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normal appearance

Chest radiographs show the superior margin of each diaphragm as a dome-shaped interface between aerated lung and the opaque soft tissues of the abdomen. Pneumoperitoneum may reveal the thickness of the diaphragm by intraperitoneal free air silhouetting the inferior margin of the diaphragm (Fig 1). Variations in diaphragmatic contour such as scalloping and prominence of the costophrenic muscle slips are fairly frequent. On CT, the diaphragm can be visualized as a separate thin line structure only when its outer aspect is surrounded by the air in the lungs, or extraperitoneal fat, and its inner aspect is marginated by intraperitoneal or retroperitoneal fat (Fig 2). The plane of CT scan is not well suited to identifying the domes of the diaphragm, although this can be accomplished by using spiral CT and multiplanar reformations. On MR imaging, the diaphragm has the signal intensity similar to that of skeletal muscle, liver and spleen on all pulse sequences. The diaphragm is usually well visualized when it is surrounded by high signal-intensity abdominal or mediastinal fat. Given the superior contrast resolution and capability of direct multiplanar imaging, MR may prove of value in the assessment of diaphragmatic and peridiaphragmatic disease.

Fig 1: NORMAL DIAPHRAGM.

A. Posteroanterior radiograph shows well the shape and thickness of the diaphragm (big arrows) in a patient with a large pneumoperitoneum due to sigmoid perforation. Central anterior part of the diaphragm (small arrows) is also silhouetted by the air. B. Lateral radiograph: The right diaphragm (small arrows) is visible to the anterior chest wall. The left diaphragm (big arrows) is obscured anteriorly by the heart.