Re-evaluating the anatomy of iatrogenic chylothorax - lymphangiography imaging of the transverse branch of the thoracic duct.

Iatrogenic chylothorax is generally attributed to injury to the main thoracic duct and its tributaries. However, the current anatomic classification of the thoracic duct primarily focuses on the morphology and outlet of the main duct. Using thoracic ductography, this study aimed to identify the presence of a large-caliber transverse branch of the thoracic duct and to evaluate its role as a cause of chylothorax. This retrospective study included 25 patients who underwent thoracic ductography for chylous leakage between May 2020 and May 2025. Thoracic duct branching patterns and leakage sites were correlated with surgical history, and clinical outcomes following lymphatic embolization were analyzed. A single thoracic duct was identified in 52% of patients, whereas 48% had at least one large-caliber transverse branch crossing the mediastinum at the carinal or upper tracheal level. All patients (n = 12) who developed chylothorax after surgery at the mediastinum had a transverse branch, which was confirmed as the source of lymphatic leakage in 100% of these cases. In contrast, leaks following surgery at the left mediastinal border originated from the main thoracic duct. There was statistically significant lower pretreatment daily drainage volume in patients with transverse branch injury than in those with main duct injury (p = 0.048). Large-caliber transverse branches of the thoracic duct may be more prevalent than previously recognized and represent a frequent cause of iatrogenic chylothorax when injured. Improved awareness of this anatomic variant may generate hypotheses for future preventive strategies during mediastinal procedures.