Anatomy of the major fissure: evaluation with standard and thin-section CT.

The major fissures of the right and left lungs were studied with standard computed tomography (CT) (10-mm-thick sections) and thin-section CT (2-mm-thick sections) in 50 patients. On standard CT scans, the major fissures were seen in 90%-100% of cases at each of three selected levels. They usually appeared as hypoattenuating bands and less often as lines or hyperattenuating bands. Although in most cases the major fissure was seen as a line on thin-section CT scans, this appearance was more common in the upper portion of the left major fissure than in the upper portion of the right major fissure. A "double-fissure sign" was most frequently seen at the base of the left lung; however, the sign was also seen at higher levels, with approximately equal frequency in the right and left lungs. An incomplete major fissure was noted in the right lung in 32 cases (64%) and in the left lung in 26 cases (52%). The upper and middle portions of the left major fissure were less frequently incomplete than were the comparable portions of the right major fissure. Thin-section CT provided better delineation of the major interlobar fissures than did standard CT.