Case - Anomalous Right Pulmonary Artery from Ascending Aorta - April 2024

Background

• In hemitruncus arteriosus, one of the pulmonary arteries (PA), usually the right PA, arises from the ascending aorta (1).

• Associated defects such as a patent ductus arteriosus, a ventricular septal defect or a tetralogy of Fallot are occasionally present (1,2).

• When it is associated with interrupted aortic arch and distal aorto-pulmonary window, it is called "Berry syndrome" (2).

• Rarely, it occurs as an isolated lesion. In most cases, it is the right PA that arises abnormally (2).

• Hemodynamically, one lung receives blood directly from the aorta, as in a PDA, with resulting volume or pressure overload. The other lung receives the entire RV output, resulting in volume overload to that lung. Therefore, pulmonary hypertension of both lungs develops (1).

• It causes severe pulmonary hypertension and heart failure (2).

Echocardiography (trans-thoracic)

There was evidence of right ventricular dysfunction, characterized by a tricuspid annular plane systolic excursion (TAPSE) measuring 8 mm, alongside severe tricuspid regurgitation with a pressure gradient (PG) of 90mmHg. The interventricular septum (IVS) displayed a D-shaped configuration during diastole, indicative of right ventricular dilation. Additionally, mild mitral regurgitation was present. The echocardiography indicated normal coronary artery origin and a left aortic arch without coarctation or patent ductus arteriosus (PDA). Pulmonary venous return to the left atrium appeared normal. Turbulent flow into the right pulmonary artery (RPA) originating from the ascending aorta was noted. An atrial septal defect (ASD-Ostium secundum defect) measuring 2mm, with a bidirectional shunt primarily right to left, was identified. Importantly, no ventricular septal defect (VSD) or pericardial effusion was observed. The left ventricular ejection fraction (LVEF) was 50%.

Right pulmonary artery originating from the ascending aorta.

Right pulmonary artery is seen originating at the level of the ascending aorta, which is seen coming off the systemic left ventricle. 

Pulmonary venous return with normal configuration draining into the left atrium. In this view, one may also appreicate the course of the RPA coming off the aortic root. 

Bidirectional inter-atrial shunt, outlining relative similar pressure at the atrial level. This is likely secondary to the increased RV end-diastolic pressure from the RV pressure and volume overload (i.e. increased Qp:Qs from the Aorta to RPA pressure and volume transmission). There is possibly some reactive pulmonary vasoconstriction affecting both lungs secondary to the increased pressure and volume transmission to the right pulmonary vascular territory.  There is also a contribution of the significant TR, possibly elevating RA pressure leading to the bidirectional shunting at the PFO level. 

Cardiac CT-scan

The origin of the RPA from the ascending aorta. The left pulmonary artery originates from the main pulmonary artery normally. No associated ventricular septal defect or patent ductus arteriosus.

Intraoperative findings

Echocardiography post-repair

Post repair. One may appreciate that the right pulmonary artery has been reconnected to the main pulmonary artery. 

Discussion

The origin of a branch pulmonary artery (PA) from the ascending aorta represents a rare congenital cardiac anomaly. While its developmental etiology remains incompletely understood, various theories propose incomplete migration of the affected branch PA towards the contralateral PA or failure of fusion of one of the sixth arches with the main pulmonary artery (MPA). This anomaly often occurs concomitantly with other cardiac anomalies such as tetralogy of Fallot, pulmonary atresia, interrupted aortic arch, and chromosome 22q11 microdeletion. Typically, the anomalous branch pulmonary artery arises from the posterolateral wall of the ascending aorta above the aortic sinus, although it may also originate distally near the innominate artery. The right pulmonary artery (RPA) more commonly exhibits anomalous origin from the ascending aorta compared to the left pulmonary artery (LPA), with the former invariably associated with a left aortic arch and often a left-sided patent ductus arteriosus (PDA). Physiologically, this anomaly may lead to abnormal pulmonary vasculature in the associated lung. Stenosis of the affected branch PA is infrequent.

Conclusion

In the past, the origin of a branch pulmonary artery from the ascending aorta was termed a "hemitruncus." This anomaly is morphologically and embryologically distinct from truncus arteriosus, occurring despite the normal separation of the aortic and pulmonary valves. In affected infants, congestive heart failure manifests early in infancy, often accompanied by respiratory distress and inadequate weight gain. Regardless of the underlying mechanism, early diagnosis and prompt surgical correction are imperative to prevent the progression to irreversible pulmonary vascular disease.

References

1. Park, Myung K., and Mehrdad Salamat. Park's Pediatric Cardiology for Practitioners - 7th edition. Elsevier Health Sciences, 2020. Chapter 15: Miscellaneous Congenital Cardiac Conditions. "Hemitruncus arteriosus". pages 230-231.

2. Park, In Sook, and Hyun Woo Goo. "Abnormalities of the Right Ventricular Outflow Tract and Pulmonary Arteries." An Illustrated Guide to Congenital Heart Disease: From Diagnosis to Treatment–From Fetus to Adult (2019): 99-123.