Anterior diaphragm: variations in the CT appearance.

The anterior portion of the diaphragm has three typical appearances on computed tomographic (CT) scans, depending on the cephalocaudal relation of the xiphoid to the central tendon of the diaphragm. The anterior diaphragm most often appears as a relatively smooth or slightly undulating soft-tissue curve, concave posteriorly and continuous across the midline with the lateral diaphragmatic arcs. In the next most frequent CT appearance, the diaphragmatic line is discontinuous in the midline. On each of these images, the muscular line diverges rather than converges as it approaches the anterior chest wall. Less commonly, the anterior portions of the diaphragm are imaged on CT not as a thin line but instead as a broad band with irregular, ill-defined, or angular margins. Occasionally, the anterior diaphragmatic muscle is not identified on CT because the muscle fibers are inseparable from adjacent structures, or are extremely short or even absent. An understanding of these anatomic variations permits the correct diagnosis of Morgagni hernias and explains previously described variants of plain radiographic configurations of pneumoperitoneum.