Discussion

Hemitruncus is best defined as a condition in which one branch of the pulmonary artery originates from the ascending aorta and the other branch of the pulmonary artery courses normally from the main pulmonary artery, which arises from the right ventricle.

It has been suggested that the anomalous origin of one pulmonary artery from the ascending aorta should be suspected when unexplained pulmonary hypertension is diagnosed and no structural intracardiac defects are observed.Reference Santos and Azevedo ³ It has been emphasised that even the lung supplied by the pulmonary artery arising from the right ventricle has high pressure and histopathological changes of pulmonary hypertension.Reference Santos and Azevedo ^{3 –} Reference Fontana, Spach and Effman ⁵ A crossover mechanism of a circulating vasoconstrictor or neurogenic pulmonary hypertensionReference Penkoske, Castaneda, Fyler and Van Praagh ^{6 ,} Reference Griffiths, Levine and Anderson ⁷ from the anomalously supplied lung to the normally supplied lung was given as a possible cause of pulmonary vascular changes in the unaffected lung. More so, increased pulmonary blood flow – as the contralateral lung receives all the cardiac output in addition to the occasional blood flow of the associated anomalies, such as ductus arteriosus, aortopulmonary window, and interatrial and interventricular septal defects – has also been suggested as a critical factor in the development of pulmonary vascular disease in the normally supplied lung because patients with Tetralogy of Fallot and hemitruncus show unilateral changes only on the affected side.Reference Fong, Anderso and Siewers ⁴ The pulmonary vascular changes have been found at a very young age. Some studies found no significant differences between the lungs on biopsy,Reference Griffiths, Levine and Anderson ^{7 ,} Reference Porter, Canent, Spach and Baylin ⁸ whereas other studies showed more advanced changes on the non-affected side.Reference Yamaki, Suzuki and Ishizawa ^{9 ,} Reference Weintraub, Fabian and Adams ¹⁰

Our case is unique as hemitruncus in an adult is rarely reported.Reference Sechtem, Jungehülsing and de Vivie ¹¹ Another unique feature, which to the best of our knowledge, has not been reported till date is entirely normal pressures in the right ventricle and normally connected right pulmonary artery.

In a multi-centre study about the pathogenesis and associated anomalies in 108 cases, Kutche et alReference Kutsche and Van Mierop ¹ reported that the incidence of the anomalous origin of the right pulmonary artery is not only more frequent, but is also pathogenically unrelated to the anomalous origin of the left pulmonary artery. The anomalous origin of the left pulmonary artery from the ascending aorta is an anomaly of the aortic arch, because, in all cases studied, Tetralogy of Fallot or anomalies of the aortic arch, or both, were associated. In our case also, anomalous left pulmonary artery was associated with right-sided aortic arch but without any other associated intracardiac structural heart defect.

Our case is unique because to the best of our knowledge origin of the left pulmonary artery from the ascending aorta without intracardiac structural heart defect in an adult has never been reported in the literature. Such an anomaly is usually associated with other structural defects of the heart and increased pressure in the normally connected pulmonary artery. In our case, the only associated anomaly was the right-sided aortic arch. The pulmonary artery pressure in the normally connected pulmonary artery was normal. The case was clinically suspected because of left ventricular hypertrophy on electrocardiogram with enlargement of the pulmonary artery on the chest X-ray, which was actually a silhouette of the anomalous left pulmonary artery, without increased right ventricular systolic pressure or shunt lesion on echocardiography.