An unusual venous anomaly: direct drainage of an accessory bronchial vein into the left atrium: a case report

Introduction: The bronchial circulation primarily supplies oxygenated blood to the airways, pulmonary vessels, and other supporting structures of the lungs. Normally, this blood drains into the azygos system on the right or, on the left, through the hemiazygos or accessory hemiazygos veins, ultimately returning to the right atrium. Anatomical and imaging studies have demonstrated that deeper bronchial veins can form direct connections with pulmonary veins, which carry oxygenated blood to the left atrium. These rare connections create a small physiologic right-to-left shunt, allowing a minor fraction of bronchial venous blood to bypass the usual pulmonary circulation and mix with oxygen-rich blood in the left heart.

Case reports and anatomical studies, including cadaveric dissections, have documented similar anomalous venous pathways, highlighting the heterogeneity of pulmonary and bronchial venous anatomy. For instance, accessory pulmonary veins and partial anomalous pulmonary venous connections (PAPVC) have been reported both in living patients and during anatomical studies, emphasizing that venous drainage patterns can vary widely and occasionally create direct drainage routes into the left atrium. Recognition of these variants is clinically relevant for imaging interpretation, surgical planning, and understanding potential sources of paradoxical embolism or hypoxemia.

Methods: During a routine anatomy cadaver lab dissection of the thoracic cavity, the heart and lungs were carefully examined and exposed. The bronchial venous system was traced from the peri bronchial plexus to its site of cardiac termination. Vascular structures were identified based on anatomical landmarks and vessel caliber, and the anomalous venous connection was documented through direct visualization and photographic recording and faculty review.

Results: An accessory bronchial vein opening was identified at the termination site directly into the left atrium, bypassing the typical azygos/hemiazygos venous pathways. The anomalous vessel was distinct from the pulmonary veins based on its smaller caliber and course. The pulmonary venous anatomy otherwise appeared typical, with normally positioned pulmonary veins draining into the left atrium. No additional major thoracic vascular anomalies or congenital cardiac defects were observed in the specimen.

Discussion: This case highlights a variant of bronchial venous drainage identified in a cadaveric specimen. The presence of a discrete bronchial venous ostium into the left atrium is rarely documented and expands the recognized spectrum of thoracic venous variability. Prior reports of PAPVC highlight the heterogeneity of pulmonary and systemic venous anatomy, and this case provides direct anatomical confirmation of an uncommon systemic pulmonary venous connection. Recognition of such anomalies is important for anatomical education, radiologic interpretation, and procedural planning in thoracic and cardiovascular interventions.