Right to left patent ductus arteriosus, acute bronchointerstitial pneumonia, pulmonary hypertension and cor pulmonale in a foal

Summary Patent ductus arteriosus (PDA) is a rare congenital cardiac defect in foals causing left to right shunting from the aorta to pulmonary artery. In extremely rare conditions, complications with pulmonary hypertension can result in right to left shunting (Eisenmenger's physiology); however, reversed or right to left shunting has not yet been precisely described in PDA‐affected equids. This report describes a unique and unusual case of right to left PDA associated with acute respiratory distress syndrome in a 20‐day‐old male foal. A holosystolic murmur over the tricuspid valve area and adventitious pulmonary sounds respectively on cardiac and thoracic auscultations, caudodorsally interstitial and bronchointerstitial pulmonary opacities on thoracic radiography, right atrial and ventricular dilatations with paradoxical ventricular septal motion, increased ratio of pulmonary artery internal diameter to the aorta and tricuspid valve regurgitation on echocardiography were detected. Post‐mortem and histopathological examinations revealed consolidated, dark red and diffusely enlarged lungs with granular appearance, marked enlargement of the right atrium and ventricle, pulmonary artery thickening and enlargement, patency of the ductus arteriosus, hyaline membrane formation, type II pneumocyte proliferation, hypertrophy and thickening of the pulmonary arteries medial layers and right ventricular myocardial cells distortion and hypertrophy. The findings suggest a right to left shunting through the persistent patency of the ductus arteriosus, pulmonary hypertension and cor pulmonale. We proposed pulmonary hypertension associated with bronchointerstitial pneumonia as a cause of this unusual case of PDA with reversed shunt direction.