CT of the bronchus intermedius: frequency and cause of a nodule in the posterior wall on normal scans.

OBJECTIVE: A focal nodule in the posterior wall of the bronchus intermedius is occasionally observed on normal CT scans. The purpose of this study was to determine the frequency and the anatomic cause of this finding.
MATERIALS AND METHODS: We prospectively analyzed helical CT scans (10-mm collimation and 10-mm/sec table speed) for evaluating nodules in the posterior wall of the bronchus intermedius from 280 consecutive subjects. A focal round elevation in the posterior wall of the bronchus intermedius was considered a nodule. Frequency of visualization of the nodule was recorded. In patients showing such nodularity, additional enhanced CT scans with thinner slices (5-mm collimation and 5-mm/sec table speed) were obtained to elucidate the nature of the nodularity.
RESULTS: Nodularity in the posterior wall of the bronchus intermedius was observed in 14/280 total subjects (5%) on 10-mm collimation CT scans. On thin-section CT scans, the nodularity was caused by a branch of the vein from the posterior segment of the right upper lobe (10/14, 71%) or by a branch of the vein from the superior segment of the right lower lobe (4/14, 29%). The vein from the upper lobe that caused nodularity in the posterior wall of the bronchus intermedius drained into either the inferior pulmonary vein (7/10) or the superior pulmonary vein (3/10). In all patients whose nodularity was caused by the vein from the superior segment of the right lower lobe, the vein drained into the inferior pulmonary vein.
CONCLUSION: Focal nodularity in the posterior wall of the bronchus intermedius was caused by the draining pulmonary vein, and it was observed in 5% of normal subjects. This nodularity should be differentiated from uniform or lobular thickening associated with abnormality in the bronchus intermedius.