Assessment of usefulness of endobronchial ultrasonography in determination of depth of tracheobronchial tumor invasion

Study objective: We assessed the usefulness of endobronchial ultrasonography in the determination of the depth of tumor invasion of the tracheobronchial wall. Methods: We performed a needle-puncture experiment on normal tissue of 45 specimens to determine the laminar structure of the tracheobronchial wall. In addition, we compared the ultrasonographic determinations of tumor invasion from 24 lung cancer cases with the histopathologic findings. Results: The cartilaginous portions of the extrapulmonary bronchi and the intrapulmonary bronchi exhibited a five-layer structure. Starting on the luminal side, the first layer (hyperechoic) was a marginal echo, the second layer (hypoechoic) was the submucosal tissue, the third layer (hyperechoic) was the marginal echo on the inner side of the bronchial cartilage, the fourth layer (hypoechoic) was bronchial cartilage, and th fifth layer (hyperechoic) was the marginal echo on the outer side of the cartilage. In the membranous portions, the first layer (hypoechoic) was a marginal echo, the second layer (hypoechoic) was smooth muscle, and the third layer (hyperechoic) corresponded to the adventita. Comparisons between the ultrasonograms and the histopathologic findings in 24 lung cancer cases revealed that depth diagnosis was the same in 23 lesions (95.8%) and was different in 1 lesion (4.2%). In the single case in which the findings were different, lymphocytic infiltration that protruded between the cartilage rings was mistakenly interpreted as tumor infiltration. Conclusions: This method allows visualization of the laminar structure of the tracheobronchial wall, which is impossible with other diagnostic imaging methods.