Epidemiological studies of accessory cardiac bronchus and a new variant.

Accessory cardiac bronchus (ACB) is a rare tracheobronchial branching abnormality which originates from the medial wall of the intermediate or main bronchus and is directed to the heart. Three types of ACB have been recognized: type (a) is similar to a short diverticulum, type (b) is a long bronchus ventilating a small undeveloped lobule, and type (c) is an intermediate type with a long diverticulum but no bronchial or alveolar arborization. Herein, we report 40 consecutive cases of ACB detected in 10,287 routine spiral computed tomography (CT) examinations of the chest. The frequency of the anomaly was 0.39%. The study included 17 females and 23 males (female to male ratio 1:1.35). A total of 24 cases belonged to type (a), 14 cases were type (b), and 2 cases were type (c). The mean largest diameter of ACB was 7.9 (range, 4.0 to 12.0) mm and the mean length was 7.5 (range, 3.0 to 18.0) mm. The mean ratio of the largest diameter to length was 1.1, the ratio for (a) was often greater than 1, and the ratios of (b) and (c) were often less than 1. The ACB originated from the intermediate bronchus in 29 cases, which accounted for the largest proportion. The ACB originated from the basal bronchus of the lower lobe in 11 cases (6 cases from the right lower lobe and 5 from the left), which has never been reported before and may be a new variant.