Abstract
Although noted in the 19th century, it was not until 1938 that Scheid published the combination of left pulmonary artery sling and narrowing of the airway due to annular tracheal cartilages. Unaware of these prior descriptions, and without a precise preoperative diagnosis, Willis Potts in Chicago performed the first successful sling repair in 1953. In 1976, Cohen and Landing described Scheid’s combination of left pulmonary artery sling and stenosis caused by complete tracheal rings, and the term “ring-sling complex” was introduced by Berdon in 1984. Four years later, Wells and Landing noted characteristic tracheobronchial malformations associated with these lesions and proposed a classification that has been confirmed to be clinically relevant in recent cross-sectional imaging studies.
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Introduction
Pulmonary slings present as an airway disease in infants with stridor. During the last half century, it became obvious that this entity comprises a combination of different malformations of the pulmonary arteries, the airway configuration and the tracheal cartilage rings. About one-third of slings are characterized by an otherwise normal airway with a carina at the level of T4-5 and the left pulmonary artery wrapping around the trachea posteriorly above the right mainstem bronchus. However, two-thirds typically have a low-lying carina at T6-7 with airway narrowing and much of the right lung supplied by a bridging bronchus from the left bronchus, which the left pulmonary artery encircles posteriorly and back toward the left (Fig. 1); this latter group may cause significant morbidity and mortality in affected infants, and many may require repair of the stenotic parts of the airway. The airway narrowing may be due to compression of the anomalous artery, complete tracheal rings with lack of a membranous portion, malacia as a result of in utero compression of the developing airways or a combination of the above.
Although simple sling was described by Glaevecke and Doehle in 1897, the detailed description by German pathologist Paul Scheid in 1938, covers the first successful repair of a pulmonary sling by Potts, and moves on toward a discussion during the last half century on the complex classification introduced by Wells and Landing, and Zhong, who based her assessment on CT reconstructions.
Timeline
In 1897, Glaevecke and Doehle presented the case of an infant with congenital worsening stridor who died at age 7 months from a concomitant upper respiratory tract infection at the meeting of the Physiologischer Verein (Physiologic association) in Kiel, Germany. A short report from this presentation was published in Münchener Medizinische Wochenschrift [1]. The postmortem exam describes the findings of a left pulmonary artery sling with narrowing of the trachea, but it does not mention ring cartilages.
More than 40 years later, Scheid, a young pathologist-in-training at the University of Frankfurt in Germany, published the case of another 7-month-old boy who succumbed to worsening stridor and respiratory failure, providing a detailed description and sketch of the malformation, including the tracheal narrowing due to cartilaginous rings (Fig. 2) [2]. Of note, Scheid did not quote Glaevecke.
After World War II, Holinger, a member of an Ear, Nose and Throat surgical group in Chicago noted several young patients with stridor and extrinsic compression of the trachea on bronchoscopy. One of the children underwent thoracotomy by Willis Potts (Fig. 3) in 1953, who, without knowing of Glaevecke or Scheid, noted an anomalous left pulmonary artery coursing around the trachea during the operation. He transected the vessel and reanastomosed it anterior to the trachea, which alleviated the symptoms of the child [3]. The case was republished in 1958 [4], at which time Scheid was referenced for the first time. Similar findings were reported in Boston at the same time by Wittenborg [5], who also noted the indentation of the esophagus on barium swallow and found that most of these patients had normal plain film chest radiographs.
During the 1960s, most published cases discussed simple and complex slings with and without intrinsic airway narrowing [6, 7]. In 1971, however, in a paper on pulmonary artery sling, Capitano et al. [8] published a complex case with a low carina in which the right lower lobe of the lung was supplied by a large aberrant branch coming off the left mainstem bronchus. This observation was later confirmed in another case and the name bridging bronchus was coined by Gonzalez-Crussi and collaborators [9] in Indianapolis.
The pathologist Benjamin Landing and the otorhinolaryngologist Cohen at the Children’s Hospital Los Angeles found the combination of this bizarre tracheobronchial anomaly combined with left pulmonary artery sling and airway narrowing in children with rigid, unpassable airways during tracheobronchoscopy (Fig. 4) [10]. During the following two decades, Landing and his associate Theadis Wells, a laboratory assistant who later was appointed honorary clinical associate professor, noted the heterogeneity of these malformations (Fig. 4). Aware of the 1986 publication by Berdon et al. [11] on the ring-sling complex in a description of 5 patients with long-segmental tracheal stenosis due to cartilaginous rings and a low carina, Wells and Landing proposed a classification in 1988 [12]. They also performed 3-D wax plate reconstructions of the airways based on CT images that show the profound airway narrowing associated with low carina (type II) anomalies [13].
Recent studies from Stanford University [14] and Shanghai, China, [15] using high-resolution contrast CT have corroborated Wells and Landing’s classification, defined the relationship of the airway and vascular anomalies, and shown that the numeric distribution among the different types is about equal.
Discussion
When Willis Potts performed the first repair of a pulmonary artery sling, he did not know about the previous descriptions by Glaevecke and Scheid. He essentially stumbled upon a relatively simple type IA malformation, and relieved the extrinsic compression of the trachea by transposing the left pulmonary artery anterior to the trachea.
In the following decades, historic pre-World War II reports resurfaced and were eventually integrated with newer descriptions on combined malformations of the airways and the left pulmonary artery into the landmark classification proposed by Wells and Landing in 1988. It became apparent that type II slings were a particular cause of morbidity and mortality, and that these could not be treated by reanastomosis of the pulmonary artery alone, but that the narrow airways most often required repair of the stenotic airway by tracheoplasty at the same time.
The technique of repair has evolved toward using cardiopulmonary bypass in most cases and a median sternotomy. The tracheal repair is accomplished by either pericardial patch tracheoplasty, tracheal autograft or slide tracheoplasty. In patients with absent or severely hypoplastic right lung, the left pulmonary artery is translocated anterior to the trachea. In the other patients, the left pulmonary artery is generally reimplanted into the main pulmonary artery. Using these techniques, the long-term patency rates of the pulmonary artery are excellent.
Despite the availability of cardiopulmonary bypass, the more complex type II associations therefore pose a considerable challenge in diagnosis and treatment. They require a multidisciplinary approach for preoperative planning and successful repair.
The imaging workup has evolved from bronchograms and angiograms to CT with intravenous contrast, which shows both the vascular anatomy and the airway configuration in fine details. In particular, coronal and sagittal reformatted images can be useful for preoperative planning, along with volume-rendered airway images. An esophogram is still a useful initial study for screening purposes and may show a typical indentation at the level of the sling. MRI has the drawback of motion artifact and lower resolution compared to CT. Also, the longer examination times limit the utility of MRI in unstable patients with airway compromise. The major drawback of CT is the relatively high radiation dose absorbed during the exam, although newer imaging protocols using 80 or 100 kVp afford good imaging quality despite lower radiation doses. For screening, it is unfortunate that techniques such as barium swallow and airway imaging, which uses low-dose, high-kV, heavily filtered plain film techniques thereby decreasing radiation exposure in many children, are not commonly used anymore. It is important to note that plain film chest radiographs in most cases are either normal or in rare cases may show a variable degree of obstruction and pulmonary overinflation, usually right-sided.
Echocardiography can only visualize the vascular sling; it does not show the configuration or stenosis of the airways.
Conclusion
The two entities of isolated pulmonary sling and high carina (types Ia, b) and pulmonary sling with low carina, airway narrowing and cartilage rings (types IIa, b) have been confounded for almost a century until a systematic classification was published by Wells and Landing in 1988. Modern spiral CT with intravenous contrast and coronal reconstruction is becoming the standard for the diagnosis of these complex anomalies.
References
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Acknowledgement
The authors are grateful to Dr. Patricia Clarkson, Dr. Richard Jaffe, Dr. Beverley Newman, Dr. J. Bruce Beckwith and Dr. Marvin Nelson Jr. for sharing their insights and memories.
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Berdon, W.E., Muensterer, O.J., Zong, YM.M. et al. The triad of bridging bronchus malformation associated with left pulmonary artery sling and narrowing of the airway: the legacy of Wells and Landing. Pediatr Radiol 42, 215–219 (2012). https://doi.org/10.1007/s00247-011-2273-2
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DOI: https://doi.org/10.1007/s00247-011-2273-2