Accessory fissures of the upper lobe of the left lung: CT and plain film appearance

The purpose of this study was to assess CT and chest radiographic features of accessory fissures of the upper lobe of the left lung. Eighteen accessory fissures of the upper lobe of the left lung were identified on CT scans of 17 adult patients. The collimation was 10 mm in 12 patients and 8 mm in five patients. Additional, thinner sections (1.5-5.0 mm) were available for 12 patients. The segments separated by each fissure were identified by means of the individual segmental bronchi and vessels. Available chest radiographs were correlated with CT studies in 12 patients. The fissures separated the anterior segment of the left upper lobe from the superior segment of the lingula (left minor fissure) in 13 cases (72%), the superior from the inferior segment of the lingula in three cases (17%), and the apico-posterior from the anterior segment in two cases (11%). Ten (56%) of the 18 fissures could be seen only on thin sections. Eleven (61%) of the accessory fissures were incomplete. The fissures were classified into four types: convex laterally (n = 8), convex medially (n = 2), anteromedial (n = 5), and transverse (n = 3). On posteroanterior chest radiographs, the accessory fissure was evident in 10 (83%) of 12 patients. CT studies showed that nine of the 10 fissures seen on radiographs represented a left minor fissure, and the remaining fissure separated the two segments of the lingula. Accessory fissures of the upper lobe of the left lung, as shown by CT, can separate any two contiguous segments, are frequently incomplete, and occur in four different configurations. The left minor fissure is the most common of these fissures and the most frequently seen on chest radiographs. The ability to recognize accessory fissures of the left upper lobe should help in the segmental and topographic localization of pulmonary lesions.