The problem of direct lymph drainage of the bronchopulmonary segments into the mediastinal and hilar lymph nodes

The phenomenon of skip metastases depends on the occurrence of direct metastases of non-small cell lung cancer into mediastinal lymph nodes without the involvement of hilar lymph nodes. The medical literature suggests that this prevalence ranges between 13 and 37.8% of cases. The goal of our study was to evaluate the prevalence of subpleural superficial lymphatic vessels carrying the lymph from the bronchopulmonary segments directly to the mediastinal nodes thus skipping the hilar nodes and determine whether there is a tendency towards differentiation in lymph drainage between males and females. During autopsy, 27 left and 27 right lungs were removed from 19 male and eight female cadavers. The lymphatic vessels were visualized at the mediastinal and interlobar surface of the lung by visual inspection. These vessels were then cannulated and injected with drawing ink. The first lymph node to become ink-colored via injection was dissected and histologically examined. The lymph flowed into hilar lymph nodes in 79.5% of the cases and into the mediastinal nodes in 20.5% of all the 83 vessels injected; of these 13.2% were from the right lung and in 7.2% from the left lung. The upper right lobe (5/14 vessels) and its anterior segment (3/14 vessels) were the most common source of the direct lymph drainage to the mediastinum. Vessels of 15.4% in female cadavers (4/26) and 22.8% vessels in male cadavers (13/57) traveled directly to mediastinal nodes skipping the hilar nodes. This difference was not statistically significant.