CT visualization of the major pulmonary fissures: value of 25 degrees cranially tilted axial scans

CT visualization of the major (oblique) pulmonary fissures is often hampered by partial volume effects of adjacent lung parenchyma. We attempted to improve visualization of the fissures by using 25 degrees cranially tilted axial scans. An initial in vitro study also was performed.

Both conventional and 25 degrees tilted axial CT scans were obtained in 40 adult patients. After scans with 2-mm collimation were obtained at 1 cm and 6 cm below the carina, the gantry was tilted 25 degrees cranially to be perpendicular to the plane of the major fissures, and scans with 2-, 5-, and 10-mm collimation were obtained at the same two levels. The appearance of the fissures was classified as linear opacity, band-like opacity, or avascular area for each lung at each level.

On 2-mm conventional axial scans, the major fissures were seen as linear opacities in three to 23 patients (8-58%), as band-like opacities in 13-31 (32-78%), and as avascular areas in one to seven (2-18%). (Ranges indicate lowest and highest values when data for the two levels in the two lungs are grouped separately.) On 2-mm tilted scans, the ranges were 32-38 patients (80-95%), one to eight (2-20%), and zero to one (0-2%), respectively. The 2-mm tilted scans were significantly superior to the 2-mm conventional axial scans for showing the fissures (p < .01). Direct visualization as linear or band-like opacities was possible even on 10-mm tilted scans in 15-32 cases (38-80%).

Our results show that visualization of the major fissure is improved when tilted CT scans rather than conventional axial scans are used.