Diaphragm

The position of the diaphragm varies considerably with the phase of respiration, and also from one individual to the next. In children and patients who have a deep thorax, or are overweight, the level of the diaphragm is higher than in tall thin individuals. The diaphragm is also higher on films taken with the patient supine or in lateral decubitus.

Table 1. Causes of elevation of both dames of the diaphragm

Table 2. Causes of elevation of one dame of the diaphragm

Volume loss of the lung produces elevation of the diaphragm, causing a triangular shape of the dome, as though it had been pulled up by a fibrous cord. Phrenic paresis is discovered by observation of inverse mobility during fluoroscopy.

a  b

Figure 25. Kyphoscoliosis and hiatus hernia. a) Wide lower mediastinal shadow because of scoliosis. Fluid level projected over the heart shadow. b) Lateral view with contrast in the esophagus and cardiac part of the stomach. The fluid level is behind the heart, and is caused by herniation of the body of the stomach (paraoesophageal hernia).

The diaphragm has several weak points that may give rise to hernias. The most frequent is hiatal hernia through the oesophageal hiatus (Fig. 25 a, b). Parts of the stomach herniate up into the chest cavity. This condition is suspected when a frontal view shows a horizontal line (fluid level) projected over the cardiac shadow. The diagnosis is confirmed by finding an air-filled cavity behind the cardiac shadow on the lateral film. For further confirmation, a barium swallow can be done.

Figure 26. Rounded opacity in the right cardiodiaphragmatic angle. Air filled haustra (arrows) in the opacity. Morgagni hernia containing omentum and a loop of the colon.

Hernia can also arise between the diaphragmatic fibers that originate from the sternum and those originating from the ribs. These may contain omentum, and give rise to a well-defined, upwards convex opacity beside the heart. The differential diagnosis is between a cardiophrenic fat pad, which is a normal variant of no pathological significance, and a pericardial cyst. An air-bubble indicates herniated intestine in addition to omentum, and this can be verified by barium enema, or possibly a barium swallow. Anterior hernias of this type are called Morgagni hernias (Fig. 26).

Posterior hernias (Bochdalek hernias) are seen as a localized, upward convex, rounded swelling of the diaphragm, paravertebrally. The opening is situated between the fibres of the diaphragm that originate from the tendinous arch over the psoas and quadratus lumborum muscles, and the fibres originating from the ribs posteriorly. This type of hernia usually contains retroperitoneal fat, but the upper pole of the kidney, the adrenal gland, and parts of the liver can also herniate. Sometimes it may be difficult to decide whether there is in fact a hernia, or whether there is only a localized relaxation of the diaphragm, an eventration. This is a congenital condition where parts or most of the diaphragm lack musculature and only consist of a thin membranous sheet.

With rupture of the diaphragm, which most often involves the left dome, the contents of the abdomen, often the stomach, herniate up into the chest cavity. When the body and antrum of the stomach herniate, the greater curvature will lie with its convexity upwards, and obstruction with distention may occur, so that the herniated greater curvature is confused with the dome of the diaphragm, and the rupture may be overlooked. A barium swallow can confirm the diagnosis because the cardiac part of the stomach does not usually herniate, and the outline of the edge of the hernia can be seen against the stomach. ACT scan may also contribute to a correct diagnosis.

Alf Kolbenstvedt, Arnulf Skjennald and Charles B. Higgins