Diaphragmatic eventration ( Box 19-1 ) is an anomaly that can be defined as a permanent elevation of part or of an entire hemidiaphragm without loss in the continuity in the pleuroperitoneal layers. It is characterized by normal peripheral muscular insertions of the diaphragm but marked decrease in muscular fibers in the eventrated part, which has the appearance of a thin, translucent membrane. It is generally thought that diaphragmatic eventration is a congenital anomaly resulting from an incomplete migration of myoblasts during the fourth week of embryologic development. It has a marked left-sided predominance and does not generally result in paradoxical diaphragmatic motion.
Congenital in origin
Can be total or partial (anterior, posterolateral, medial)
Characterized by normal muscular insertions and thin membranous abnormal eventrated area
Nearly always acquired
Characterized by atrophic muscle
Can occur with or without phrenic nerve involvement
Involves loss of continuity of one or more of the layers constituting the diaphragm
Diaphragmatic paralysis is usually an acquired disorder in which the diaphragm, even if somewhat atrophic, is still muscular. It may manifest in childhood or adulthood and can be associated with phrenic nerve involvement. In many cases, especially in the adult, the exact cause of diaphragmatic paralysis will remain unexplained despite extensive investigation and follow-up.
Diaphragmatic herniation, with or without a hernia sac, involves the loss of continuity in one or more of the layers constituting the diaphragm.
The mature diaphragm is a dome-shaped muscle that is anchored to the bony structures of the thorax and is considered the most important inspiratory muscle. When it contracts, the dome moves inferiorly and becomes flattened, thus decreasing the intrathoracic pressure and allowing air to be taken into the lungs. The muscular parts that originate from the lower six ribs bilaterally, the posterior aspect of the xiphoid, and the external and internal arcuate ligaments unite at the central tendon. As such, the diaphragm should be viewed as a single muscular unit with two halves.
The diaphragm receives its motor supply through the phrenic nerves, which are formed at the lateral border of the anterior scalenus muscles, chiefly from the C4 nerve roots but with contributions from the C3 and C5 nerve roots. From there, the phrenic nerves enter the superior mediastinum between the ipsilateral subclavian artery and innominate vein and pass anterior to the pulmonary hilum along the pericardium. It is at that level that they are most susceptible to surgical injury, which may result in complete paralysis and eventual muscular atrophy of the corresponding half of the diaphragm. The right phrenic nerve reaches the diaphragm lateral to the inferior vena cava, and the left phrenic nerve joins the diaphragm lateral to the left border of the heart. They both divide into several terminal branches whose anatomy delineates safe areas in the diaphragm where incisions can be made without creating loss of diaphragmatic function.
Arterial supply to the diaphragm is through the pericardiophrenic and intercostal arteries; venous drainage is through the right and left inferior phrenic veins, which drain medially into the inferior vena cava.
In the adult population, symptoms related to an elevated diaphragm are predominantly respiratory, mainly dyspnea, cough, and retrosternal discomfort. The diagnosis can usually be made on standard posteroanterior chest films ( Fig. 19-1A ) which show a diaphragm in higher position than normal, forming a round, unbroken line arching from the mediastinum to the costal arch laterally. Often the mediastinum will be shifted toward the unaffected side. If there is diaphragmatic paralysis, paradoxical motion can be observed on fluoroscopic examination. Although seldom done, diagnostic pneumoperitoneum might be useful to distinguish between an elevated diaphragm and frank herniation (see Fig. 19-1B ). Computed tomography (CT) scanning and ultrasonography are not particularly helpful in differentiating between an elevated diaphragm and true herniation, but magnetic resonance imaging (MRI) allows one to acquire high-quality images in several planes, which provides a better evaluation of the entire diaphragm.