all normal layers of the tracheal wall.
Acquired tracheal diverticula are most likely caused by increased
intraluminal pressure related to chronic cough and emphysema
[21]. Acquired diverticula can
occur anywhere along the trachea and typically have a wider mouth than do
congenital diverticula. Acquired diverticula are lined by respiratory
epithelium but do not contain other elements of the tracheal wall, such as
smooth muscle and cartilage
[20]. Management of acquired
tracheal diverticula may include antibiotics and, in rare instances,
surgery.
Normal variants such as a tracheal bronchus (Fig.
11A,
11B,
11C) can be identified with
VB. Tracheal bronchus is a congenital aberrant bronchus present along the
right side of the trachea above the carina, supplying the right upper lobe.
Tracheal bronchus is usually an incidental finding but can be symptomatic if
it acts as a reservoir for secretions or infection. An association between
tracheal bronchus and other bronchopulmonary abnormalities has been reported
[22]. Tracheal bronchus in
patients with Down syndrome and in patients with tracheal stenosis has been
described [22]. If patients
have recurrent infections, surgical resection of the aberrant bronchus and the
associated lobe it supplies may be indicated
[22]. Vascular anatomic
variants causing tracheal stenosis can be identified with a combination of VB
and axial and MPR images, as in imaging of tracheobronchial stenosis.
Foreign Body Aspiration
Foreign body aspiration is a common and serious cause of respiratory
difficulties in children. Many cases of foreign body aspiration may not be
recognized initially, and the child may be incorrectly treated for asthma or
bronchiolitis [1]. A study by
Applegate et al. [23] showed
that the diagnosis of foreign body aspiration is made in only 59% of cases
within the first 24 hours. Prompt recognition of foreign body aspiration is
essential. Delay in diagnosis can lead to wheezing, infection, and
life-threatening airway obstruction. In cases of suspected foreign body
aspiration, radiographs are usually obtained and can be helpful. However,
radiographic findings are normal in as many as 30% of cases. It is estimated
[23] that only 10% of
aspirated foreign bodies are radiopaque. In this clinical setting, CT can be
useful for detecting aspirated foreign objects, including plastic items and
food [1,
23] (Fig.
12A,
12B). Applegate et al. used
low-dose CT to visualize plastic toys in the airways of cadavers with a
sensitivity and specificity of 89%. Kosucu et al.
[1] performed low-dose MDCT and
VB on 23 children with clinically suspected foreign body aspiration. All
patients also underwent conventional bronchoscopy. In 15 patients, the foreign
object was identified with CT and conventional bronchoscopy. CT also has the
advantage of showing secondary signs, such as hyperaeration, atelectasis, and
infiltrates. In a study involving 21 consecutively registered patients with
suspected foreign body aspiration, Kocaoglu et al.
[24] found no added benefit of
VB over standard axial images and MPRs.
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Fig. 12A —73-year-old man who arrived in emergency department with
shortness of breath and wheezing, remote history of right upper lobectomy for
lung cancer, and recent history of bladder cancer managed with
cystoprostatectomy 2 weeks previously. CT evaluation to rule out pulmonary
embolism revealed filling defect (arrow) in right lower lobe bronchus
not reported after initial review of axial images but later found on coronal
multiplanar reformations. Bronchoscopy revealed aspirated food. Axial
image.
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Fig. 12B —73-year-old man who arrived in emergency department with
shortness of breath and wheezing, remote history of right upper lobectomy for
lung cancer, and recent history of bladder cancer managed with
cystoprostatectomy 2 weeks previously. CT evaluation to rule out pulmonary
embolism revealed filling defect (arrow) in right lower lobe bronchus
not reported after initial review of axial images but later found on coronal
multiplanar reformations. Bronchoscopy revealed aspirated food. Coronal
multiplanar reformation.
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Imaging Guidance
VB can be used to direct transbronchial needle aspiration of mediastinal
and hilar nodes and masses
[25]. The success rate for
transbronchial biopsy is only 50% for nodes and tumors not visible to the
bronchoscopist [26]. McAdams
et al. [25] reported great
success using VB as a guide for transbronchial needle aspiration during
fiberoptic bronchoscopy. Those authors found the sensitivity for malignancy on
a per node basis was 88%, considerably higher than the sensitivity reported
for non-CT-guided transbronchial needle aspiration. They attributed their
success to their ability to better correlate node location and angle of needle
approach using VB instead of standard axial images. They also believed VB
imaging gave them greater confidence in biopsying small nodes and nodes in
difficult locations. In that study, use of VB decreased procedure time. VB
also can be used to guide biopsy of peripheral lesions. For example, Shinagawa
et al. [27] found that VB can
be used to guide transbronchial biopsy with an ultrathin bronchoscope. Small
peripheral lesions (< 20 mm) were successfully biopsied with this
technique.
Miscellaneous Applications
VB may play a role in a variety of clinical applications.
Tracheoesophageal Fistula
Patients with esophageal atresia can have an associated tracheoesophageal
fistula. Lam et al. [28]
successfully used 3D CT with VB to locate the site of a fistula and to measure
the gap between the upper and lower portions of the esophagus.
Burn Injuries
Gore et al. [29] found that
VB can play a role in identifying inhalation injuries in burn patients with
suspected airway involvement. Ten burned patients with clinical suspicion of
inhalation injury underwent CT, and in eight of the cases the diagnosis was
confirmed on the VB images.
Stent Planning and Follow-up
Because it has been shown accurate in imaging of the airways, CT with VB
can be used in planning of placement of metallic bronchial stents. In patients
who have had stents inserted, CT can be used to confirm patency and to
diagnosis stenosis and migration (Fig.
13A,
13B,
13C). In a study involving 25
patients with 28 endobronchial stents, Ferretti et al.
[30] found CT with VB useful
for evaluating the stents. In that study, CT with VB was compared with
fiberoptic bronchoscopy. CT showed all but two clinically significant
abnormalities. Both of the missed cases were related to granuloma formation at
the origin of the stent.
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Fig. 13B —49-year-old man with lung cancer obstructing left mainstem
bronchus treated with stent placement. Stent (arrows) has migrated
and protrudes into carina. Coronal multiplanar reformation.
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Trauma
Moriwaki et al. [31] found
3D CT with VB useful for the diagnosis of tracheal injury in patients in
hemodynamically stable condition. In that small series, CT depicted a defect
or depression in the wall at the site of the injury diagnosed at bronchoscopy.
The CT depiction of the site and size of the injury was comparable to that of
fiberoptic bronchoscopy.
Conclusion
Although 3D CT with VB has been used for more than 10 years, enthusiasm for
the technique is increasing in both the radiologic and pulmonary medicine
communities owing to advances in CT scanner hardware and software. It is clear
that VB can be a useful adjunct to conventional axial CT in the evaluation of
patients with suspected airway abnormalities.
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Abstract
Introduction
