Case report: the ‘vanished’ left pulmonary artery

Abstract Background We report a case of isolated ductal origin of pulmonary artery (DOPA) diagnosed in an asymptomatic newborn. The primary aim of this case is to highlight the need to investigate for DOPA in patients diagnosed with an ‘absent branch pulmonary artery’. Case summary Our patient was an asymptomatic newborn infant, with normal intracardiac anatomy. He was initially diagnosed post-natally with ‘absent left pulmonary artery’ (LPA), though the LPA was seen in antenatal scans. He underwent angiography and was re-diagnosed with bilateral arterial ducts, with ductal origin of the LPA from the left arterial duct. The LPA was salvaged by first stenting the left arterial duct on Day 11 of life, with subsequent surgery to connect the LPA to the main pulmonary artery at 4.5 months old. The patient had an uneventful recovery after the surgery. Discussion Ductal origin of pulmonary artery is a rare vascular anomaly characterized by continuity of the left or right pulmonary artery (PA) with the distal end of the arterial duct, and discontinuity with the main PA. It is commonly misdiagnosed as pulmonary artery agenesis when the patent arterial duct constricts, with cessation of blood flow into the affected pulmonary artery. A high index of suspicion is necessary for diagnosis of DOPA. Once diagnosed, this lesion is clearly amenable to intervention, with benefits from unifocalization, to prevent late onset pulmonary hypertension or cardiac failure.


Discussion
Ductal origin of pulmonary artery is a rare vascular anomaly characterized by continuity of the left or right pulmonary artery (PA) with the distal end of the arterial duct, and discontinuity with the main PA.It is commonly misdiagnosed as pulmonary artery agenesis when the patent arterial duct constricts, with cessation of blood flow into the affected pulmonary artery.A high index of suspicion is necessary for diagnosis of DOPA.Once diagnosed, this lesion is clearly amenable to intervention, with benefits from unifocalization, to prevent late onset pulmonary hypertension or cardiac failure.

Learning points
• This case highlights the importance of investigating for ductal origin of pulmonary artery with angiography in patients diagnosed with absent branch pulmonary artery or pulmonary artery agenesis.
• Patients may be initially asymptomatic.If left untreated, however, they may develop pulmonary hypertension or cardiac failure.
• In neonates or young infants, a staged approach of stenting the ductus arteriosus prior to unifocalization may be favoured, allowing for phys- ical growth of the baby, as well as the pulmonary artery, improving the surgical outcome.
• Antenatal diagnosis of the condition is possible, and should be suspected, if confluent branch pulmonary arteries cannot be demonstrated.

Introduction
Ductal origin of pulmonary artery (DOPA) is a rare vascular anomaly characterized by continuity of a branch pulmonary artery (PA) with the distal end of the arterial duct, and discontinuity with the main PA.Its incidence is estimated at 1:200 000, however this may be underestimated as many cases are misdiagnosed as pulmonary artery agenesis or 'absent pulmonary artery'. 1 Untreated, long-term consequences include unilateral lung hypoplasia, pulmonary hypertension, and cardiac failure.Early diagnosis and repair have good prognosis. 2,3

Summary figure
We report a case of an asymptomatic neonate with right aortic arch, bilateral arterial ducts, discontinuous pulmonary arteries with ductal origin of left pulmonary artery, who underwent successful staged repair, in a low volume cardiac centre.

Case summary
A baby boy with an antenatal diagnosis of double aortic arch was born well at term, birth weight 3224 g.His saturations were ≥95% in room air.Post-natal echocardiography done on Day 2 of life showed normal intracardiac anatomy, right aortic arch, right pulmonary artery arising normally from main pulmonary artery (MPA), with left pulmonary artery (LPA) not visualized (Figure 1A).
Computer tomography (CT) angiography scan (Figure 1B) performed on Day 9 of life confirmed echocardiographic findings of absent left pre-hilar LPA.Post-hilar left upper and lower lobe pulmonary arteries were visualized.There were no major aortopulmonary collateral arteries.The ampulla of the right arterial duct was seen at the aortic isthmus.A short tubular vessel was seen arising from the left brachiocephalic artery, suspected to be the ampulla of a constricted left arterial duct (PDA).Both lungs were well developed.
On retrospective review of the antenatal echocardiogram performed at 32 weeks gestational age, we were able to trace the LPA from the lung parenchyma to the origin of left brachiocephalic artery (Figure 2A-D, Supplementary material online, Video S1A and B).We postulated that this patient had bilateral PDAs in utero, discontinuous branch pulmonary arteries, with the LPA being supplied by the left PDA.High dose prostaglandin E1 was commenced, however the PDA did not reopen.The patient remained asymptomatic, maintaining oxygen saturations ≥ 95% in room air.
Cardiac catheterization study was performed on Day 11 of life.Contrast injected at the origin of the left brachiocephalic artery demonstrated a thread-like connection with the LPA via the left PDA, confirming the diagnosis of ductal origin of the LPA.The left PDA was stented, with good pulmonary arterial blood flow established in all lobes of the left lung, and good pulmonary venous return (Figure 3A and B, Supplementary material online, Videos S2 and S3).
Post-intervention, there was initial left lung reperfusion injury with pulmonary haemorrhage.This was medically managed with high positive end-expiratory pressure and diuresis.The patient also developed thrombo-embolic stroke presenting with focal seizures, for which he was treated with subcutaneous enoxaparin, titrated to maintain therapeutic anti-factor Xa levels (0.5-1.0 units/mL), along with oral  phenobarbitone at 5 mg/kg/day.There was no neurological deficit clinically.However, magnetic resonance imaging (MRI) of the brain showed evidence of small areas of acute infarcts.
He was discharged on Day 25 of life.Good growth and saturations were noted on outpatient follow-up.Serial echocardiograms showed patent left PDA stent.The left atrium and ventricle were dilated, The 'vanished' left pulmonary artery with mild mitral regurgitation.A repeat CT angiography at 3 months of age (Figure 3C) showed good interval growth of the post-hilar distal LPA.Repeat MRI brain showed mild gliosis from old infarcted areas, hence enoxaparin was discontinued while phenobarbitone was to be continued till re-assessment at 1 year of age.
At 4.5 months old, he underwent surgery to reconnect the LPA to MPA via direct anastomosis, using MPA flap to augment the anastomotic site, with removal of the left PDA stent.He was extubated hours after surgery uneventfully.Pre-discharge fluoroscopy and echocardiography (Figure 4A and B) demonstrated confluent and good-sized branch PAs, with non-turbulent flow across them.He was discharged well on post-operative Day 4.
He was last reviewed at 5.5 months of age in clinic.He remained well, with appropriate growth and development for age, and no further reported seizures.Echocardiography again demonstrated normal sized and non-turbulent branch pulmonary arteries.At 6 months of age, he and his family relocated back to their home country, and further followup was continued in their home country.

Discussion
Ductal origin of pulmonary artery can occur with other congenital heart lesions, and less commonly, in isolation. 3Isolated DOPA may  result in delayed diagnosis as it is frequently asymptomatic during childhood.
Embryologically, the distal intrapulmonary arteries arise from their respective lung buds, then join the proximal part of the sixth arch, forming the left and right pulmonary arteries.The distal portion of the sixth arches become the arterial duct.Regression of the proximal sixth arch, with persistence of its distal portion, results in ductal origin of the pulmonary artery. 4True pulmonary artery agenesis may occur if there is unilateral lung agenesis.
A high index of suspicion is required for the diagnosis, and should be considered in the absence of identifying confluent pulmonary arteries.
CT angiography or MRI may be performed to determine if intrapulmonary arteries are present.A PDA or ligamentum arteriosus may also be identified on the ipsilateral side of the 'absent' PA. 3 Angiography is the gold standard in diagnosis.Pulmonary venous wedge injections may depict hypoplastic intrapulmonary vessels. 5][8][9][10][11][12][13] When confluent branch pulmonary arteries cannot be demonstrated in the three-vessels (3V) or three-vessels trachea view (3VT), a transverse sweep (3VT view) is performed from the level of the bifurcation of pulmonary arteries to the level above the aortic arch, demonstrating the head and neck vessels.Identification of the origin of the affected vessel arising from the base of the brachiocephalic artery via the ipsilateral patent arterial duct in this sweep clinches the diagnosis of DOPA. 13actors contributing to our missed antenatal diagnosis included late presentation to our centre, suboptimal echocardiographic windows, and false reassurance from visualizing normal intraparenchymal pulmonary arteries, with normal intracardiac anatomy.The observation that the LPA had 'vanished' post-natally made us suspicious of DOPA, which was confirmed with angiography.
Management strategies involve either (1) direct unifocalization, or (2) staged procedure with either stenting of the arterial duct or placement of a surgical shunt.If the lesion was detected antenatally, prostaglandin E1 infusion may be immediately commenced post-natally to maintain ductal patency, before proceeding to either options.
Two large case series evaluating the outcomes of children with DOPA 2,3 showed the benefit of intervention even in late presentation.Pulmonary blood flow was re-established in the affected lung, and none of the patients developed pulmonary hypertension during the followup period.The oldest reported patient in the study by Mery et al. 2 was a child who underwent PDA stent at 9 years old, followed by unifocalization at 11 years old.In both case series, reinterventions (transcatheter or surgical) were required in the majority of patients to augment the growth of the reimplanted pulmonary artery, regardless of the initial approach chosen.
We chose a staged approach with ductal stenting followed by unifocalization for our patient, after discussion with our cardiothoracic surgeon.This approach allowed for good interim physical growth for our patient, as well as distal LPA growth, reducing the technical challenges of surgery, and the patient had a quick post-operative recovery.A recent multicentre review 14 found that in children with isolated pulmonary artery of ductal origin (IPADO), with or without structural heart defects, a staged repair was associated with larger isolated PA size and symmetry at late follow-up, as compared to primary unifocalization.We have proposed a management approach to isolated DOPA (Figure 5).

Conclusion
In conclusion, isolated DOPA is a rare condition that should be considered when the diagnosis of 'absent pulmonary artery' is made.It can be diagnosed antenatally if the affected pulmonary artery is demonstrated to arise from the ipsilateral brachiocephalic artery.Reconnecting the isolated PA to MPA should always be attempted, which reduces the risk of long-term consequences such as pulmonary hypertension and cardiac failure.A staged procedure may improve the surgical risk profile in young infants in a low volume cardiac unit.

Figure 1
Figure 1 (A) Post-natal transthoracic echocardiography parasternal short axis view demonstrating flow from MPA to RPA.LPA was not visualized.(B) CT angiography demonstrating RPA arising from MPA. LPA again not visualized.A stump appearing from left IA can be seen, likely ampulla of left ductus arteriosus.MPA, main pulmonary artery; RPA, right pulmonary artery; SVC, superior vena cava; IA, innominate artery; Ao, aorta; aLDA, ampulla of left ductus arteriosus; PA, pulmonary artery; LA, left atrium.

Figure 2 (
Figure 2 (A and B) Antenatal echocardiography at 32 weeks gestational age: a sweep depicting blood flow from PA to LDA to the isolated LPA.The LDA arises from the base of the left IA.(C and D) Sweep from four-chamber view, to three-vessel view, to the neck vessels, demonstrates that the LPA and RPA are discontinuous (see Supplementary material online, Video S1A and B).

Figure 3 (
Figure 3 (A) Anteroposterior view of angiography showing thread-like LDA connecting from left innominate artery to LPA. (B) LPA stent reestablishes flow to distal LPA (see Supplementary material online, Video S2A and B).(C) CT angiography repeated 2 months post-stenting.The stent was patent, with good growth of distal LPA.DAo, descending aorta; LDA, left ductus arteriosus; LPA, left pulmonary artery; IA, innominate artery; Ao, aorta; PA, pulmonary artery.

Figures 4 (
Figures 4 (A and B) Post-operative fluoroscopy demonstrates confluent branch pulmonary arteries.This was also demonstrated on echocardiography, with non-turbulent flow across both PAs seen.This is also demonstrated on fluoroscopy.RPA, right pulmonary artery; MPA, main pulmonary artery; LPA, left pulmonary artery; Ao, aorta.

Figure 5
Figure 5Flow chart: proposed management approach to isolated DOPA.