Analysis of the Internal Structure of Peripheral Pulmonary Lesions Using Endobronchial Ultrasonography: Histopathology
The use of miniature ultrasound probes for diagnosing peripheral pulmonary lesions has been reported previously. Hurter and Hanarath reported the successful visualization of peripheral lung lesions in 19 of 26 cases, and Goldberg et al reported that EBUS provided unique information that complement other diagnostic modalities in 18 of 25 cases (including 6 peripheral lesions and 19 hilar tumors). This is the first report to focus on the internal structure of peripheral pulmonary lesions and to correlate these findings with the histopathology of the surgical specimen.
We also evaluated the spatial resolution of EBUS using the 20-MHz probe. Spatial resolution, which refers to resolution in the direction of the propagated wave front, and is theoretically defined as follows: spatial resolution (Ax) = nA/2 (where X is the wavelength and n is an empirically derived coefficient that is 4 to 5). At a frequency of 20 MHz, the speed of sound transmission through soft tissue in vivo is 1,540 m/s, and the spatial resolution (Ax) is approximately 0.38 mm. In one case of well-differentiated adenocarcinoma, the tumor vessel was visualized by EBUS that had a diameter of 0.68 mm on histopathologic examination review contraceptive pills. This indicates that blood vessels of this caliber can be visualized using the 20-MHz probe.
We developed our classification system with the aim of distinguishing between benign and malignant diseases, identifying the type of lung cancer, and determining the degree of differentiation.
Two patients with type Ia lesions had a disease other than pneumonia. One of these patients had pulmonary metastasis from pancreatic cancer, and the other had moderately differentiated adenocarcinoma. In both cases, blood vessels and bronchi within the lesion were preserved. However, blood vessels and bronchi could not be visualized in some areas of the lesions. Because of such heterogeneity, we think that it may be necessary to further divide type Ia into subtypes depending on whether the preserved blood vessels and bronchi are distributed homogeneously or heterogeneously. Type IIIa lesions included a variety of different types of lung cancer. Three lesions contained multiple cysts, and the tumors were moderately differentiated squamous cell carcinomas in all three cases. Thus, the presence of multiple cysts is suggestive of squamous cell carcinoma.