2. Figure 1. Prenatal and postnatal echocardiography, CT, and intraoperative findings of case 1 with a PA sling. A, Fetal echocardiography
shows the left PA arising distally from the right PA and surrounding the trachea. B, Schematic drawing illustrates the relationship between
PA branches and the trachea. C, Postnatal echocardiography shows the left arising distally from the right PA. D, Computed tomography
shows that the left PA originates from the right PA and passes posterior to the trachea. The arrow shows the compressed trachea. E, The
Intraoperative photograph shows reimplantation of the left PA from the right PA to the main PA. F, Postoperative echocardiography shows
that the left PA arises from the main PA. AAO indicates ascending aorta; ANT, anterior; AO, aorta; DA, ductus arteriosus; LPA, left PA; MPA,
main PA; RA, right atrium; RPA, right PA; RV, right ventricle; SP, spine; and T, trachea.
Peng et al—3-Vessel and 3-Vessel and Trachea Views of a Pulmonary Artery Sling
540 J Ultrasound Med 2019; 38:539–544
3. 3-vessel and trachea view, it showed the left
PA distally arising from right PA and coursing
between the trachea and esophagus, indicating
the existence of a PA sling (Figure 1, A and
B). A male neonate was born at 40 weeks’ ges-
tation via a cesarean delivery, without respira-
tory complications. Postnatal
echocardiography on the first day after birth
revealed a PA sling with the left PA arising
from the right PA (Figure 1C). Postnatal com-
puted tomography (CT) also showed the
anomalous left PA and stenosis of the airway
(Figure 1D). At 8 months of age, the infant
underwent surgical repair of the PA sling
(Figure 1E) and ligation of the ductus arterio-
sus. Postoperative echocardiography showed
that the left PA was transplanted to the main
PA (Figure 1F). At the time of writing, he was
faring well.
Case 2
A 26-year-old pregnant woman was referred to our
hospital at 25 weeks’ gestation for a fetal cardiovascu-
lar anomaly evaluation. When we scanned between
the 3-vessel and 3-vessel and trachea views, the axial
planes showed that the aberrant left PA anomalously
originated from the right PA, turned sharply leftward
at the right side of the trachea, and then reached the
left lung through the space between the distal trachea
and esophagus (Figure 2, A and B). Furthermore, the
fetus had a prenatal diagnosis of cleft lip and palate.
Because of these congenital malformations, the
parents chose pregnancy termination. With the con-
sent of the parents and the approval of the Ethics
Committee, a cardiovascular cast was made from this
induced fetal specimen. The cast clearly revealed that
the left PA anomalously originated from the right PA
with a retrotracheal course (Figure 2C).
Case 3
A 30-year-old pregnant woman was referred to our
hospital at 31 weeks’ gestation for a suspected fetal
congenital heart defect. Prenatal echocardiography
showed the anomalous left PA arising from the right
PA between the 3-vessel and 3-vessel and trachea
views, with the ductus arteriosus coursing left anterior
and the proximal left PA right posterior to the trachea
(Figure 3, A–C). Fetal echocardiography also showed
a perimembranous ventricular septal defect and
enlarged oval foramen. At 39 weeks’ gestation, a
female neonate was born by a cesarean delivery. The
Apgar scores were 8 and 9 at 1 and 5 minutes after
birth, respectively. Postnatal echocardiography con-
firmed the diagnosis of a PA sling, perimembranous
ventricular septal defect, and patent oval foramen. In
addition, color Doppler postnatal echocardiography
indicated that the peak systolic velocity of the left PA
was 2.6 m/s, suggesting left PA stenosis (Figure 3D).
Discussion
A PA sling, also known as a left PA sling, is a very
rare congenital cardiovascular anomaly.4
The
Figure 2. Prenatal echocardiography and cardiovascular cast depiction of case 2 with a PA sling. A, Fetal echocardiography shows the left
PA originating from the rear of the right PA, passing between the esophagus and trachea to reach the left hilum. B, Schematic drawing illus-
trates the view in A. C, Cardiovascular cast shows the left PA arising distally from the right PA. The trachea is surrounded by the left PA and
left-sided ductus arteriosus. ARCH indicates aortic arch; and DAO, descending aorta; other abbreviations are as in Figure 1.
Peng et al—3-Vessel and 3-Vessel and Trachea Views of a Pulmonary Artery Sling
J Ultrasound Med 2019; 38:539–544 541
4. estimated prevalence of PA slings was 59 per million
in a large-scale pre–sports participation cardiovascu-
lar screening study of 186,213 school-aged children
by Yu et al.5
It is hypothesized that if the left lung
capillary plexus is not connected to the left sixth
branchial arch, but instead bypasses the trachea and
consequently connects to the right sixth branchial
arch, then this connection contributes to the forma-
tion of a PA sling.6
The aberrant left PA can cause
varying compression of the lower trachea, right main
bronchus, and esophagus. The associated cardiac
anomalies with a PA sling include a persistent left
superior vena cava, an atrial septal defect, a
ventricular septal defect, and a patent ductus arterio-
sus. Clinically, 90% of patients have airway obstruc-
tion symptoms, with only 10% asymptomatic.
Dyspneic respiration caused by incomplete airway
obstruction is the most prominent manifestation of
a PA sling in children.2
Therefore, prenatal diagnosis
of a PA sling can be helpful for postnatal manage-
ment of tracheal compression. Compared to postna-
tal echocardiography, CT is more effective in the
evaluation of tracheal anomalies and stenosis. How-
ever, with its safe, noninvasive, real-time imaging
capability, fetal echocardiography is crucial for the
prenatal diagnosis of a PA sling.
Figure 3. Prenatal and postnatal echocardiography of case 3 with a PA sling and a ventricular septal defect. A, Slightly cranial axial plane to
the 3-vessel and trachea view shows an aberrant distal origin of the left PA. B, Color Doppler imaging shows the left PA turning leftward in
the rear of the trachea, which surrounds the trachea together with the left-sided ductus arteriosus. C, Schematic drawing illustrates the rela-
tionship of the ductus arteriosus, left PA, right PA, and trachea. D, Postnatal echocardiography shows that the left PA arises distally from the
right PA. Color Doppler imaging indicates the accelerated flow of the left PA. Abbreviations are as in Figure 1.
Peng et al—3-Vessel and 3-Vessel and Trachea Views of a Pulmonary Artery Sling
542 J Ultrasound Med 2019; 38:539–544
5. To date, few studies have reported PA slings in
fetuses.7
In this report, we have described 3 cases of
PA slings with postnatal follow-ups. In case 1, postna-
tal echocardiography, CT, and intraoperative findings
all confirmed the prenatal diagnosis of a PA sling. In
case 2, a cardiovascular cast of the fetal specimen
showed the existence of a PA sling. In case 3, postnatal
echocardiography also confirmed the prenatal diagno-
sis of a PA sling and other associated cardiac anoma-
lies. In our previous study, we applied cardiovascular
casts to display 3-dimensional anatomy of fetal con-
genital cardiovascular anomalies.8,9
In case 2, not only
the cardiac chambers and great vessels but also the
trachea were cast with different colors. The cast viv-
idly showed the interrelationship between the PA
branches and trachea. Fetal cardiac screening of the
3 cases indicated that the aberrant left PA was poste-
rior to the trachea by sweeping from the 3-vessel view
to the 3-vessel and trachea view. As we know, the
3-vessel and 3-vessel and trachea views play a vital
role in the evaluation of great vascular anomalies. The
relationship of the PA, aorta, ductus arteriosus, supe-
rior vena cava, and trachea in the upper mediastinum
can be observed via the 3-vessel and 3-vessel and tra-
chea views, which is of crucial importance in the iden-
tification of a PA sling.10
In normal conditions, the
PAs are located anterior to the primary bronchi and
form an inverted Y shape in the 3-vessel view,
whereas the aorta and ductus arteriosus are located
on the left side of the trachea and form a V shape in
Figure 4. Prenatal echocardiography of a healthy fetus. A, The 3-vessel view shows the PA branches forming an inverted Y shape in front of
the primary bronchi. B, Schematic drawing illustrates the relationship of the main PA, left PA, right PA, and principal bronchus in the 3-vessel
and trachea view. C, Aorta and ductus arteriosus forming a V shape in the left side of the trachea in the 3-vessel and trachea view. D, Sche-
matic drawing illustrates the relationship of the great vessels and trachea in the 3-vessel and trachea view. LB indicates left bronchus; RB,
right bronchus; and SVC, superior vena cava; other abbreviations are as in Figures 1 and 2.
Peng et al—3-Vessel and 3-Vessel and Trachea Views of a Pulmonary Artery Sling
J Ultrasound Med 2019; 38:539–544 543
6. the 3-vessel and trachea view (Figure 4). No vessels
should be observed posterior to the trachea in the
3-vessel or 3-vessel and trachea view in a healthy
fetus. Conversely, if the aberrant left PA is found pos-
terior to the trachea in the above views, a PA sling
should be suspected. Moreover, we can assess the
dimension of the pulmonary trunk and its branches
in the 3-vessel view. If the diameter of the left PA is
substantially lower than that of the right PA, the fetus
may have left PA stenosis.
Although a PA sling has typical echocardio-
graphic manifestations, it is still easy to misdiagnose.
By reviewing the literature, we suppose there are
2 reasons. First, the left PA is not routinely observed
in obstetric ultrasound screens; thus, an aberrant left
PA may be ignored in the prenatal examination. Sec-
ond, the sonographer may not distinguish the left PA
from the ductus arteriosus in the 3-vessel and 3-vessel
and trachea views during the fetal cardiac screen and
mistakenly may mistake the ductus arteriosus as the
left PA. Therefore, if the left PA is not able to be
detected in the 3-vessel view, a PA sling should be
highly suspected.
In summary, fetal echocardiography plays a
vital role in the prenatal diagnosis of a PA sling.
The abnormal position between the left PA and the
trachea in the axial plane between the 3-vessel and
3-vessel and trachea views may contribute to the
prenatal diagnosis of a PA sling. We emphasize the
importance of the 3-vessel and 3-vessel and trachea
views in the prenatal diagnosis of a PA sling.
References
1. Contro S, Miller RA, White H, Potts WJ. Bronchial obstruction
due to pulmonary artery anomalies, I: vascular sling. Circulation
1958; 17:418–423.
2. Gikonyo BM, Jue KL, Edwards JE. Pulmonary vascular sling:
report of seven cases and review of the literature. Pediatr Cardiol
1989; 10:81–89.
3. Sade RM, Rosenthal A, Fellows K, Castaneda AR. Pulmonary
artery sling. J Thorac Cardiovasc Surg 1975; 69:333–346.
4. Ochiai D, Miyakoshi K, Koinuma G, Matsumoto T, Tanaka M.
Prenatal sonographic images of left pulmonary artery sling. Eur J
Obstet Gynecol Reprod Biol 2017; 211:217–218.
5. Yu JM, Liao CP, Ge S, et al. The prevalence and clinical impact of
pulmonary artery sling on school-aged children: a large-scale
screening study. Pediatr Pulmonol 2008; 43:656–661.
6. Pu WT, Chung T, Hoffer FA, Jonas RA, Geva T. Diagnosis and
management of agenesis of the right lung and left pulmonary
artery sling. Am J Cardiol 1996; 78:723–727.
7. Yorioka H, Kasamatsu A, Kanzaki H, Kawataki M, Yoo SJ. Prena-
tal diagnosis of fetal left pulmonary artery sling. Ultrasound Obstet
Gynecol 2011; 37:245–246.
8. Cao HY, Wang Y, Hong L, et al. Morphological features of complex
congenital cardiovascular anomalies in fetuses: as evaluated by cast
models. J Huazhong Univ Sci Technolog Med Sci 2017; 37:596–604.
9. Wang Y, Cao HY, Xie MX, et al. Cardiovascular cast model fabri-
cation and casting effectiveness evaluation in fetus with severe con-
genital heart disease or normal heart. J Huazhong Univ Sci
Technolog Med Sci 2016; 36:259–264.
10. Brandt JS, Wang E, Rychik J, Soffer D, McCann ML, Schwartz N.
Utility of a single 3-vessel view in the evaluation of the ventricular
outflow tracts. J Ultrasound Med 2015; 34:1415–1421.
Peng et al—3-Vessel and 3-Vessel and Trachea Views of a Pulmonary Artery Sling
544 J Ultrasound Med 2019; 38:539–544
