Bridging Bronchus and Left Pulmonary Artery Sling: Two Cases Differing in Clinical Presentation and Management

To the Editor, Bridging bronchus (BB) is rare congenital anomaly in which the right lower and the right middle lobe is supplied by an aberrant bronchus, arising from the left main bronchus (LMB), which crosses (bridges) the mediastinum [1]. The right upper lobe (RUL) is supplied by the right main bronchus (RMB), branching directly off the trachea. BB is frequently associated with the left pulmonary artery sling (LPAS), a vascular anomaly in which LPA originates from the right pulmonary artery (RPA), runs between the trachea and the esophagus, heading to the left lung. When LPAS is associated with BB, compression of the LMB is often detected [1, 2]. A 6 months-old girl, in whom LPAS was detected by antenatal ultrasound, was admitted because of recurrent episodes of dyspnea, persistent coughing, and noisy breathing during respiratory tract infections. At admission, an echocardiography showed that the LPA, originating from the RPA, had a slightly reduced caliber at its origin (7 mm) (not shown). The the contrast-enhanced chest Computed Tomography (CT) scan axial reconstruction showed the LPA passing behind the LMB and causing bronchial compression and, the coronal reconstruction, the presence of a BB, originating from LMB, bridging the mediastinum (Figure 1A,B). Tracheobronchial endoscopy, performed with a pediatric fiberoptic bronchoscope (distal-end outer diameter 2.8 mm) showed a significant reduction of the LMB lumen, impeding the bronchoscope progression (Figure 1C). Complete cartilage rings were present at LMB origin. Bronchography demonstrated that the LMB and BB diameters were respectively 2.4 and 2.1 mm, and that the stenotic LMB length, from the true to the secondary carina, was 16.1 mm (Figure 1D). One year after, the child was re-evaluated. Fiberoptic bronchoscopy showed the unchanged LMB narrowing (not shown). Following a multidisciplinary consultation, it was planned to correct both the LMB stenosis and the LPAS. Repair of the LPAS involved its transection and reimplantation to the left anterolateral side of the pulmonary trunk. The stenotic LMB segment with complete rings was resected, with anastomosis of the proximal and distal ends of the remaining portion, in an end-to-end fashion. At the follow-up, 6 months after discharge, the echocardiogram showed that the re-implanted LPA had no vessel tortuosity nor stenosis and no significant flow alteration up to the pulmonary hilum (not shown). Fiberoptic bronchoscopy visualized the trifurcated main carina, result of LMB resection and anastomosis, with good patency of RMB, LMB and BB (Figure 1E). Bronchography showed that the LMB and BB diameters were respectively 3.6 and 2.7 mm (Figure 1F). A 2-year-old boy, was admitted because of persistent/recurrent dry cough and mild respiratory distress during respiratory infections. Decreased breath sounds over the left hemithorax were detected by physical examination. Fiberoptic bronchoscopy showed an extrinsic pulsating compression on the LMB severely reducing its lumen (Figure 2A), but not preventing the progression of the pediatric videobronchoscope (distal-end outer diameter 4 mm), with vision of a secondary carina with two bronchi (the BB and the LLB). Bronchography demonstrated a good patency of the LMB at its origin (diameter 5.4 mm), with progressive reduction of the lumen, reaching a minimum diameter of 2.3 mm. The contrast media did not progress into the bronchus originating on the right of the secondary carina (the BB) (Figure 2B). The axial and coronal reconstructions of the contrast-enhanced chest CT scan showed an abnormal origin of the LPA, arising from the RPA, passing behind and compressing the posterior and right wall of the LMB (Figure 2C,D). The presence of a BB was detected, originating from the LMB, and crossing the median line to supply the RLL. The LPAS was confirmed by transthoracic echocardiography (not shown). The patient underwent corrective LPAS surgery, with transection and reimplantation of the LPA to the left anterolateral side of the pulmonary trunk. Intra-operative bronchoscopy after LPAS surgery showed resolution of the extrinsic compression with a mild LMB residual malacia, not requiring surgical correction (Figure 2E). Three months after the surgical procedure the patient was re-evaluated. Parents reported only occasional episodes of wheezing, occurring during upper respiratory tract infections. Echocardiogram allowed a good visualization of the reimplanted LPA without sign of stenosis (not shown). A new fiberoptic bronchoscopy showed the good patency of the left bronchial branches. During bronchography, the contrast media easily spread along the LMB, the BB and the LLB. The diameter of the three bronchi were respectively 4.8, 5.6 and 7.6 mm (Figure 2F). BB is a rare congenital airway anomaly commonly accompanied by diffuse or focal airway stenosis, causing respiratory distress shortly after birth or less severe symptoms in infants and young children. In the moderate-to-severe forms, the clinical presentation can be complicated by signs and symptoms related to the often-associated congenital cardiovascular malformations, most frequently with the left pulmonary artery sling [1, 2]. In mild cases the diagnosis can be challenging because symptoms may mimic those of some more common conditions, such as viral bronchiolitis, asthma, and foreign body aspiration. The presence of BB therefore can be discovered incidentally, during diagnostic evaluation for other respiratory diseases. Bronchial branching malformation must be included in the differential diagnosis in infants with persistent respiratory distress and in children with an atypical history of recurrent wheezing episodes, despite appropriate long-term therapy [1, 2]. Chest radiography fails to identify bronchial tree and vascular anomalies [3, 4]. The two cases here presented highlight the importance of bronchoscopy, bronchography, CT scan, and ultrasounds to achieve an accurate diagnosis and a personalized preoperative planning [3, 4]. Surgical management of BB is indicated for patients with significant respiratory symptoms and the degree of airway stenosis are crucial for the preoperative planning [4-6]. Repair of the LPAS can relieve respiratory distress due to airway compression. In patients with complete cartilage rings, surgical bronchoplasty should be performed at the same time as LPAS repair [4-6]. Intraoperative and postoperative bronchoscopies are usually performed to evaluate the effectiveness of LPA reimplantation on the LMB patency and, in case of persistent stenosis, to evaluate the need for the stenotic segment resection and anastomosis [4-6]. Angelo Florio: conceptualization, data curation, writing–original draft. Pietro Salvati: conceptualization, investigation, formal analysis. Paola Borgia: conceptualization, data curation, investigation, writing–original draft. Francesca Rizzo: methodology, data curation, visualization. Giovanni A. Rossi: conceptualization, supervision, data curation, formal analysis, writing–review and editing. Michele Torre: conceptualization, formal analysis, supervision, writing–review and editing. Oliviero Sacco: conceptualization, investigation, validation, formal analysis, writing–review and editing. All investigations were carried out with full-informed written consent. Written informed consent was obtained from the patient's parents for publication of the two cases. A copy of the written consent is available for review by the Editor of this journal. This retrospective report was approved by the Institutional Review Board of the University Hospital IRCCS Giannina Gaslini (N° 06/24). The authors declare no conflicts of interest. Data about the patient are available on request due to privacy restrictions.