Radiology Quiz 91043 | Radiopaedia.org

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On the coronal CT image, the horizontal fissure appears sharper than the oblique fissure. Can you explain why?

The horizontal fissure is closer to perpendicular to the reformat plane. Volume averaging across the 3mm slice width produces blurring. The degree of blurring depends on slice width and orientation of the interface which determine how much the position of the fissure changes across the slice.

The orientation of the fissures explains why the boundaries of the consolidated right middle lobe are not visible on the PA CXR: they are not tangential to the X-ray beam. Lateral CXR would clearly demonstrate the sharply outlined RML, but they are not routinely performed.