Acquired Diaphragmatic Hernia

The diaphragm is a modified half-dome of musculofibrous tissue that separates the thorax from the abdomen. The thoracic side is covered with parietal pleura and the abdominal side with peritoneum. Four embryologic components arise during the formation of the diaphragm, as follows:

• Septum transversum
• Two pleuroperitoneal folds
• Cervical myotomes
• Dorsal mesentery

Development begins during week 3 of gestation and concludes by week 8. Failure of the development of the pleuroperitoneal folds, with subsequent muscular migration, results in congenital defects.

The muscular diaphragm originates from the six lowest ribs on both sides, from the posterior xiphoid process, and from the external and internal arcuate ligaments. Different structures traverse the diaphragm, including three distinct apertures that allow the aorta, esophagus, and vena cava to pass, as follows:

• The aortic aperture is the lowest and most posterior of the openings, lying at the level of T12; it also transmits the thoracic duct and, sometimes, the azygos and hemiazygos veins
• Diaphragmatic muscle surrounds the esophageal aperture, which lies at the level of T10
• The vena caval aperture is the highest of the three openings and lies level to the disk space between T8 and T9

Because of its combination of fast-twitch oxidative-glycolytic fibers and slow-twitch oxidative fibers, the diaphragm is a muscle resistant to fatigue. Loss of movement of the diaphragm is indicative of fatigue and can be measured by the contractile force. Many patients with chronic obstructive pulmonary disease (COPD) can live at the brink of fatigue.[6]

The arterial supply to the diaphragm derives from the right and left phrenic arteries, the intercostal arteries, and the musculophrenic branches of the internal thoracic arteries. Small branches of the pericardiophrenic arteries that course with the phrenic nerve, mainly where the nerves penetrate the diaphragm, provide some arterial blood. Venous drainage is through the inferior vena cava (IVC) and azygos vein on the right and the adrenal/renal and hemizygos veins on the left.

The diaphragm receives its sole muscular neurologic impulse from the phrenic nerve, which primarily originates from the fourth cervical ramus; however, it also has contributions from the third and fifth rami. (As the saying goes, "C3, C4, and C5 keep the diaphragm alive.")

Originating around the level of the scalenus anterior, the phrenic nerve courses inferiorly through the neck and thorax before reaching its end point, the diaphragm. Because the phrenic nerve has such a long course before it reaches its final destination, any process that disrupts transmission of neurologic impulses through the nerve directly affects the diaphragm.

The pathophysiology of acquired diaphragmatic hernias includes circulatory and respiratory depression secondary to decreased function of the diaphragm, intrathoracic abdominal contents leading to compression of the lungs, shifting of the mediastinum, and cardiac compromise.[7] Smaller diaphragmatic hernias are often not found until months or years later, when patients present with strangulation of intra-abdominal organs, dyspnea, or nonspecific gastrointestinal complaints.

By far the most common cause of acquired diaphragmatic disorders is trauma, either blunt or penetrating. Motor vehicle accidents (MVAs) are the leading cause of blunt diaphragmatic injury,[8] whereas penetrating injuries result from gunshot or stab wounds. In contrast to earlier work, several later retrospective studies found 75% of their patients to have tears from penetrating injuries.[9, 10] This may stem from increasing awareness of the part of providers or from improved ability to detect small tears via minimally invasive methods.

Other rare causes of traumatic rupture include labor in women with prior diaphragmatic hernia repair,[11]  barotrauma during underwater dives in patients with history of Nissen fundoplications,[12]  and liver transplantation (particularly in children).[13, 14]

The following theories have been postulated to explain the mechanism of rupture for blunt injuries:

• Shearing of a stretched membrane
• Avulsion of the diaphragm from its points of attachment
• Sudden increase in the transdiaphragmatic pleuroperitoneal pressure gradient

The resting pressure differential between the pleural (–5 to –10 cm H2O) and peritoneal (+2 to +10 cm H2O) cavities rises to 100-150 cm H2O with a large cough and does not injure the diaphragm. Forces transmitted to the abdomen from blunt trauma can raise the pressure gradient to 1000 cm H2O.

It is thought that the right side has more protection than the left and may be slightly stronger; in addition, the liver may provide another protection for the right hemidiaphragm. Thus, owing to hepatic protection and the increased strength of the right hemidiaphragm, left-side rupture is more common than right-side rupture (68.5% vs 24.2%). However, the increased prevalence of left-side hernias may also result from weaknesses in points of diaphragmatic embryologic fusion. Children have equal rates of rupture per side, likely because of laxity of liver attachments.[15]

Rarely, idiopathic spontaneous acquired diaphragmatic hernia may occur in the absence of any trauma or surgery.[16]

Of patients admitted to the hospital for trauma, 3-5% have a diaphragmatic hernia.[9, 10] The male-to-female ratio is 4:1, with most presenting in the third decade of life. Approximately 0.8-1.6% of patients with blunt trauma sustain a rupture of the diaphragm, accounting for 75% of diaphragmatic hernias. Approximately 69% of hernias are on the left side, 24% are on the right, and 15% are bilateral.

In traumatic ruptures, the outcome is generally related to concomitant injuries. Reported mortality ranges from 5.5% to 51%. People with isolated diaphragmatic injuries tend to recover without long-term disability.

Clinical findings in patients with acquired diaphragmatic hernia may include the following:

• Marked respiratory distress
• Decreased breath sounds on the affected side
• Palpation of abdominal contents upon insertion of a chest tube
• Auscultation of bowel sounds in the chest
• Paradoxic movement of the abdomen with breathing
• Diffuse abdominal pain

Chest radiography

Chest radiography is standard in the Advanced Trauma Life Support (ATLS) protocol for a trauma workup. Approximately 23-73% of traumatic diaphragmatic ruptures will be detected by initial chest radiography, with an additional 25% found on subsequent films.[17] Chest radiography is most sensitive for detecting left-side hernias. Chest radiographic findings that indicate traumatic rupture include the following:

• Abdominal contents in the thorax, with or without signs of focal constriction ("collar sign") ^[17]
• Nasogastric tube seen in the thorax (see the image below)
• Elevated hemidiaphragm (>4 cm higher on the left than on the right)
• Distortion of diaphragmatic margin

Preoperative chest radiograph in a 53-year-old woman who was a restrained passenger in an automobile accident. Note the bowel contents in the left hemithorax. Nasogastric tube can be seen in the thorax.

Computed tomography

Conventional computed tomography (CT) has been reported to have a sensitivity of 14-82%, with a specificity of 87%.[18] Helical (spiral) CT has increased sensitivity, 71-100%, with higher sensitivity on the left than on the right.[17] CT findings indicative of rupture include the following:

• Direct visualization of injury
• Segmental diaphragm nonvisualization
• Intrathoracic herniation of viscera
• "Collar sign"
• Peridiaphragmatic active contrast extravasation

Ultrasonography

Ultrasonography (US; specifically, focused assessment with sonography for trauma [FAST]) has been reported to detect diaphragmatic hernias.[3] During visualization of each upper quadrant, the movement of the diaphragm was noted to be decreased in patients with diaphragmatic hernias. This technique is limited in patients who are on mechanical ventilation because of the positive pressure of the thoracic cavity.[3]

In stable patients in whom an isolated diaphragmatic tear is suspected, diagnostic laparoscopy or video-assisted thoracoscopic surgery (VATS) is indicated.

In traumatic rupture of the diaphragm, surgical intervention is mandatory, whether the patient presents immediately or some time after the trauma. The high incidence of concomitant intra-abdominal injuries dictates the need for emergency abdominal exploration in the acute trauma setting after initial resuscitation is accomplished.

Patients who present in the latent phase or long after the trauma require repair because the hernia contents may become strangulated, leading to dead gut, stomach, liver, spleen, or other organs.

No contraindications have been reported for repair of an acquired diaphragmatic hernia. In the trauma setting, the patient must be adequately resuscitated before being transported to the operating room. Many small injuries are discovered during exploratory laparotomy for the repair of other intra-abdominal injuries.

Diaphragmatic hernias should always be repaired. Lack of repair of a diaphragmatic hernia can lead to incarceration and strangulation of intra-abdominal contents or respiratory dysfunction.

For traumatic rupture, first provide initial resuscitation according to Advanced Trauma Life Support (ATLS) protocol, with particular attention to airway control. Avoid the use of military antishock trousers (MAST).

Prepare the patient for surgery. Sometimes, as with congenital hernias, surgical intervention can be briefly delayed until the patient's condition is stabilized. However, the high incidence of concomitant injuries necessitates emergency exploration in most cases.

If the diaphragmatic injury is discovered during the acute phase of trauma, the standard surgical approach is laparotomy or, less commonly, thoracotomy. The generally accepted protocol in the acute setting has been that a diaphragmatic rupture is approached via a celiotomy because concomitant intra-abdominal injuries are more likely to be present than thoracic injuries are (84% vs 53%).[4]

The problem regarding which approach to use arises when the diaphragmatic injury goes unnoticed for months or years. More surgeons approach long-standing hernias via a transthoracic or thoracoabdominal approach because the herniated intra-abdominal contents tend to be firmly attached to intrathoracic structures, making a transabdominal approach difficult.

Minimally invasive techniques for diaphragmatic repair have become increasingly common. With advances in technology and surgical skills, repairing both acute and chronic diaphragmatic hernias is possible with laparoscopic,[19, 20] thoracoscopic, robot-assisted,[21, 22] or combined approaches. However, the success of these minimally invasive approaches is highly surgeon-dependent, and laparotomy remains more common in this setting.[23]

Operative details

As in any case of trauma, the patient's condition must be stabilized, and he or she must be resuscitated to the extent possible before operative treatment. People with traumatic hernias frequently have concomitant injuries and require emergency exploration.

With traumatic ruptures, the surgical approach depends on the timing of the diagnosis with the surgical intervention. In the acute phase of trauma, an abdominal approach is preferred.[24] In the latent phase of trauma, a transthoracic approach may be necessary because patients often have adhesions to intrathoracic organs.

Acute injuries are repaired with monofilament permanent sutures. Small lacerations may be repaired by using interrupted, horizontal mattress, or figure-eight stitches; larger lacerations may be repaired with continuous or double-layered closures. Absorbable sutures are associated with a high rate of recurrence.[9]  There is some limited evidence to suggest that the use of biologic mesh in traumatic diaphragmatic repair may be feasible, at least in chronic cases.[25]

Laparoscopic abdominal exploration in the setting of trauma has become an increasingly popular way of determining whether diaphragmatic integrity is retained. It provides a minimally invasive mechanism by which the diaphragm can be directly viewed to determine if an injury has occurred. In the absence of other intra-abdominal injuries, the diaphragm can easily be repaired by applying laparoscopic techniques.[26]

The best utility of laparoscopy is with penetrating thoracic and flank injuries when intraperitoneal penetration is being considered and if a projectile injured the diaphragm.

Recurrence is possible after traumatic herniation or a congenital diaphragmatic hernia that was repaired in an adult. Therefore, after an anatomic defect is corrected, periodic assessments of pulmonary function and chest radiography are important (see the image below). Although the spontaneous recurrence rate for repaired diaphragmatic hernias is low, small defects in the repair site have been reported; therefore, surveillance is crucial.

Postoperative chest radiograph in a 53-year-old woman who was a restrained passenger in an automobile accident.