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ucu1
lu1uzhan Özdemir1enur Ökten3it Gümele1
1 Department of Radiology, Medical School of Karadeniz Technical University,
Farabi Hospital, Trabzon 61080, Turkey.
2 Department of Pediatrics, Medical School of Karadeniz Technical University,
Farabi Hospital, Trabzon 61080, Turkey.
3 Department of Cardiovascular Surgery, Medical School of Karadeniz Technical
University, Farabi Hospital, Trabzon 61080, Turkey.
Received October 30, 2003;
accepted after revision May 20, 2004.
Address correspondence to P. Kosucu.
Abstract
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SUBJECTS AND METHODS. Low-tube-current MDCT was performed in 23 patients (10 girls, 13 boys) with a mean age of 3.3 years (9 months–13 years) with suspicion of foreign body aspiration. Chest radiographs were obtained before CT was performed. MDCT was performed using 25- to 50-mA tube currents. MDCT virtual bronchoscopy images were obtained. Neither sedation nor IV contrast medium was used during CT scanning. All patients underwent endoscopic evaluation within 24 hr after MDCT was performed. MDCT virtual bronchoscopy findings were retrospectively compared with the results of rigid bronchoscopy.
RESULTS. The mean tube current was 35 mA (range, 25–50 mA). Imaging quality was excellent in nine studies (39%), good in 12 studies (52%), and poor in two studies (9%). Motion artifacts were present on several slices in five examinations. In 15 patients, all foreign bodies detected by conventional bronchoscopy were also revealed on MDCT virtual bronchoscopy. The foreign body was in the right main bronchus in six patients, in the bronchus intermedius in one patient, and in the left main bronchus in eight patients. No discordance was found between the two techniques. MDCT revealed hyperaeration of the ipsilateral lung in five patients, atelectasis in five patients, infiltration in three patients, and infiltration and bronchiectasis in two patients; it showed infiltration in four patients and atelectasis in one of eight patients without a foreign body detected. There were no abnormal findings in three patients.
CONCLUSION. Evaluation of foreign body aspiration of the airway in children can be accomplished by using a low-tube-current MDCT protocol. It may be useful both in showing the exact location of a foreign body before bronchoscopy and in ruling out a foreign body in patients with a low level of suspicion and normal or nonspecific findings on chest radiography.
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The diagnosis and management of foreign body aspiration at the proper time are extremely important. This diagnosis is made correctly in the first 24 hr after aspiration in only 59% of cases [1]. A foreign body in the airway requires prompt removal. Missed or delayed diagnosis can result in respiratory complications ranging from chronic wheezing or recurrent pneumonias to life-threatening airway obstruction or lung abscess [3, 4].
In children with a foreign body in the airway, chest radiography findings are frequently normal and can display abnormalities uncharacteristic of foreign body aspiration [5]. Radiography features depend on the size, location, duration, and nature of the foreign body. Chest radiography may show a variety of findings, including air-trapping, consolidation, atelectasis, and bilateral overaeration [6]. The radiologic diagnosis of foreign body aspiration is also challenging for several reasons: only 10% of foreign bodies are radiopaque, the findings of chest radiography are normal in up to 30% of children who aspirate a foreign body, and the presence of pulmonary infiltrates may misdirect the management of foreign body aspiration [1].
Bronchoscopy is often performed for definitive diagnosis and management; however, it is invasive and serious complications may occur [5]. Recently developed virtual bronchoscopy is a noninvasive technique that provides realistic 3D views of the tracheobronchial tree [6]. The volumetric imaging data acquired on MDCT can be manipulated, and additional high-quality multiplanar and 3D reconstructions can be obtained. Virtual bronchoscopy of the tracheobronchial system with both single-detector CT and MDCT is well established in adults [7–10], but experience with pediatric patients is limited. To the best of our knowledge, only three studies of virtual bronchoscopy in children have been published in the English-language literature [6, 11, 12].
MDCT allows rapid acquisition of the volumetric data sets. For pediatric imaging, it is of the utmost importance to reduce radiation exposure to the minimum appropriate for diagnosis. Using a low-tube-current technique and rapid table speed can also minimize radiation exposure (the major disadvantage of CT in pediatric patients) [13]. Previous studies have shown that thin-section CT can be performed to evaluate the pulmonary parenchyma at lower-tube-current settings without significant loss of image quality [13–19]. One study has reported low-dose CT applied to 3D imaging of the chest [16]. In our study, we aimed to describe the potential use of low-tube-current MDCT virtual bronchoscopy in children with foreign body aspiration. To our knowledge, ours is the first report on the use of this technique for the evaluation of foreign body aspiration in children.
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This study included patients who were referred from the pediatric pulmonology unit with a history of aspiration, sudden-onset coughing and wheezing, or pneumonia unresponsive to treatment suggesting foreign body aspiration. In five patients, the history of aspiration was clear. Seven patients were admitted with a history of sudden onset of coughing and wheezing. The remaining 11 patients were hospitalized for pneumonia but were unresponsive to treatment. The duration of symptom onset ranged from 1 day to 2 months. Initially, posteroanterior inspiratory chest radiographs were obtained in each patient, followed by MDCT scanning; then all patients underwent endoscopic evaluation within 24 hr after MDCT.
CT
All patients were imaged on an MDCT scanner (Somatom Volume Zoom, Siemens).
MDCT was performed from the level of the larynx to the dome of the diaphragm
at end inspiration. Scanning parameters were the following: slice width, 1.25
mm; slice collimation, 4 x 1; feed–rotation, 4 mm; rotation time,
0.5 sec; pitch, 4; and 80 kVp. The tube current was selected individually
according to the size of the body (mA, 25–50). The scanning time ranged
from 17 to 55 sec. Images were reconstructed in the axial plane at 1-mm
intervals with a standard reconstruction algorithm.
The examination was performed with a single-breath-hold technique in 10 patients. Scanning was conducted during spontaneous breathing in 13 patients who were unable to hold their breath. Neither sedation nor IV contrast medium was used.
Image Processing
After scanning, we transferred the MDCT data sets to an independent
workstation (Virtuoso, Siemens) for postprocessing. Computer generation of the
tracheobronchial images was accomplished in three successive steps as
previously described [6]. For
virtual bronchoscopy visualization, the workstation screen was divided into
three parts: a global view, an endoscopic view, and a slice view. In the
global view, the generated polyhedral models of the tracheobronchial tree
could be inspected from the outside. In addition, the position of the virtual
camera was depicted and the multiplanar format of the single-detector CT data
was depicted orthogonal to the axis of the virtual camera (virtual inner
surfaces of the airway). The virtual camera could be moved interactively in
any direction. The aperture of the virtual camera could be adjusted between 0
and 170°. During the study, apertures between 70 and 110° were used.
Real-time collision detection kept the virtual camera within the lumen of the
airway and assisted the operator during airway navigation. The slice view
presented the corresponding axial CT slice at the position of the virtual
camera. The endoscopic view began at the tracheal inlet; moved to the trachea,
right lung bronchi, left lung bronchi, and upper lobes; then moved to the
middle lobe and lingula; and finally moved to the lower lobes. The radiologist
had to pull back the virtual endoscope to the bifurcation before entering
smaller branches.
Postprocessing time ranged between 25 and 35 min for each study. The virtual images for each patient were saved as digital files. The axial images and virtual bronchoscopy images were evaluated together. All images were available on an independent workstation. Hard copies were made of all transverse and virtual bronchoscopy images.
Image Analysis
Two radiologists reviewed and evaluated all CT studies and arrived at
conclusions by consensus. When observers reviewed the studies, they were
unaware of endoscopic findings. The axial images were viewed with standard
lung window settings (level, –700 H; width, 1,000 H) and standard
soft-tissue window settings (level, 50 H; width, 450 H) for the presence or
absence of foreign bodies. The CT criterion of a foreign body was its presence
in the lumen of the tracheobronchial three. Additional parenchymal and
mediastinal abnormalities were noted. The axial CT images were interpreted
first; then virtual bronchoscopy in the multiview mode was performed. The
virtual bronchoscopy studies were evaluated for image quality (excellent,
diagnostic, or poor), motion artifact (present or absent), and the usefulness
of the studies. The tracheobronchial system was carefully evaluated for the
presence of foreign bodies.
Virtual Bronchoscopy Quality
The quality of virtual bronchoscopy was assessed independently by both
reviewers using a 3-point score: excellent quality (smooth polyhedral surface
models), diagnostic quality (only minor irregularities of polyhedral surface
models), and poor quality (respiratory motion producing stairstep artifacts).
The final decision was made by consensus.
Bronchoscopy
Bronchoscopy was performed in all patients using a rigid pediatric Karl
Storz bronchoscope (model no. B482, Karl Storz Endoscopy), with the patient
under general anesthesia in the operating room. After monitoring and careful
administration of the anesthetic, the appropriate-sized pediatric ventilating
rigid bronchoscope was inserted under direct vision past the vocal cords.
First, the unaffected bronchus was evaluated for foreign bodies, anatomic
abnormalities, or inflammation. The foreign body, once visualized, could be
extracted using the optical grasping forceps. After the foreign body was
removed, the bronchoscope was reinserted to look for any retained fragments,
to aspirate trapped secretions for culture, and to evaluate the severity of
the tissue reaction and edema. Postoperatively, the children were observed in
the hospital, usually for less than 18 hr.
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Chest radiography in nine of 15 patients with foreign bodies showed hyperaeration of the ipsilateral lung, either of the lobe or of the entire lung in four patients (Fig. 1A); infiltrates in three patients; and atelectasis in two patients (Fig. 2A). Six of the 15 patients had normal findings on chest radiography. Chest radiography revealed metallic objects in the bronchial tree in two of 15 patients.
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Axial MDCT scans showed foreign bodies in all 15 patients. Hyperaeration (n = 5) (Fig. 1B) and atelectasis (n = 5) were the most common additional thoracic CT findings, followed by infiltration (n = 3) and infiltration and bronchiectasis (n = 2) (Fig. 2C).
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Axial MDCT images, virtual bronchoscopy, and conventional bronchoscopy did not reveal foreign bodies in eight patients. In this group, MDCT and chest radiography showed infiltration in four patients and atelectasis in one patient. Findings of CT and chest radiography were normal in three patients.
All patients were evaluated endoscopically after MDCT virtual bronchoscopy was performed. All foreign bodies were removed successfully. We removed the following foreign bodies: nuts in 12 patients, metallic objects in two patients, and a plastic object in one patient. Rigid bronchoscopy confirmed the same results (presence and location of foreign bodies) as those of MDCT virtual bronchoscopy. The sensitivity and specificity of MDCT virtual bronchoscopy compared with rigid bronchoscopy were 100%. The sensitivity, specificity, and accuracy of inspiratory chest radiographs compared with rigid bronchoscopy were 60%, 37%, and 52%, respectively.
Image quality was classified as excellent in nine studies (39%), diagnostic in 12 studies (52%), and poor in two studies (9%). The primary reason that the 12 studies were considered diagnostic rather than excellent was the presence of increased noise, which was related to the low tube current and rapid table speed. Motion artifacts were present on several images in five examinations. No studies were considered technically nondiagnostic. Because of low tube current, we observed artifacts from the shoulder on the axial images.
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Because of the high risk associated with overlooked foreign body aspiration, bronchoscopy is often performed for definitive diagnosis and treatment, even when there is little suspicion or doubtful history. Although the general impression is that bronchoscopy is simple and safe in pediatric patients, serious complications such as pneumothorax, pneumonia, respiratory distress, cardiac arrest, pneumomediastinum, trachea laceration, and subglottic edema may occur in 6–8% of children, even when performed by experienced radiologists [5, 20].
Diagnosis of foreign body aspiration begins with a patient history and clinical exploration and can be strengthened by radiographic findings. Metallic objects are readily identified on chest radiographs. However, most inhaled foreignFig. 2B bodies are nonradiopaque; the most common material is food, usually a vegetable [1, 21]. A radiolucent foreign body can be suggested only by secondary changes [22]. These include segmental or lobar collapse; air trapping, especially in a unilateral hyperlucent lung; postobstructive lobar or segmental infiltrates; or other chronic pulmonary changes [23]. However, these findings are nonspecific and may occur also in patients without foreign body aspiration. In addition, 9–35% of patients with endoscopically confirmed foreign bodies do not have any abnormalities on radiographs [3, 22, 24, 25]. Swedstrom et al. [26] reported that chest radiography for foreign body aspiration in 108 children has a sensitivity of 68% and a specificity of 67%. In our study, two patients with metallic foreign body aspiration were diagnosed directly on chest radiography. Whereas nine of 15 patients had secondary parenchymal findings, six (false-negative findings) had no abnormal findings on chest radiographs. In addition, secondary parenchymal changes were seen in five of eight patients who had no foreign body aspiration. In this study, the sensitivity was 60%, and the specificity was 32% regarding chest radiography for foreign body aspiration. Thus, although chest radiography may help, it seems neither sufficiently sensitive nor specific for the diagnosis of foreign body aspiration.
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The detection of unilateral air trapping with foreign body aspiration is enhanced with expiratory or bilateral decubitus radiographs. Kim et al. [27] reported that patients believed to have foreign bodies in the airway should undergo inspiratory–expiratory radiography and fluoroscopy. Of their 202 patients, 33 had normal findings on radiography. However several studies have reported that 24–34% of patients with normal radiographic findings were proven to have a foreign body during bronchoscopy [20]. These common false-negative radiographs cannot exclude the presence of foreign bodies in the airways. In this instance, CT may be helpful in diagnosing and in determining the exact location of the foreign body in patients with false-negative findings on inspiratory–expiratory and decubitus radiographs. A limitation of our study is that although expiratory chest radiography, lateral decubitus radiography, and fluoroscopic examinations are useful, we did not perform them routinely.
CT is another diagnostic technique used to detect foreign bodies. It not only can reveal foreign bodies in the bronchial tree but also is very sensitive in showing differences in density in the lung parenchyma. CT findings of three radiolucent foreign bodies were reported in children in 1980 [28]. Since then, to our knowledge, few reports mention using CT for the detection of foreign bodies. Recently, it was reported that low-dose helical CT is useful for visualizing plastic pieces (LEGO) in the airway and has a combined sensitivity of 89% and combined specificity of 89% in cadaveric specimens [1]. Zissin et al. [22] performed a CT study for the detection of foreign bodies in adults. They concluded that chronic unexplained respiratory symptoms warrant further investigation on CT to exclude foreign bodies—even if there is no pertinent history of a foreign body or if the findings of chest radiography are normal.
The most reliable CT findings of an aspirated foreign body are its presence within the lumen of the tracheobronchial three. Associated features are usually secondary parenchymal changes in the affected lobe. Reactive mediastinal findings (hilar lymphadenopathy and thickening of the surrounding bronchial walls) are also common and may be due to nonrecognition of the foreign body when its density does not differ from the surrounding parenchymal infiltration or when it is mistaken for a calcified node or bronchial mural calcification [22]. We showed that both the foreign bodies in the airway and secondary parenchymal changes such as hyperaeration, atelectasis, infiltration, and bronchiectasis are found in patients with foreign body aspiration.
Virtual endoscopy of the tracheobronchial system is a relatively new postprocessing technique, and technical solutions for routine use in clinical practice are expected in the near future for adults [29]. Virtual bronchoscopy of the tracheobronchial system with both single-detector CT and MDCT is well established in adults [6–10]. In pediatric patients, the value of virtual bronchoscopy has not been established yet. However, only four studies on the application of virtual bronchoscopy have been published, describing the technique and the comparison of virtual bronchoscopy with conventional bronchoscopy [6, 11, 12, 30]. Haliloglu et al. [30] have recently reported 23 pediatric patients with suspected foreign body aspiration. They performed standard-dose (100 mA) single-detector CT, and findings in seven patients were positive. Data regarding the precision and accuracy of virtual bronchoscopy were not included. In addition, no information was published on the age restriction of the bronchial order suitable for virtual bronchoscopy in pediatric patients [6].
Virtual bronchoscopy provides an internal rendering of the tracheobronchial walls and lumen. High-performance workstations permit computer postprocessing of complex algorithms and virtual reality techniques. Because of a perspective-rendering algorithm, virtual bronchoscopy simulates an endoscopist's view of the internal surface of the airway. The observer may interactively move through the airway. This technique may be performed with 3D surface-rendering and volume-rendering techniques [31]. These techniques allow accurate reproduction of major endoluminal abnormalities with an excellent correlation with fiberoptic bronchoscopy results regarding the location, severity, and shape of airway narrowing [32]. Despite these appreciable abilities, virtual endoscopy remains very sensitive to the partial volume averaging effect and motion artifacts. Retained secretions and artifacts may result in false-positive findings; virtual bronchoscopy cannot show the morphology, vascularity, or color of the mucosa [33].
Virtual bronchoscopy uses surface rendering, which takes advantage of the natural contrast between the airway and surrounding tissues. Therefore, the level of thresholding is important in displaying accurate simulations [10]. For reasons of standardization, we used the fixed threshold of 500 H that was used by Zeiberg et al. [34]. Our study focused on the proximal airway within the fourth-order bronchi, for which the threshold has been shown to be appropriate. Incorrect threshold values may be a considerable source of error.
Another limitation of our study is that virtual bronchoscopy could not show the segmental and subsegmental parts of the tracheobronchial system. Studies that were negative for foreign bodies on virtual bronchoscopy were also negative on conventional bronchoscopy.
In the future, when applications of virtual bronchoscopy are expanded to include the examination of segmental and subsegmental bronchi, the use of MDCT may have considerable advantages related to a further reduction in collimation.
Radiation exposure is the major disadvantage of CT, and doses in children that are equivalent to those used in adult CT protocols have been suggested to be associated with a small increase in the risk of future malignancy [13, 17, 35]. Several factors influence patient radiation dose from CT including tube voltage, tube current, scanning time, pitch, slice thickness, and scanning volume [13, 17]. Because the radiation dose is linearly related to amperage at a fixed kilovoltage and scanning time, a reduction in the milliamperage or tube current results in an equivalent reduction in dose. The reduction will, however, also result in increased image noise and may therefore reduce image quality. Mindful of the need to minimize radiation exposure, Choi et al. [16] defined the optimal CT tube current as the minimum milliamperage necessary to achieve a diagnostic-quality CT image. Therefore, low-dose CT has been recently used for lung cancer screening [36] and in the evaluation of diffuse infiltrative lung disease [37], radiation pneumonitis [38], and pediatric chest imaging [13]. To our knowledge, only one study reported applying low-dose CT to 3D imaging of the central airway. Choi et al. evaluated the influence of tube current on the quality of 3D reconstructions of MDCT data sets of the central airway in adults. This study showed that there was no significant loss of image quality for either the shaded surface display or the virtual bronchoscopy images when tube current was decreased from 240 to 50 mA. The 25- to 50-mA (mean, 35 mA) tube currents were used in our study for evaluating foreign bodies in the airways in the children. This radiation dose is only one third that used in a typical child protocol (100 mA). We found that studies performed with this technique were of good quality and without loss of diagnostic information. Virtual bronchoscopy images were excellent in quality in nine patients. However, increased noise was the primary reason that 12 of the examinations (52%) were graded as diagnostic rather than excellent in quality. Motion artifacts were present on several images in five examinations. Because of low tube current, we observed artifacts from the shoulder on the axial images. No studies were considered technically nondiagnostic.
On the basis of a limited number of patients, we concluded that virtual bronchoscopy images of the central airway could be reconstructed from low-dose thin-collimation MDCT without appreciable loss of image quality on virtual bronchoscopy. The accuracy of low-tube-current MDCT for foreign bodies was assessed by comparing the CT findings with results of endoscopic evaluation. No cases were found in which CT findings were shown to be inaccurate at endoscopy. Also, this study did not address the specific question of how much the tube-current setting can be reduced before increased noise renders an examination nondiagnostic for foreign bodies. All the findings of foreign body aspiration were seen on axial images. The added value of virtual bronchoscopy over simple thin-section axial images is that it gives both a different confirmatory perspective and pretty pictures for the clinicians.
We conclude that the use of MDCT virtual bronchoscopy should be considered in pediatric patients with pulmonary infiltrates that fail to resolve in the usual time (10–14 days). Moreover, chronic, unexplained respiratory symptoms should warrant further investigation on MDCT to rule out foreign bodies. MDCT may be also useful in ruling out a foreign body in patients with a low level of suspicion and normal or nonspecific chest radiography findings and in showing the exact location of the foreign body before bronchoscopy. Low-tube-current MDCT virtual bronchoscopy is a reliable, noninvasive method for endoluminal assessment of foreign body aspiration particularly in pediatric patients when combined with the interpretation of axial and multiplanar reformatted images.
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