Discussion:
The clinical findings associated with the occurrence of a direct fistula between the right pulmonary artery and the left atrium. Furthermore, it was vary from mild to extreme cyanosis with clubbing and exertional dyspnea. These patients with above-mentioned symptoms may experience increased blood viscosity, due to the high hemoglobin levels caused by chronic hypoxia. In addition to this, bypassing of the pulmonary vascular bed, the blood filtering function of the lung is lost, which leads to complications such as emboli, brain abscesses, cerebrovascular events and other systemic embolic events (6), one of the rare complications that may occur is fistula rupture.
De Silva et al. (8) described three patterns of fistula between the pulmonary artery and the left atrium depending on where the fistula opened on the left atrium and its relationship with the branches of the right pulmonary artery and pulmonary veins.
Type 1 : The right pulmonary artery and its branches and the pulmonary veins are normal but there is a fistula between the right pulmonary artery and the
left atrium.
Type 2: The lower right pulmonary vein is absent and the lower branch of the right pulmonary artery drains directly to the left atrium where the lower right pulmonary vein usually opens into the atrium.
Type 3: Pulmonary veins drain to an abnormal duct between the left atrium and the right pulmonary artery (a fistula).
Later, the fourth type was added by Oahu et al. 1979 (9). This pattern is similar to the second pattern, where the right pulmonary veins enter the fistula that resembles an aneurysm and connects the lower branch of the right pulmonary vein with the left atrium Fig 4)
In the case we present here, the right pulmonary artery which supplies the middle pulmonary lobe drains directly into the left atrium through a large fistula taking the form of an aneurysm where the upper right pulmonary vein usually drains into the atrium. This case doesn’t fall under any particular classification but is somewhat similar to Type-2. (Fig. 5)
There is no definite fetal origin or explanation for the fistula between the right pulmonary artery and the left atrium; some theories suggest the presence of a connection between the right pulmonary artery and the primary pulmonary vein. At a later stage, the primary pulmonary vein merges into the atrial wall resulting in the fistula (10, 11). Atrial septal defect is the most common cardiac defect associated with the fistula between the right pulmonary artery and the left atrium, the absence of the lower pulmonary lobe and right bronchial atresia are the most common pulmonary malformations (12, 13).
In this case, we found only an ASD of a 6.5 mm diameter that was closed at the surgical repair of the fistula. When diagnosed, this condition should be treated with selective surgery to close the fistula (14). This can be achieved either through outside ligation without cardiopulmonary bypass, or through open heart surgery using a patch which was performed in the case we presented. The surgical approach was selected due the presence of the ASD and the size of the fistula and the thinness of its wall causing concern of rupture. Many other cases were mentioned in the medical literature regarding the closure of the fistula using cardiac catheterization which is an effective alternative to surgical closure.