Rare Reversible Cause of Severe Pulmonary Hypertension in A Neonate - Unilateral Absence of Pulmonary Artery View PDF

*Eapen Thomas
National Heart Center, Royal Hospital, P.B.No: 1331, P.C: 111, Bausher, Muscat, Oman

*Corresponding Author:
Eapen Thomas
National Heart Center, Royal Hospital, P.B.No: 1331, P.C: 111, Bausher, Muscat, Oman
Email:dret59@gmail.com

Published on: 2020-11-05

Abstract

This case report describes the diagnostic and surgical management of a neonate with isolated unilateral absence of right pulmonary artery (UAPA). A high index of suspicion leading to early diagnosis and the importance of right pulmonary vein wedge injection angiography in a neonatal presentation of UAPA and good outcomes of timely surgery is highlighted.

Keywords

Pulmonary artery abnormalities; Pulmonary artery-diagnostic imaging; Pulmonary artery-surgery

Introduction

Neonatal presentation of the unilateral absence of pulmonary artery (UAPA) is rare. Isolated UAPA has a prevalence ranging from 1 in 200,000 to 1 in 300,000 [1-3]. It has been variably called absence, interruption, agenesis, involution, or isolation of either right or left pulmonary artery. The term ‘absence’ though technically incorrect, is retained due to its initial description. The anomaly can present as an isolated lesion or in association with other congenital heart defects. The infantile form presents with heart failure and severe pulmonary hypertension. Often, the underlying presence of UAPA may be hidden in a patient with the clinical presentation being akin to that of an increased pulmonary blood flow state, albeit to one lung. This case report highlights the elusive way UAPA presented in an infant masquerading as heart failure for which the baby was under treatment for weeks until further investigations revealed the underlying etiology. Further, the successful surgical outcome of a neonate with isolated UAPA is reported.

Case Report

A one-month-old female infant was referred to the authors’ institute with a history of intermittent central cyanosis, tachypnoea, and sweating with feeds. About a week before her presentation to us, she has admitted to a peripheral hospital with a respiratory tract infection and her respiratory viral panel study was positive for respiratory syncytial and coronaviruses.

Transthoracic echocardiogram (TTE) performed on admission revealed mildly dilated right ventricle (RV) and the main pulmonary artery (MPA). There was also a patent foramen ovale with the right to left shunt. An absent right pulmonary artery had been overlooked in the initial TTE. A contrast-enhanced computed tomography scan of the chest was undertaken to rule out a secondary etiology for pulmonary hypertension with intermittent cyanosis and this revealed an isolated absent right pulmonary artery (RPA), a left aortic arch, a dilated MPA continuing as the left pulmonary artery [LPA] and a hypertrophied right ventricle [Figure-1A&B&C]. Repeat TTE revealed features of worsening pulmonary hypertension with further dilation and hypertrophy of RV, MPA, and LPA with an estimated systolic pulmonary artery pressure of 70 mmHg. The cardiac catheterization study further confirmed the above findings. Right pulmonary vein wedge injection (RPVW) showed well-formed hilar RPA and right pulmonary arborization (Figure 2A). The baby continued to remain unwell with tachypnoea and episodes of pulmonary hypertensive crisis not abating with oral sildenafil administration and was taken up for surgery.

On normothermic beating heart cardiopulmonary bypass, hilar RPA was dissected out. It had a ligamentous continuity with an outpouching at the base of the innominate artery. This connection was divided, and a tiny lumen was seen and filleted out to the hilar RPA but was felt to be a trifle short to reach the MPA (Figure 2B). It was then divided and RPA continuity with MPA was established by the interposition of a 6 mm Polytetrafluoroethylene [PTFE] graft [W. L. Gore & Associates, Inc. Flagstaff, Arizona, USA] between the hilar RPA and the posterolateral aspect of the MPA (Figure 2 B&C). The graft was routed under the ascending aorta without any compression. She was separated from cardiopulmonary bypass easily on minimal inotrope support with good arterial oxygen saturation. The baby made a rapid clinical recovery after surgery and was discharged on the fourteenth postoperative day, on aspirin, sildenafil, and diuretics. Her repeat TTE in the out-patient clinic, seven months after surgery, showed a patent neo-RPA with no evidence of pulmonary hypertension.

Discussion

The early diagnosis and successful surgical management of a neonate with UAPA is described. The management of this anomaly is based on the symptoms of the patient, pulmonary artery anatomy, and the presence of aortopulmonary collaterals.

Isolated congenital unilateral absence of central pulmonary arteries is rare with an estimated prevalence of 1 in 200,000. This can occur on either side, with about 60% being on the right side. When associated with other cardiac anomalies congenital unilateral absence is noted predominantly on the left side [1]. UAPA can manifest either in infancy or adulthood. Congestive cardiac failure (CCF) and pulmonary hypertension (PHT) are the dominant features of the infantile presentation and require a high index of suspicion to undertake relevant investigations [2]. Clinical presentation in our patient, however, was worsened by coincidental respiratory infection and she had intermittent cyanosis, perhaps reflecting intermittent right to left shunting through the patent foramen ovale from raised pulmonary arterial pressure. Diagnosis involves echocardiography and is confirmed by CT angiography or cardiac catheterization. Pulmonary vein wedge injection at cardiac catheterization is recommended particularly in cases where CT angiography fails to demonstrate the hilar RPA. Delay in diagnosis may lead to death or irreversible hypoplasia and regression of the affected pulmonary artery with a less favorable outcome [3].

The embryological basis has been well described. The absent pulmonary artery is caused by the involution of the proximal sixth aortic arch which gives rise to the intrapericardial, extrapulmonary- parenchymal branch pulmonary arteries. However, the connection of the intrapulmonary-parenchymal PAs with the distal sixth arch persists as the ductus (arising from the innominate artery when the UAPA is on the side opposite the arch). The ductus involutes perinatally, starting distally at the far end of the intrapericardial portion and progresses proximally and can be inferred by the presence of a patent proximal end seen as a diverticulum from the innominate artery. The fate of hilar RPA rests then, perhaps, on collateralization, in the absence of which, it undergoes regression. Thus, the term ‘isolation of the right pulmonary artery’ describing the ductal origin, and the term ‘unilateral interruption of pulmonary artery’ describing the missing intrapericardial segment have been alternatively used for this condition. Other terms used include the ductal origin of distal PA, occult PA, and proximal interruption. The term unilateral absence of a pulmonary artery is, however, retained due to its original description.

Pulmonary hypertension in these patients is akin to that developing after pneumonectomy, due to the entire right heart output passing through the left pulmonary artery. The blood flow through the left pulmonary artery is significantly decreased after the restoration of blood flow to the hilar right pulmonary artery. In the absence of surgical correction, pulmonary hypertensive changes, in the left lung are expected and would become irreversible over time.

Well-developed hilar and intrapulmonary vasculature, as in this child, is an indication to establish MPA to hilar RPA continuity. Either a staged approach using a modified Blalock Taussig shunt followed by MPA to RPA continuity or single-stage establishment of MPA to RPA continuity using the autologous pericardial tube, homograft or prosthetic (Dacron or PTFE) interposition graft or rarely direct anastomosis have been reported [4-6]. We chose the conduit option as the tissue from the ligament was very ragged and the distance quite large for a direct anastomosis; and PTFE was chosen due to the non-availability of homograft. Although prosthetic material lacks growth potential and will require further surgeries to replace it, and requires indefinite aspirin thromboprophylaxis, it was preferred in this case for its simplicity, non-collapsibility, and familiarity with PTFE conduit use in neonates.

Conclusion

In conclusion, UAPA is a rare cause of CCF and PHN in neonates and infants and requires a high index of suspicion to diagnose the condition. In infancy, it presents with CCF and signs of severe PHN. Therapeutic intervention is dictated by clinical manifestations and timely surgery is imperative to attain a good outcome. Single-stage surgical repair using PTFE conduit, though limited by lack of growth potential and need for repeat surgery, is relatively simple and has a good short-term outcome.

References

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