Anatomy of the minor fissure: evaluation with thin-section CT.

The minor fissure was studied with thin computed tomographic (CT) sections in 40 patients. It was absent in eight (20%) and seen in 32 (80%) patients; of these 32 the fissure was complete in seven (22%), incomplete in 23 (72%), and of indeterminate completeness in two (6%). Appearance of the minor fissure on CT scans can be categorized into two major configurations, which are determined by variation in contour of the middle lobe upper surface. The location of the highest point along this surface is either medial (type I configuration) or lateral (type II configuration). The lowest tributary of the vein draining the anterior segment of the upper lobe was seen in 75% of the patients. This vessel was a reliable landmark in delineating boundaries between upper and middle lobes, even when the fissure was radiologically incomplete or absent. In the authors' experience, familiarity with these configurations of the minor fissure has been useful in localization of a lesion in a lobe or determination of its possible extension beyond the fissure into the neighboring lobe.