Discussion
UPAD is rare congenital malformation and usually demonstrated as an
absence of proximal unilateral pulmonary artery on prenatal
echocardiography; therefore, it has also been referred to as unilateral
absence of the pulmonary artery.1 As the distal
segment of the affected pulmonary artery actually exists, UPAD is a more
accurate term to describe this malformation.1 It also
should be distinguished from the other rare form of CHD, hemitruncus
arteriosus, which is defined as an anomalous origin of one of the branch
pulmonary arteries (PAs) from the aorta and a normal origin of other PAs
from the RVOT.2 If untreated, it results in a large
left-to-right shunt, with the whole cardiac output from the right
ventricle directed to the unaffected lung while the other lung receives
blood at a systemic pressure from the systemic aorta; its 1-year
survival rate has been reported to be
<30%.2,3
Unlike patients with hemitruncus arteriosus, those with UPAD receive
blood supply to one lung from ductus-like collateral vessels, not the
systemic aorta, and it is often associated with other CHDs, especially
tetralogy of Fallot (TOF).2 Although, its
pathophysiology is not fully understood most studies on UPAD have
described that a failure in the connection of the sixth aortic arch with
the pulmonary trunk results in this developmental
anomaly.1,4 Clinical presentations vary depending on
the affected site.1,4,5 In case of LPAD, 75% of
patients have an associated congenital heart disease, including TOF,
right-side aortic arch, septal defect, or persistent
DA.1,5,6 By contrast, most patients with RPA
discontinuity have the isolated form without other intracardiac
anatomies. The affected pulmonary artery is on the side opposite the
aortic arch.6 As known previously, in this case, the
LPA was affected, and the neonate showed a right aortic arch. This
implies that the confirmation of the aortic arch location has an
important clinical significance.
As previous mentioned, the initial diagnosis was PAVSD only. In the case
of PAVSD, the initial maintenance of DA is also important because the
pulmonary circulation is dependent on DA. However, the atretic MPA was
not dependent on DA and was responsible for the right lung circulation
in the present case. If PGE1 was administered for a certain period to
maintain DA without prenatal detection of UPAD in our case, it would be
associated with a decrease in the size of the right PA, resulting in PA
size discrepancy. Meanwhile, an isolated form of UPAD (usually affecting
the right PA) could be missed during prenatal care. Diagnosis is often
delayed in patients with pulmonary hypertension, recurrent pulmonary
infections, congestive heart failure, and
haemoptysis.4 Prenatal detection is important because
it aids in the prompt initiation of PGE1 administration to ensure early
rehabilitation of the affected lung.7
No consensus has been reached regarding the treatment for UPAD. In cases
complicated by other CHDs, treatment would depend on major cardiac
abnormalities. In our case, the prenatal detection of UPAD in addition
to PAVSD allowed the paediatric cardiologist to make a precise operative
plan. Our paediatric cardiologist knew the size difference between the
LPA and the MPA, which made it possible to prepare the Gore-Tex graft
patch for pulmonary angioplasty. In cases of the isolated form of UPAD,
early intervention for UPAD has been supported owing to the concern for
regression of the affected PA after DA closure. However, the operation
timing should be determined on the basis of many other clinical
situations, including the neonatal condition or
birthweight.7 If early intervention is unavailable,
administration of PGE1 is usually required. In cases of delayed
diagnosis made in the adolescent or adult period, lobectomy and ligation
of the affected PA are required.5 In conclusion, UPAD
is relatively rare, but when undetected, it could affect neonatal
prognosis. Therefore, clinicians should examine the route of the both
pulmonary arteries regardless of the existence of other intracardiac
abnormalities.