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Original Report |
1
Department of Radiology, Queen Mary Hospital, 102 Pokfulam Rd., Hong Kong,
China
2
Department of Surgery, Division of Paediatric Surgery, University of Hong
Kong, Queen Mary Hospital, Hong Kong, China.
Received July 15, 1999;
accepted after revision September 8, 1999.
Address correspondence to W. W.-m. Lam.
Abstract
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CONCLUSION. Long-gap (n = 1) and short-gap (n = 5) esophageal atresia, long-segment stenosis (n = 2), patent poststenting trachea (n = 1), normal trachea without fistula (n = 1), and tracheal bronchus (n = 1) were studied. Fistulas between the lower esophagus and carina were noted in all six cases of esophageal atresia. All CT findings correlated with operative or bronchoscopy findings. Sensitivity and specificity were 100%. Three-dimensional CT and virtual bronchoscopy are accurate and useful techniques in the preoperative assessment of esophageal atresia and tracheal stenosis in neonates, infants, and children.
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2 cm), whereas
either delayed primary anastomosis or esophageal replacement may be required
for patients with long gaps (length, >2 cm). The basis of delayed primary
anastomosis is that the distance between the two ends of esophagus will often
decrease as the upper pouch elongates with time
[1]. By placing a feeding tube
into the esophagus or using conventional contrast-enhanced studies, we can
show only the lower limit of the upper esophagus and fistula between the upper
esophageal segment and trachea. We cannot visualize the gap or fistula from
the lower esophageal segment. Congenital tracheal stenosis can be classified as a focal or segmental variety, a generalized hypoplasia—type, or a carrot- or funnellike stenosis. Other abnormalities of the trachea include tracheal fistula, tracheal bronchus, bridging bronchus, tracheobronchomegaly, and tracheomalacia. In these cases, the trachea and bronchus are mainly assessed using bronchoscopy.
The purpose of this study was to evaluate the use of three-dimensional (3D) CT and virtual bronchoscopy in the treatment of neonates, infants, and children with tracheoesophageal fistula and tracheal stenosis.
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Techniques
Unenhanced helical CT examination was performed on a HiSpeed Advantage
scanner (General Electric Medical Systems, Milwaukee, WI) at a pitch of 1 or
1.5. An infant feeding tube was placed in the upper esophagus and air was
injected to distend the upper esophagus before CT in patients with esophageal
atresia. All images were obtained in the axial plane with 3-mm contiguous
sections and 1.5 mm overlapping. The scanning time ranged from 25 to 30 sec.
3D CT and virtual bronchoscopy reconstruction were performed on the Advantage
Windows workstation (General Electric Medical Systems) using 3D analysis and
software (Navigator [version 2.0.8W]; General Electric Medical Systems).
Interactive navigation through the tracheobronchial tree was accomplished by
rotating the virtual camera in all directions within the lumen. Stored
screen-saved images were obtained and correlated with surgical and flexible
bronchoscopy findings obtained within 40 days of CT.
In patients with esophageal atresia, the distance between the upper and
lower esophageal pouches was measured. The presence or absence of fistula,
position of fistula, short- (distance between two esophageal pouches, 2
cm) or long-gap (distance between two esophageal pouches, >2 cm) atresia,
presence or absence of tracheal stenosis, and length of stenosis were
compared.
Sedation
Oral sedation was administered before examination (chloral hydrate, 50
mg/kg body weight). If the initial dose failed, more chloral hydrate was given
up to a maximal dose of 1 g. Additional IV midazolam (Dormicum; F. Hoffmann-La
Roche, Basel, Switzerland) was given (0.2-0.5 mg/kg body weight) if oral
sedation failed. The patients were carefully monitored for vital signs such as
pulse rate and oxygen saturation during and after the examination.
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In the six cases of esophageal atresia, five were short-gap (Fig. 1A,1B) and one was a long-gap atresia. Fistulas connecting the lower esophagus and posterior aspect of the carina were noted in all six cases. All imaging findings corresponded to the surgical findings, with sensitivity and specificity being 100%. In one case, direct sagittal CT showed a short gap between the two esophageal pouches; this case was defined as short-gap atresia. Despite the short craniocaudal distance between the two esophageal pouches, they were found to be widely separated in transverse and anteroposterior dimensions on 3D CT. This case was thus reclassified as long-gap atresia and this diagnosis was confirmed at surgery.
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In three cases of tracheal stenoses, all were long-segment stenoses. Two stenoses involved more than half the length of the trachea (Fig. 2A,2B,2C); the remaining stenosis involved more than half of the trachea and the origins of both main bronchi. Abnormal branching of right upper lobe bronchus directly from the trachea was present in the third case (Fig. 3A,3B,3C); this is a case of tracheal bronchus associated with stenosis of the distal trachea and carina. In such cases, the main trachea and the anomalous origin of the right upper lobe bronchus occasionally may be difficult to differentiate on a routine axial scan. 3D CT helped solve this problem and provided a clear image of the 3D relationship between different branches.
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Patent trachea with good luminal diameter was seen in the patient with tracheal stenting (Fig. 4A,4B), indicating that the procedure was successful. All CT findings correlated with the findings at flexible bronchoscopy. The sensitivity and specificity were 100%.
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In the suspected H-type fistula (presented as repeated aspiration), neither 3D CT nor virtual bronchoscopy showed abnormal fistula. A dimple with suspected fistula was detected using flexible bronchoscopy. Because of the discrepancy between these two findings, rigid bronchoscopy and bronchography were performed. No abnormal fistula was detected. A blind-ended dimple was seen at the posterior aspect of the trachea.
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Virtual bronchoscopy is a new, evolving technique that produces a bronchoscopy-like view of the trachea, carina, and main bronchi. Its advantages over flexible bronchoscopy in adults have been described [4,5,6]. A report of the use of virtual bronchoscopy in infants and children has been published [7]. The quality of virtual images in neonates, infants, and children might be expected to be inferior to that in adults because of the smaller size of the airways. Like other 3D reconstructions, virtual bronchoscopy does not add information to that provided by the axial images; however, virtual bronchoscopy is helpful to referring surgeons and pulmonologists who are familiar with bronchoscopic images. Virtual bronchoscopy is less invasive than flexible bronchoscopy and can be performed under simple sedation without general anesthesia; it also has the advantage of going beyond a stenosed airway, thus allowing 3D CT visualization of the trachea beyond the stenosis, whereas bronchoscopy does not have this capability. Virtual bronchoscopy provides more information to help design accurate stents than bronchoscopy. The inherent severe perspective distortion of real bronchoscopy makes it difficult to assess distance and length correctly even when the structures are unobstructed.
In cases of a tracheal stenosis, 3D CT gives a 3D overview of the trachea and its branches. The site of stenosis and its abnormal branches are located. Virtual bronchoscopy and 3D CT provide both endoluminal and extraluminal information in any viewing direction. The user can navigate through the virtual anatomy with ease.
One pitfall of 3D CT and virtual bronchoscopy is that the software relies on the presence of air. Mucous plugs or secretions inside the lumen can make an airway appear suspiciously stenosed. Occluding foreign bodies cannot be differentiated from complete stenosis in cases of complete airway occlusion seen on virtual bronchoscopy. Virtual bronchoscopy provides no information on the color or texture of the airway mucosa because this is not represented in the CT data. A real bronchoscopy vividly portrays airway mucosal surfaces. In our patient with suspected H-type fistula, virtual bronchoscopy failed to detect mucosal details such as a dimple on the posterior wall of the carina, but virtual bronchoscopy was more accurate than flexible bronchoscopy in the assessment of the fistula.
The quality of the views generated by virtual bronchoscopy is limited by the resolution of the image data. Two factors limit virtual bronchoscopic imaging in children: small airway size and the inability of infants to suspend respiration during data acquisition. The respiratory motion from breathing then creates zigzag artifacts on 3D CT and virtual bronchoscopy. Other limitations include the high cost, the use of surface rendering instead of volume rendering, and the need for substantial off-line display computation. Surface rendering can quickly provide high-quality views. However, it requires that surfaces of interest, such as the endoluminal walls of the airways, be predefined by image segmentation before rendering. Volume rendering does not require that surfaces be predefined and requires no preprocessing step. Unfortunately, most of the recently proposed virtual endoscopy systems provide only surface-rendered endoluminal views.
3D CT and virtual bronchoscopy can give 3D road maps to surgeons. These techniques are noninvasive, accurate, and useful in the preoperative assessment of esophageal atresia and tracheal stenosis in neonates, infants, and children. Although virtual bronchoscopy appears more susceptible to artifacts in pediatric patients than in adults, it adds to the information obtained from flexible bronchoscopy in the evaluation of the pediatric tracheobronchial tree. Virtual bronchoscopy is complementary to flexible bronchoscopy in preoperative planning and for postoperative follow-up.
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