Chylothorax after patent ductus arteriosus ligation in a dog with persistent left cranial vena cava.

This report is the first to document chylothorax after patent ductus arteriosus (PDA) ligation in a dog with a persistent left cranial vena cava (PLCVC), highlighting potential complications arising from concurrent cardiovascular anomalies. A nine-month-old female desexed Pomeranian was referred for PDA. Echocardiography confirmed a left-to-right shunt with mild left-sided cardiac changes from volume overload. At left fourth intercostal thoracotomy, an aberrant vein (5 mm) coursing over the PDA within the mediastinum was retracted proximally to facilitate PDA ligation. Retraction was released before thoracotomy closure, and the vein remained grossly unaltered. The dog represented 3 days postoperative for dyspnoea and had bilateral chylous pleural effusion. Thoracic computed tomography with intravenous contrast identified a complete PLCVC, which was continuous with the left brachiocephalic vein and inserted into the right atrium without any venous connection to the normal right cranial vena cava. A thoracostomy tube was placed, and the chylothorax resolved spontaneously. Repeat echocardiogram eight weeks postoperative showed normal laminar trans-pulmonic flow and reversal of cardiac changes. It is hypothesised that an acute increase in hydrostatic venous pressure from transient obstruction of the PLCVC during intraoperative retraction impeded thoracic duct emptying into the venous system. This in turn may have caused chyle leakage through afferent lymphatics with chylothorax. It is unlikely PLCVC thrombosis was a cause given chylothorax was transient and the PLCVC was normal on computed tomography (CT); nor iatrogenic thoracic duct damage given the surgical approach was left-sided and the duct courses through the right.