Case Presentation
The mother was a 43-year-old G2P2 woman. She was referred to our
hospital when the fetus was suspected to have heart disease at 26 weeks
of gestational age. Fetal echocardiography at gestational week 33 showed
that the main pulmonary artery arose from the right single ventricle; on
the right side of the main pulmonary artery, a hypoplastic ascending
aorta with reverse blood flow from the ductus arteriosus was observed.
The fetus was diagnosed as having hypoplastic left heart syndrome (Fig.
1a). The interatrial septum was completely absent, presenting
anatomically as a single atrium; however, the inferior vena cava and
right superior vena cava returned to the right side of the atrium. A
residual left superior vena cava (SVC), which returned to the left side
of the single atrium, was observed. The pulmonary veins did not return
to the atrium. The right pulmonary veins returned to the right SVC and
the left pulmonary veins to the left SVC. Therefore, the fetus was
diagnosed with a mixed form of supracardiac TAPVC. The left pulmonary
veins returning to the left SVC were severely constricted to a diameter
of 1.3 mm, with an increased velocity of 1.2 m/s. Part of the left
pulmonary veins ran to the right, through the narrow tortuous abnormal
vessels behind the atrium, to join the right pulmonary veins. The
diameters of these anomalous vessels were small (1.0 mm). They were
tortuous and did not have a structure that could be described as a
common chamber (Fig. 1b). Doppler waveforms from the pulmonary veins
were normal and biphasic on the right side; however, they showed
non-pulsatile continuous flow on the left side, suggesting left
pulmonary congestion (Fig. 1c).
Fetal MRI performed at 35 weeks of gestation revealed no difference in
appearance between the left and right lungs, indicating no laterality of
the lungs. No nutmeg lung pattern was observed (Fig. 1d). However,
because fetal echocardiographic findings were suggestive of advanced
left pulmonary venous stenosis, interventions such as stent placement at
the site of stenosis could be required directly following birth.
Therefore, a cesarean section was performed.
The baby was born with a birthweight of 2618 g at 38 weeks and 2 days of
gestation. Immediately after birth, the following conditions were
observed: an oxygen saturation (SpO2) of 90% on room
air, tachypnea, and retractive breathing. High-flow nasal cannula
therapy with a low oxygen concentration was administered. Based on the
findings of chest computed tomography (CT) and echocardiography
performed on the day of birth, it was determined that the diagnosis had
not changed since gestation (Fig. 2a–d). Marked congestion was observed
in the left lung (Fig. 2a). On echocardiography, blood flow velocity was
approximately 1.5 m/s at sites where the left pulmonary veins returned
to the left SVC, and blood flow to the left pulmonary artery was
maintained. As the patient was inhaling low-oxygen air (17% of oxygen)
under hypoxia inhalation therapy with a nitrogen gas mixture and the
patient’s SpO2 was 80–89%, it was determined that the
patient’s course could be observed without performing additional
interventions. Therefore, no interventions were performed for pulmonary
venous stenosis during the early neonatal period. Bilateral pulmonary
artery banding was performed at 6 days of age. The patient has been
scheduled to undergo another operation after weight gain has occurred.
Discussion
The peripheral pulmonary venous plexus and systemic archenteron plexus
are initially connected; however, their connection regresses after the
pulmonary veins and left atrium connect to each other. The common
pulmonary vein develops from the posterior wall of the left atrium
embryologically. TAPVC occurs if the fusion of the pulmonary veins and
left atrium via the common pulmonary vein is interrupted before the
network between the pulmonary venous plexus and archenteron plexus
regresses.
In the present case, narrow tortuous networks of anomalous vessels
between the left and right pulmonary veins were observed on the
posterior side of the atrium; however, the common pulmonary venous
chamber could not be clearly observed. Therefore, it may be deduced that
the fusion of the pulmonary veins and left atrium was not the result of
the agenesis of the common pulmonary vein, leading to TAPVC. Rather, it
is thought that the anomalous vessels on the posterior side of the left
atrium were part of the remaining archenteron venous plexus.
Meanwhile, there was only a single atrium, in which complete absence of
the septum was observed. The left atrial appendage was present, and
there were no issues with the returning systemic veins. Hence, it was
thought that laterality was maintained while the atria were developing,
although a single atrium was formed due to the malformation of the
interatrial septum.
During normal development, the atria are formed by the following four
components: (1) smooth-walled lower atrial rim derived from the
atrioventricular canal myocardium; (2) atrial appendages derived from
the primitive cardiac tube; (3) caval vein myocardium (systemic inlet);
and (4) mediastinal myocardium (pulmonary inlet), including the atrial
septa derived from the dorsal mesocardium.6 In this
case, the absence of the common pulmonary vein, which would have formed
an inflow portion to receive blood from the pulmonary veins and
interatrial septum, was observed. Hence, it was believed that the
sequence of cardiac malformations in the present case occurred due to
the incomplete development of the dorsal mesocardium.
The nutmeg lung pattern can be observed in pulmonary lymphangiectasia on
fetal MRI. Secondary pulmonary lymphangiectasia due to congenital heart
disease is caused by the following conditions: pulmonary venous
stenosis/atresia, mitral stenosis/atresia, cor triatriatum, and
hypoplastic left heart syndrome.4 Furthermore, the
pulmonary venous flow has been reported to be continuous or monophasic
on fetal echocardiography in TAPVC patients with pulmonary venous
stenosis.7 However, no studies have reported the
relationship between the nutmeg lung pattern and pulmonary venous flow
patterns. In this case, fetal echocardiography showed non-pulsatile
continuous flow in the left pulmonary veins as well as increased flow
velocity at the entry point of the pulmonary vein to the left SVC,
suggesting severe pulmonary congestion. On the other hand, no marked
nutmeg lung pattern was observed on fetal MRI. Additionally, while left
pulmonary congestion was suggested on postnatal CT, blood flow in the
left pulmonary artery was maintained. Therefore, it was not necessary to
perform interventions for pulmonary venous stenosis directly following
birth. The above findings suggest that the nutmeg lung pattern can only
be observed if more severe pulmonary congestion and more advanced
pulmonary lymphangiectasia are present, compared with non-pulsatile
continuous pulmonary venous flow patterns. Going forward, it is
necessary to report more cases such as this in order to more accurately
predict the postnatal course of fetuses with TAPVC accompanied by
pulmonary venous stenosis based on fetal echocardiography and pulmonary
MRI. This may help develop effective treatment plans.
A cknowledgement
The authors gratefully acknowledge the valuable support received from
the study staff, which had made this investigation possible.
Statement of Ethics
This study was approved by the Institutional Review Board of Osaka City
General Hospital (approval number: 2012135). Informed consent was
obtained in the form of opt-out on the website of Osaka City General
Hospital.
Conflict of Interest Statement
The authors have no conflicts of interest to declare.
Author Contributions
All authors discussed and planned the treatment. WM, TS, EE, and KK
carried out the treatment. WM and YK drafted the manuscript. All authors
critically reviewed and approved the final manuscript.