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Tracheobronchial Foreign Bodies in Children: Imaging Assessment
Tracheobronchial Foreign Bodies in Children: Imaging Assessment Shilpa V. Hegde, MD,* Peter K.T. Hui, MBBS, FRCR,† and Edward Y. Lee, MD, MPH‡,§ Tracheobronchial foreign-body aspiration is a relatively frequent pediatric emergency and a cause of substantial morbidity and mortality especially in preschool children. Although foreignbody aspiration may cause sudden airway obstruction and subsequent death, quite often symptoms are mild and nonspecific; therefore, the correct diagnosis may be delayed particularly in the pediatric population. A delay in diagnosis increases the rate of complications and can cause substantial morbidity. Early and accurate diagnosis combined with intervention through foreign-body retrieval is critical for proper patient management. For evaluation of both radiopaque and non-radiopaque airway foreign bodies in pediatric patients, imaging plays an important role in initial detection and follow-up evaluation. In this article, we discuss the currently available imaging modalities and techniques for evaluating tracheobronchial foreign bodies in infants and children. Imaging findings of various tracheobronchial foreign bodies and mimics of foreign bodies are also discussed. In addition, information regarding management of tracheobronchial foreign-body aspiration is included. Semin Ultrasound CT MRI ]:]]]-]]] C 2014 Elsevier Inc. All rights reserved.
Introduction
F
oreign-body aspiration is a common pediatric emergency and is the sixth most common cause of accidental deaths in children.1 More than 300 deaths occur in the United Sates per year as a result of foreign-body aspiration.2 Majority of cases occur in preschool children with a peak incidence in second year.1 Young children, owing to their poor chewing ability, are prone to aspiration while eating, crying, or playing.1 Symptoms of foreign-body aspiration are related to size, shape, and nature of foreign body. An organic foreign body causes more airway inflammation, whereas an inorganic foreign body may go undetected for a long time.1 Radiopaque foreign bodies are more easily diagnosed on imaging studies, whereas
*Department of Radiology, University of Arkansas for Medical Sciences, Little Rock, AR. †Department of Radiology, Queen Mary Hospital, Hong Kong SAR, China. ‡Department of Radiology, Boston Children's Hospital and Harvard Medical School, Boston, MA. §Department of Medicine, Boston Children's Hospital and Harvard Medical School, Boston, MA. Address reprint requests to Edward Y. Lee, MD, MPH, Division of Thoracic Imaging, Boston Children's Hospital and Harvard Medical School, 300 Longwood Ave, Boston, MA 02115. E-mail: Edward.Lee@Childrens. Harvard.Edu
http://dx.doi.org/10.1053/j.sult.2014.10.001 0887-2171/& 2014 Elsevier Inc. All rights reserved.
non-radiopaque foreign bodies may not be suspected owing to nonspecific symptoms. A large foreign body may cause complete airway obstruction and sudden subsequent death. A sharp object may cause direct injury to the airway. However, in most cases, the symptoms of tracheobronchial foreign-body aspiration are nonspecific and constitute cough, wheeze, dyspnea, fever, and pneumonia.1 For evaluation of both radiopaque and non-radiopaque airway foreign bodies in pediatric patients, imaging plays an important role in initial detection and follow-up evaluation. This article describes the currently available imaging modalities and techniques as well as imaging findings of tracheobronchial foreign-body aspiration in the pediatric population. The differential diagnostic considerations and mimickers of tracheobronchial foreign bodies in pediatric patients are also reviewed. Additionally, management of tracheobronchial foreign-body aspiration is discussed.
Imaging Techniques Currently, the 3 most commonly used imaging modalities for assessing tracheobronchial foreign-body aspiration in children are plain radiographs, airway fluoroscopy, and computed tomography (CT). The current role and imaging technique of these modalities are briefly reviewed and addressed in the following section. 1
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Plain Radiographs Plain radiographs are usually the first line of imaging study in a child who presents with respiratory distress including suspected tracheobronchial foreign-body aspiration. Plain radiographs are frequently used as the first-line imaging modality, because they are relatively inexpensive and widely available. Radiographs are very sensitive in directly showing radiopaque foreign bodies (Fig. 1). However, 90% of foreign bodies are non-radiopaque and the indirect signs of air trapping, atelectasis, and consolidation are not always present in these cases.3 Hence a normal appearing radiograph does not exclude a foreign body. Up to 80% of children with laryngotracheal foreign bodies and 30%-50% of children with bronchial foreign bodies have been reported with a normal chest radiograph.4 Although frontal and lateral views are the most commonly recommended views in the setting of evaluating children suspected of having tracheobronchial foreign-body aspiration, additional views such as decubitus views that can demonstrate air trapping may be also obtained in selected equivocal cases and in noncooperative young children (r5 years old)5 (Fig. 2). In cooperative older pediatric patients (45 years old), end inspiratory and end expiratory radiographs can be performed (Fig. 3). The technical parameters for chest radiographs in children are summarized in Tables 1 and 2. Though air trapping was suggested in 77% of the expiratory radiographs in one series of pediatric patients with airway foreign-body aspiration, other studies have questioned their usefulness.4,6 In a recent study of 328 pediatric patients with suspected foreign-body aspiration, the addition of expiratory radiograph was found to increase the number of true positives; however, the accuracy was low and the clinical benefit of the expiratory radiographs remains unclear.6 The same study also
reported that the decubitus radiographs increased the false positive rate and had no clear clinical benefit.6
Airway Fluoroscopy Traditionally, this technique was used to demonstrate mediastinal shift or decreased excursion of the diaphragm in cases of air trapping owing to foreign-body aspiration in the absence of findings on the chest radiograph in noncooperative young pediatric patients with high clinical suspicion of having tracheobronchial foreign-body aspiration. However, this operator-dependent technique now has a limited role because of the wide availability and recent advances in CT, although it can still be valuable in areas where CT is not readily available.7 With the child in the supine position on the fluoroscopic table, the lower extremities and upper extremities are stabilized by the radiologist who is performing the procedure or trainees, technologists, or nurses who are assisting the radiologist. After adjusting the fluoroscopic field that covers both hemithoraces sufficiently, the chest is then carefully observed fluoroscopically during quiet and deep breathing (or crying) in real time to detect abnormal side-to-side shifting of the mediastinum or decreased excursion of the diaphragm produced by the imbalance of air flow between the 2 hemithoraces because of the presence of the foreign body.
Computed Tomography There has been an increase in the use of CT in investigating large airway abnormalities in children. Though CT is fast to perform and easily available, the associated radiation risk should be carefully considered and its usage made judiciously. Direct demonstration of foreign body and indirect evidences
Figure 1 A 13-month-old girl who presented with persistent cough for 2 weeks with an aspirated metallic pin lodged in the right main stem bronchus. (A) A frontal chest radiograph shows a metallic pin (arrow) projecting over the right hilar region. (B) A lateral chest radiograph demonstrates a metallic pin (arrow) located in the right main stem bronchus. Case courtesy of Chan Hau Yee, MD, Department of Surgery, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong SAR.
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Figure 2 A 2-year-old boy who presented with a history of choking episodes almost a month before admission. A nut was removed from the right main stem bronchus during bronchoscopy. (A) A frontal chest radiograph shows slight hyperlucency of the right lung in comparison with the left lung. (B) Left side down decubitus view of the chest radiograph demonstrates normally decreased aeration of the left lung. (C) Right side down decubitus view of the chest radiograph shows persistent air trapping in the right lung.
such as air trapping, lung atelectasis or collapse are easily and accurately demonstrated by CT (Fig. 4). CT is also superior in demonstrating other airway pathologies (ie, alternative diagnoses) such as tracheobronchial branching anomalies, extrinsic compressions, and intraluminal lesions such as tumors and vascular anomalies that may mimic a foreign body. With the development of multidetector CT (MDCT) with multiple arrays of detectors, the speed of performing a CT scan has increased dramatically. This has substantially decreased the frequency of sedation required to image children, which is an important benefit in pediatric patients.8 For evaluation of a large airway, CT can be obtained in a single phase at end inspiration or in 2 phases at both end inspiration and end expiration. Low radiation techniques are possible and are adequate for imaging large airways owing to the inherent contrast between the air-filled airways and the
adjacent soft tissues.8 With the advent of state-of-the art, 320 MDCT scanner in recent years, dynamic imaging of the large airways can now be performed in real time without the need of sedation or anesthesia8 (Fig. 5). Such advanced fourdimensional (4D) large airway imaging is particularly beneficial in severely ill and unstable infants and young children with respiratory distress who may not tolerate intubation, sedation, or anesthesia for large airway CT imaging. In addition to the increase in number of detectors in CT imaging in recent years, there has also been a great progress in the postprocessing techniques of the axial CT data set generated from CT imaging. Two-dimensional multiplanar reformatted (MPR) reconstructions in sagittal and coronal planes can now be easily obtained on any MDCT scanner (Fig. 6A and B). A straightened view of the large airway can be obtained using a curved coronal reconstruction (Fig. 6C). For
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Table 2 Technical Parameters for Chest Radiograph in Children Z5 Years of Age Frontal view Lateral view
Distance (Inches)
kVp
mAs
72 72
85 85-95
2.5 2.5
kVp, peak kilovoltage; mAs, milliampere per second.
Figure 3 A 5-year-old girl who accidentally aspirated pop corns. A frontal chest radiograph shows hyperinflated right lung with an area of atelectasis (arrow) in the right middle and lower lobes. Bronchoscopy showed an aspirated pop corn lodged in the right main stem bronchus and the bronchus intermedius.
evaluation of large airway abnormality, 3D volume-rendered imaging of the large airway from the external perspective (ie, virtual bronchography) (Fig. 6D) and the internal perspective (ie, virtual bronchoscopy) (Fig. 6E) can be generated using the axial CT data.8 These 2D and 3D images of the large airway are helpful in accurately diagnosing a subtle abnormality that can be easily missed on axial CT images or an abnormality in a distal airway beyond a high-grade narrowing in which a conventional bronchoscope cannot pass. Furthermore, 4D imaging of the large airways is now feasible with the advent of state-of-the-art 320 MDCT, which provides real-time, dynamic 3D images of the entire large airway in infants and young children without sedation or intubation8 (Fig. 5). The principal CT parameters for imaging chest in children at our institution are summarized in Tables 3 and 4. A CT scan is superior to plain radiographs in demonstration of relatively less dense and non-radiopaque foreign bodies. Plastic foreign bodies and “LEGO” foreign bodies that may not be detected on plain radiographs are well visualized on CT scans.9 Foreign bodies can be demonstrated directly in the airway or indirectly as a defect in the air column. However, a mucous plug in the airway can mimic an airway foreign body and may lead to a false-positive result (Fig. 7). In a small study comparing CT virtual bronchoscopy and conventional bronchoscopy, there was no discordance between the findings for the presence and location of the foreign body by the 2 Table 1 Technical Parameters for Chest Radiograph in Children o5 Years of Age Frontal view Lateral view
Distance (Inches)
kVp
mAs
40 40
75 75-85
2 2
kVp, peak kilovoltage; mAs, milliampere per second.
methods, demonstrating the high diagnostic accuracy of CT virtual bronchoscopy.10 The foreign bodies in this study were composed of nut fragments, plastic objects, and vegetable matter.10 Though routine performance of CT should not be advocated, CT does seem to have an important role in cases of high clinical suspicion where the findings of plain radiography have been inconclusive as conventional bronchoscopy has its own associated risks. CT in fact can reduce the rigid bronchoscopy time as it provides precise information regarding the location of the foreign body and any associated airway abnormality.7 CT is also better than chest radiograph in demonstration of lung parenchymal abnormalities and diagnosing other conditions that can mimic airway foreign body.7 Additionally, in a recent study consisting of 9 pediatric patients who underwent CT for the evaluation of a clinically suspected residual foreign body in the airway after bronchoscopy, the investigators found that CT after bronchoscopy can provide additional information regarding the presence and pattern of bronchial obstruction in children with a suspected residual foreign body, suggesting the important role of CT in this setting.11
Spectrum of Imaging Findings Imaging findings of aspirated foreign bodies in the tracheobronchial tree mainly depend on whether they are radiopaque or nonradiopaque. Additionally, imaging findings of aspirated foreign body can be grouped into: (1) primary findings (ie, direct visualization of aspirated foreign body) and (2) secondary findings (ie, sequelae of aspirated foreign body).
Radiopaque Foreign Bodies Most aspirated foreign bodies in the tracheobronchial tree in children are radiolucent (Figs. 2 and 3). Obviously, radiopaque foreign bodies pose less of a diagnostic challenge (Fig. 1). Glass and most animal bones are radiopaque, whereas most fish bones, plastic and wooden objects are non-radiopaque.12 All metallic objects except aluminum are radiopaque on plain radiographs12 (Fig. 1). Although some of the metallic objects such as aluminum do not have enough radio-opacity for the plain radiograph, they can be demonstrated directly on CT scans.13 Examples of aspirated radiopaque foreign bodies in the tracheobronchial tree are pins, pen caps, whistle, needles, thumbtack, apricot stone, nails, springs, and jewelry pieces especially in girls.1,14,15 Overall, 70% of the aspirated foreign bodies in the large airways are found in the proximal airways (ie, trachea and the main stem bronchi), and the right main stem bronchus is more
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Figure 4 A 3-year-old boy who had acute shortness of breath and respiratory distress while eating peanuts. (A) A frontal chest radiograph shows markedly hyperinflated left lung and mediastinal shift to the right side. (B) An oblique axial reformatted CT image shows an aspirated peanut located in the left main stem bronchus (arrow). Hyperinflated left lung is also seen.
often involved than the left because the right main stem bronchus is wider, shorter, and more vertical in orientation than the left main stem bronchus2 (Fig. 1). The complications of foreign-body aspiration demonstrated using imaging include air trapping, atelectasis, pneumothorax, subcutaneous emphysema, and pneumonia (Fig. 8). Unilateral, bilateral, or segmental air trapping is a common finding followed by pneumonia, atelectasis, and mediastinal shift.2 Late complications include empyema, bronchiectasis, and abscess.1 Bronchiectasis is usually seen in patients diagnosed more than 30 days after aspiration2 (Fig. 9).
Nonradiopaque Foreign Bodies Nonradiopaque foreign bodies in the tracheobronchial tree constitute of organic and inorganic foreign bodies. Organic foreign bodies cause more tissue reaction and tend to produce complications such as atelectasis and air trapping (Figs. 2 and 4). However, inert foreign bodies are more likely to remain in one place for a longer time without an increase in the obstruction over time and hence are less likely to cause complications.2 Inorganic foreign bodies include toys like LEGO, balloons, plastic pieces, and pen top. Organic foreign bodies include nuts and seeds, bones, meat, and fruits like apple and carrot.16 Peanuts are the
Figure 5 An 8-month-old boy who presented with a persistent right upper lobe collapse and hyperinflation of the remaining right lung. (A) A 3D volume-rendered CT image obtained at end inspiration shows patent large airways. (B) A 3D volumerendered CT image obtained at end expiration demonstrates markedly decreased right upper, middle, and lower lobe bronchi (circle), consistent with right-sided bronchomalacia. Hyperinflated right lung is also seen. (Color version of figure is available online.)
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Figure 6 Normal large airways of a 9-year-old girl. (A) A coronal reformatted CT image of the large airways shows partially visualized central airways. (B) A sagittal reformatted CT image of the large airways shows a reference line through the center of the airway for reconstruction of a curved coronal reformatted image. (C) A curved coronal reformatted CT image shows a straightened view of the entire trachea (T) and the right main stem bronchus (R) and the left main stem bronchus (L). (D) A 3D external volume-rendered image shows patent trachea (T) and bilateral bronchi. (E) A 3D internal volumerendered image obtained at the level of carina. The bilateral main stem bronchi are patent. (Color version of figure is available online.)
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Table 3 CT Parameters for Imaging Chest in Children Using Either a 320-Detector or a 64-Detector CT Scanner With Dose Modulation Technique Weight (kg)
kVp
mA (Minimum/ Maximum)
Rotation Time (s)
o15 15-30 31-45 46-60 61-75 76-90 91-149 4150
80 80 100 100 100 100 120 120
60/200 80/300 90/300 90/300 100/400 120/400 120/400 140/500
0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
kVp, peak kilovoltage; mA, milliamperes. A z-axis of 16 cm can be covered in a single gantry rotation using a 320detector CT scanner. For older children, either helical scanning or wide volume scanning can be used. In the latter, the entire field of view is scanned using multiple volumes.
most commonly aspirated foreign bodies reported in English literature, but seeds account for most of the cases in the Middle East.2 Cough, wheezing, and dyspnea are the 3 most common symptoms in cases of organic foreignbody inhalation.2 The rate of complications is higher in cases of organic foreign-body inhalation, which could be partly related to a delayed diagnosis in these cases.2 The overall incidence of air trapping, atelectasis, and pneumonia has been reported to increase from 41%-64%, 8%-33%, and 10%-24%, respectively, in pediatric patients with aspirated nonradiopaque foreign bodies.2 However, in 7%-30% of the patients, the findings of the chest radiographs have been normal, and hence they do not exclude tracheobronchial foreign-body aspiration. In fact, when a chest radiography shows no abnormalities, it might delay the diagnosis. In spite of this fact and also that more than 90% of the aspirated tracheobronchial foreign bodies are nonradiopaque, chest radiography is the first line of investigation in cases of foreign-body aspiration.
Indirect Radiologic Findings of Foreign-Body Aspiration When direct radiologic findings of aspirated foreign bodies in the tracheobronchial tree are not present, clear understanding and accurate knowledge of indirect radiologic findings of foreign-body aspiration are crucial for reaching an accurate diagnosis or guiding to proper next step in management in pediatric patients who present with aspirated foreign body Table 4 CT Parameters for Imaging Chest in Infants and Young Children Where the z-Axis is 16 cm or Less, Using a 320-Slice Scanner With Dose Modulation Technique. The Entire Field of View is Covered With 1 Rotation Weight (kg)
kVp
mA (Minimum/ Maximum)
Rotation Time (s)
o15 15-30
80 80
60/200 80/300
0.35 0.35
KVp, peak kilovoltage; mA, milliamperes.
in the tracheobronchial tree. Common indirect radiologic findings of aspirated foreign bodies in the tracheobronchial tree in the pediatric population are reviewed in the following section. Hyperinflation Unilateral, bilateral, or segmental hyperinflation is the most common indirect sign of tracheobronchial foreign-body aspiration2,17 (Fig. 4A). Unilateral hyperinflation is more common than bilateral hyperinflation. Bilateral hyperinflation is usually caused by tracheal foreign bodies.17 Hyperinflation is caused by a ball valve type of obstruction caused by the foreign body. Air trapping causes reflex oligemia in the affected lung and is demonstrated as hyperlucency.17 Unlike other indirect signs, hyperinflation is seen in both early and delayed presentation following foreign-body aspiration.17 Atelectasis and Pneumonia The findings of chest radiography show atelectasis in approximately 25% of cases of foreign-body aspiration and pneumonia develops in 9%-26% of cases of persistent obstruction.17 Atelectasis and pneumonia are more often seen in cases with delayed presentation (Figs. 8 and 10). The organic foreign bodies may eventually cause complete obstruction owing to the progressive inflammation and migration of the foreign body into the distal airway.17 A case of shifting atelectasis has also been reported in children owing to a change in the position of the aspirated foreign body.18 Bronchiectasis Bronchiectasis is defined as an irreversible dilatation of the bronchi and is the end result of chronic inflammation and infection of the bronchi19 (Fig. 9). The risk of developing complications rises with increasing elapsed time from the time of foreign-body aspiration to diagnosis. In a study of 174 patients with foreign-body aspiration, bronchiectasis was seen in 25% of patients with a delay in diagnosis of more than 30 days.2 Hyperinflation or Obstructive Emphysema With Atelectasis in the Same Hemithorax and Aeration Within an Area of Atelectasis Both hyperinflation and atelectasis in the same hemithorax were found in 18%, and aeration was seen within an area of atelectasis in 6% of cases in a series of 133 children with foreign-body aspiration (Fig. 3).20 These radiographic signs are not specific to foreign-body aspiration. Atelectasis can be seen adjacent to a hyperinflated lobe or segment because any cause of overinflation and aeration within an area of atelectasis can be also be seen in cases of bronchial obstruction due to any cause where the absorption of air is not yet complete. These radiographic signs are not diagnostic of foreign-body aspiration but may be indicators of bronchoscopy.21 Air Leaks Pneumothorax is a relatively rare complication of foreign-body aspiration. In a study of 749 children with foreign-body aspiration, pneumothorax was seen in 1.9% of the cases.22
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Figure 7 A 3-year-old girl with indwelling tracheostomy and respiratory distress. An axial CT image shows low attenuation materials (HU ¼ 8) mixed with air (arrow) located within the right main stem bronchus consistent with mucus plug. HU, Hounsfield unit.
Pneumothorax can occur during the time of foreign-body inhalation. Spontaneous pneumothorax and pneumomediastinum can also occur after 1-3 days foreign-body inhalation. Pneumomediastinum rarely occurs in children with foreignbody inhalation and the reported prevalence is 1%.23 Pneumothorax occurs owing to increased intrapulmonary pressure secondary to obstruction from the foreign body. Pneumomediastinum may result from perforation of a tracheobronchial tree. However, it more commonly occurs secondary to alveolar rupture with the air dissecting along the pulmonary interstitium into the mediastinum.24 Subcutaneous emphysema usually is due to extension of air into the subcutaneous soft tissues from the mediastinum.24,25 Very rarely epidural emphysema (eg, pneumorachis) is seen with foreign-body aspiration.26
Mimics of Tracheobronchial Foreign-Body Aspiration in Children Mucus Plug Mucous plug results from inspissation of secretions within the airway and most often occurs in the bronchi and the bronchioles (Fig. 7). A mucous plug can cause partial or complete airway obstruction.27 Children who are ventilated by either an endotracheal or a tracheostomy tube is more prone to develop mucous plugs, as are children with cystic fibrosis and asthma. The incidence of mucous plugs in children without the predisposing factors is not known and probably low.28 There was a reported incidence of mucous plug in 3% of
Figure 8 A 10-year-old boy with swallowing dysfunction who had an acute respiratory distress while eating. (A) A frontal chest radiograph shows an opacity (arrow) with volume loss of the right lower lobe, consistent with atelectasis. (B) A coronal reformatted CT image demonstrates an atelectasis (arrow) of the right lower lobe.
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Figure 9 A 14-year-old boy with left lower lobe foreign-body aspiration who later had postobstructive bronchiectasis. (A) An axial CT image shows a calcified aspirated foreign body (arrow) located in the left lower lobe bronchus. (B) An axial CT image demonstrates dilated left lower lobe bronchi with mucus plugging (arrows). (C) A follow-up axial CT image shows bronchiectasis (arrows).
children in a study of 85 children who underwent bronchoscopy for various reasons.28 A mucous plug in the airway can mimic a foreign body.27 Mucous plug can cause sudden respiratory distress or chronic symptoms like a foreign body. Imaging findings of a mucous plug can also mimic a foreign body. In a study of CT findings in 27 children with suspected foreign body, mucous plug was associated with atelectasis, atelectasis and pneumonia, or pneumonia alone. In this study, air trapping was notably not associated with mucous plugs unlike foreign-body aspiration.29 However, a case of unilateral obstructing emphysema and contralateral opaque hemithorax has been described in which the dual pathology was most likely caused by a shifting or migrating mucous plug.28 It may not be possible to make a definite diagnosis of mucous plug using imaging techniques, including CT. Some features suggestive of mucous plug on CT scan are relatively low density of the mucous plug with an attenuation value of 0-10 Hounsfield Units, presence of a linear branching pattern, and possibly absence of air trapping29 (Fig. 7).
Large Airway Infections The 2 most common infections that can infect and narrow the large airways in children are tuberculosis and fibrosing mediastinitis caused by histoplasmosis.8 Involvement of the airways in tuberculosis could be either due to a direct infection of the tracheobronchial wall with distal trachea and proximal main bronchi being most commonly involved, or could be due to extrinsic compression by enlarged lymph nodes.8 Endobronchial involvement in tuberculosis is related to mucosal involvement such as inflammation, ulceration, or granuloma formation.30 Nontuberculous mycobacteria such as mycobacterium avium can also cause endobronchial granulomas and has been reported even in immunocompetent children.31 Fibrosing mediastinitis, also known as mediastinal fibrosis or sclerosing mediastinitis, is characterized by abnormal proliferation of acellular collagen and fibrous tissue in the mediastinum. Symptoms are related to obstruction and compression of mediastinal structures including large airways.8 Histoplasma capsulatum is the most common of mediastinal
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postinfectious stricture following endobronchial tuberculosis, and rarely conditions such as mucopolysaccharidosis with accumulation of glycosaminoglycans in the airway. Congenital tracheal and tracheobronchial stenosis are defined by the presence of complete tracheal rings extending for a variable length of the trachea and presence of complete tracheal rings in at least one bronchus, respectively35 (Fig. 12). These congenital tracheobronchial stenosis are less common compared with the acquired stenosis. In approximately 75% of patients, there are associated anomalies such as tracheal bronchus, pulmonary sling, vascular rings, left superior vena cava, and cardiac defects.34 Though chest radiography can be helpful, CT is essential to confirm the diagnosis of tracheal or tracheobronchial stenosis. CT is also required to assess the site and the degree of narrowing and evaluate any vascular anomaly. Postprocessing techniques such as MPR and 3D reconstructions are particularly helpful in preoperative assessment of both congenital and acquired tracheobronchial stenosis.34 Figure 10 A 5-year-old boy who presented with cough, fever, and right-sided chest pain several days after aspirating incompletely chewed chicken nuggets. A frontal chest radiograph shows a consolidation in the right lower lobe. Bronchoscopy showed aspirated chicken nugget pieces in the right lower lobe bronchus.
fibrosis in pediatric patients, and the involvement is typically at the level of carina and the main bronchi.8 Two different patterns of mediastinal fibrosis have been described. Focal form of mediastinal fibrosis is known to be more often associated with histoplasma infection, whereas the diffuse form is seen in patients with other idiopathic fibrosing disorders.8
Large Airway Neoplasms Persistent symptoms combined with worsening atelectasis or recurrent pneumonia in the same location can be caused by an obstructing lesion such as foreign body or an endobronchial neoplasm. Endobronchial tumors, though rare in children, can mimic an aspirated foreign body and this differential should be carefully considered because the management differs depending upon the type of the neoplasms.32 Benign endobronchial tumors in children include hamartoma, hemangiomas, papillomas, leiomyomas, mucus gland tumors, and inflammatory myofibroblastic tumor (Fig. 11). Malignant tumors include carcinoid tumors, mucoepidermoid tumors, and adenoid cystic carcinomas.33 Endobronchial lymphoma is also rarely encountered in children.33
Tracheobronchial Stenosis The most common cause of acquired tracheal stenosis is related to prolonged intubation and hence more often seen in children who were born premature. Tracheal stenosis or stricture results in 10%-15% of patients after intubation and is seen at the level of the endotracheal tube tip.34 Other causes of acquired tracheal stenosis include granulomatosis with polyangitis (formerly known as Wegener granulomatosis),
Tracheobronchomalacia Tracheobronchomalacia is the most common congenital anomaly of the central airways. The condition results from weakness of the tracheobronchial wall, resulting in excessive collapsibility of more than 50% in expiration.36 Congenital tracheobronchomalacia occurs secondary to impaired cartilage maturation, whereas the acquired form results from the degeneration of the normal cartilage following conditions such as intubation, trauma, and infection36 (Fig. 5). Tracheobronchomalacia is often misdiagnosed as asthma. Similar to tracheobronchial foreign-body aspiration, it predisposes to frequent lung infections. On chest radiographs, the findings of tracheobronchomalacia are usually nonspecific and comprise hyperinflation or atelectasis mimicking foreign-body aspiration or both. Historically, fluoroscopy-guided large airway study was used to diagnose tracheobronchomalacia. The child is immobilized with the head in an extended position, and fluoroscopic images are obtained in inspiration and expiration in both the anteroposterior and the lateral projections. Inspiration and expiration are defined by diaphragmatic movements.37 The tracheal caliber change is observed for more than 50% narrowing of the airway in expiration, which is a diagnostic criterion for tracheobronchomalacia. The limitations of this technique are poor anatomical details of the trachea and the paratracheal structures, difficulty in visualizing the entire airway especially the bronchi and the distal airway, and the inability to simultaneously assess the anteroposterior and the lateral walls of the trachea.38 However using the MDCT, radiologists can now obtain an objective and quantitative assessment of tracheobronchomalacia with accuracy similar to that of bronchoscopy.36 To be able to achieve this, end inspiratory and end expiratory CT images are obtained. MPR and 3D images of the entire central airways are subsequently reconstructed to aid the evaluation (Fig. 5). 4D imaging of the large airways can now be performed with the 320 multidetector volume scanner for detection of dynamic large airway disorder such as tracheobronchomalacia, where imaging is
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Figure 11 A 6-year-old girl who presented with prolonged wheezing and productive cough. An axial CT image shows a heterogeneously enhancing intraluminal mass located at the level of carina. Pathology of this mass was consistent with inflammatory myofibroblastic tumor.
performed over entire respiratory cycle. Postprocessing techniques allow the dynamic 4D visualization of the airway in real time, which provides more accurate detection of subtle large airway malacia and its accurate extension.
Management of Tracheobronchial Foreign-Body Aspiration Prevention of tracheobronchial foreign-body aspiration by parental and caregiver education and increasing public
awareness is important in reducing the incidence of tracheobronchial foreign-body aspiration in infants and young children.39 In pediatric patients who present with clinically suspected tracheobronchial foreign-body aspiration, the most important step in management is to ensure airway support. Although imaging evaluation such as plain radiographs can be performed in stable pediatric patients, endotracheal intubation or other form of airway maintenance is required in unstable pediatric patients.1 Because clinical signs and plain radiographs have a low positive predictive value particularly in nonradiopaque tracheobronchial foreign-body aspiration, some physicians advocate
Figure 12 A 10-month-old boy with worsening wheezing and stridor. Foreign-body aspiration was suspected, and CT was performed for further evaluation. (A) A 3D volume-rendered CT image of the large airways from the external perspective (ie, virtual bronchography) shows a congenital tracheal stenosis (arrow). No aspirated foreign body was seen. (B) A 3D volume-rendered CT image of the large airways from the internal perspective (ie, virtual bronchoscopy) demonstrates a markedly narrowed distal trachea (arrow) consistent with a congenital tracheal stenosis.
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12 emergency bronchoscopy in cases that are highly suggestive when plain radiographs do not reveal tracheobronchial foreign-body aspiration.39 Prompt bronchoscopy is essential as a delay of more than 24 hours increases the incidence of complications.1 Most authors consider rigid bronchoscopy as the standard for retrieving airway foreign bodies in children.7 However, rigid bronchoscopy in pediatric patients is associated with potentially serious complications such as vocal cord injury, tracheobronchial laceration, subglottic edema, pneumothorax, bradycardia, and cardiac arrest.40 An alternative is to perform CT in suspected foreign-body aspiration to reduce negative bronchoscopy rates. The reported sensitivity for detecting airway foreign body is 94% for MDCT and 100% for 3D reconstructed CT images in pediatric patients.40,41 It is crucial that radiation dose should be kept as low as reasonably achievable and usage of CT should be done judiciously. The duration and the nature of the foreign body affect the outcome with increased delayed complications seen in association with organic foreign bodies.2 Persistent respiratory symptoms after removal of foreign bodies may need anti-inflammatory treatment such as steroids and bronchodilators. Bronchiectasis is usually managed medically with antibiotics, bronchodilators, and physiotherapy. Rarely, lobectomy may be needed in pediatric patients with persistent symptoms and permanent damage such as bronchiectasis.2 Almost 75% of pediatric patients recover completely within a week after removal of tracheobronchial foreign bodies.42 However, pediatric patients with preoperative inflammation of the airways, a prolonged procedure time in retrieving the foreign body and worsening of the chest radiograph findings in the immediate postoperative period, such as atelectasis or pneumonia, may require more intense treatment with physiotherapy and medical management.42
Conclusion Foreign-body aspiration is a cause of substantial morbidity and mortality in children. Though the diagnosis of a radiopaque foreign body is often straightforward, most foreign bodies are nonradiopaque, and imaging findings in these cases are nonspecific or even noncontributory. Though chest radiography is often the first line of investigation, when chest radiography does not show any abnormalities, it does not exclude the presence of tracheobronchial foreign body. Bronchoscopy can be both diagnostic and therapeutic; however, this procedure has associated risks particularly in pediatric patients. CT has a high sensitivity in detecting airway foreign bodies and associated airway and parenchymal complications. On the other hand, the radiation risk has to be considered carefully while imaging children. CT, however, can be used as a problem-solving tool in selected cases and is particularly useful in distinguishing and diagnosing the various mimickers of foreign bodies.
References 1. Sahin A, Meteroglu F, Eren S, et al: Inhalation of foreign bodies in children: Experience of 22 years. J Trauma Acute Care Surg 74(2): 658-663, 2013 2. Karakoc F, Karadag B, Akbenlioglu C, et al: Foreign body aspiration: What is the outcome? Pediatr Pulmonol 34(1):30-36, 2002 3. Hong SJ, Goo HW, Roh JL: Utility of spiral and cine CT scans in pediatric patients suspected of aspirating radiolucent foreign bodies. Otolaryngol Head Neck Surg 138(5):576-580, 2008 4. Assefa D, Amin N, Stringel G, et al: Use of decubitus radiographs in the diagnosis of foreign body aspiration in young children. Pediatr Emerg Care 23(3):154-157, 2007 5. Lee EY, Restrepo R, Dillman JR, et al: Imaging evaluation of pediatric trachea and bronchi: Systematic review and updates. Semin Roentgenol 47(2):182-196, 2012 6. Brown JC, Chapman T, Klein EJ, et al: The utility of adding expiratory or decubitus chest radiographs to the radiographic evaluation of suspected pediatric airway foreign bodies. Ann Emerg Med 61(1):19-26, 2013 7. Hitter A, Hullo E, Durand C, et al: Diagnostic value of various investigations in children with suspected foreign body aspiration: Review. Eur Ann Otorhinolaryngol Head Neck Dis 128(5):248-252, 2011 8. Lee EY, Greenberg SB, Boiselle PM: Multidetector computed tomography of pediatric large airway diseases: State-of-the-art. Radiol Clin North Am 49(5):869-893, 2011 9. Applegate KE, Dardinger JT, Lieber ML, et al: Spiral CT scanning technique in the detection of aspiration of LEGO foreign bodies. Pediatr Radiol 31(12):836-840, 2001 10. Haliloglu M, Ciftci AO, Oto A, et al: CT virtual bronchoscopy in the evaluation of children with suspected foreign body aspiration. Eur J Radiol 48(2):188-192, 2003 11. Shin SM, Kim WS, Cheon JE, et al: CT in children with suspected residual foreign body in airway after bronchoscopy. Am J Roentgenol 192(6): 1744-1751, 2009 12. Hunter TB, Taljanovic MS: Foreign bodies. Radiographics 23(3):731-757, 2003 13. Fidkowski CW, Zheng H, Firth PG: The anesthetic considerations of tracheobronchial foreign bodies in children: A literature review of 12,979 cases. Anesth Analg 111(4):1016-1025, 2010 14. Gang W, Zhengxia P, Hongbo L, et al: Diagnosis and treatment of tracheobronchial foreign bodies in 1024 children. J Pediatr Surg 47 (11):2004-2010, 2012 15. Rizk H, Rassi S: Foreign body inhalation in the pediatric population: Lessons learned from 106 cases. Eur Ann Otorhinolaryngol Head Neck Dis 128(4):169-174, 2011 16. Foltran F, Ballali S, Rodriguez H, et al: Inhaled foreign bodies in children: A global perspective on their epidemiological, clinical, and preventive aspects. Pediatr Pulmonol 48(4):344-351, 2013 17. Tokar B, Ozkan R, Ilhan H: Tracheobronchial foreign bodies in children: Importance of accurate history and plain chest radiography in delayed presentation. Clin Radiol 59(7):609-615, 2004 18. Wu CT, Wang CJ: Alternate lung collapse in a 9-year-old boy with peanut aspiration. Pediatr Radiol 36(12):1327, 2006 19. Boren EJ, Teuber SS, Gershwin ME: A review of non-cystic fibrosis pediatric bronchiectasis. Clin Rev Allergy Immunol 34(2):260-273, 2008 20. Girardi G, Contador AM, Castro-Rodriguez JA: Two new radiological findings to improve the diagnosis of bronchial foreign-body aspiration in children. Pediatr Pulmonol 38(3):261-264, 2004 21. Pitcher R, Zar H: Re: “Two new radiological findings to improve the diagnosis of bronchial foreign-body aspiration in children” by Girardi et al. (Pediatr Pulmonol 2004;38:261-264). Pediatr Pulmonol 39(6):568, 2005. [author reply 569] 22. Li Y, Wu W, Yang X, et al: Treatment of 38 cases of foreign body aspiration in children causing life-threatening complications. Int J Pediatr Otorhinolaryngol 73(12):1624-1629, 2009 23. Damore DT, Dayan PS: Medical causes of pneumomediastinum in children. Clinical Pediatr 40(2):87-91, 2001
Tracheobronchial foreign bodies in children 24. Findlay CA, Morrissey S, Paton JY: Subcutaneous emphysema secondary to foreign-body aspiration. Pediatr Pulmonol 36(1):81-82, 2003 25. Hu M, Green R, Gungor A: Pneumomediastinum and subcutaneous emphysema from bronchial foreign body aspiration. Am J Otolaryngol 34(1):85-88, 2013 26. Tambe P, Kasat LS, Tambe AP: Epidural emphysema associated with subcutaneous emphysema following foreign body in the airway. Pediatr Surg Int 21(9):721-722, 2005 27. Xue FS, Luo MP, Liao X, et al: Delayed endotracheal tube obstruction by mucus plug in a child. Chin Med J 122(7):870-872, 2009 28. Debnath J, Jain NK, Adhikari KM, et al: A child with respiratory distress having unilateral obstructive emphysema and contralateral opaque hemithorax on chest radiograph: Role of multi-detector computerized tomography with multi-planar reconstruction and virtual bronchoscopy. Aust Radiol 51(suppl):B217-220, 2007 29. Hong WS, Im SA, Kim HL, et al: CT evaluation of airway foreign bodies in children: Emphasis on the delayed diagnosis and differentiation from airway mucus plugs. Jpn J Radiol 31(1):31-38, 2013 30. Prada Arias M, Jardon Bahia JA, Rodriguez Barca P, et al: Endobronchial tuberculous granuloma in children. Eur J Pediatr Surg 16(4):265-268, 2006 31. del Rio Camacho G, Soriano Guillen L, Flandes Aldeyturriaga J, et al: Endobronchial atypical mycobacteria in an immunocompetent child. Pediatr Pulmonol 45(5):511-513, 2010 32. Fauroux B, Aynie V, Larroquet M, et al: Carcinoid and mucoepidermoid bronchial tumours in children. Eur J Pediatr 164(12):748-752, 2005
13 33. Kobayashi T, Hyodo M, Honda N: Primary endobronchial Burkitt 's lymphoma in a child: A case report. Int J Pediatr Otorhinolaryngol 77(5):875-878, 2013 34. Lee EY, Siegel MJ: MDCT of tracheobronchial narrowing in pediatric patients. J Thorac Imaging 22(3):300-309, 2007 35. Speggiorin S, Torre M, Roebuck DJ, et al: A new morphologic classification of congenital tracheobronchial stenosis. Ann Thorac Surg 93(3):958-961, 2012 36. Lee EY, Boiselle PM: Tracheobronchomalacia in infants and children: Multidetector CT evaluation. Radiology 252(1):7-22, 2009 37. Sanchez MO, Greer MC, Masters IB, et al: A comparison of fluoroscopic airway screening with flexible bronchoscopy for diagnosing tracheomalacia. Pediatr Pulmonol 47(1):63-67, 2012 38. Tan JZ, Ditchfield M, Freezer N: Tracheobronchomalacia in children: Review of diagnosis and definition. Pediatr Radiol 42(8):906-915, 2012. [quiz 1027-1028] 39. Passali D, Lauriello M, Bellussi L, et al: Foreign body inhalation in children: An update. Acta Otorhinolaryngol Ital 30(1):27-32, 2010 40. Huang HJ, Fang HY, Chen HC, et al: Three-dimensional computed tomography for detection of tracheobronchial foreign body aspiration in children. Pediatr Surg Int 24(2):157-160, 2008 41. Manach Y, Pierrot S, Couloigner V, et al: Diagnostic performance of multidetector computed tomography for foreign body aspiration in children. Int J Pediatr Otorhinolaryngol 77(5):808-812, 2013 42. Chung MK, Jeong HS, Ahn KM, et al: Pulmonary recovery after rigid bronchoscopic retrieval of airway foreign body. Laryngoscope 117(2): 303-307, 2007
Introduction
F
oreign-body aspiration is a common pediatric emergency and is the sixth most common cause of accidental deaths in children.1 More than 300 deaths occur in the United Sates per year as a result of foreign-body aspiration.2 Majority of cases occur in preschool children with a peak incidence in second year.1 Young children, owing to their poor chewing ability, are prone to aspiration while eating, crying, or playing.1 Symptoms of foreign-body aspiration are related to size, shape, and nature of foreign body. An organic foreign body causes more airway inflammation, whereas an inorganic foreign body may go undetected for a long time.1 Radiopaque foreign bodies are more easily diagnosed on imaging studies, whereas
*Department of Radiology, University of Arkansas for Medical Sciences, Little Rock, AR. †Department of Radiology, Queen Mary Hospital, Hong Kong SAR, China. ‡Department of Radiology, Boston Children's Hospital and Harvard Medical School, Boston, MA. §Department of Medicine, Boston Children's Hospital and Harvard Medical School, Boston, MA. Address reprint requests to Edward Y. Lee, MD, MPH, Division of Thoracic Imaging, Boston Children's Hospital and Harvard Medical School, 300 Longwood Ave, Boston, MA 02115. E-mail: Edward.Lee@Childrens. Harvard.Edu
http://dx.doi.org/10.1053/j.sult.2014.10.001 0887-2171/& 2014 Elsevier Inc. All rights reserved.
non-radiopaque foreign bodies may not be suspected owing to nonspecific symptoms. A large foreign body may cause complete airway obstruction and sudden subsequent death. A sharp object may cause direct injury to the airway. However, in most cases, the symptoms of tracheobronchial foreign-body aspiration are nonspecific and constitute cough, wheeze, dyspnea, fever, and pneumonia.1 For evaluation of both radiopaque and non-radiopaque airway foreign bodies in pediatric patients, imaging plays an important role in initial detection and follow-up evaluation. This article describes the currently available imaging modalities and techniques as well as imaging findings of tracheobronchial foreign-body aspiration in the pediatric population. The differential diagnostic considerations and mimickers of tracheobronchial foreign bodies in pediatric patients are also reviewed. Additionally, management of tracheobronchial foreign-body aspiration is discussed.
Imaging Techniques Currently, the 3 most commonly used imaging modalities for assessing tracheobronchial foreign-body aspiration in children are plain radiographs, airway fluoroscopy, and computed tomography (CT). The current role and imaging technique of these modalities are briefly reviewed and addressed in the following section. 1
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Plain Radiographs Plain radiographs are usually the first line of imaging study in a child who presents with respiratory distress including suspected tracheobronchial foreign-body aspiration. Plain radiographs are frequently used as the first-line imaging modality, because they are relatively inexpensive and widely available. Radiographs are very sensitive in directly showing radiopaque foreign bodies (Fig. 1). However, 90% of foreign bodies are non-radiopaque and the indirect signs of air trapping, atelectasis, and consolidation are not always present in these cases.3 Hence a normal appearing radiograph does not exclude a foreign body. Up to 80% of children with laryngotracheal foreign bodies and 30%-50% of children with bronchial foreign bodies have been reported with a normal chest radiograph.4 Although frontal and lateral views are the most commonly recommended views in the setting of evaluating children suspected of having tracheobronchial foreign-body aspiration, additional views such as decubitus views that can demonstrate air trapping may be also obtained in selected equivocal cases and in noncooperative young children (r5 years old)5 (Fig. 2). In cooperative older pediatric patients (45 years old), end inspiratory and end expiratory radiographs can be performed (Fig. 3). The technical parameters for chest radiographs in children are summarized in Tables 1 and 2. Though air trapping was suggested in 77% of the expiratory radiographs in one series of pediatric patients with airway foreign-body aspiration, other studies have questioned their usefulness.4,6 In a recent study of 328 pediatric patients with suspected foreign-body aspiration, the addition of expiratory radiograph was found to increase the number of true positives; however, the accuracy was low and the clinical benefit of the expiratory radiographs remains unclear.6 The same study also
reported that the decubitus radiographs increased the false positive rate and had no clear clinical benefit.6
Airway Fluoroscopy Traditionally, this technique was used to demonstrate mediastinal shift or decreased excursion of the diaphragm in cases of air trapping owing to foreign-body aspiration in the absence of findings on the chest radiograph in noncooperative young pediatric patients with high clinical suspicion of having tracheobronchial foreign-body aspiration. However, this operator-dependent technique now has a limited role because of the wide availability and recent advances in CT, although it can still be valuable in areas where CT is not readily available.7 With the child in the supine position on the fluoroscopic table, the lower extremities and upper extremities are stabilized by the radiologist who is performing the procedure or trainees, technologists, or nurses who are assisting the radiologist. After adjusting the fluoroscopic field that covers both hemithoraces sufficiently, the chest is then carefully observed fluoroscopically during quiet and deep breathing (or crying) in real time to detect abnormal side-to-side shifting of the mediastinum or decreased excursion of the diaphragm produced by the imbalance of air flow between the 2 hemithoraces because of the presence of the foreign body.
Computed Tomography There has been an increase in the use of CT in investigating large airway abnormalities in children. Though CT is fast to perform and easily available, the associated radiation risk should be carefully considered and its usage made judiciously. Direct demonstration of foreign body and indirect evidences
Figure 1 A 13-month-old girl who presented with persistent cough for 2 weeks with an aspirated metallic pin lodged in the right main stem bronchus. (A) A frontal chest radiograph shows a metallic pin (arrow) projecting over the right hilar region. (B) A lateral chest radiograph demonstrates a metallic pin (arrow) located in the right main stem bronchus. Case courtesy of Chan Hau Yee, MD, Department of Surgery, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong SAR.
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Figure 2 A 2-year-old boy who presented with a history of choking episodes almost a month before admission. A nut was removed from the right main stem bronchus during bronchoscopy. (A) A frontal chest radiograph shows slight hyperlucency of the right lung in comparison with the left lung. (B) Left side down decubitus view of the chest radiograph demonstrates normally decreased aeration of the left lung. (C) Right side down decubitus view of the chest radiograph shows persistent air trapping in the right lung.
such as air trapping, lung atelectasis or collapse are easily and accurately demonstrated by CT (Fig. 4). CT is also superior in demonstrating other airway pathologies (ie, alternative diagnoses) such as tracheobronchial branching anomalies, extrinsic compressions, and intraluminal lesions such as tumors and vascular anomalies that may mimic a foreign body. With the development of multidetector CT (MDCT) with multiple arrays of detectors, the speed of performing a CT scan has increased dramatically. This has substantially decreased the frequency of sedation required to image children, which is an important benefit in pediatric patients.8 For evaluation of a large airway, CT can be obtained in a single phase at end inspiration or in 2 phases at both end inspiration and end expiration. Low radiation techniques are possible and are adequate for imaging large airways owing to the inherent contrast between the air-filled airways and the
adjacent soft tissues.8 With the advent of state-of-the art, 320 MDCT scanner in recent years, dynamic imaging of the large airways can now be performed in real time without the need of sedation or anesthesia8 (Fig. 5). Such advanced fourdimensional (4D) large airway imaging is particularly beneficial in severely ill and unstable infants and young children with respiratory distress who may not tolerate intubation, sedation, or anesthesia for large airway CT imaging. In addition to the increase in number of detectors in CT imaging in recent years, there has also been a great progress in the postprocessing techniques of the axial CT data set generated from CT imaging. Two-dimensional multiplanar reformatted (MPR) reconstructions in sagittal and coronal planes can now be easily obtained on any MDCT scanner (Fig. 6A and B). A straightened view of the large airway can be obtained using a curved coronal reconstruction (Fig. 6C). For
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Table 2 Technical Parameters for Chest Radiograph in Children Z5 Years of Age Frontal view Lateral view
Distance (Inches)
kVp
mAs
72 72
85 85-95
2.5 2.5
kVp, peak kilovoltage; mAs, milliampere per second.
Figure 3 A 5-year-old girl who accidentally aspirated pop corns. A frontal chest radiograph shows hyperinflated right lung with an area of atelectasis (arrow) in the right middle and lower lobes. Bronchoscopy showed an aspirated pop corn lodged in the right main stem bronchus and the bronchus intermedius.
evaluation of large airway abnormality, 3D volume-rendered imaging of the large airway from the external perspective (ie, virtual bronchography) (Fig. 6D) and the internal perspective (ie, virtual bronchoscopy) (Fig. 6E) can be generated using the axial CT data.8 These 2D and 3D images of the large airway are helpful in accurately diagnosing a subtle abnormality that can be easily missed on axial CT images or an abnormality in a distal airway beyond a high-grade narrowing in which a conventional bronchoscope cannot pass. Furthermore, 4D imaging of the large airways is now feasible with the advent of state-of-the-art 320 MDCT, which provides real-time, dynamic 3D images of the entire large airway in infants and young children without sedation or intubation8 (Fig. 5). The principal CT parameters for imaging chest in children at our institution are summarized in Tables 3 and 4. A CT scan is superior to plain radiographs in demonstration of relatively less dense and non-radiopaque foreign bodies. Plastic foreign bodies and “LEGO” foreign bodies that may not be detected on plain radiographs are well visualized on CT scans.9 Foreign bodies can be demonstrated directly in the airway or indirectly as a defect in the air column. However, a mucous plug in the airway can mimic an airway foreign body and may lead to a false-positive result (Fig. 7). In a small study comparing CT virtual bronchoscopy and conventional bronchoscopy, there was no discordance between the findings for the presence and location of the foreign body by the 2 Table 1 Technical Parameters for Chest Radiograph in Children o5 Years of Age Frontal view Lateral view
Distance (Inches)
kVp
mAs
40 40
75 75-85
2 2
kVp, peak kilovoltage; mAs, milliampere per second.
methods, demonstrating the high diagnostic accuracy of CT virtual bronchoscopy.10 The foreign bodies in this study were composed of nut fragments, plastic objects, and vegetable matter.10 Though routine performance of CT should not be advocated, CT does seem to have an important role in cases of high clinical suspicion where the findings of plain radiography have been inconclusive as conventional bronchoscopy has its own associated risks. CT in fact can reduce the rigid bronchoscopy time as it provides precise information regarding the location of the foreign body and any associated airway abnormality.7 CT is also better than chest radiograph in demonstration of lung parenchymal abnormalities and diagnosing other conditions that can mimic airway foreign body.7 Additionally, in a recent study consisting of 9 pediatric patients who underwent CT for the evaluation of a clinically suspected residual foreign body in the airway after bronchoscopy, the investigators found that CT after bronchoscopy can provide additional information regarding the presence and pattern of bronchial obstruction in children with a suspected residual foreign body, suggesting the important role of CT in this setting.11
Spectrum of Imaging Findings Imaging findings of aspirated foreign bodies in the tracheobronchial tree mainly depend on whether they are radiopaque or nonradiopaque. Additionally, imaging findings of aspirated foreign body can be grouped into: (1) primary findings (ie, direct visualization of aspirated foreign body) and (2) secondary findings (ie, sequelae of aspirated foreign body).
Radiopaque Foreign Bodies Most aspirated foreign bodies in the tracheobronchial tree in children are radiolucent (Figs. 2 and 3). Obviously, radiopaque foreign bodies pose less of a diagnostic challenge (Fig. 1). Glass and most animal bones are radiopaque, whereas most fish bones, plastic and wooden objects are non-radiopaque.12 All metallic objects except aluminum are radiopaque on plain radiographs12 (Fig. 1). Although some of the metallic objects such as aluminum do not have enough radio-opacity for the plain radiograph, they can be demonstrated directly on CT scans.13 Examples of aspirated radiopaque foreign bodies in the tracheobronchial tree are pins, pen caps, whistle, needles, thumbtack, apricot stone, nails, springs, and jewelry pieces especially in girls.1,14,15 Overall, 70% of the aspirated foreign bodies in the large airways are found in the proximal airways (ie, trachea and the main stem bronchi), and the right main stem bronchus is more
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Figure 4 A 3-year-old boy who had acute shortness of breath and respiratory distress while eating peanuts. (A) A frontal chest radiograph shows markedly hyperinflated left lung and mediastinal shift to the right side. (B) An oblique axial reformatted CT image shows an aspirated peanut located in the left main stem bronchus (arrow). Hyperinflated left lung is also seen.
often involved than the left because the right main stem bronchus is wider, shorter, and more vertical in orientation than the left main stem bronchus2 (Fig. 1). The complications of foreign-body aspiration demonstrated using imaging include air trapping, atelectasis, pneumothorax, subcutaneous emphysema, and pneumonia (Fig. 8). Unilateral, bilateral, or segmental air trapping is a common finding followed by pneumonia, atelectasis, and mediastinal shift.2 Late complications include empyema, bronchiectasis, and abscess.1 Bronchiectasis is usually seen in patients diagnosed more than 30 days after aspiration2 (Fig. 9).
Nonradiopaque Foreign Bodies Nonradiopaque foreign bodies in the tracheobronchial tree constitute of organic and inorganic foreign bodies. Organic foreign bodies cause more tissue reaction and tend to produce complications such as atelectasis and air trapping (Figs. 2 and 4). However, inert foreign bodies are more likely to remain in one place for a longer time without an increase in the obstruction over time and hence are less likely to cause complications.2 Inorganic foreign bodies include toys like LEGO, balloons, plastic pieces, and pen top. Organic foreign bodies include nuts and seeds, bones, meat, and fruits like apple and carrot.16 Peanuts are the
Figure 5 An 8-month-old boy who presented with a persistent right upper lobe collapse and hyperinflation of the remaining right lung. (A) A 3D volume-rendered CT image obtained at end inspiration shows patent large airways. (B) A 3D volumerendered CT image obtained at end expiration demonstrates markedly decreased right upper, middle, and lower lobe bronchi (circle), consistent with right-sided bronchomalacia. Hyperinflated right lung is also seen. (Color version of figure is available online.)
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Figure 6 Normal large airways of a 9-year-old girl. (A) A coronal reformatted CT image of the large airways shows partially visualized central airways. (B) A sagittal reformatted CT image of the large airways shows a reference line through the center of the airway for reconstruction of a curved coronal reformatted image. (C) A curved coronal reformatted CT image shows a straightened view of the entire trachea (T) and the right main stem bronchus (R) and the left main stem bronchus (L). (D) A 3D external volume-rendered image shows patent trachea (T) and bilateral bronchi. (E) A 3D internal volumerendered image obtained at the level of carina. The bilateral main stem bronchi are patent. (Color version of figure is available online.)
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Table 3 CT Parameters for Imaging Chest in Children Using Either a 320-Detector or a 64-Detector CT Scanner With Dose Modulation Technique Weight (kg)
kVp
mA (Minimum/ Maximum)
Rotation Time (s)
o15 15-30 31-45 46-60 61-75 76-90 91-149 4150
80 80 100 100 100 100 120 120
60/200 80/300 90/300 90/300 100/400 120/400 120/400 140/500
0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
kVp, peak kilovoltage; mA, milliamperes. A z-axis of 16 cm can be covered in a single gantry rotation using a 320detector CT scanner. For older children, either helical scanning or wide volume scanning can be used. In the latter, the entire field of view is scanned using multiple volumes.
most commonly aspirated foreign bodies reported in English literature, but seeds account for most of the cases in the Middle East.2 Cough, wheezing, and dyspnea are the 3 most common symptoms in cases of organic foreignbody inhalation.2 The rate of complications is higher in cases of organic foreign-body inhalation, which could be partly related to a delayed diagnosis in these cases.2 The overall incidence of air trapping, atelectasis, and pneumonia has been reported to increase from 41%-64%, 8%-33%, and 10%-24%, respectively, in pediatric patients with aspirated nonradiopaque foreign bodies.2 However, in 7%-30% of the patients, the findings of the chest radiographs have been normal, and hence they do not exclude tracheobronchial foreign-body aspiration. In fact, when a chest radiography shows no abnormalities, it might delay the diagnosis. In spite of this fact and also that more than 90% of the aspirated tracheobronchial foreign bodies are nonradiopaque, chest radiography is the first line of investigation in cases of foreign-body aspiration.
Indirect Radiologic Findings of Foreign-Body Aspiration When direct radiologic findings of aspirated foreign bodies in the tracheobronchial tree are not present, clear understanding and accurate knowledge of indirect radiologic findings of foreign-body aspiration are crucial for reaching an accurate diagnosis or guiding to proper next step in management in pediatric patients who present with aspirated foreign body Table 4 CT Parameters for Imaging Chest in Infants and Young Children Where the z-Axis is 16 cm or Less, Using a 320-Slice Scanner With Dose Modulation Technique. The Entire Field of View is Covered With 1 Rotation Weight (kg)
kVp
mA (Minimum/ Maximum)
Rotation Time (s)
o15 15-30
80 80
60/200 80/300
0.35 0.35
KVp, peak kilovoltage; mA, milliamperes.
in the tracheobronchial tree. Common indirect radiologic findings of aspirated foreign bodies in the tracheobronchial tree in the pediatric population are reviewed in the following section. Hyperinflation Unilateral, bilateral, or segmental hyperinflation is the most common indirect sign of tracheobronchial foreign-body aspiration2,17 (Fig. 4A). Unilateral hyperinflation is more common than bilateral hyperinflation. Bilateral hyperinflation is usually caused by tracheal foreign bodies.17 Hyperinflation is caused by a ball valve type of obstruction caused by the foreign body. Air trapping causes reflex oligemia in the affected lung and is demonstrated as hyperlucency.17 Unlike other indirect signs, hyperinflation is seen in both early and delayed presentation following foreign-body aspiration.17 Atelectasis and Pneumonia The findings of chest radiography show atelectasis in approximately 25% of cases of foreign-body aspiration and pneumonia develops in 9%-26% of cases of persistent obstruction.17 Atelectasis and pneumonia are more often seen in cases with delayed presentation (Figs. 8 and 10). The organic foreign bodies may eventually cause complete obstruction owing to the progressive inflammation and migration of the foreign body into the distal airway.17 A case of shifting atelectasis has also been reported in children owing to a change in the position of the aspirated foreign body.18 Bronchiectasis Bronchiectasis is defined as an irreversible dilatation of the bronchi and is the end result of chronic inflammation and infection of the bronchi19 (Fig. 9). The risk of developing complications rises with increasing elapsed time from the time of foreign-body aspiration to diagnosis. In a study of 174 patients with foreign-body aspiration, bronchiectasis was seen in 25% of patients with a delay in diagnosis of more than 30 days.2 Hyperinflation or Obstructive Emphysema With Atelectasis in the Same Hemithorax and Aeration Within an Area of Atelectasis Both hyperinflation and atelectasis in the same hemithorax were found in 18%, and aeration was seen within an area of atelectasis in 6% of cases in a series of 133 children with foreign-body aspiration (Fig. 3).20 These radiographic signs are not specific to foreign-body aspiration. Atelectasis can be seen adjacent to a hyperinflated lobe or segment because any cause of overinflation and aeration within an area of atelectasis can be also be seen in cases of bronchial obstruction due to any cause where the absorption of air is not yet complete. These radiographic signs are not diagnostic of foreign-body aspiration but may be indicators of bronchoscopy.21 Air Leaks Pneumothorax is a relatively rare complication of foreign-body aspiration. In a study of 749 children with foreign-body aspiration, pneumothorax was seen in 1.9% of the cases.22
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Figure 7 A 3-year-old girl with indwelling tracheostomy and respiratory distress. An axial CT image shows low attenuation materials (HU ¼ 8) mixed with air (arrow) located within the right main stem bronchus consistent with mucus plug. HU, Hounsfield unit.
Pneumothorax can occur during the time of foreign-body inhalation. Spontaneous pneumothorax and pneumomediastinum can also occur after 1-3 days foreign-body inhalation. Pneumomediastinum rarely occurs in children with foreignbody inhalation and the reported prevalence is 1%.23 Pneumothorax occurs owing to increased intrapulmonary pressure secondary to obstruction from the foreign body. Pneumomediastinum may result from perforation of a tracheobronchial tree. However, it more commonly occurs secondary to alveolar rupture with the air dissecting along the pulmonary interstitium into the mediastinum.24 Subcutaneous emphysema usually is due to extension of air into the subcutaneous soft tissues from the mediastinum.24,25 Very rarely epidural emphysema (eg, pneumorachis) is seen with foreign-body aspiration.26
Mimics of Tracheobronchial Foreign-Body Aspiration in Children Mucus Plug Mucous plug results from inspissation of secretions within the airway and most often occurs in the bronchi and the bronchioles (Fig. 7). A mucous plug can cause partial or complete airway obstruction.27 Children who are ventilated by either an endotracheal or a tracheostomy tube is more prone to develop mucous plugs, as are children with cystic fibrosis and asthma. The incidence of mucous plugs in children without the predisposing factors is not known and probably low.28 There was a reported incidence of mucous plug in 3% of
Figure 8 A 10-year-old boy with swallowing dysfunction who had an acute respiratory distress while eating. (A) A frontal chest radiograph shows an opacity (arrow) with volume loss of the right lower lobe, consistent with atelectasis. (B) A coronal reformatted CT image demonstrates an atelectasis (arrow) of the right lower lobe.
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Figure 9 A 14-year-old boy with left lower lobe foreign-body aspiration who later had postobstructive bronchiectasis. (A) An axial CT image shows a calcified aspirated foreign body (arrow) located in the left lower lobe bronchus. (B) An axial CT image demonstrates dilated left lower lobe bronchi with mucus plugging (arrows). (C) A follow-up axial CT image shows bronchiectasis (arrows).
children in a study of 85 children who underwent bronchoscopy for various reasons.28 A mucous plug in the airway can mimic a foreign body.27 Mucous plug can cause sudden respiratory distress or chronic symptoms like a foreign body. Imaging findings of a mucous plug can also mimic a foreign body. In a study of CT findings in 27 children with suspected foreign body, mucous plug was associated with atelectasis, atelectasis and pneumonia, or pneumonia alone. In this study, air trapping was notably not associated with mucous plugs unlike foreign-body aspiration.29 However, a case of unilateral obstructing emphysema and contralateral opaque hemithorax has been described in which the dual pathology was most likely caused by a shifting or migrating mucous plug.28 It may not be possible to make a definite diagnosis of mucous plug using imaging techniques, including CT. Some features suggestive of mucous plug on CT scan are relatively low density of the mucous plug with an attenuation value of 0-10 Hounsfield Units, presence of a linear branching pattern, and possibly absence of air trapping29 (Fig. 7).
Large Airway Infections The 2 most common infections that can infect and narrow the large airways in children are tuberculosis and fibrosing mediastinitis caused by histoplasmosis.8 Involvement of the airways in tuberculosis could be either due to a direct infection of the tracheobronchial wall with distal trachea and proximal main bronchi being most commonly involved, or could be due to extrinsic compression by enlarged lymph nodes.8 Endobronchial involvement in tuberculosis is related to mucosal involvement such as inflammation, ulceration, or granuloma formation.30 Nontuberculous mycobacteria such as mycobacterium avium can also cause endobronchial granulomas and has been reported even in immunocompetent children.31 Fibrosing mediastinitis, also known as mediastinal fibrosis or sclerosing mediastinitis, is characterized by abnormal proliferation of acellular collagen and fibrous tissue in the mediastinum. Symptoms are related to obstruction and compression of mediastinal structures including large airways.8 Histoplasma capsulatum is the most common of mediastinal
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postinfectious stricture following endobronchial tuberculosis, and rarely conditions such as mucopolysaccharidosis with accumulation of glycosaminoglycans in the airway. Congenital tracheal and tracheobronchial stenosis are defined by the presence of complete tracheal rings extending for a variable length of the trachea and presence of complete tracheal rings in at least one bronchus, respectively35 (Fig. 12). These congenital tracheobronchial stenosis are less common compared with the acquired stenosis. In approximately 75% of patients, there are associated anomalies such as tracheal bronchus, pulmonary sling, vascular rings, left superior vena cava, and cardiac defects.34 Though chest radiography can be helpful, CT is essential to confirm the diagnosis of tracheal or tracheobronchial stenosis. CT is also required to assess the site and the degree of narrowing and evaluate any vascular anomaly. Postprocessing techniques such as MPR and 3D reconstructions are particularly helpful in preoperative assessment of both congenital and acquired tracheobronchial stenosis.34 Figure 10 A 5-year-old boy who presented with cough, fever, and right-sided chest pain several days after aspirating incompletely chewed chicken nuggets. A frontal chest radiograph shows a consolidation in the right lower lobe. Bronchoscopy showed aspirated chicken nugget pieces in the right lower lobe bronchus.
fibrosis in pediatric patients, and the involvement is typically at the level of carina and the main bronchi.8 Two different patterns of mediastinal fibrosis have been described. Focal form of mediastinal fibrosis is known to be more often associated with histoplasma infection, whereas the diffuse form is seen in patients with other idiopathic fibrosing disorders.8
Large Airway Neoplasms Persistent symptoms combined with worsening atelectasis or recurrent pneumonia in the same location can be caused by an obstructing lesion such as foreign body or an endobronchial neoplasm. Endobronchial tumors, though rare in children, can mimic an aspirated foreign body and this differential should be carefully considered because the management differs depending upon the type of the neoplasms.32 Benign endobronchial tumors in children include hamartoma, hemangiomas, papillomas, leiomyomas, mucus gland tumors, and inflammatory myofibroblastic tumor (Fig. 11). Malignant tumors include carcinoid tumors, mucoepidermoid tumors, and adenoid cystic carcinomas.33 Endobronchial lymphoma is also rarely encountered in children.33
Tracheobronchial Stenosis The most common cause of acquired tracheal stenosis is related to prolonged intubation and hence more often seen in children who were born premature. Tracheal stenosis or stricture results in 10%-15% of patients after intubation and is seen at the level of the endotracheal tube tip.34 Other causes of acquired tracheal stenosis include granulomatosis with polyangitis (formerly known as Wegener granulomatosis),
Tracheobronchomalacia Tracheobronchomalacia is the most common congenital anomaly of the central airways. The condition results from weakness of the tracheobronchial wall, resulting in excessive collapsibility of more than 50% in expiration.36 Congenital tracheobronchomalacia occurs secondary to impaired cartilage maturation, whereas the acquired form results from the degeneration of the normal cartilage following conditions such as intubation, trauma, and infection36 (Fig. 5). Tracheobronchomalacia is often misdiagnosed as asthma. Similar to tracheobronchial foreign-body aspiration, it predisposes to frequent lung infections. On chest radiographs, the findings of tracheobronchomalacia are usually nonspecific and comprise hyperinflation or atelectasis mimicking foreign-body aspiration or both. Historically, fluoroscopy-guided large airway study was used to diagnose tracheobronchomalacia. The child is immobilized with the head in an extended position, and fluoroscopic images are obtained in inspiration and expiration in both the anteroposterior and the lateral projections. Inspiration and expiration are defined by diaphragmatic movements.37 The tracheal caliber change is observed for more than 50% narrowing of the airway in expiration, which is a diagnostic criterion for tracheobronchomalacia. The limitations of this technique are poor anatomical details of the trachea and the paratracheal structures, difficulty in visualizing the entire airway especially the bronchi and the distal airway, and the inability to simultaneously assess the anteroposterior and the lateral walls of the trachea.38 However using the MDCT, radiologists can now obtain an objective and quantitative assessment of tracheobronchomalacia with accuracy similar to that of bronchoscopy.36 To be able to achieve this, end inspiratory and end expiratory CT images are obtained. MPR and 3D images of the entire central airways are subsequently reconstructed to aid the evaluation (Fig. 5). 4D imaging of the large airways can now be performed with the 320 multidetector volume scanner for detection of dynamic large airway disorder such as tracheobronchomalacia, where imaging is
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Figure 11 A 6-year-old girl who presented with prolonged wheezing and productive cough. An axial CT image shows a heterogeneously enhancing intraluminal mass located at the level of carina. Pathology of this mass was consistent with inflammatory myofibroblastic tumor.
performed over entire respiratory cycle. Postprocessing techniques allow the dynamic 4D visualization of the airway in real time, which provides more accurate detection of subtle large airway malacia and its accurate extension.
Management of Tracheobronchial Foreign-Body Aspiration Prevention of tracheobronchial foreign-body aspiration by parental and caregiver education and increasing public
awareness is important in reducing the incidence of tracheobronchial foreign-body aspiration in infants and young children.39 In pediatric patients who present with clinically suspected tracheobronchial foreign-body aspiration, the most important step in management is to ensure airway support. Although imaging evaluation such as plain radiographs can be performed in stable pediatric patients, endotracheal intubation or other form of airway maintenance is required in unstable pediatric patients.1 Because clinical signs and plain radiographs have a low positive predictive value particularly in nonradiopaque tracheobronchial foreign-body aspiration, some physicians advocate
Figure 12 A 10-month-old boy with worsening wheezing and stridor. Foreign-body aspiration was suspected, and CT was performed for further evaluation. (A) A 3D volume-rendered CT image of the large airways from the external perspective (ie, virtual bronchography) shows a congenital tracheal stenosis (arrow). No aspirated foreign body was seen. (B) A 3D volume-rendered CT image of the large airways from the internal perspective (ie, virtual bronchoscopy) demonstrates a markedly narrowed distal trachea (arrow) consistent with a congenital tracheal stenosis.
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12 emergency bronchoscopy in cases that are highly suggestive when plain radiographs do not reveal tracheobronchial foreign-body aspiration.39 Prompt bronchoscopy is essential as a delay of more than 24 hours increases the incidence of complications.1 Most authors consider rigid bronchoscopy as the standard for retrieving airway foreign bodies in children.7 However, rigid bronchoscopy in pediatric patients is associated with potentially serious complications such as vocal cord injury, tracheobronchial laceration, subglottic edema, pneumothorax, bradycardia, and cardiac arrest.40 An alternative is to perform CT in suspected foreign-body aspiration to reduce negative bronchoscopy rates. The reported sensitivity for detecting airway foreign body is 94% for MDCT and 100% for 3D reconstructed CT images in pediatric patients.40,41 It is crucial that radiation dose should be kept as low as reasonably achievable and usage of CT should be done judiciously. The duration and the nature of the foreign body affect the outcome with increased delayed complications seen in association with organic foreign bodies.2 Persistent respiratory symptoms after removal of foreign bodies may need anti-inflammatory treatment such as steroids and bronchodilators. Bronchiectasis is usually managed medically with antibiotics, bronchodilators, and physiotherapy. Rarely, lobectomy may be needed in pediatric patients with persistent symptoms and permanent damage such as bronchiectasis.2 Almost 75% of pediatric patients recover completely within a week after removal of tracheobronchial foreign bodies.42 However, pediatric patients with preoperative inflammation of the airways, a prolonged procedure time in retrieving the foreign body and worsening of the chest radiograph findings in the immediate postoperative period, such as atelectasis or pneumonia, may require more intense treatment with physiotherapy and medical management.42
Conclusion Foreign-body aspiration is a cause of substantial morbidity and mortality in children. Though the diagnosis of a radiopaque foreign body is often straightforward, most foreign bodies are nonradiopaque, and imaging findings in these cases are nonspecific or even noncontributory. Though chest radiography is often the first line of investigation, when chest radiography does not show any abnormalities, it does not exclude the presence of tracheobronchial foreign body. Bronchoscopy can be both diagnostic and therapeutic; however, this procedure has associated risks particularly in pediatric patients. CT has a high sensitivity in detecting airway foreign bodies and associated airway and parenchymal complications. On the other hand, the radiation risk has to be considered carefully while imaging children. CT, however, can be used as a problem-solving tool in selected cases and is particularly useful in distinguishing and diagnosing the various mimickers of foreign bodies.
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