Long-segment tracheal stenosis with left pulmonary artery sling in a low- to middle-income country setting: Value of imaging and bronchoscopy

Editorial

To the editor: Congenital lung and lower airway abnormalities are rare, but are important differential diagnoses in children with respiratory diseases. Some lesions cause severe symptoms shortly after birth, while others may not present for years. The latter are often not diagnosed in childhood, and present in adults as episodes of recurrent pneumonia or as malignancies.^[1–3] In the developing world there is limited access to antenatal ultrasound, and congenital lesions will only be diagnosed much later.^[4]

Diagnosis of congenital airway lesions in low- and middle-income country (LMIC) settings may be delayed, as these conditions are frequently misdiagnosed. Clinical signs and symptoms are often attributed to infectious diseases such as tuberculosis (TB) with airway involvement or to severe viral infections. Despite the availability of advanced imaging in the developed world, the chest radiograph remains important in the LMIC setting. The airways of young infants should be carefully evaluated for any narrowing and deviations, and they should be visible in their entirety. In most cases of TB, mediastinal lymph nodes are visible on the chest radiograph and can be identified as having an effect on the airway.^[5] In the presence of airway abnormalities on the radiograph in the absence of mediastinal lymph nodes, congenital airway abnormalities should be considered.

A 6-month-old boy presented with a history of noisy breathing since birth. He had previously been admitted twice for wheezing episodes. There was no known TB contact, and he had a negative polymerase chain reaction test. At the age of 1 month, the boy was admitted for the first time for noisy breathing and wheezing. The chest radiograph (Figure 1A) was reported normal, and he was discharged. He was readmitted at the age of 6 months because of persistent symptoms and seen by an ear, nose and throat surgeon, who performed an upper airway endoscopy and excluded glottic and subglottic pathology, and then referred the baby for a bronchoscopy. Chest radiographs and lateral neck radiographs were performed. They demonstrated a very narrow trachea, involving the whole length of the trachea, and an abnormal T-shaped carina (Figure 1B).

Fig. 1.

Plain radiograph series. A 6-month-old boy who presented with noisy breathing was diagnosed with a long-segment tracheal stenosis and left pulmonary artery sling and underwent corrective surgery. An initial AP chest radiograph (A) failed to demonstrate the airway adequately. A follow-up AP chest radiograph (B), 5 months later, demonstrated narrowing of the mid-trachea (arrows) with a T-shaped carina (rectangle). (C) shows the postoperative AP chest radiograph with improved tracheal and carinal morphology. (AP = anteroposterior.)

The lateral neck radiograph showed a narrow trachea about 1.5 cm below the subglottic area. Computed tomography angiography (CTA) of the chest was performed. Long-segment tracheal stenosis from just below the vocal cords to just above the carina and left pulmonary artery (LPA) sling was demonstrated. The chest computed tomography (CT) scan also showed focal narrowing and rightward bowing of the mid-trachea, as well as the low position of a splayed T-shaped carina without any true right upper lobe bronchus visualised (Figs 2A and 2B). An echocardiogram confirmed the LPA arising from the right pulmonary artery (RPA), but no other cardiac abnormalities.

Bronchoscopy was performed before surgery (Figs 2E and 2F). The top part of the stenosis was identified about 1 cm below the subglottic area (3.0 mm video bronchoscope). Solid tracheal rings were visible, and the trachea was not straight, with the most severe narrowing just above the carina with pulsation from posterior (2.2 mm fibreoptic bronchoscope). The 2.2 mm fibreoptic bronchoscope could not be passed through the narrowest part of the trachea, so the carina was not reached. This confirmed the picture that was seen on the three dimensional airway segmentation (Figure 3A). With a 3.5 endotracheal tube positioned just through the vocal cords, a median sternotomy was performed.

Fig. 2.

Post-contrast CT scans of the chest. (A) Preoperative coronal reconstruction using MinIP, thick-slab technique and lung windowing to demonstrate the trachea and carina in full, showing focal narrowing and rightward bowing of the mid-trachea (arrow) as well as the low position of a splayed, T-shaped carina (rectangle), without any true RUL bronchus visualised. (B) Preoperative axial post-contrast chest CT using MIP and soft-tissue windowing to demonstrate the aberrant left pulmonary artery sling (curved arrow), coursing posterior to the trachea (straight arrow). (C) Postoperative coronal reconstruction using MinIP, thick-slab technique and lung windowing to demonstrate the trachea and carina in full, showing the corrected morphology of the carina to a higher position and with a narrower angle (rectangle), as well as a normal-appearing calibre of the mid-trachea (arrow). (D) Postoperative axial post-contrast chest CT using MIP and soft-tissue windowing to demonstrate the corrected position of the left main pulmonary artery (curved arrow), anterior to the trachea (straight arrow). Bronchoscopy images. (E) Image demonstrating the top part of the tracheal stenosis, just below the subglottic area with solid tracheal rings present. (F) Image demonstrating the severe narrowing just above the carina with both anterior and posterior vascular compression visible. Bronchoscopy was performed with a 2.2 mm Olympus fibreoptic bronchoscope. (CT = computed tomography; MinIP = minimum intensity projection; RUL = right upper lobe; MIP = maximum intensity projection.)

The trachea was exposed from the cricoid cartilage down to the carina. The ductus arteriosus was tied and divided. The LPA was identified, originating from the RPA and passing posterior to the distal trachea. It was dissected free, and the tracheal bifurcation was identified. The tracheal stenosis measured ~5 cm in length. The trachea was divided midway between the cricoid and the carina, about 2.5 cm. The LPA was released from its posterior position and transposed anteriorly, lying without tension after mobilisation of the main and right pulmonary arteries (Figure 3B).

Fig. 3.

(A) Three-dimensional airway segmentation demonstrating not only the length of the tracheal stenosis but also the abnormal shape of the trachea and near-complete obstruction at the site of the LPA. The abnormal T-shaped carina and absent RUL bronchus are also visible. (B) Intraoperative image showing the solid tracheal rings and the LPA that has been moved to anterior to the trachea. (C) Bronchoscopy image at 1 week after the slide tracheoplasty showing the repair and the abnormal carina. The stitches are visible, but no granulation tissue. (D) Three-dimensional airway segmentation at 1 month after the surgery showing the enlarged trachea, which is shorter and straighter compared with the original segmentation. (LPA = left pulmonary artery; RUL = right upper lobe.)

A posterior longitudinal incision was made in the distal trachea down to the carina. The superior trachea was incised anteriorly up to the cricoid cartilage and a slide tracheoplasty was then performed. A 3.5 mm endotracheal tube was placed with a GlideScope (Verathon, USA) and fibreoptic bronchoscope with the tip above the carina. Bronchoscopy demonstrated a normal right bronchial tree but an abnormally long left main bronchus.

Postoperative care was complicated by difficult ventilation and reduced perfusion of the left lung, as confirmed by echocardiography. This improved on day 3, and the baby was extubated on day 6 (Figure 1C). Bronchoscopy was repeated before extubation on day 4, and showed a good-calibre trachea, well-perfused mucosa, and no granulation tissue on the stitch lines (Figure 3C). CTA was repeated at 1 month, and showed sufficient flow in the LPA (Figure 2C and D, 3D).

Congenital tracheal stenosis (CTS) is an abnormality characterised by the presence of complete tracheal rings along the stenotic segment, creating a fixed narrow tracheal lumen. Symptoms are associated more with severity than with the length of the stenosis. CTS is associated with several other lesions, including tracheal bronchus, other airway/ lung anomalies, pulmonary sling, congenital heart disease and H-type tracheo-oesophageal fistula. Long-segment tracheal stenosis is strongly associated with type I pulmonary artery (PA) sling, occurring in 2 out of 3 cases.^[6,7]

In the PA sling anomaly, the LPA arises from the postero-superior aspect of the RPA and courses to the left hilum between the trachea and oesophagus, causing tracheobronchial compression at the level of the distal trachea and carina. The symptoms range from asymptomatic to severe airway obstruction, which is related to the extent of tracheobronchial stenosis.

Type II left pulmonary artery sling (LPAS) is strongly associated with long-segment tracheal stenosis caused by complete cartilaginous rings extending from the normal carinal level to the low ‘inverted T’ carina. Because of this strong association, the presence of either LPAS or congenital airway stenosis warrants evaluation for the other.^[7] When performing surgical repair of the LPAS, it is feasible to translocate the LPA anterior to the tracheobronchial tree when the trachea is divided for the slide tracheoplasty. Patency of the LPA can be determined by postoperative echocardiography, magnetic resonance imaging (MRI), CT or a pulmonary perfusion nuclear scan.^[8]

CT or MRI is essential to study associated vascular malformations. The gold standard for the diagnosis and assessment of the severity of CTS is rigid and flexible airway endoscopy. Bronchoscopy can be used to determine the presence of solid rings and the length and diameter of the stenosis.^[9–11]

Postoperative bronchoscopy is needed to evaluate the airway reconstruction and determine granulation tissue formation. Paediatric lung and airway surgery in LMICs presents several challenges owing to resource limitations, healthcare infrastructure and social factors. Despite the challenges faced in LMICs, it has been shown that children with complicated pulmonary conditions can still experience positive outcomes after surgery.^[12]

Chest radiography remains an essential initial screening tool for detecting airway abnormalities. However, advanced imaging techniques such as three-dimensional airway segmentation provide a more accurate and realistic representation of airway morphology, including lumen size, length, and the extent of narrowing.

Computer-aided detection has been developed for TB diagnosis in children.^[13,14] While it is important for TB diagnosis, it may have an additional advantage if it can detect airway abnormalities.

This case demonstrates that long-segment tracheal stenosis with LPA can be successfully managed even in LMICs. Advanced imaging remains important in the management of these patients. In this case, chest radiographs were very helpful in identifying the tracheal stenosis and provided information about the length of stenosis, the abnormal carina and the abnormal perfusion of the left lung.