Discussion

Right pulmonary artery-to-left atrium fistula is a rare congenital anomaly initially reported by Friedlich et alReference Fredlich, Bing and Blount ¹ and surgically corrected for the first time by Blalock in 1950. Subsequently, more than 100 cases have been reported, managed either surgicallyReference Zeebregts, Nijved, Lam, Van Oart and Lacquet ² or by transcatheter techniques using coils or one of the devices from the Amplatzer family.Reference Francis, Sirakumar and Kumar ³ To the best of our knowledge, this is the first report of spontaneous closure of such a fistula.

This anomaly can present at different ages depending on the size of the fistula, which in turn determines the magnitude of the shunt. Those presenting late usually have good prognosis compared with those who present in infancy because they have a much smaller shunt.Reference Ali, Nainar, Kona and Kotturathu ⁴ The clinical presentation is due to right-to-left shunt and is characterised by shortness of breath, easy fatigability, cyanosis, and clubbing.Reference Fredlich, Bing and Blount ¹ In the case of our patient, the shunt was minimal, and hence he remained completely asymptomatic. As the pulmonary artery directly communicates with the left atrium, some patients may present with paradoxical embolism or with cerebral abscesses.Reference Ohara, Ito and Kohguchi ⁵ Therefore, this anomaly should be considered in children who present with unexplained cerebral or systemic embolisation.

Right pulmonary artery-to-left atrium communication can mimic a pulmonary arteriovenous fistula in terms of its clinical presentation as both present with extracardiac right-to-left shunt in the presence of normal right ventricular pressure; two-dimensional echocardiography with colour Doppler and CT angiography can help differentiate the two.

On the basis of the presence or absence of the aneurysm and the drainage of the pulmonary veins, the right pulmonary artery-to-left atrium fistula has been classified angiographically into four types.Reference Ohara, Ito and Kohguchi ⁵ Type 1 is characterised by a normally branching right pulmonary artery with normal pulmonary venous return and a fistulous channel connecting the right pulmonary artery to the left atrium. In Type 2, the lower lobe branch of the right pulmonary artery communicates with an aneurysmally dilated right inferior pulmonary vein. In Type 3, all pulmonary veins drain into the aneurysmal pouch between the right pulmonary artery and the left atrium, whereas Type 4 has a very proximal right pulmonary arteriovenous fistula, which joins the left atrium via the right pulmonary veins. On the basis of this classification, our patient demonstrated a Type 1 fistula.

The diagnosis of right pulmonary artery–left atrium fistula is usually established using two-dimensional echocardiography and colour Doppler as in our patient. Contrast echocardiography is helpful in confirming the diagnosis in adults where colour flow imaging is suboptimal. A CT pulmonary angiogram is considered as the gold standard for establishing the diagnosis.Reference Sheikhzadeh, Hakim, Ghabusi, Ataii and Tarbiat ⁶ In our patient, the diagnosis was unequivocally confirmed in the neonatal period on two-dimensional echocardiography, the shunt was small, and no intervention was contemplated. Hence, we did not feel it was necessary to subject the child to CT pulmonary angiography as it involves exposure to radiation and injection of radiographic contrast.

Early repair is recommended in patients with right pulmonary artery–left atrium fistula to avoid complications, particularly systemic embolism, infective endocarditis, cerebral abscess, and rupture of aneurysmal communications. Surgical ligation of the fistula was the preferred treatment for this condition until recently. Of late, transcatheter coil occlusion and device closure have been performed successfully. As our patient had no symptoms and a small right-to-left shunt, it was decided not to intervene early. Fortunately, the fistula closed spontaneously and the child was saved from any form of intervention.

Although the exact mechanism of spontaneous closure remains unknown, it is likely that a fall in pulmonary vascular resistance in the postnatal period resulted in a significant drop in the pressure head with reduced flow through the restricted fistulous orifice. The flow eventually fell to a critical level, allowing the endothelium to grow and bridge the gap. The second mechanism that can be contemplated is that the duct-like tissue forming the fistulous tract constricted because of increased oxygenation in the postnatal period after the lungs became operational.