The term “diaphragm” originates from the Greek words dia (in between) and phragma (fence). This reflects the diaphragm’s anatomical role in separating the torso into the thoracic and abdominal cavities. Functionally, the diaphragm is the principal muscle of respiration.

To review, embryologic development of the diaphragm is a process that occurs between the fourth and eighth week of gestation.¹ The organ is formed by the fusion of tissues from four different sources. First, the septum transversum, a mass of mesodermal tissue located between the primitive heart tube and liver, gives rise to the central tendon of the diaphragm. This process produces two spaces (pleuroperitoneal canals) for the development of the lungs. As the lungs develop, they form bilateral folds, which fuse with the septum transversum to form bilateral pleuroperitoneal membranes.¹ Myoblasts penetrate the pleuroperitoneal membranes to form the muscular part of the diaphragm. Also, the dorsal mesentery of the esophagus becomes invaded by myoblasts and ultimately forms the crura of the adult diaphragm. Finally, the body wall contributes portions to the peripheral diaphragm. During the fourth week of fetal development, the primitive diaphragm becomes innervated by the phrenic nerves (C3, C4, and C5). By week 8, the diaphragm descends as a result of displacement by the rapidly growing neural tube. A delay or alteration in the embryologic structuring can result in a diaphragmatic hernia or congenital eventration.

Anatomically, the diaphragm is skeletal muscle composed of two distinct parts—the costal and crural aspects.¹ The costal muscle, located peripherally, is thin and causes downward displacement of the diaphragm. The costal part of the diaphragm allows the diaphragm to flatten and the lower ribs to lift, resulting in inspiration. The crural aspect of the diaphragm is thicker, supports the heart, and plays a lesser role in respiration. Both groups are innervated by the phrenic nerve. The pericardiacophrenic artery, musculophrenic artery, and superior phrenic arteries extend to the superior side of the diaphragm while the caudal area is supplied by the inferior phrenic arteries. The inferior phrenic arteries branch off the aortal hiatus directly from the aorta or from the celiac trunk. Direct branches of the aorta also vascularize the dorsal part of the diaphragm.

In the adult, the diaphragm is the primary muscle of inspiration and is responsible for 75 to 80 percent of the air brought into the lungs during quiet breathing.² During light inspiration, the 2 domes of the diaphragm flatten to some extent, whereas the central tendon remains almost stationary. The diaphragm typically descends 1 to 2 cm during quiet breathing but may lower as much as 6 to 7 cm with forced inspiration. The peripheral parts of the diaphragm unwrap from the lateral walls of the chest by contraction during deep breathing. Both movements widen the costodiaphragmatic recesses, which the lungs subsequently expand to partially fill.

There are four hernias we will consider (Fig. 22-1): two congenital hernias (Bochdalek and Morgagni) and two acquired defects (sliding and paraesophageal).

Congenital Diaphragmatic Hernias

Bochdalek (Posterolateral) Hernia

Despite major advances in prenatal diagnosis and management, infants with Bochdalek diaphragmatic hernias diagnosed at birth (1/4000 live births) have a poor prognosis.³ Bochdalek hernia is a posterolateral hiatal defect in the diaphragm caused by a failure of the pleuroperitoneal canal fusion during fetal development. More than 80 percent occur in the left hemithorax, and typically are through a small circular defect (Fig. 22-2). Only 10 percent have a true hernia sac. When the intestines return to the abdomen from the yolk sac at 10 weeks gestation, the abdominal organs may herniate into the thorax through this defect. The pressure of abdominal viscera in the thoracic cavity results in a decrease in the number of bronchial branches, total number of acini, and number of vessels. Typically this results in impaired growth of the ipsilateral lung. However, in extreme cases, when the mediastinum is forced to the contralateral side of the chest, the contralateral lung may also be affected. Herniation of the viscera through the defect usually occurs during the pseudoglandular stage of lung development.

They are commonly associated with additional anomalies including congenital heart defects, hydronephrosis, renal agenesis, intestinal atresia, extralobular sequestration, hydrocephalus, anencephaly, and spina bifida.

Bochdalek hernias may result in life-threatening respiratory compromise as early as the first hours or days of life.³ The timing of presentation is dependent on the degree of pulmonary hypoplasia, which is the main cause of morbidity and mortality associated with this disorder. Occasionally, the defect may result in respiratory distress or feeding intolerance in later infancy or childhood or may be identified on a radiograph obtained for unrelated reasons. The other element that contributes to the pathophysiology of this disease is pulmonary hypertension—this condition mimics normal fetal circulation and is termed persistent fetal circulation. This condition may result in hypoxemia and acidosis (Fig. 22-3). Severe pulmonary hypertension forces right-to-left shunting through the persistent foramen ovale and the patent ductus arteriosus.

Almost 50 percent of these congenital diaphragmatic hernias are identified during prenatal ultrasound examination.⁴ The diagnosis can later be confirmed by a chest radiograph that characteristically demonstrates abdominal contents in the chest with mediastinal deviation away from the affected side (Fig. 22-4). The differential diagnosis includes congenital cystic adenomatoid malformation, other cystic diseases of the lung, and eventration of the diaphragm. Visualization of the naso- or oralgastric tube above the diaphragm also supports the diagnosis. The prenatal diagnosis of right-sided defects is extremely difficult because of the similar echogenicity of the liver and lung.

If a patient presents with respiratory distress at birth, the child should be promptly intubated and nasogastric decompression initiated to minimize visceral distention. Mechanical ventilation with 100 percent F_io₂ and low airway pressures (<25 mm Hg and 5 of positive end-expiratory pressure (PEEP)) should be used. The patient should then be transported to a facility capable of extracorporeal membrane oxygenation (ECMO). Indication to place a baby on ECMO includes an alveolar–arterial oxygen gradient greater than 600 for 8 h, oxygen index greater than 40, pH <7.15, P_ao₂ <55, and progressive barotrauma. ECMO is contraindicated if the patient has preexisting weights less than 2 kg, intraventricular hemorrhage, or has other abnormalities incompatible with life.

Repair of a Bocadaleck hernia has previously been considered a surgical emergency; however, the scheme of emergency operative repair immediately after birth has resulted in mortality rates greater than 50 percent. Recent trends include alternative forms of management, such as delayed operation, ECMO, inhaled nitric oxide, and partial liquid ventilation, all with improved results. Recent studies have demonstrated preoperative stabilization results in improvement of pulmonary compliance prior to repair.⁴ Once stable, the repair can be performed through a paramedian incision or subcostal incision. A transthoracic approach has also been advocated by some for right-sided hernias. From the abdominal approach, the viscera can be returned from the chest and the hernia sac may need to be excised if present. The lung tissue should be examined; however, attempts to expand the hypoplastic lung should be avoided. Extralobar pulmonary sequestrations are resected at the time of hernia repair.

A small diaphragmatic defect is closed with permanent suture and Teflon pledgets. Larger defects, or defects whose edges may be under tension, can be closed with synthetic sheet material. Typically, bilateral chest tubes are left in place and connected to water-seal. Intra-abdominal anomalies may be corrected at the time of hernia repair if the patient’s condition is stable, although there remain center-to-center preferences regarding this step. In some cases, abdominal wall fascia may not be closed primarily and these circumstances should be managed as large abdominal wall defects.

Postoperative management should aim to reduce pulmonary vascular resistance, improve oxygenation, and treat persistent fetal circulation. Frequent arterial blood gas determinations coupled with continuous pulse oximetry or transcutaneous partial pressure of oxygen and carbon dioxide monitoring provide a reliable mechanism of ventilatory status. A variety of vasodilators have been used to prevent and reverse pulmonary hypertension. It is important to realize that minor changes in ventilation can precipitate intense pulmonary vasoconstriction. Finally, one should consider that the lungs are at risk of barotrauma. As a last resort, ECMO may need to be initiated to reverse pulmonary hypertension if conventional methods fail.

In the absence of additional lethal anomalies, mortality is directly related to the degree of pulmonary hypoplasia. Other prognostic indications associated with poor outcome include additional anomalies, polyhydramnios, presence of an intrathoracic stomach bubble, and underdevelopment of the left heart region. Although the majority of these patients present within the first few days of life, patients may present later in life. This cohort of patients often presents with a variety of respiratory symptoms or sometimes bowel obstruction.

Morgagni (Retrosternal) Hernia

Morgagni hernia was initially described by Morgagni in 1769. Morgagni hernias are rare and account for less than 5 percent of all diaphragmatic hernias. Unlike Bochdalek hernias, patients with Morgagni hernias typically present later in life.³ Morgagni hernias are hypothesized to arise from the incomplete fusion of the transverse septum to fuse with the sternum and resulting abnormalities of the foramen of Morgagni (Fig. 22-2). These hernias typically are true hernias and possess a hernia sac. Commonly, the defect contains a piece of omentum that enlarges as the person grows and produces the mass within the hernia sac. However, colon and small intestine are capable of passing through larger defects. A right-sided defect occurs in 90 percent of the cases because the left side is protected by the pericardium.