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Imaging the upper airways
PAEDIATRIC RESPIRATORY REVIEWS (2001) 2, 46–56 doi: 10.1053/prrv.2000.0101, available online at http://www.idealibrary.com on
SERIES: IMAGING
Imaging the upper airways K. Bradshaw Radiology Department,The Birmingham Children’s Hospital, Steelhouse Lane, Birmingham B4 6LH, UK KEYWORDS paediatric, head/neck, tracheo-bronchial tree, radiography, radiology, imaging
Summary Radiological evaluation of the airway has been used as a screening tool and an adjunct to endoscopy for many years. It provides non-invasive data on the structure of the airway, often avoiding the risk of general anaesthesia. Standard radiographs provide some information on the intricate anatomy of the paediatric airway aided by fluoroscopy. More recently, CT and MRI are proving to have a valuable role and are approaching near endoscopic detail of airway anatomy.The purpose of this article is to highlight areas where radiology can aid in the evaluation of the airway of infants and children. © 2001 Harcourt Publishers Ltd
INTRODUCTION The most common indication for imaging the paediatric airway is suspected airway obstruction. Partial or complete obstruction of the upper airway occurs at multiple levels and can be due to a number of causes. Radiological evaluation should be performed after thorough clinical work-up, including flexible fibre-optic laryngoscopy where appropriate. The plan of investigation detailed in this article is symptom and suspected pathology driven. Whilst the spectrum of aetiologies is diverse, the investigations are more specific. The soft tissue lateral radiograph of the neck (Fig. 1) and an upper gastrointestinal barium study with airway screening are the standard investigations. Computed tomography (CT) scanning and magnetic resonance imaging (MRI) should be reserved for specific cases. In all cases, the conditions mentioned in infants are relevant to older children and vice versa; however, I have attempted specific segregation into infant and childhood causes.
INVESTIGATION OF STERTOR Stertor is described as noisy breathing due to nasal or pharyngeal causes of airway obstruction.
Nasal causes of stertor in infants Failure to pass an 8 French catheter through the nasal cavity should confirm the clinical suspicion of obstruction to 1526–0550/01/010046 + 11 $35.00/0
the airway at the nasal level. The most common cause is posterior choanal atresia (Fig. 2). Less commonly, anterior piriform aperture stenosis is present and this has an identical clinical presentation (Fig. 3). High resolution CT is the investigation of choice in the diagnosis of nasal obstruction in the newborn. Respiratory distress alleviated by crying is the classical presentation of nasal obstruction in neonates, as they are obligate nasal breathers.1 In view of this, the child is not sedated but instead imaged after a feed when hopefully the child will be asleep. The child is placed on the scanning table supine. A lateral tomogram is performed, from which continuous 2 mm cuts are taken through the nose and nasopharynx avoiding the orbits and the radiosensitive lens. Sagittal reconstructions can subsequently be performed to aid diagnosis in difficult cases. In the evaluation of choanal atresia, vomer bone width and choanal air space distance are important landmarks.2 The main vomer bone width in neonates is 0.23 cm and this thickens to 0.28 cm by the eighth year of life. The choanal air space distance refers to the space from the lateral wall of the nasal cavity to the vomer. This is normally 0.67 cm at birth, and it increases by 0.027 cm per year until the age of 19 years. In choanal atresia the vomer is widened and the choanal air space is absent with, in 90% , a complete bony obstruction. In 10% there is a mixed bony/membranous or very rarely a purely membranous cause. There is a high incidence of associated anomalies in choanal atresia, e.g. CHARGE syndrome and Treacher Collins syndrome. © 2001 Harcourt Publishers Ltd
IMAGING THE UPPER AIRWAYS
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Figure 1 Normal lateral soft tissue neck. P, piriform fossa;V, vallecula; L, larynx;T, trachea; E, epiglottis.
Figure 2 CT scan of choanal atresia. Arrow indicates the posterior narrowing.
CT scanning is also performed to identify the rare congenital nasal piriform aperture stenosis (CNPAS). This is clinically indistinguishable from the more common bilateral choanal atresia. The nasal airway is narrowed anteriorly by bony overgrowth of the nasal process of the maxilla. As yet no normal values have been determined for the anterior aperture but radiological signs are inward convexity of the nasal bone. This condition may occur in isolation or in association with a mid-facial
Figure 3 CT scan of piriform aperture stenosis. Arrow indicates the anterior narrowing.
dysostosis (single central incisor) or with associated endocrine pathology (pituitary) or a central nervous system abnormality (holoprosencephaly spectrum). Further imaging of these associated abnormalities by CT or MRI should be performed at a later date when the airway has
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Figure 4 T1W saggital MRI showing large encephalocele obstructing the nasal airway.
Figure 5 Lateral soft tissue neck. Pierre Robin Syndrome, narrowing of the oropharynx due to micrognathia.
been stabilised, as sedated scans are usually required due to the complexity and length of time of the imaging, particularly when MRI is performed. Anterior encephalocele can present with nasal obstruction due to the mass – this is normally unilateral and MRI is the investigation of choice (Fig. 4).
child. Tumours and non-accidental injury can also cause retropharyngeal widening, although these are rare causes. These should be investigated as in the older child.
Oropharyngeal causes of stertor in the Infant In newborn infants there are a variety of causes. The initial radiological investigation is a lateral soft tissue radiograph of the face and neck. The air within the airway provides a negative contrast, which allows the patency and calibre of the oropharyngeal airway anteroposteriorly to be assessed. Craniofacial dysostosis with mandibular hypoplasia is seen in the ‘first arch’ or related syndromes, particularly Pierre Robin syndrome (Fig. 5), Goldenhars syndrome and Weyers mandibulofacial dysostosis. Mandibular hypoplasia is also seen in trisomies 17–18 and 13–15, and the Cri-du-Chat syndrome. This can cause severe airway compromise because the micrognathia causes posterior displacement of the tongue. In the neonatal period vascular and lymphatic malformations are the most likely causes of enlargement of the oropharyngeal soft tissues, as nasopharyngeal lymphoid tissue is sparse at this age. These malformations are often extensive and cause airway compromise at multiple levels. Retropharyngeal abscess is exceptionally rare in the neonatal period and if it does occur is more likely to have arisen in a congenital cyst than in the older
Nasal and oropharyngeal causes of stertor in children The initial radiological investigation is the lateral soft tissue of the upper airways, as in infants. Precise prevertebral soft tissue dimensions in children are impossible. In infants and young children the prevertebral space is wider because the vertebrae are not fully ossified: however, as a guide, with the neck fully extended the soft tissue space from C1 to C4 is equal to one half of the vertebral body. In the older child the vertebral bodies become larger and wider and the prevertebral space smaller. (However, the degree of lymphoid hyperplasia should be considered.) Below C4, the prevertebral space normally equals the adjacent vertebral body. In a child, if the prevertebral space is greater than the adjacent vertebral body below C3 it is abnormal, provided the radiograph is adequate and the neck is not flexed.
Acute Enlargement of the prevertebral soft tissues on the lateral radiograph in the context of a toxic child with airway obstruction suggests retropharyngeal inflammation. Plain film findings of retropharyngeal inflammation are straightening of the normal curve of the spine with smooth forward displacement and compression of the airway. Rarely, in cases of retropharyngeal abscess pathological
IMAGING THE UPPER AIRWAYS
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Figure 6 Lateral soft tissue neck. Retropharyngeal abscess, widening of the prevertebral soft tissue and pseudosubluxation of C1 on C2, Grisels Syndrome. Stretching and narrowing of the trachea anteriorly indicated by the arrows.
slip of C1 on C2 can be falsely suggested on a lateral soft tissue neck; this is termed Grisels syndrome (Fig. 6). The retropharyngeal space extends from the skull base to T4. Further investigation is by cross-sectional imaging to assess the deep tissues of the neck and upper mediastinum (Fig. 7). Magnetic resonance imaging is preferable because there is no radiation dose, the risks of iodinated contrast media are avoided and the multiplanar imaging capability allows easy identification of mediastinal extension, particularly on sagittal sequences. If access to MRI is difficult then CT will adequately assess the extent of the abscess. In both modalities it is important to scan to at least the carina to exclude mediastinal extension. Neoplastic causes of retropharyngeal distension are uncommon and should be investigated with CT and MRI, as in retropharyngeal infection. In neoplastic lesions in this region often both CT and MRI will have to be performed: CT for the bony destruction and MRI for the soft tissue characteristics.
Figure 7 Saggital T2W MRI showing high signal prevertebral inflammation due to the retropharyngeal abscess.
of the nasopharyngeal lymphoid tissue is 3–5 years. A lateral neck radiograph, however, does not predict the severity of the obstruction when a child is sleeping or supine. Sleep fluoroscopy has been advocated in the investigation of this condition but currently is not used routinely. Juvenile angiofibroma can present with stertor, although more commonly with epistaxsis. This is investigated by cross-sectional imaging and can be identified by the location centred in the pterygopalatine fossa and the intense enhancement post-contrast: this will alert the radiologist to the diagnosis, averting any biopsy as these can bleed profusely. Rarely, children can present with insidious stertor due to neoplastic disease, i.e. rhabdomyosarcoma, lymphoma and nasopharyngeal carcinoma in the older child (Figs 8 and 9).
Stridor Chronic Nasopharyngeal causes of airway obstruction in older children most commonly take the form of obstructive sleep apnoea syndrome. This is diagnosed by assessing the degree of obstruction of the nasopharygeal airway secondary to adenoidal or tonsillar hypertrophy on the lateral soft tissue neck radiograph. The peak age for maximum growth
Stridor is a harsh high-pitched sound in breathing, caused by air passing through constricted air passages. Diagnostic evaluation of the infant and child with stridor should initially involve flexible fibreoptic layrngoscopy to examine the hypopharynx and larynx. AP and lateral soft tissue radiographs of the neck using the Cincinatti high KV technique plus a chest X-ray are indicated. Video
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Causes of stridor in infants Bilateral vocal cord paralysis. Subglotic haemangioma. Subglotic stenosis. Laryngomalacia and tracheomalacia. Extrinsic compression. fluoroscopy with airway screening and a barium swallow are useful in certain cases. Airway fluoroscopy provides a dynamic view of the airway below the vocal cords. Fluoroscopy is performed with the neonate supine on the table for AP screening; the child can then be turned laterally to further assess the airway. The upper airway is dynamically assessed throughout the respiratory cycle; due to this, patient compliance is less crucial than in plain films and most neonates can be adequately immobilised for screening. Spot films and video recording of the examination are performed for review later. Airway screening can determine whether an obstruction is fixed or varies with the respiratory cycle. A barium swallow can be performed at the same time as airway screening. Pulsed fluoroscopy can be used for much of the swallowing study; this has been shown to reduce radiation dose.3 Barium swallow can assess conditions such as posterior laryngeal clefts, tracheooesophageal fistula, pharyngeal inco-ordination with resultant laryngeal or tracheal aspiration and extrinsic compression on the trachea. The barium swallow evaluates the oesophagus, stomach, duodenum and proximal jejunum.
Figure 8 CT, left nasopharyngeal lymphoma.
The examination is performed after the child has missed a feed and is therefore hungry and will readily drink the barium. The child’s regular feeding apparatus is used. In the case of breast-fed infants, a dummy with a 6 French feeding tube fed into the teat via a small hole made with a scalpel, with a hole in the tip and a syringe attached to the end of the feeding tube normally gives good results. The addition of glycerol to the tip of the dummy can help the infant ‘to latch on’. As a last resort the barium can be directly syringed in to the infants mouth. Thin barium 50 w/v is used, up to a max of 3.5 ml/kg. Lateral screening provides detailed information on the oral and pharyngeal phases of swallowing and can document aspiration. Adequate distension of the oesophagus will normally demonstrate a tracheo-oesophageal fistula, but where there is strong clinical suspicion then prone lateral screening views should be performed. This will make the fistulous track dependent and thus the barium more likely to enter. Antero-posterior screening should be performed too, as this will help assess any extrinsic oesophageal compression. Careful examination at the end of the procedure to assess gastrooesophageal reflux should also be performed.
Laryngeal causes of stridor in the infant Laryngeal pathology is the most common cause of stridor in infants and the majority of congenital laryngotracheal abnormalities present in the neonatal period. Laryngomalacia is the most common laryngeal abnormality in the neonatal period4 and 60% of laryngeal causes of stridor are attributed to this self-limiting condition.5 The diagnosis of laryngomalacia is made with flexible fibre-optic laryngoscopy; however, research has demonstrated an 80% incidence of gastro-oesophagea reflux6
Figure 9 T1W post gadolinium axial MRI, large left nasopharyngeal carcinoma.
IMAGING THE UPPER AIRWAYS
Figure 10 Ph probe correctly positioned to assess gastrooesophageal reflux.
and also an increased incidence of additional laryngotracheal abnormalities (Fig. 10).7 Subsequent to direct examination of the larynx and hypopharynx, whether the finding is normal or a laryngeal abnormality is found, a barium swallow and airway screening should normally be performed. This determines the cause of the stridor in cases where no abnormality was detected at direct examination and where an abnormality was found; coexistent distal pathology can then be excluded and laryngeal competence can be assessed. The exception to this pathway is in bilateral vocal cord paralysis, which is found at flexible laryngoscopy in 10% of cases of congenital laryngeal causes of stridor.8 This is the second most common upper airway anomaly encountered in infants and children. Once the diagnosis is established and the child stabilised then, unlike other laryngeal causes of airway obstruction, a barium examination is not required. The child with bilateral vocal cord paralysis should undergo a detailed MRI scan of the brain and thorax. Due to the length of the examination (45 mins) and the need for complete immobilisation to reduce artefacts, the MRI needs to be performed either under general anaesthetic or sedated with the airway stabilised. A cranial MRI is performed as 25–35% of vocal cord paralysis has a central nervous system cause,9 which is normally in the midbrain or brainstem. The most common CNS cause is the Arnold Chiari malformation (Fig. 11). There are two forms of Arnold Chiari malformation. In type one there is tonsillar herniation as an isolated feature. In type two there is an associated meningomylocele. The downward herniation of the cerebellar tonsils and brainstem is thought to cause traction on the vagus nerves. Posterior fossa decompression may lead to resolution of the vocal cord paralysis. The thorax should also be imaged to
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Figure 11 Saggital T1W MRI head, arrow showing tonsillar herniation, Arnold Chiari 1.
exclude thoracic causes of recurrent laryngeal nerve pathology.
Subglottic causes of stridor in the infant Subglottic stenosis This is the third most common upper airway anomaly in this age group. This is identified as a fixed narrowing in the subglottic region throughout the respiratory cycle. It may be acquired or congenital. In acquired cases prolonged intubation is an important cause, particularly in the premature infant. Additionally, reflux with aspiration is thought to contribute. Computed tomography occasionally may be helpful to assess the integrity of the cartilaginous support of the cricoid.
Subglottic haemangioma These lesions have a characteristic radiographic appearance of asymmetric subglottic narrowing. They are seen on plain radiographs, but the diagnosis is made by direct examination (Fig. 12).
Tracheal causes of stridor in the infant Tracheomalacia Tracheomalacia is diagnosed radiologically by expiratory collapse of the trachea on airway screening causing greater than 10%–20% tracheal obstruction.10 Tracheooesophageal fistulae are associated with focal areas of tracheomalacia (Fig. 13). If vascular compression or cardiac compression is thought to be a causative factor, then MRI or CT should be performed to further assess this (see later text).
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Figure 12 Asymmetric airway narrowing, sub-glottic haemangioma.
Extrinsic causes of stridor in the infant MRI or CT can be used to assess the mediastinum. Ideally MRI scanning is preferred, although availability and clinical condition may necessitate CT. MRI is the best technique for imaging the thorax to assess whether respiratory compromise is due to extrinsic lesions. By accounting for cardiac movement and respiratory artefact, a variety of sequences in multiple planes can be used to demonstrate the adjacent vascular structures or massess. MRI provides additional information over CT about the location and extent of disease and can confirm the cystic nature of lesions which appear solid on CT (Fig. 14). MRI is particularly invaluable in neurogenic tumours, as it can optimally demonstrate the number and extent of the lesions, particularly the intraspinal extension. MRI has no radiation burden and as yet has no known adverse effects. MRI is rather time-consuming and children up to the age of 5–6 years need sedation for the scan. CT should be performed after intravenous contrast. This is a higher resolution modality but lacks the multiplanar capability of MRI and incurs a radiation burden. On newer helical scanners, however, manipulation of the axial data can be performed to create multiplanar reformats, shaded surface display three-dimensional reconstructions and virtual bronchoscopy. Additionally, contrast enhanced CT is rapid in modern scanners so this technique can often be performed unsedated in a younger
Figure 13 Tracheo-oesophageal fistula, lateral swallow.
age group and in conditions where prolonged supine positioning may lead to respiratory compromise. The technique used in our institution for a CT thorax is that the child is placed supine on the scanner, approx. 35 s
IMAGING THE UPPER AIRWAYS
after the start of a fast bolus injection of non-ionic iodinated contrast media and 8 mm contiguous slices with a pitch of 1.5 are performed. The scanner takes approximately 1 second per slice, making an average of 20second scanning time depending on the size of the child. There are many lesions causing extrinsic compression. These are often related to anomalies of the surrounding anatomical structures but local or metastatic neoplasms may present in this way (Fig. 15 a,b). A list of some of the more common causes is shown below.
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Vascular malformations. Haemangioma is the most common tumour of infancy and over 50% occur in the head and neck region. Venolymphatic malformations are also an important cause of pathology in this region (Fig. 17). MRI is the investigation of choice for vascular malformations, as it can not only give exquisite anatomical detail of the extent of the lesion but can also give specific information as to the histological nature of the lesion.
Lesions causing extrinsic compression Bronchogenic cyst. Oesophageal duplication cysts. Neurogenic tumour. Thymic mass. Lymph node mass. Vascular anomalies. Venolymphatic malformations.
Vascular compression This may consist of a complete ring or an incomplete pulmonary sling. MRI can occasionally be misleading if a ligamentous arch completes the ring or duct and therefore the barium swallow must not be excluded. Vascular compression tends to cause symptoms in infancy, although it can present later (Fig. 16 a,b).
(a) Figure 14 Axial T2W MRI with left branchial cleft cyst.
(b)
Figure 15 T-cell lymphoma. (a) Chest X-ray showing large mediastinal mass. (b) Post-contrast CT showing large anterior mediastinal mass with compression of the carina (arrow).
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(a)
Figure 17 Axial fat suppressed T2W MRI showing a macrocystic lymphangioma, marked airway narrowing noted.
(b)
Epiglotitis Although a swollen epiglottis can be demonstrated on lateral soft tissue neck, this investigation is not recommended due to the risk of acute airway obstruction during positioning.
Croup
Figure 16 Right-sided aortic arch. (a) Coronal T1W MRI, arrow indicating a Kommerel diverticulum. (b) Axial T1W MRI: note anterior and posterior compression of the airway.
A chest X-ray is the investigation of choice in croup to exclude additional lower respiratory tract infection that could be exacerbating the situation and would require treatment. A plain lateral soft tissue neck X-ray should be performed if there is a suspicion of a complicating factor. In croup there is loss of clarity of the tracheal airway on radiographs. Table 1 illustrates the relative narrowing that 1 mm of subglottic oedema causes in various ages.
Causes of stridor more specific to the child
Inhaled foreign body
In the older child acquired causes have a greater role to play, particularly infectious causes.
Providing the ingested item is radio-opaque, AP and lateral radiographs will clearly identify the location (Fig. 18a,b).
Table 1 Relative narrowing caused by subgloltic oedema. Age group
Term Newborn
1-year-old
3-year-old
10-year-old
Normal diameter of airway Percentage loss in airway due to 1mm oedema
D = 4.5 mm 70%
D = 5.5 mm 60%
D = 7.00 mm 50%
D = 9.00 mm 40%
IMAGING THE UPPER AIRWAYS
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(a)
(b)
Figure 19 Barium swallowing demonstrating laryngeal and tracheal aspiration.
Figure 18 Foreign body in the oesophagus. (a) Lateral soft tissue neck, tracheal compression at level of foreign body indicated by the arrow. (b) AP chest X-ray.
Dysphagia Dysphagia can present with a multiplicity of airway symptoms, including stridor and coughing. An important examination in the assessment of the upper airway in the younger child is the feeding study. In older children a modified feeding study is used, tailored to the feeding capabilities of the child. The evaluation is performed by a speech therapist and a radiologist. The examination is videotaped for future review. Silent aspiration has been noted in
59–94% during feeding studies (Fig. 19). Children with wheezing or chronic pulmonary disorders can be assessed for aspiration or gastro-oesophageal reflux. If the child aspirates thin liquids then semi-thick and thickened liquids can be tried. If there is aspiration of all liquids then, depending on the child’s feeding status, semi-solid to solid food can be tried. Feeding can be assessed with all consistency of foods, including iced food.
CONCLUSION Imaging of the upper airways involves multiple modalities. The investigative pathway is targeted to the likely level of pathology. Therefore, radiological investigations should only be undertaken after a complete clinical evaluation by an experienced clinician and in many cases only after direct laryngoscopy.
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RESEARCH DIRECTIONS
•
•
Virtual bronchoscopy with CT or MRI provides a non-invasive method of examination; however, further work is necessary in both resolution, speed of scanning (to minimise respiratory artefact) and post-processing software. Clinical trials of comparison with the current gold standard direct laryngoscopy and bronchoscopy will be necessary to determine sensitivity and specificity.
REFERENCES 1. Healy GB, Mc Gill T, Strong MS et al. Management of choanal atresia with the carbon dioxide laser. Ann Otol Rhinol Laryngol 1978; 87: 658–662. 2. Slovis TL, Renform B, Watts FB et al. Choanal atresia precise CT evaluation. Radiology 1985; 155: 345–348.
3. Brown PH, Thomas RD et al. Optimization of a fluoroscope to reduce radiation exposure in pediatric imaging. Pediatr Radiol 2000; 30: 229–235. 4. Holinger LD, Konior RJ. Surgical management of severe laryngomalacia. Laryngoscope 1989; 99: 136–142. 5. Friedman EM, Vastola AP, McGill TJ et al. Chronic pediatric stridor: etiology and outcome. Laryngoscope 1990; 100: 222–280. 6. Giannoni C, Sulek M, Frieman EM et al. Gastroesophageal reflux association with laryngomalacia: a prospective study. Int J Pediatr Otorhinolaryngol 1998; 43: 11–20. 7. Schild JA, Holinger LD. Peroralendoscopy in neonates. Int J Pediatr Otorhinolaryngol 1980; 2: 133–138. 8. Dedo D. Pediatric vocal cord paralysis [abstract]. Laryngoscope 1979; 89: 1378. 9. De Gaudemar I, Roudaire M, Francois M et al. Outcome of laryngeal paralyis in neonates: a long-term retrospective study of 113 cases. Int J Pediatr Otorhinolaryngol 1996; 34: 101–110. 10. Benjamin B. Tracheomalacia in infants and children. Ann Otol Rhinol Laryngol 1984; 93: 438–442. 11. Linden P, Siebens A. Dysphagia: predicting laryngeal penetration. Arch Phys Med Rehabil 1983; 64: 281. 12. Smith CH, Logemann JA, Colangelo LA, Rademaker AW et al. Incidence and patient characteristics associated with silent aspiration in the acute care setting. Dysphagia 1999; 14: 1.
SERIES: IMAGING
Imaging the upper airways K. Bradshaw Radiology Department,The Birmingham Children’s Hospital, Steelhouse Lane, Birmingham B4 6LH, UK KEYWORDS paediatric, head/neck, tracheo-bronchial tree, radiography, radiology, imaging
Summary Radiological evaluation of the airway has been used as a screening tool and an adjunct to endoscopy for many years. It provides non-invasive data on the structure of the airway, often avoiding the risk of general anaesthesia. Standard radiographs provide some information on the intricate anatomy of the paediatric airway aided by fluoroscopy. More recently, CT and MRI are proving to have a valuable role and are approaching near endoscopic detail of airway anatomy.The purpose of this article is to highlight areas where radiology can aid in the evaluation of the airway of infants and children. © 2001 Harcourt Publishers Ltd
INTRODUCTION The most common indication for imaging the paediatric airway is suspected airway obstruction. Partial or complete obstruction of the upper airway occurs at multiple levels and can be due to a number of causes. Radiological evaluation should be performed after thorough clinical work-up, including flexible fibre-optic laryngoscopy where appropriate. The plan of investigation detailed in this article is symptom and suspected pathology driven. Whilst the spectrum of aetiologies is diverse, the investigations are more specific. The soft tissue lateral radiograph of the neck (Fig. 1) and an upper gastrointestinal barium study with airway screening are the standard investigations. Computed tomography (CT) scanning and magnetic resonance imaging (MRI) should be reserved for specific cases. In all cases, the conditions mentioned in infants are relevant to older children and vice versa; however, I have attempted specific segregation into infant and childhood causes.
INVESTIGATION OF STERTOR Stertor is described as noisy breathing due to nasal or pharyngeal causes of airway obstruction.
Nasal causes of stertor in infants Failure to pass an 8 French catheter through the nasal cavity should confirm the clinical suspicion of obstruction to 1526–0550/01/010046 + 11 $35.00/0
the airway at the nasal level. The most common cause is posterior choanal atresia (Fig. 2). Less commonly, anterior piriform aperture stenosis is present and this has an identical clinical presentation (Fig. 3). High resolution CT is the investigation of choice in the diagnosis of nasal obstruction in the newborn. Respiratory distress alleviated by crying is the classical presentation of nasal obstruction in neonates, as they are obligate nasal breathers.1 In view of this, the child is not sedated but instead imaged after a feed when hopefully the child will be asleep. The child is placed on the scanning table supine. A lateral tomogram is performed, from which continuous 2 mm cuts are taken through the nose and nasopharynx avoiding the orbits and the radiosensitive lens. Sagittal reconstructions can subsequently be performed to aid diagnosis in difficult cases. In the evaluation of choanal atresia, vomer bone width and choanal air space distance are important landmarks.2 The main vomer bone width in neonates is 0.23 cm and this thickens to 0.28 cm by the eighth year of life. The choanal air space distance refers to the space from the lateral wall of the nasal cavity to the vomer. This is normally 0.67 cm at birth, and it increases by 0.027 cm per year until the age of 19 years. In choanal atresia the vomer is widened and the choanal air space is absent with, in 90% , a complete bony obstruction. In 10% there is a mixed bony/membranous or very rarely a purely membranous cause. There is a high incidence of associated anomalies in choanal atresia, e.g. CHARGE syndrome and Treacher Collins syndrome. © 2001 Harcourt Publishers Ltd
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Figure 1 Normal lateral soft tissue neck. P, piriform fossa;V, vallecula; L, larynx;T, trachea; E, epiglottis.
Figure 2 CT scan of choanal atresia. Arrow indicates the posterior narrowing.
CT scanning is also performed to identify the rare congenital nasal piriform aperture stenosis (CNPAS). This is clinically indistinguishable from the more common bilateral choanal atresia. The nasal airway is narrowed anteriorly by bony overgrowth of the nasal process of the maxilla. As yet no normal values have been determined for the anterior aperture but radiological signs are inward convexity of the nasal bone. This condition may occur in isolation or in association with a mid-facial
Figure 3 CT scan of piriform aperture stenosis. Arrow indicates the anterior narrowing.
dysostosis (single central incisor) or with associated endocrine pathology (pituitary) or a central nervous system abnormality (holoprosencephaly spectrum). Further imaging of these associated abnormalities by CT or MRI should be performed at a later date when the airway has
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Figure 4 T1W saggital MRI showing large encephalocele obstructing the nasal airway.
Figure 5 Lateral soft tissue neck. Pierre Robin Syndrome, narrowing of the oropharynx due to micrognathia.
been stabilised, as sedated scans are usually required due to the complexity and length of time of the imaging, particularly when MRI is performed. Anterior encephalocele can present with nasal obstruction due to the mass – this is normally unilateral and MRI is the investigation of choice (Fig. 4).
child. Tumours and non-accidental injury can also cause retropharyngeal widening, although these are rare causes. These should be investigated as in the older child.
Oropharyngeal causes of stertor in the Infant In newborn infants there are a variety of causes. The initial radiological investigation is a lateral soft tissue radiograph of the face and neck. The air within the airway provides a negative contrast, which allows the patency and calibre of the oropharyngeal airway anteroposteriorly to be assessed. Craniofacial dysostosis with mandibular hypoplasia is seen in the ‘first arch’ or related syndromes, particularly Pierre Robin syndrome (Fig. 5), Goldenhars syndrome and Weyers mandibulofacial dysostosis. Mandibular hypoplasia is also seen in trisomies 17–18 and 13–15, and the Cri-du-Chat syndrome. This can cause severe airway compromise because the micrognathia causes posterior displacement of the tongue. In the neonatal period vascular and lymphatic malformations are the most likely causes of enlargement of the oropharyngeal soft tissues, as nasopharyngeal lymphoid tissue is sparse at this age. These malformations are often extensive and cause airway compromise at multiple levels. Retropharyngeal abscess is exceptionally rare in the neonatal period and if it does occur is more likely to have arisen in a congenital cyst than in the older
Nasal and oropharyngeal causes of stertor in children The initial radiological investigation is the lateral soft tissue of the upper airways, as in infants. Precise prevertebral soft tissue dimensions in children are impossible. In infants and young children the prevertebral space is wider because the vertebrae are not fully ossified: however, as a guide, with the neck fully extended the soft tissue space from C1 to C4 is equal to one half of the vertebral body. In the older child the vertebral bodies become larger and wider and the prevertebral space smaller. (However, the degree of lymphoid hyperplasia should be considered.) Below C4, the prevertebral space normally equals the adjacent vertebral body. In a child, if the prevertebral space is greater than the adjacent vertebral body below C3 it is abnormal, provided the radiograph is adequate and the neck is not flexed.
Acute Enlargement of the prevertebral soft tissues on the lateral radiograph in the context of a toxic child with airway obstruction suggests retropharyngeal inflammation. Plain film findings of retropharyngeal inflammation are straightening of the normal curve of the spine with smooth forward displacement and compression of the airway. Rarely, in cases of retropharyngeal abscess pathological
IMAGING THE UPPER AIRWAYS
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Figure 6 Lateral soft tissue neck. Retropharyngeal abscess, widening of the prevertebral soft tissue and pseudosubluxation of C1 on C2, Grisels Syndrome. Stretching and narrowing of the trachea anteriorly indicated by the arrows.
slip of C1 on C2 can be falsely suggested on a lateral soft tissue neck; this is termed Grisels syndrome (Fig. 6). The retropharyngeal space extends from the skull base to T4. Further investigation is by cross-sectional imaging to assess the deep tissues of the neck and upper mediastinum (Fig. 7). Magnetic resonance imaging is preferable because there is no radiation dose, the risks of iodinated contrast media are avoided and the multiplanar imaging capability allows easy identification of mediastinal extension, particularly on sagittal sequences. If access to MRI is difficult then CT will adequately assess the extent of the abscess. In both modalities it is important to scan to at least the carina to exclude mediastinal extension. Neoplastic causes of retropharyngeal distension are uncommon and should be investigated with CT and MRI, as in retropharyngeal infection. In neoplastic lesions in this region often both CT and MRI will have to be performed: CT for the bony destruction and MRI for the soft tissue characteristics.
Figure 7 Saggital T2W MRI showing high signal prevertebral inflammation due to the retropharyngeal abscess.
of the nasopharyngeal lymphoid tissue is 3–5 years. A lateral neck radiograph, however, does not predict the severity of the obstruction when a child is sleeping or supine. Sleep fluoroscopy has been advocated in the investigation of this condition but currently is not used routinely. Juvenile angiofibroma can present with stertor, although more commonly with epistaxsis. This is investigated by cross-sectional imaging and can be identified by the location centred in the pterygopalatine fossa and the intense enhancement post-contrast: this will alert the radiologist to the diagnosis, averting any biopsy as these can bleed profusely. Rarely, children can present with insidious stertor due to neoplastic disease, i.e. rhabdomyosarcoma, lymphoma and nasopharyngeal carcinoma in the older child (Figs 8 and 9).
Stridor Chronic Nasopharyngeal causes of airway obstruction in older children most commonly take the form of obstructive sleep apnoea syndrome. This is diagnosed by assessing the degree of obstruction of the nasopharygeal airway secondary to adenoidal or tonsillar hypertrophy on the lateral soft tissue neck radiograph. The peak age for maximum growth
Stridor is a harsh high-pitched sound in breathing, caused by air passing through constricted air passages. Diagnostic evaluation of the infant and child with stridor should initially involve flexible fibreoptic layrngoscopy to examine the hypopharynx and larynx. AP and lateral soft tissue radiographs of the neck using the Cincinatti high KV technique plus a chest X-ray are indicated. Video
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Causes of stridor in infants Bilateral vocal cord paralysis. Subglotic haemangioma. Subglotic stenosis. Laryngomalacia and tracheomalacia. Extrinsic compression. fluoroscopy with airway screening and a barium swallow are useful in certain cases. Airway fluoroscopy provides a dynamic view of the airway below the vocal cords. Fluoroscopy is performed with the neonate supine on the table for AP screening; the child can then be turned laterally to further assess the airway. The upper airway is dynamically assessed throughout the respiratory cycle; due to this, patient compliance is less crucial than in plain films and most neonates can be adequately immobilised for screening. Spot films and video recording of the examination are performed for review later. Airway screening can determine whether an obstruction is fixed or varies with the respiratory cycle. A barium swallow can be performed at the same time as airway screening. Pulsed fluoroscopy can be used for much of the swallowing study; this has been shown to reduce radiation dose.3 Barium swallow can assess conditions such as posterior laryngeal clefts, tracheooesophageal fistula, pharyngeal inco-ordination with resultant laryngeal or tracheal aspiration and extrinsic compression on the trachea. The barium swallow evaluates the oesophagus, stomach, duodenum and proximal jejunum.
Figure 8 CT, left nasopharyngeal lymphoma.
The examination is performed after the child has missed a feed and is therefore hungry and will readily drink the barium. The child’s regular feeding apparatus is used. In the case of breast-fed infants, a dummy with a 6 French feeding tube fed into the teat via a small hole made with a scalpel, with a hole in the tip and a syringe attached to the end of the feeding tube normally gives good results. The addition of glycerol to the tip of the dummy can help the infant ‘to latch on’. As a last resort the barium can be directly syringed in to the infants mouth. Thin barium 50 w/v is used, up to a max of 3.5 ml/kg. Lateral screening provides detailed information on the oral and pharyngeal phases of swallowing and can document aspiration. Adequate distension of the oesophagus will normally demonstrate a tracheo-oesophageal fistula, but where there is strong clinical suspicion then prone lateral screening views should be performed. This will make the fistulous track dependent and thus the barium more likely to enter. Antero-posterior screening should be performed too, as this will help assess any extrinsic oesophageal compression. Careful examination at the end of the procedure to assess gastrooesophageal reflux should also be performed.
Laryngeal causes of stridor in the infant Laryngeal pathology is the most common cause of stridor in infants and the majority of congenital laryngotracheal abnormalities present in the neonatal period. Laryngomalacia is the most common laryngeal abnormality in the neonatal period4 and 60% of laryngeal causes of stridor are attributed to this self-limiting condition.5 The diagnosis of laryngomalacia is made with flexible fibre-optic laryngoscopy; however, research has demonstrated an 80% incidence of gastro-oesophagea reflux6
Figure 9 T1W post gadolinium axial MRI, large left nasopharyngeal carcinoma.
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Figure 10 Ph probe correctly positioned to assess gastrooesophageal reflux.
and also an increased incidence of additional laryngotracheal abnormalities (Fig. 10).7 Subsequent to direct examination of the larynx and hypopharynx, whether the finding is normal or a laryngeal abnormality is found, a barium swallow and airway screening should normally be performed. This determines the cause of the stridor in cases where no abnormality was detected at direct examination and where an abnormality was found; coexistent distal pathology can then be excluded and laryngeal competence can be assessed. The exception to this pathway is in bilateral vocal cord paralysis, which is found at flexible laryngoscopy in 10% of cases of congenital laryngeal causes of stridor.8 This is the second most common upper airway anomaly encountered in infants and children. Once the diagnosis is established and the child stabilised then, unlike other laryngeal causes of airway obstruction, a barium examination is not required. The child with bilateral vocal cord paralysis should undergo a detailed MRI scan of the brain and thorax. Due to the length of the examination (45 mins) and the need for complete immobilisation to reduce artefacts, the MRI needs to be performed either under general anaesthetic or sedated with the airway stabilised. A cranial MRI is performed as 25–35% of vocal cord paralysis has a central nervous system cause,9 which is normally in the midbrain or brainstem. The most common CNS cause is the Arnold Chiari malformation (Fig. 11). There are two forms of Arnold Chiari malformation. In type one there is tonsillar herniation as an isolated feature. In type two there is an associated meningomylocele. The downward herniation of the cerebellar tonsils and brainstem is thought to cause traction on the vagus nerves. Posterior fossa decompression may lead to resolution of the vocal cord paralysis. The thorax should also be imaged to
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Figure 11 Saggital T1W MRI head, arrow showing tonsillar herniation, Arnold Chiari 1.
exclude thoracic causes of recurrent laryngeal nerve pathology.
Subglottic causes of stridor in the infant Subglottic stenosis This is the third most common upper airway anomaly in this age group. This is identified as a fixed narrowing in the subglottic region throughout the respiratory cycle. It may be acquired or congenital. In acquired cases prolonged intubation is an important cause, particularly in the premature infant. Additionally, reflux with aspiration is thought to contribute. Computed tomography occasionally may be helpful to assess the integrity of the cartilaginous support of the cricoid.
Subglottic haemangioma These lesions have a characteristic radiographic appearance of asymmetric subglottic narrowing. They are seen on plain radiographs, but the diagnosis is made by direct examination (Fig. 12).
Tracheal causes of stridor in the infant Tracheomalacia Tracheomalacia is diagnosed radiologically by expiratory collapse of the trachea on airway screening causing greater than 10%–20% tracheal obstruction.10 Tracheooesophageal fistulae are associated with focal areas of tracheomalacia (Fig. 13). If vascular compression or cardiac compression is thought to be a causative factor, then MRI or CT should be performed to further assess this (see later text).
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Figure 12 Asymmetric airway narrowing, sub-glottic haemangioma.
Extrinsic causes of stridor in the infant MRI or CT can be used to assess the mediastinum. Ideally MRI scanning is preferred, although availability and clinical condition may necessitate CT. MRI is the best technique for imaging the thorax to assess whether respiratory compromise is due to extrinsic lesions. By accounting for cardiac movement and respiratory artefact, a variety of sequences in multiple planes can be used to demonstrate the adjacent vascular structures or massess. MRI provides additional information over CT about the location and extent of disease and can confirm the cystic nature of lesions which appear solid on CT (Fig. 14). MRI is particularly invaluable in neurogenic tumours, as it can optimally demonstrate the number and extent of the lesions, particularly the intraspinal extension. MRI has no radiation burden and as yet has no known adverse effects. MRI is rather time-consuming and children up to the age of 5–6 years need sedation for the scan. CT should be performed after intravenous contrast. This is a higher resolution modality but lacks the multiplanar capability of MRI and incurs a radiation burden. On newer helical scanners, however, manipulation of the axial data can be performed to create multiplanar reformats, shaded surface display three-dimensional reconstructions and virtual bronchoscopy. Additionally, contrast enhanced CT is rapid in modern scanners so this technique can often be performed unsedated in a younger
Figure 13 Tracheo-oesophageal fistula, lateral swallow.
age group and in conditions where prolonged supine positioning may lead to respiratory compromise. The technique used in our institution for a CT thorax is that the child is placed supine on the scanner, approx. 35 s
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after the start of a fast bolus injection of non-ionic iodinated contrast media and 8 mm contiguous slices with a pitch of 1.5 are performed. The scanner takes approximately 1 second per slice, making an average of 20second scanning time depending on the size of the child. There are many lesions causing extrinsic compression. These are often related to anomalies of the surrounding anatomical structures but local or metastatic neoplasms may present in this way (Fig. 15 a,b). A list of some of the more common causes is shown below.
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Vascular malformations. Haemangioma is the most common tumour of infancy and over 50% occur in the head and neck region. Venolymphatic malformations are also an important cause of pathology in this region (Fig. 17). MRI is the investigation of choice for vascular malformations, as it can not only give exquisite anatomical detail of the extent of the lesion but can also give specific information as to the histological nature of the lesion.
Lesions causing extrinsic compression Bronchogenic cyst. Oesophageal duplication cysts. Neurogenic tumour. Thymic mass. Lymph node mass. Vascular anomalies. Venolymphatic malformations.
Vascular compression This may consist of a complete ring or an incomplete pulmonary sling. MRI can occasionally be misleading if a ligamentous arch completes the ring or duct and therefore the barium swallow must not be excluded. Vascular compression tends to cause symptoms in infancy, although it can present later (Fig. 16 a,b).
(a) Figure 14 Axial T2W MRI with left branchial cleft cyst.
(b)
Figure 15 T-cell lymphoma. (a) Chest X-ray showing large mediastinal mass. (b) Post-contrast CT showing large anterior mediastinal mass with compression of the carina (arrow).
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(a)
Figure 17 Axial fat suppressed T2W MRI showing a macrocystic lymphangioma, marked airway narrowing noted.
(b)
Epiglotitis Although a swollen epiglottis can be demonstrated on lateral soft tissue neck, this investigation is not recommended due to the risk of acute airway obstruction during positioning.
Croup
Figure 16 Right-sided aortic arch. (a) Coronal T1W MRI, arrow indicating a Kommerel diverticulum. (b) Axial T1W MRI: note anterior and posterior compression of the airway.
A chest X-ray is the investigation of choice in croup to exclude additional lower respiratory tract infection that could be exacerbating the situation and would require treatment. A plain lateral soft tissue neck X-ray should be performed if there is a suspicion of a complicating factor. In croup there is loss of clarity of the tracheal airway on radiographs. Table 1 illustrates the relative narrowing that 1 mm of subglottic oedema causes in various ages.
Causes of stridor more specific to the child
Inhaled foreign body
In the older child acquired causes have a greater role to play, particularly infectious causes.
Providing the ingested item is radio-opaque, AP and lateral radiographs will clearly identify the location (Fig. 18a,b).
Table 1 Relative narrowing caused by subgloltic oedema. Age group
Term Newborn
1-year-old
3-year-old
10-year-old
Normal diameter of airway Percentage loss in airway due to 1mm oedema
D = 4.5 mm 70%
D = 5.5 mm 60%
D = 7.00 mm 50%
D = 9.00 mm 40%
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(a)
(b)
Figure 19 Barium swallowing demonstrating laryngeal and tracheal aspiration.
Figure 18 Foreign body in the oesophagus. (a) Lateral soft tissue neck, tracheal compression at level of foreign body indicated by the arrow. (b) AP chest X-ray.
Dysphagia Dysphagia can present with a multiplicity of airway symptoms, including stridor and coughing. An important examination in the assessment of the upper airway in the younger child is the feeding study. In older children a modified feeding study is used, tailored to the feeding capabilities of the child. The evaluation is performed by a speech therapist and a radiologist. The examination is videotaped for future review. Silent aspiration has been noted in
59–94% during feeding studies (Fig. 19). Children with wheezing or chronic pulmonary disorders can be assessed for aspiration or gastro-oesophageal reflux. If the child aspirates thin liquids then semi-thick and thickened liquids can be tried. If there is aspiration of all liquids then, depending on the child’s feeding status, semi-solid to solid food can be tried. Feeding can be assessed with all consistency of foods, including iced food.
CONCLUSION Imaging of the upper airways involves multiple modalities. The investigative pathway is targeted to the likely level of pathology. Therefore, radiological investigations should only be undertaken after a complete clinical evaluation by an experienced clinician and in many cases only after direct laryngoscopy.
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RESEARCH DIRECTIONS
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Virtual bronchoscopy with CT or MRI provides a non-invasive method of examination; however, further work is necessary in both resolution, speed of scanning (to minimise respiratory artefact) and post-processing software. Clinical trials of comparison with the current gold standard direct laryngoscopy and bronchoscopy will be necessary to determine sensitivity and specificity.
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3. Brown PH, Thomas RD et al. Optimization of a fluoroscope to reduce radiation exposure in pediatric imaging. Pediatr Radiol 2000; 30: 229–235. 4. Holinger LD, Konior RJ. Surgical management of severe laryngomalacia. Laryngoscope 1989; 99: 136–142. 5. Friedman EM, Vastola AP, McGill TJ et al. Chronic pediatric stridor: etiology and outcome. Laryngoscope 1990; 100: 222–280. 6. Giannoni C, Sulek M, Frieman EM et al. Gastroesophageal reflux association with laryngomalacia: a prospective study. Int J Pediatr Otorhinolaryngol 1998; 43: 11–20. 7. Schild JA, Holinger LD. Peroralendoscopy in neonates. Int J Pediatr Otorhinolaryngol 1980; 2: 133–138. 8. Dedo D. Pediatric vocal cord paralysis [abstract]. Laryngoscope 1979; 89: 1378. 9. De Gaudemar I, Roudaire M, Francois M et al. Outcome of laryngeal paralyis in neonates: a long-term retrospective study of 113 cases. Int J Pediatr Otorhinolaryngol 1996; 34: 101–110. 10. Benjamin B. Tracheomalacia in infants and children. Ann Otol Rhinol Laryngol 1984; 93: 438–442. 11. Linden P, Siebens A. Dysphagia: predicting laryngeal penetration. Arch Phys Med Rehabil 1983; 64: 281. 12. Smith CH, Logemann JA, Colangelo LA, Rademaker AW et al. Incidence and patient characteristics associated with silent aspiration in the acute care setting. Dysphagia 1999; 14: 1.