Introduction
Truncus arteriosus is an uncommon congenital cardiac malformation, accounting for less than 1% of CHDs. It is defined by a single arterial trunk overriding the ventricles and supplying both systemic and pulmonary circulations.Reference Hazekamp, Barron and Dangel1 Within this group, an exclusive right ventricular origin of the truncal root is extremely rare, having been described only in pathological series, and an association with an inlet ventricular septal defect has never been reported to our knowledge.Reference Adachi, Seale and Uemura2
This anatomical variant challenges the usual relationships between the ventricles and the arterial trunk and presents specific technical difficulties for achieving unobstructed left ventricular outflow. We describe a case illustrating its distinctive features, operative management, and the value of three-dimensional modelling in understanding this complex morphology.
Case description
A two-year-old child born in Africa was referred for persistent fatigue and growth retardation.
Echocardiography revealed a large type 2 arterial trunk arising entirely from the right ventricle. The left ventricle was well developed but connected to the right ventricle only through a small, posteriorly positioned, restrictive inlet-type ventricular septal defect.
CT confirmed the exclusive right ventricular origin of the truncal root and normal pulmonary artery branching (Figure 1).
Pre-operative CT scan showing the truncus arteriosus arising completely from the right ventricle and the posterior inlet ventricular septal defect.
Surgical correction was performed at two years of age. The truncal root was fully committed to the right ventricle and separated from both atrioventricular valves by a muscular infundibular fold. Through a right atriotomy, the restrictive inlet muscular ventricular septal defect was enlarged anteriorly to establish unobstructed left ventricular outflow, and an autologous pericardial patch was used to construct an intraventricular tunnel from the left ventricle to the truncal root. The pulmonary branches were harvested from the truncal root, and a 16 mm Contegra conduit (Medtronic Inc., Minneapolis, MN, USA) was used for right ventricular outflow tract reconstruction. Intraoperative echocardiography showed no residual lesion, and separation from cardiopulmonary bypass was achieved without difficulty.
The early post-operative course was complicated by a failure to wean from mechanical ventilation, associated with high pulmonary arterial pressures. Echocardiography demonstrated a high-velocity jet across the left ventricle-to-aorta tunnel, consistent with inadequate tunnel size. Surgical re-exploration on post-operative day 3 confirmed narrowing of the tunnel, related to the remote restrictive ventricular septal defect. The tunnel was augmented, and the ventricular septal defect enlarged, resulting in immediate haemodynamic improvement. Recovery was uneventful, and the patient was discharged on post-operative day 14. At the latest follow-up, echocardiography showed good biventricular function, unobstructed left ventricular outflow, a competent truncal valve, and no residual shunt.
Discussion
Morphologically, the truncal valve was entirely supported by the right ventricular heart muscle, while the ventricular septal defect was in the inlet position. The persistence of a muscular fold between the truncal root and both atrioventricular valves indicates incomplete absorption of conal tissue, resulting in a double mitral and tricuspid discontinuity with the truncal valve. A similar configuration was reported in an autopsy series, with the truncal valve fully committed to the right ventricle and separated from the atrioventricular valves by a persistent ventriculo-infundibular fold and associated with a remote ventricular septal defect.Reference Crupi, Macartney and Anderson3 The mitro-truncal discontinuity is a singular feature, contrasting with the usual truncal roots overriding both ventricles, where continuity is constant. The present case could be regarded as an anatomical equivalent of a double-outlet right ventricle.
Rather than representing an absence of septation, this pattern likely reflects abnormal alignment or partial resorption of conal musculature during cardiac development.Reference Van Praagh and Van Praagh4 It emphasises the morphological variability within the conotruncal spectrum, where septation, alignment, and rotation combine differently to shape ventricular–arterial connections.
From a surgical perspective, the restrictive posterior ventricular septal defect required extensive enlargement to achieve unobstructed outflow. In such extreme conotruncal malalignment, even subtle underestimation of tunnel size or trajectory may result in left ventricular outflow tract obstruction. In this case, the left ventricular outflow tract obstruction was highly dynamic, which likely explains why it was not clearly identified on intraoperative transesophageal echocardiography. Three-dimensional imaging and modelling are essential for understanding such unique morphologies.Reference Hoogerbeets, Roest and Valverde5 We therefore emphasise the necessity for particularly careful pre-operative three-dimensional reconstruction to anticipate the spatial relationship between the ventricular septal defect, the truncal root, and the intended tunnel and to guide adequate enlargement and orientation of the intraventricular baffle.
Conclusion
Truncus arteriosus arising exclusively from the right ventricle with a restrictive inlet-type ventricular septal defect is a rare but instructive variant of the conotruncal malalignment spectrum.
Three-dimensional modelling plays a crucial role in translating complex morphologies into practical surgical strategies capable of achieving durable biventricular repair.
Financial support
This research received no specific grant.
Competing interests
None.
Ethical standard
Ethical approval was not required for this single-patient case report. The case was managed as part of routine clinical care, and no experimental procedures were performed.
