Large Airways



Large Airways


Evan J. Zucker

Bernard F. Laya

Mark C. Liszewski

Ricardo Restrepo

Sara O. Vargas

Edward Y. Lee



INTRODUCTION

Disorders of the large airways occur frequently in the pediatric population. Many pose a risk of life-threatening airway obstruction and respiratory distress, and thus, early recognition is essential. Combined with physical and laboratory findings, imaging plays a key role in the assessment, from diagnosis to preoperative planning.

In this chapter, the major pediatric large airway disorders are discussed. First, the embryology and normal anatomy of the large airways, with attention to normal variants, are reviewed. Then, the major and evolving imaging modalities available for evaluating the pediatric large airways are summarized. Finally, the broad spectrum of pediatric large airway disorders, including pathophysiology, clinical features, imaging assessment, pertinent pathological findings, and treatment approaches, are reviewed.


ANATOMY

The large airways are classified as either upper or lower airways (Fig. 2.1). The upper airways consist of the air passages from the nasal cavity to the cervical trachea above the thoracic inlet. The lower airways begin below the thoracic inlet level and include the thoracic trachea and bronchi.1


Embryology

The larynx and lower airways begin forming at 3 to 4 weeks of gestation and continue developing beyond 2 years of age.2 Initially, budding of the ventral foregut leads to formation of a respiratory diverticulum. Esophagotracheal ridges then develop and eventually fuse to separate the respiratory diverticulum from the foregut (Fig. 2.2). The larynx remains as a communication between the respiratory tree and oropharynx, and growth continues to 3 years of age. The laryngeal muscles and cartilages (including the epiglottis and arytenoid, cricoid, thyroid, corniculate, and cuneiform cartilages) arise from mesenchyme of the 4th and 6th pharyngeal arches.2 Tracheal rings develop from hyaline cartilage; 15 to 20 provide adequate support to ensure patency of the tracheal lumen at birth (Fig. 2.3). Lung buds form by the end of the 4th week of gestation, growing longer and giving rise to the primary and segmental bronchi (Fig. 2.4).2 The more distal airways develop progressively thinner walls, and alveoli arise between 32 and 36 weeks of gestation (Fig. 2.5).2


Normal Development and Anatomy

The airway includes the nose, paranasal sinuses, pharynx (subdivided into nasopharynx, oropharynx, and hypopharynx), larynx, trachea, main bronchi, peripheral bronchi, and bronchioles.1 The intrathoracic large airways are the subject of this chapter.

The trachea is a membranous and cartilaginous tube. It begins below the larynx at approximately the level of C6 and extends to the upper border of T5. However, in newborns, the trachea starts at the C4 level, and in older children, may begin as high a the C5 level.1 The trachea subdivides into right and left main bronchi (Fig. 2.6). The right main bronchus divides into the right upper lobe bronchus and bronchus intermedius. The bronchus intermedius further branches into right middle and lower lobe bronchi. The left main bronchus gives rise to left upper and lower lobe bronchi. There are typically three segmental right upper lobe bronchi (apical, anterior, and posterior), two segmental right middle lobe bronchi (lateral and medial), and five segmental right lower lobe bronchi (superior, medial basal, anterior basal, lateral basal, and posterior basal). There are four segmental left upper lobe bronchi (apicoposterior, anterior, superior lingular, inferior lingular) and four segmental left lower lobe bronchi (superior, anteromedial, lateral basal, and posterior basal).







FIGURE 2.1. Diagram of the large airways, which can be classified as either upper or lower airways. (Adapted from McArdle WD, Katch FI, Katch VL. Exercise Physiology; 2014. Figure 12.1. © LWW/Wolters Kluwer, with permission.)


Anatomic Variants

In children under 5 years of age, lateral deviation of the trachea may occur normally and should not be misconstrued as pathologic (Fig. 2.7). This phenomenon is believed to be caused by the relatively long tracheal length with respect to the child’s short neck and rib cage, and typically occurs at or just superior to the thoracic inlet opposite to the side of the aortic arch.3,4 Other common normal variants include anterior tracheal buckling and retropharyngeal soft tissue widening during expiration and neck flexion, findings that may mimic a retropharyngeal abscess (Fig. 2.8).5






FIGURE 2.2. Diagram of development of the lower airways. The lower airways develop in successive stages from the primitive foregut: A: First, a respiratory diverticulum or “lung bud” is formed ventrally. B: Subsequently, the respiratory diverticulum is separated from the foregut (dorsal) by the tracheoesophageal ridges that join to form a septum. C: Finally, the respiratory diverticulum develops into the trachea and bronchial buds and the foregut forms the esophagus. (Adapted from Sadler TJ. Langman’s Essential Medical Embryology; 2004. Figure 6.1. © Wolters Kluwer, with permission.)

Many normal variations in airway branching anatomy exist and usually occur in the upper lobes. In fact, according to one series, a bifurcation rather than the expected trifurcation of right upper lobe segmental bronchi occurs in 70% of normal individuals; the apical bronchus is absent in 22%. A superior-inferior division of the middle lobe paralleling the normal lingular anatomy is seen in 23%, while a lateral-medial division of the lingular bronchi paralleling the normal middle lobe anatomy is seen in 25%. A subsuperior bronchus may be present in 56% of individuals in the right lung and 26% of individuals in the left lung. A medial basal subsegmental bronchus, seen normally in the right lung, occurs in the left lung in 14% of healthy volunteers.6 In contrast, abnormal bronchi originating from the trachea or main bronchi are rare and more likely to be pathologic, as detailed later in this chapter.


IMAGING TECHNIQUES


Radiography

Frontal and lateral radiographs of the neck and chest remain first-line in the imaging assessment of pediatric patients presenting with suspected large airway disorders (Table 2.1).


Widely available and inexpensive, radiographs help to exclude foreign body aspiration and other causes of acute respiratory distress. The airway is best evaluated using magnification high kilovoltage (kV) technique.3,7 The anteroposterior (AP) view is tightly coned to the neck and selectively filtered to eliminate overlap from the cervical spine.8 The lateral neck view should be performed in inspiration with moderate neck extension. Neck rotation, flexion, or expiration may cause radiographic appearances mimicking pathology, and thus proper positioning is critical. However, in actual practice, performing optimal lateral radiographs in crying, moving infants proves challenging.3,7 Pacifiers and a variety of immobilization devices may be helpful for children <4 years old. Nevertheless, it is vital to note that patients with suspected airway obstruction should never be forced into positions they find uncomfortable.3,7 This may lead to acute, life-threatening respiratory decompensation.






FIGURE 2.3. Anatomy of the trachea. (Modified from Premkumar K. Anatomy & Physiology: The Massage Connection. Baltimore, MD: LWW/Wolters Kluwer; 2004, with permission.)






FIGURE 2.4. Developmental embryology of lung buds.






FIGURE 2.5. Development of the distal airways. A: Right upper (superior) lobe. B: Right middle lobe. C: Right lower (inferior) lobe. D: Left upper (superior) lobe. E: Left lower (inferior) lobe.

Chest radiographs are optimally performed near the end of quiet inspiration. In infants, supine AP views are satisfactory because the degree of magnification is similar compared to that of posteroanterior (PA) erect radiographs. AP views are also easier to perform. Lateral radiographs are rarely indicated. In cooperative children over 4 years of age, PA and lateral erect views are best, performed either in the seated or
standing position.3 Evaluation for air trapping, a secondary sign of tracheobronchial foreign body obstruction, can be further evaluated with expiratory views in cooperative older children or the less technically onerous lateral decubitus views in younger uncooperative patients.3 Gonadal shielding can help limit radiation exposure.






FIGURE 2.6. Trachea and major bronchi of the lungs.






FIGURE 2.7. A 2-year-old girl with normal lateral deviation of the trachea. Frontal radiograph shows normal deviation (arrow) of the trachea to the right of midline at the thoracic inlet level.


Ultrasound

In general, ultrasound (US) is an ideal imaging modality in pediatric patients due to the lack of ionizing radiation and need for sedation and ability for real-time assessment in multiple planes. However, its applications for airway imaging remain limited due to poor sound conduction by air-filled structures.9,10

Although still in their infancy, sonographic airway imaging techniques have been described. A typical protocol involves scanning patients supine with a pillow under the shoulders, the head extended, and the neck flexed (“sniffing” position). A linear high-frequency transducer is used to image the superficial airway structures (2 to 3 cm from the skin) in the transverse plane (Fig. 2.9A). A low-frequency curved transducer is best for sagittal and parasagittal views of structures in the supraglottic and submandibular regions (Fig. 2.9B). Recent investigations have examined the use of sonography in performing quantitative analysis of upper airway luminal patency throughout respiration.9,10 US may also complement the physical examination and direct visualization methods such as laryngoscopy. Moreover, US is an ideal modality for providing imaging guidance during procedures such as percutaneous tracheostomy, which might otherwise be performed blindly.


Fluoroscopy

Fluoroscopy is useful for evaluating dynamic abnormalities including laryngomalacia and tracheomalacia and may be combined with a barium swallow study (Fig. 2.10).7 The entire
airway from nasopharynx to bronchi can be evaluated rapidly and noninvasively in any projection. Radiation-dose reduction techniques such as pulsed fluoroscopy and restricted fluoroscopic time should be emphasized to keep exposure “As Low As Reasonably Achievable” (ALARA). Uncooperative infants and young children and older children with large body habitus may prove difficult to image.3,7






FIGURE 2.8. A 2-year-old boy with normal anterior buckling of the trachea. A: Lateral soft tissue neck radiograph shows anterior buckling (arrow) of the trachea and retropharyngeal soft tissue widening (asterisk) during expiration and neck flexion. B: Repeat lateral soft tissue neck radiograph demonstrates resolution of anterior buckling of the trachea and retropharyngeal soft tissue widening during inspiration.

Dynamic sleep airway fluoroscopy may be used to assess patients with obstructive sleep apnea. The patient is sedated, with continuous pulse oximetry and monitoring of vital signs. When signs of airway occlusion become apparent, fluoroscopy is performed for 10 to 20 seconds at selected anatomical sites in the lateral supine position and correlated with clinical findings. Typically evaluated structures include the oropharynx at the level of the tongue base, the hypopharynx, and the intrathoracic trachea. Pulling the arms downward optimizes visualization of the neck structures, while visualization of the intrathoracic trachea is optimized with the arms held above the head. Targeting a maximum of 2 minutes fluoroscopy time helps limit radiation exposure.11








TABLE 2.1 Radiograph Technique for Soft Tissue Neck



































































































































Age


View


kVp


mAs


AEC


Grid


SID


FSS


0-3 mo


AP


60


1.5


Off


No


40″


Small


3-12 mo


AP


60


2


Off


No


40″


Small


1-3 y


AP


65


2


Off


No


40″


Small


3-6 y


AP


65


5


Active


Grid


40″


Small


6-10 y


AP


70


5


Active


Grid


40″


Small


>10 y


AP


75


8


Active


Gird


40″


Small


Age


View


kVp


mAs


AEC


grid


SID


FSS


0-3 mo


Lateral


60


4


Off


No


72″


Small


3-12 mo


Lateral


60


5


Off


No


72″


Small


1-3 y


Lateral


67


6


Off


No


72″


Small


3-6 y


Lateral


67


6.5


Off


No


72″


Small


6-10 y


Lateral


70


7


Off


No


72″


Small


>10 y


Lateral


75


15


Off


Grid


72″


Large


kVp, kilovoltage peak; mAs, milliampere-second (current); AEC, automatic exposure control; SID, source to image receptor distance; FSS, focal spot size; mo, months; y, years.


Reprinted from Table 8.1 from Lee EY, ed. Pediatric Radiology: Practical Imaging Evaluation of Infants and Children. Philadelphia: Wolters Kluwer; 2018, with permission.








FIGURE 2.9. A 3-year-old boy with normal sonographic view of the trachea. A: Transverse ultrasound image of the trachea obtained in supine position shows air within the nondependent portion of the trachea (T), manifested as a curved hyperechoic line (arrow) with posterior shadowing. B: Sagittal ultrasound image of the trachea obtained in supine position demonstrates air as a hyperechoic line (arrows) within the nondependent portion of the trachea (T). Asterisks demarcate tracheal cartilages.


Computed Tomography

Multidetector computed tomography (MDCT) with multiplanar two-dimensional (2D) and three-dimensional (3D) reformats is the gold standard for noninvasively evaluating the pediatric airway (Fig. 2.11). With rapid acquisition providing precise anatomical detail and diagnostic image quality, MDCT often eliminates the need for sedation and intubation. Newer techniques, such as paired inspiratoryexpiratory MDCT, cine MDCT, and four-dimensional (4D) MDCT, allow dynamic airway assessment.12,13,14 Of course, CT utilization is tempered by ever-increasing concerns about the risks of radiation exposure in children.15






FIGURE 2.10. A 6-month-old girl with bronchoscopy-confirmed tracheomalacia who presented with chronic cough. A: Lateral radiograph obtained at end-inspiration during airway fluoroscopy shows a patent trachea (arrows). B: Lateral radiograph obtained at end-expiration during airway fluoroscopy demonstrates substantial (>50%) collapse of the trachea (arrows), consistent with tracheomalacia.

Specific parameters for large airway CT depend on the type of scanner. In general, diagnostic imaging can be achieved with ≥16 row MDCT and the following parameters: 0.75 mm collimation for a 16-MDCT scanner, 0.625 mm collimation for a 32-MDCT scanner, and 0.6 mm collimation for a 64-MDCT scanner; high-speed mode; and a pitch equivalent of 1.0 to 1.5. The advent of 128- 256-, and 320-slice scanners heralds a new era of even faster airway imaging.16 Age- and weight-adjusted

milliamperage (mA), lowest-possible kilovoltage (kV), and anatomically based real-time automated exposure control help to decrease radiation exposure (Table 2.2). The intrinsic contrast between the air-filled large airways and nearby mediastinal soft tissue structures also allows for lower-dose technique. In addition to traditional coronal and sagittal reconstructions, curved planar reformats along the long axis of the large airways are commonly performed to allow more accurate measurements of the trachea and bronchi.3,7,12,16






FIGURE 2.11. A 10-year-old boy with normal large airways. A: Axial contrast-enhanced CT image at the level of the aortic arch (AA) shows a normal, round, patent trachea (T) at end-inspiration. E, Esophagus. B: Axial contrast-enhanced CT image at the level of the proximal mainstem bronchi demonstrates a normal, patent right mainstem bronchus (RB) and left mainstem bronchus (LB). AA, Ascending aorta; DA, Descending aorta. C: Coronal lung window CT image shows the trachea (T) and bilateral mainstem bronchi. RB, Right mainstem bronchus; LB, Left mainstem bronchus. D: Sagittal reformatted lung window CT image demonstrates a reference line (green line and yellow stars) through the center of the airway for reconstruction of a curved coronal reformatted CT image. E: Curved coronal reformatted CT image shows a straightened view of the large airways.






FIGURE 2.11. (Continued) F: Three-dimensional volume-rendered CT image (virtual bronchography) shows the normal large airways. G: Three-dimensional volume-rendered CT image (virtual bronchoscopy) of the normal large airways at the level of carina shows patent bilateral mainstem bronchi.


Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) offers superb contrast discrimination without ionizing radiation. However, long scan times may necessitate sedation and even intubation to prevent patient motion. A typical MRI airway imaging protocol may take 30 to 60 minutes (Table 2.3). However, recent research suggests that a comprehensive evaluation of the airways, lungs, and pulmonary vasculature may be achieved using a free-breathing ultrashort echo time (UTE) acquisition strategy.17 Intravenous gadolinium contrast is useful for assessing suspected neoplastic or infectious causes of upper airway obstruction.7 Gadofosveset (Ablavar), a gadolinium-based compound that binds to serum
albumin, and ferumoxytol (Feraheme), an iron oxide nanoparticle, have shown excellent promise as vascular contrast agents, although use remains off-label, and gadofosveset is no longer being marketed. Moreover, recently, heightened safety concern has been raised about ferumoxytol, which is approved only for the treatment of iron deficiency anemia. Nevertheless, ferumoxytol is not excreted through the kidneys and remains an attractive contrast option for patients with renal failure.18








TABLE 2.2 Tube Current and kV by Patient Weight for Central Airway MDCT







































Weight (kg)


Tube Current (mAs) Insp./Exp.


kV


<10


40/20


80


10-14


50/25


80


15-24


60/30


80


25-34


70/35


80


35-44


80/40


80


45-54


90/40


90


55-70


100-120/40


100-120


For tube current and kilovoltage by patient weight for end-expiratory MDCT examination, mAs should be reduced by 50% to a maximum of 40 mA while maintaining the same level of kV for end-expiratory MDCT examination. Insp., Inspiratory; Exp., Expiratory; mA, milliamperage; kV, kilovoltage; MDCT, Multidetector computed tomography.


Reprinted from Lee EY, Boiselle PM. Tracheobronchomalacia in infants and children: multidetector CT evaluation. Radiology. 2009;252:7-22, with permission.









TABLE 2.3 Static MRI Airway Imaging Protocol


































MRI Sequence


Imaging Plane


3D spoiled gradient-recalled echo (3D SPGR)


Axial, coronal, and sagittal


T2-weighted coronal single-shot half Fourier turbo spin echo


Coronal


Balanced steady-state free precession


Coronal


STIR


Axial


Bright blooda


Axial and coronal


T2-weighted periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER)b


Axial


Contrast-enhanced T1-weighted 3D gradient-recalled echo (3D GRE)c


Axial, coronal, and sagittal


Contrast-enhanced 3D MR angiography (3D MRA)a


Axial, coronal, and sagittal


a Can be performed for evaluation for vascular ring.

b Can be performed in patients who have difficulty following breathing instructions.

c Can be used to evaluate for contrast enhancement, depending on the indication.


Reprinted from Liszewski MC, Ciet P, Sodhi KS, Lee EY. Updates on MRI evaluation of pediatric large airways. AJR Am Roentgenol. 2017;208:971-981, with permission.


While static MRI is standard for anatomical assessment, cine MRI with fast gradient-echo sequences is an emerging modality that allows dynamic airway assessment in conditions such as obstructive sleep apnea, velopharyngeal insufficiency, and tracheobronchomalacia (TBM) (Table 2.4). Studies can be performed at 1.5 or 3.0 Tesla (T).7,19,20,21,22,23,24 The patient is sedated and placed in a head/neck vascular coil. In smaller children, the entire airway, from the upper nasal passages to the carina, can be fully visualized. In larger pediatric patients, the lower trachea may be outside the field of view. Following 3D localizers, sagittal and axial T1-weighted spin-echo (SE) (representative parameters: repetition time [msec]/echo time [msec] of 400/minimal, 22-cm field of view, 4-mm section thickness with 1-mm gap, 256 × 192 matrix, two signals acquired) and sagittal and axial fast SE inversion-recovery (IR) (representative parameters: 5,000/34, echo train length of 12, 22-cm field of view, 6-mm section thickness with 2-mm gap, 256 × 192 matrix, two signals acquired) sequences are typically obtained.7,23

Cine MR is performed in midline sagittal and axial planes at the midportion of the tongue using a fast gradient-echo sequence (representative parameters: 8,200/3,600, 80 degree flip angle, 12-mm section thickness). One hundred twentyeight consecutive images are obtained in ˜2 minutes and can be viewed in cine mode.7,23 Another evolving use of MRI is hyperpolarized gas imaging using inhaled 129Xe or 3He (Fig. 2.12).25 While potentially helpful in assessing ventilation patterns, the scarce and expensive nature of these gases limits widespread use of this technique.








TABLE 2.4 Dynamic MRI Airway Imaging Protocol




















MRI Sequence


Imaging Plane


3-plane gradient-recalled echo localizer at IVC


Axial, coronal, and sagittal


3D SPGR at IVC and EVC with wide FOV including the complete thorax


Axial, coronal, and sagittal


3D SPGR at IVC and EVC with narrow FOV focused on the large airways


Axial, coronal, and sagittal


Multiphase 3D SPGR with parallel imaging or temporally resolved imaging of contrast kinetics (TRICKS) throughout the respiratory cycle


Dynamic axial, coronal, and sagittal (4D)


Note: Protocol is performed with MRI-compatible spirometer. IVC, Inspiratory vital capacity; EVC, Expiratory vital capacity; SPGR, Spoiled gradient-recalled echo. Reprinted from Liszewski MC, Ciet P, Sodhi KS, Lee EY. Updates on MRI evaluation of pediatric large airways. AJR Am Roentgenol. 2017;208:971-981, with permission.







FIGURE 2.12. Hyperpolarized 3He MR lung ventilation image in a patient with cystic fibrosis causing severe respiratory disease (FEV1 = 34%). In addition to wedge-shaped regions of hypointensity due to underlying lung disease, large airways are also visualized. (Reprinted from Liszewski MC, Hersman FW, Altes TA, et al. Magnetic resonance imaging of pediatric lung parenchyma, airways, vasculature, ventilation, and perfusion: state of the art. Radiol Clin North Am. 2013;51(4):573, with permission.)


Nuclear Medicine

The use of nuclear medicine studies for evaluation of the airways is currently limited. While offering the unique ability to image physiologic processes, nuclear medicine techniques are generally inferior in spatial resolution and pose the usual risks of ionizing radiation. One technique that can be helpful is the radionuclide salivagram for assessing aspiration (Fig. 2.13). In this technique, a very small amount (<1 mL) of radiolabeled technetium 99m sulfur colloid is placed under the patient’s
tongue. The patient is dynamically imaged using the gamma camera. Aspiration is suggested by the presence of radiotracer within the tracheobronchial tree. Relatively sensitive and safe, the radionuclide salivagram can be performed in children who are not yet feeding orally, and it requires minimal patient cooperation.26 It is thus a viable alternative to the fluoroscopic modified barium swallow study. As in other body regions, positron emission tomography (PET) using 18F-fluorodeoxyglucose (18F-FDG), combined with anatomical imaging, provides added diagnostic value in characterizing neoplastic, inflammatory, and infectious processes of the airways.27






FIGURE 2.13. A 2-year-old girl with developmental delay and aspiration. Salivagram shows aspiration into both mainstem bronchi.


SPECTRUM OF LARGE AIRWAY DISORDERS


Congenital Disorders


Upper Large Airway Anomalies


Choanal Atresia/Stenosis

Choanal atresia is a congenital obstruction of the nasopharynx. It is characterized by narrowing and closure of the posterior choanae, and medialization of the pterygoid plates and lateral walls of the nose.7,29 The most common etiology of neonatal nasal obstruction, choanal atresia has an estimated incidence of 1 in 5,000 to 1 in 9,000 births. It arises twice as frequently in females as in males and is more commonly unilateral than bilateral.7,29,30 Osseous obstruction of the choanae was previously thought to be most common (90%), with membranous obstruction comprising the remaining 10%.29 However, more recent data point to a mixed bony/membranous etiology in 70% of cases and a pure bony abnormality in 30%. Unilateral choanal atresia may be asymptomatic; later in life, the patient may present with nasal stuffiness, rhinorrhea, or infection. Inability to pass a nasal enteric tube should raise clinical suspicion. Bilateral choanal atresia can cause severe respiratory distress because neonates are obligate nose breathers.7 Approximately 50% of patients with choanal atresia have associated anomalies such as coloboma, heart defects, and mental retardation, and syndromes including CHARGE (coloboma, heart disease, choanal atresia, growth and mental retardation, genital hypoplasia, ear anomalies with deafness), Crouzon, Pfeiffer, Antley-Bixler, Marshall-Smith, Schinzel-Giedion, and Treacher Collins.7,29,31

CT is most useful for demonstrating the precise anatomic abnormalities.7,32 Characteristic findings include narrowing of the posterior choanae to a width <0.34 cm in children under 2 years of age, inward bowing of the posterior maxilla, fusion or thickening of the vomer, and a bone or soft tissue septum across the posterior choanae (Fig. 2.14).7,33 Severe choanal stenosis may mimic atresia. CT virtual endoscopy is a 3D postprocessing technique that requires ˜10 additional minutes per examination, but no additional radiation, and can be helpful in diagnosis and preoperative planning.34 Some advocate instillation of 1 to 3 drops diluted nonionic contrast material through the nostril to better assess communication of the posterior choanae with the nasopharynx.35






FIGURE 2.14. A 2-day-old boy with choanal atresia who presented with grunting and clinical failure to pass a nasogastric tube through the left nostril. Axial bone window CT image at the level of the choanae shows complete obliteration of the left nasal passage (arrow) compared to the open contralateral side (asterisk).

Surgery is the management of choice for choanal atresia/stenosis. This consists of perforation of the obstructing septum to create a permanently patent airway.7 Many surgical techniques are available, including transnasal puncture, transpalatal resection, stent placement, endoscopic resection, and choanal resection, although there is no clearly preferred strategy.7,29,31 Correction of unilateral choanal atresia can be delayed until 6 to 9 years of age, when the midface reaches near-adult size.7 In contrast, bilateral choanal atresia mandates immediate intervention to reestablish airway patency. CT-navigation systems may be useful in complex cases. Adjuncts such as mitomycin C and laser therapy demonstrate no definite benefit.29 Ultimately, surgical success depends on the type of atresia, approach used, type of stent and duration of placement, and presence of other anomalies.7


Congenital Pyriform Aperture Stenosis

Congenital nasal pyriform aperture stenosis (CNPAS) is characterized by excessive growth of the medial nasal processes of the maxilla.7 It is a rare cause of upper airway obstruction in the newborn. The clinical presentation may include respiratory distress, episodic apnea, cyclical cyanosis, or sudden complete airway obstruction.36,37 Inability to pass a 5 French (F) catheter or endoscope through the nasal cavity is a classic history.36 Clinically, CNPAS cannot be distinguished from bilateral choanal atresia.7 The disorder may be part of the holoprosencephaly spectrum; a single central maxillary incisor is reported in up to 75% of cases, along with central nervous system (CNS) abnormalities.7,33,36,37 Additional associations include pituitary hormonal deficiencies and chromosomal abnormalities.7,36,37

CT is the imaging test of choice. Thin (1.5 to 2 mm) contiguous axial images are typically acquired parallel to the hard palate and roof of the orbits. Multiplanar 2D reformats are helpful but not mandatory to make the diagnosis. Findings include soft tissue density extending across the nostrils just
inside the nares, overgrowth and medial displacement of the nasal processes of maxilla, and narrowing of the pyriform aperture (Fig. 2.15). The pyriform aperture is bounded by the nasal bones superiorly, the nasal processes of the maxilla laterally, and the horizontal processes inferiorly; a width <11 mm in a term infant is considered diagnostic of CNPAS.7,36,38,39 MR is used to assess for associated intracranial abnormalities.40






FIGURE 2.15. A 1-day-old girl with congenital pyriform aperture stenosis and midline incisor who presented with grunting, difficulty breathing, and clinical failure to pass a nasogastric tube on either side. An orogastric tube was inserted instead. A: Axial bone window CT image obtained at the level of the nostrils shows marked narrowing (asterisk) of the pyriform aperture. B: Axial bone window CT image obtained at the level of the maxillary alveolar ridge demonstrates a solitary median maxillary central incisor (arrow), a commonly associated finding in patients with congenital pyriform aperture stenosis.

Mild CNPAS can be treated conservatively with humidification, topical nasal decongestants, nasal stenting, and placement of an oropharyngeal airway. More severe disease may necessitate surgical intervention.7,36,37,40 However, with treatment, the prognosis is excellent.36


Adenoid and Palatine Tonsil Enlargement

Pathologic enlargement of the normally immunoprotective adenoid and palatine tonsils is a frequent cause of upper airway obstruction in children (Fig. 2.16). The adenoid is an aggregation of lymphoid tissue located in the nasopharyngeal roof just beneath the sphenoid sinus and anterior to the basiocciput. It is absent at birth and rapidly grows during infancy, reaching a maximum size of 7 to 12 mm by 2 years of age, and progressively decreasing in size during puberty.7,21,41,42,43,44,45 The palatine (faucial) tonsils are also masses of lymphoid tissue, bounded by the glossopalatine and pharyngopalatine arches. Chronic inflammation or infection leading to hypertrophy/enlargement of the adenoid and palatine tonsils can ultimately cause nasopharyngeal and oropharyngeal obstruction. In turn, affected pediatric patients may develop chronic hypoxemia and hypercarbia from hypoventilation and obstructive sleep apnea.

Radiography remains first-line in the evaluation. The adenoid is considered enlarged if it appears to touch the hard palate on a lateral upper airway view (Fig. 2.17). Some advocate calculating the adenoidal-nasopharyngeal ratio (size of the adenoid relative to the nasopharynx). A value >0.8 is suggestive of adenoidal enlargement. The palatine tonsils are considered enlarged when they extend into the hypopharynx.7,46,47 The tonsillar-pharyngeal (T/P) ratio, or width of the tonsil divided by depth of the pharyngeal space on a lateral neck radiograph, may be used to screen children with suspected obstructive sleep apnea.2,48 Traditionally, sedated video fluoroscopy has been used for dynamic airway evaluation.2,48 A more recent alternative is cine MRI, which can provide volumetric measurements of the tonsils and adenoid in addition to dynamic airway assessment.2,21,49

Antibiotics are used to treat active adenoid and tonsillar infection (with associated lymphoid tissue enlargement). For chronic enlargement, especially when associated with airway compromise or obstructive sleep apnea, adenoidectomy and/or tonsillectomy may be necessary. Surgery may also help manage recurrent ear and sinus infections.7






FIGURE 2.16. A 12-year-old girl with tonsillar hyperplasia. The cut surfaces of the resected palatine tonsils show fleshy pale tan lymphoid tissue with deep slit-like crypts.







FIGURE 2.17. A 12-year-old boy with adenoid and palatine tonsillar hypertrophy who presented with sleep apnea. Lateral soft tissue neck radiograph shows moderate adenoid (black asterisk) and palatine tonsillar (white asterisk) hypertrophy.


Macroglossia

Macroglossia is characterized by chronic and painless enlargement of the tongue, defined by protrusion of the tongue beyond the teeth or alveolar ridge at rest. It should be distinguished from acute glossitis, in which there is painful and rapid tongue enlargement.7,50 Causes of macroglossia include hypothyroidism, idiopathic hyperplasia, and a number of syndromes including the mucopolysaccharidoses, Down, and Beckwith-Wiedemann.7,51,52 A variant known as relative macroglossia refers to a normal-sized tongue that is large relative to a small-sized mandible (micrognathia). Macroglossia may present with noisy breathing, drooling, dysphagia, and speech difficulty, with potential for upper airway obstruction.7,52,53

Sleep fluoroscopy can be used to evaluate for progressive respiratory distress in affected pediatric patients. During sleep, the enlarged tongue may fall posteriorly and obstruct the posterior pharynx.7,54 Cross-sectional imaging with CT and MRI is also helpful in assessing the tongue and excluding underlying masses (Fig. 2.18).7,55

Medical management may be sufficient for macroglossia related to an underlying systemic process. In other cases, surgery with reduction glossectomy is the treatment of choice in symptomatic patients, helping to prevent airway, speech, and orthodontic sequelae. Acute upper airway obstruction mandates immediate evaluation and intervention such as tracheostomy.7,55






FIGURE 2.18. A 3-year-old girl with macroglossia who presented with dysphagia and drooling. Sagittal T1-weighted magnetic resonance image shows marked enlargement of the tongue (asterisks) with anterior protrusion outside of the oral cavity.


Laryngomalacia

Laryngomalacia is characterized by abnormal laxity of the pharyngeal soft tissues due to immaturity of the laryngeal cartilages and muscles. It is a benign and often transient condition. The laxity causes inspiratory collapse of the epiglottis, arytenoids, and aryepiglottic folds with resultant partial upper airway obstruction. Laryngomalacia is the most frequent congenital laryngeal anomaly, accounting for >75% of such cases.7,56,57 In addition, it is the most common cause of symptomatic airway obstruction in infants presenting with stridor that worsens with rest and improves with activity.7,56,57

Airway fluoroscopy characteristically shows downward and posterior bending of the epiglottis and anterior buckling of the aryepiglottic folds, with narrowing and eventually occlusion of the upper airway (Fig. 2.19). Although airway fluoroscopy demonstrates high specificity for the diagnosis, its sensitivity is poor. Therefore, even when fluoroscopy is normal, further evaluation with laryngoscopy should be performed if there is persistent clinical concern.7,56,58,59,60

The majority of cases of laryngomalacia resolve without intervention by the end of the first year of life.7 Acid-suppressing medication should be given in patients with concurrent feeding symptoms.60 Persistent symptoms require surgical intervention to prevent complications such as airway obstruction and even sudden death. Relevant surgical techniques include tracheostomy, supraglottoplasty, aryepiglottic fold incision, and epiglottopexy.7,61


Laryngeal Cleft

Laryngeal cleft is a congenital anomaly characterized by failure of fusion of the posterior aspect of the larynx, resulting in abnormal communication between the airway and esophagus.







FIGURE 2.19. A 2-month-old girl with laryngomalacia who presented with stridor. A: Lateral soft tissue neck radiograph shows the normal position of the epiglottis (arrow). B: Lateral soft tissue neck radiograph demonstrates laxity of the epiglottis (arrow), with posterior and downward movement obstructing the airway. (Reprinted from Laya BF, Lee EY. Congenital causes of upper airway obstruction in pediatric patients: updated imaging techniques and review of imaging findings. Semin Roentgenol. 2012;47[2]:147-158, with permission. Case courtesy of Khristine Grace C. Pulido, MD, Manila, Philippines.)

There are four types according to the Benjamin and Inglis classification scheme: Type I is an interarytenoid soft-tissue defect that does not involve the cricoid cartilage; type II extends into the cricoid cartilage; type III extends through the cricoid cartilage and may involve the cervical trachea; and type IV extends into the posterior wall of the thoracic trachea and, potentially, the carina (Fig. 2.20).62 Laryngeal cleft has traditionally been considered rare, reportedly representing <0.5% of all congenital larynx anomalies.63,64 However, with increasing diagnosis in recent years, the actual prevalence may be higher. There is a slight male predominance. Associations include laryngomalacia; absent tracheal rings; pulmonary agenesis; anomalies of the cardiovascular, genitourinary, and gastrointestinal systems; and syndromes such as Opitz G/BBB, Pallister-Hall, VACTERL, and CHARGE. The clinical presentation may include chronic cough and choking, cyanosis during feeding, aspiration, recurrent pneumonia, respiratory distress, and stridor. Because symptoms are nonspecific and the disorder uncommon, the diagnosis may be delayed.63,64

Direct laryngoscopy with visualization of the interarytenoid area remains the most reliable method of diagnosis. However, a variety of imaging modalities are used in the workup. Chest radiographs may be normal or show findings compatible with chronic aspiration or pneumonia, including consolidation and reticular opacities more often occurring in
the lower lobes (Fig. 2.21).63,64 Chest CT demonstrates similar findings, but with greater sensitivity and anatomic precision (Fig. 2.22). Modified barium swallow study is useful for assessing aspiration. Barium swallow study may show passage of contrast into the trachea, potentially leading to misdiagnosis of tracheoesophageal fistula (TEF) rather than laryngeal cleft.63,64 CT or MRI may occasionally demonstrate the abnormal communication and lack of soft tissue between the trachea and esophagus. An abnormally anterior or intratracheal position of a nasogastric tube is also a clue to the diagnosis. Ultimately, advanced modalities are more often used for assessing associated anomalies.63,64






FIGURE 2.20. Diagram showing the types of laryngeal cleft. Type I is the mildest form of laryngeal cleft. The gap between the larynx and the esophagus is located above the vocal cords. Type II laryngeal cleft extends into the lower cartilage of the larynx, below the vocal chords. Type III laryngeal cleft extends beyond the larynx and into the trachea. Type IV is the most severe form of laryngeal cleft. The gap extends even further down into the trachea, even sometimes extending to the carina.






FIGURE 2.21. A 10-year-old boy with delayed diagnosis of type II laryngeal cleft who presented with recurrent pneumonia. Frontal chest radiograph shows a consolidation and an internal air-fluid level (arrow), likely representing a lung abscess caused by aspiration.






FIGURE 2.22. A 7-year-old boy with delayed diagnosis of type II laryngeal cleft who presented with recurrent aspiration pneumonia. Coronal lung window CT image shows bronchiectasis and chronicappearing atelectasis in both lower lobes, left side greater than right side, due to recurrent aspiration pneumonia.

Initial conservative medical management includes acidsuppressive treatment for gastroesophageal reflux, change in food texture, and alternative positioning before and after feeding. These strategies help to maintain adequate ventilation and feeding while preventing aspiration. Respiratory distress may require endotracheal intubation, but endoscopic guidance is recommended to mitigate the high risk of tube misplacement. Refractory cases merit surgery. New endoscopic techniques may be adequate for milder cases, while more severe cases require the classical, systematic, external approach (anterior laryngotracheal or lateral pharyngotomy). The overall prognosis depends on the type of cleft, the patient’s pulmonary status, and associated anomalies; early surgery helps mitigate complications of gastroesophageal reflux and aspiration.64


Lower Large Airway Anomalies


Tracheal Agenesis

Congenital tracheal agenesis is a rare and usually lethal anomaly (Fig. 2.23). The pathogenesis is uncertain. However, the disorder is postulated to result from failed embryologic separation of the trachea and esophagus during anterior budding of the proximal foregut.65 The incidence is estimated at 1 in 50,000 newborns, with a male/female ratio of 2:1.66 Over 150 cases have been reported since the initial description by Payne in 1900.66,67 More than half of patients are premature; over 50% of pregnancies are associated with polyhydramnios.66,68 Associated congenital anomalies are present in 50% to 94% of cases.66 Affected patients present acutely with cyanosis, severe respiratory distress, inadequate gas exchange, lack of audible crying, and failed endotracheal intubation.66,67,68

Anatomically, the trachea is typically blind-ending below the level of the larynx. Gas exchange occurs through a distal esophageal fistula.69 As originally described by Floyd et al., there are three subtypes.70 In type I, the proximal trachea is atretic, and the preserved short distal trachea communicates with the esophagus via a TEF. In type II, the trachea is nearly or completely absent, and the main bronchi join to form a midline carina that fistulizes with the esophagus. This is the most common type, occurring in 60% of cases. In type III, the trachea and carina are absent, and the main bronchi arise directly from the distal esophagus at separate origins.65,66,67,68,69,70

Chest radiographs are generally nondiagnostic. They may demonstrate an absent tracheal air column, an abnormally low position of the tracheal bifurcation, an abnormally posterior “endotracheal” tube/esophageal intubation, or gaseous distention of the distal esophagus, stomach, and proximal small bowel. Historically, barium studies were performed to assess for bronchoesophageal fistulas. They are now usually avoided due to potential airway compromise.65,69,71 CT with multiplanar reformations (MPRs) is the imaging modality of
choice, as it is able to show the entire length of the atretic trachea and precisely localize the esophageal fistula.65,69






FIGURE 2.23. Spectrum of pathological phenotypes of the tracheal cartilages showing normal anatomy (A-F) and cross-section through the tracheal cartilages (A’-F’). Cartilages are depicted in blue, epithelium in purple, and esophagus/stomach in orange. E, esophagus; Hy, hyoid; Th, thyroid cartilage; Cr, cricoid cartilage; Al, annular ligaments; Ca, carina; Br, bronchus; St, stomach. A’: Schematic cross-section through tracheal cartilages. E, esophagus; TM, trachealis muscle; RE, respiratory epithelium; TC, tracheal cartilage. B and B’: Depiction of tracheal agenesis shows absence of the tracheal cartilages below the larynx. C and C’: Tracheomalacia results from a weakness in the cartilage rings that makes the trachea prone to collapse. This can be seen as a flattening of the tracheal rings in cross-section (C’). D and D’: Tracheal stenosis is a narrowing of the tracheal lumen. Rather than the normal C-shaped cartilage rings with intervening tissue allowing expansion, in tracheal stenosis the cartilage rings are O-shaped, and therefore unable to grow. E and E’: In tracheal cartilaginous sleeve, cartilage rings are fused, leading to a loss of the intervening fibrous annular ligaments. F and F’: Tracheo-esophageal fistula occurs when the foregut fails to separate into the trachea and esophagus. (Reprinted from Sher ZA, Liu KJ. Congenital tracheal defects: embryonic development and animal models. AIMS Genetics. 2016;3(1):60-73. Figure 1, with permission.)

Few treatment options currently exist. If tracheal agenesis is diagnosed prenatally by fetal US and MRI, the ex utero intrapartum tracheotomy (EXIT) procedure may be successful if the distal trachea is patent. Surgical attempts to reconstruct the upper airway using the esophagus or synthetic material thus far have not been effective for long-term survival.72


Ectopic Bronchus


Tracheal Bronchus

Tracheal bronchus was originally narrowly defined as a right upper lobe bronchus arising from the trachea (also known as “bronchus suis” or pig bronchus due to similar anatomy in pigs). The term now covers a broad spectrum of anomalous bronchi originating from the trachea or main bronchi, directed towards the upper lobes. The prevalence of right and left tracheal bronchus is 0.1% to 0.2% and 0.3% to 1%, respectively, based on bronchographic and bronchoscopic series.3,12,72,73 Tracheal bronchus is generally isolated and incidental. However, reported associations include Down syndrome, rib anomalies, TEF, VATER (vertebral anomalies, anal atresia, tracheoesophageal fistula, and renal malformations) syndrome, partial anomalous pulmonary venous return, congenital lobar emphysema, and cystic lung malformations.72,73,74 Affected pediatric patients are usually asymptomatic but may develop recurrent pneumonia, atelectasis or air-trapping, persistent cough, stridor, acute respiratory distress, or hemoptysis (Fig. 2.24).72,73 A classic history is nonresolving right upper lobe atelectasis following endotracheal intubation, related to obstruction of the unsuspected aberrant bronchus by the endotracheal tube.3,12







FIGURE 2.24. A 2-year-old girl with tracheal bronchus who presented with recurrent right upper lobe pneumonia. Axial enhanced CT image shows a tracheal bronchus (arrow) arising at the right lateral aspect of the trachea (T) and leading to the consolidated right upper lobe (asterisk). E, Esophagus.

A “true tracheal bronchus” arises from the trachea usually <2 cm and no more than 6 cm from the carina, typically at the right lateral aspect (Fig. 2.25).3,12,72,73 If the segmental bronchi of the parent anatomic bronchus supplying the same lobe as the tracheal bronchus are intact, the tracheal bronchus is termed supernumerary. Otherwise, the aberrant bronchus is termed displaced. Blind-ending supernumerary bronchi are known as tracheal diverticula. Supernumerary bronchi ending in aerated or bronchiectatic lung are known as apical accessory lungs or tracheal lobes.73

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May 8, 2019 | Posted by in PEDIATRIC IMAGING | Comments Off on Large Airways
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