Study objectives: Previously, we reported that small pulmonary adenocarcinomas (tumor diameter 20 mm or less) could be classified according to attenuation on thin-section CT (TS-CT) images as either 'air-containing type' or 'solid-density type' (Lung Cancer 2002;36:49-57). Air-containing type was defined as having areas where TOM (tumor opacity on mediastinal window images) was half or less than half the size of those noted on lung window images. Solid-density type was defined as having areas where TOM was greater than half the size of those noted on lung window images. Our findings indicated that there was no microscopic evidence of metastasis with air-type nor any relapses nor deaths, after resection. By contrast, patients with solid-density types demonstrated a poor prognosis. At this time, the histopathological characteristics of areas of TOM have not been fully investigated. The purpose of this study is to define the correlations between TOM and histopathological findings of small lung adenocarcinomas.
Method: We retrospectively reviewed the records and CT scans of 134 patients, who had undergone surgical resection of peripheral adenocarcninomas. All tumor diameters were 20 mm or less in size. All 134 patients had undergone TS-CT prior to surgery. TS-CT Images were acquired by a model X-Vigor/Real or an Aquillion CT scanner (Toshiba Medical Systems). Thin-section images of tumors were obtained at 135 kVp at 250 mAs with 1-2 mm section thicknesses. All images were photographed using mediastinal (level, 40 HU; width, 400 HU) and lung (level, -600 HU; width, 1600 HU) window settings. We researched the histopathological components corresponding to the areas of TOM.
Results: Areas of TOM demonstrated five possible histopathological findings; (1) collapse (C), (2) collapse with bronchioloalveolarcell carcinoma (CwB), (3) adenocarcinoma cells (Cells), (4) fibroblasts (F), and (5) mucus (M). Areas of TOM in air-containing type adenocarcinomas (52 cases) demonstrated predominantly C and/or CwB (C/CwB type, 44 cases). Areas of TOM in solid-density type adenocarcinomas (82 cases), in comparison, demonstrated predominantly Cells and/or Cells/F (Cell/F type, 67 cases). We noted a statistically significant difference between the histopathological findings of the areas of TOM of air-containing type and solid-density type tumors. The 39 cases of Cell/F type adenocarcinomas revealed microscopic evidence of metastasis (pleural involvement, vascular invasion, lymphatic permeation, or lymphnode metastasis). Whereas, no C/CwB type adenocarcinomas cases revealed any microscopic metastasis. The prognosis of C/CwB type after resection is better than for Cell/F type.
Conclusion: We found that air-containing type adenocarcinomas demonstrated C/CwB type, and that solid-density type adenocarcinomas demonstrated Cell/F type. The histopathological findings of small pulmonary adenocarcinomas could be classified into three groups: C/CwB type, Cell/F type and M type. The prognosis of C/CwB type is better than for Cell/F type. Our results indicate that there are clear correlations between the areas of TOM and the histopathological components of small pulmonary adenocarcinomas. Therefore TS-CT findings are a useful aid in determining the best surgical methods.
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