The bronchus sign on CT represents the presence of a bronchus leading directly to a peripheral pulmonary lesion. We investigated the value of this sign in predicting the results of transbronchial biopsy and brushing in 33 consecutive cases of proved peripheral bronchogenic carcinoma studied with thin-slice CT (2-mm-thick sections). The bronchus sign was seen on CT in 22 patients and was absent in 11. Transbronchial biopsy and brushing showed peripheral carcinoma in 13 (59%) of 22 patients in whom the bronchus sign was seen on CT and in only two (18%) of 11 patients in whom it was not seen. The difference is statistically significant (Fisher's exact test, p = .029). When analyzed by the order of involved bronchus, a 90% success rate of transbronchial biopsy and brushing was found in patients in whom the bronchus sign was seen at a fourthorder bronchus (p = .01). This compared with a success of 33% when the bronchus sign was seen at fifth-, sixth-, or seventh-order branches. Our results suggest that the bronchus sign at a fourth-order bronchus is valuable in predicting the success of transbronchial biopsy and brushing. The presence of the sign on CT may be useful in determining if the workup should include transbronchial biopsy and brushing or transthoracic needle aspiration in patients with peripheral lung lesions.

Our study shows that air-space lung metastasis from GI carcinomas is uncommon but not rare. On CT as well as microscopically, differential diagnosis between air-space metastasis and bronchioloalveolar carcinoma may be impossible.

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To investigate the value of computed tomography (CT) for depicting the relationship between carcinomatous solitary pulmonary nodules and the bronchial tree and predicting the results of various bronchoscopic biopsy techniques, the authors retrospectively reviewed CT scans from 27 consecutive patients with solitary pulmonary nodules associated with a positive bronchus sign. All patients underwent bronchoscopy and transbronchial biopsy. Macroscopic demonstration of the tumor-bronchi relationship was obtained in 18 patients. Five basic types of tumor-bronchus relationships were identified with CT: (a) bronchus cut off by the tumor, (b) bronchus contained within the tumor, (c) bronchus compressed by the tumor, (d) thickening and smooth narrowing of the bronchus leading to the tumor, and (e) thickening and irregular narrowing of the bronchus leading to the tumor. The diagnostic yield of transbronchial forceps biopsy and bronchial brushing was significantly higher in nodules characterized by a cut-off or contained bronchus. Transbronchial needle aspiration was performed in six patients, and results were positive in five, all of whom had a compressed or thickened bronchus. These results confirm that yield of transbronchial biopsy is determined by the type of tumor-bronchus relationship and the biopsy technique performed.

Our series demonstrates that focal BAC may progress to diffuse pulmonary involvement by bronchogenic spread. The presence of a large area of ground-glass attenuation associated with a nodular BAC might be the CT sign of an aggressive biologic behavior. In these cases there is a high likelihood for diffuse disease to develop from bronchogenic spread.