BACKGROUND: Pleural anthracosis (PA) appears as superficial black discoloration or scattered focal black spots on the surface of the pleura. Few studies have investigated the relationship between PA and changes in pleural structure. The aim of this study is to perform a detailed morphometric characterization of pleura in patients with different degrees of PA at both macroscopic and microscopic levels. METHODS: Preoperative, intraoperative, and postoperative data were collected for all patients. Lung tissue (far away from the tumor) was obtained from patients with pulmonary nodules who required surgical treatment. According to different degrees of PA, the pleura were classified into four degrees. In addition to using grade data, we also calculated the ratio of PA. Slices were stained with Hematoxylin-eosin (HE) and D2-40 to obtain the results of pleural structures. RESULTS: We prospectively evaluated 48 subjects between March 12, 2024 and August 17, 2024. There was no significant difference in PA levels between people living in urban and rural areas (P=0.32). However, the proportion of rural population in patients with PA level 3 was 2.6 times that of urban population. Patients who were male demonstrated significantly higher level of PA (P=0.01). With the increase of the smoking index, the patients with PA levels increased. PA levels increased with age (P=0.02). With the decrease of the FEV1/FVC, the patients with PA levels also increased (P=0.03), and the patients with PA ratio also increased (P=0.007). With the continuous improvement of PA ratio and upgrading of PA level, the pleural thickness continued to decrease(R=-0.75, P <
0.01), the number of subpleural lymphatic vessels (SLVs) increased (P<
0.01), cross-sectional area of SLVs increased (P<
0.01), length of SLVs increased (P<
0.01), and SLVs density increased (P<
0.01). CONCLUSIONS: The current study demonstrated that the proportion of PA is negatively correlated with pleural thickness and positively correlated with the number of SLVs, cross-sectional area of SLVs, length of SLVs, and SLVs density. This study provides us with new evidence for the subpleural lymphatic metastasis pathways.