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pulmonary sling is a vascular abnormality wherein the left pulmonary artery arises from the right pulmonary artery and then traverses between the esophagus and the trachea toward the hilum of the left lung .
it was first described by glaevecke and doehle in 1897 . since then , about 100 cases have been reported in the world .
the average age at the onset of symptoms , such as respiratory distress and cyanosis , is 2 months and about half have symptoms from birth .
so , adult cases are very rare , are most often asymptomatic and usually found incidentally .
when combined with complete cartilaginous tracheal rings in the absence of posterior membranous portion , it is called  ring - sling complex  . in that case ,
we here report an adult case who was diagnosed as pulmonary sling with complete tracheal ring by ct and bronchoscopy along with a literature review .
she had had symptoms of airway obstruction , such as wheezing , hoarseness and mild dyspnea since a young infant .
blood pressure was 140/90 mmhg , pulse rate was 80/min , body temperature was 36.5c and respiration rate was 16/min . on physical examination , she was alert , but had a slight dyspneic appearance . there were no cyanosis , chest deformities and cardiac murmurs .
fev1 was 1.52l ( 66.2% of predicted value ) and fvc was 1.90l ( 54.5% of predicted value ) on pulmonary function test .
complete cartilaginous ring without posterior membranous portion was found on the entire trachea ( fig .
1 ) . the plain chest x - ray showed a right mediastinal mass - like density and a long - segment tracheal narrowing ( fig .
2 ) . the chest ct revealed the anomalous left pulmonary artery originating from the right pulmonary artery and its posterior course between the trachea and the esophagus ( fig .
she was discharged without specific treatment because of mild symptoms which are mainly caused by complete tracheal ring and not by tracheal compression due to vascular anomaly .
the term  vascular ring  was introduced to describe the mediastinal vascular anomalies causing tracheobronchial compression by dr .
the pulmonary sling is a kind of vascular ring and the term was first used by contro et al . in 1958 to distinguish it from other vascular anomalies .
carl et al . reported that when vascular rings were classified into four groups , as follows , 1 ) complete vascular rings with double aortic arch or right aortic arch 2 ) pulmonary sling 3 ) innominate artery compression and 4 ) miscellaneous , pulmonary sling was about 4.5% .
embryologically , it has been suggested that it is caused by a maldevelpment of the left ventral pulmonary artery bud due to growth failure or reabsorption .
the left lung may capture its arterial supply by connection of the left postbronchial plexus with the right sixth arch through capillaries caudal to the lung bud .
then , as the lung bud grows caudally , the course of the left pulmonary artery is behind the developing trachea - bronchial tree . about half have cardiac or tracheo - bronchial anomalies which determine the prognosis . according to christoph dohleman s review , the associated cardiac anomalies were 49% and among those , patent ductus arteriosus , ventricular septal defect and atrial septal defect were most common .
tracheal stenosis with complete tracheal rings was the most common anomaly , followed by stenosis of main stem bronchus , tracheal bronchus and tracheo - esophageal fistula .
wells et al . proposed a classification system assigning pulmonary sling without complete tracheal rings to type 1 and pulmonary sling with complete tracheal ring to type 2 .
ring - sling complex can be classified into a lethal form and a form in which there is enough pars membranacea left to allow sufficient tracheal growth .
the two forms can be distinguished only by their clinical course , i.e. , either severe respiratory symptoms with progression or mild symptoms without progression .
bronchoscopy and echocardiography should be performed to evaluate the combined cardiac or tracheo - bronchial anomalies .
the plain radiographic features include unequal aeration due to compression of the right main bronchus by the anomalous vessel , low carina , horizontal equal - length right and left mainstem bronchi and long - segment tracheal stenosis .
diagnostic considerations such as dilated azygous vein , lymphadenopathy , foregut cyst or esophageal neoplasm should be excluded .
most cases can be diagnosed by ct or mri , but misinterpretation can occur because of a bifurcation - like structure of the pulmonary artery . the left pulmonary artery can be missed because of its different level of crossing the carina or main bronchus .
was the first to propose the now most common corrective surgical procedure : division and reimplantation of the anomalous left pulmonary artery into the pulmonary trunk anterior to the trachea with division of the ligamentum arteriosum .
because of high operation mortality and loss of function of the left lung due to obstruction of the reconstructed vessel , a conservative approach with symptomatic management was recommended initially .
but recent development of operation technique has resulted in low operation mortality and good patencty of the reconstructed vessel .
so , in view of the seriousness of this condition and the fact that reports of surgical management have been encouraging , current policy is to offer an operation as soon as the diagnosis is made .
pulmonary sling is a rare congenital condition in which the left pulmonary artery arises from the right pulmonary artery forming a sling around the trachea causing tracheal compression . 
 many cases are associated with cardiovascular and tracheo - bronchial anomalies . 
 when combined with complete tracheal ring , it is called  ring - sling complex  . 
 the average onset of symptoms is 2 months and about half have symptoms from birth . 
 the anomaly , if not corrected , can be fatal within the first year of life . in an adult , it is most often asymptomatic and usually found incidentally . 
 we report an adult case who was diagnosed as pulmonary sling with complete tracheal ring by ct and bronchoscopy along with a literature review .