Eventration of the Diaphragm
Daniel Von Allmen
Diaphragmatic eventration (DE) is a pathologic condition defined by a permanent elevation of an immobile hemidiaphragm that cannot participate actively in respiration. Peripheral muscular attachments are normal, the diaphragmatic apertures are sealed normally, and there is no interruption in the pleural or peritoneal layers as is seen with diaphragmatic hernias. The defect can be unilateral, localized, or bilateral. DE may be a congenital anomaly caused by failure of muscularization of the dome of a hemidiaphragm, or it may be acquired as a result of dysfunction of the phrenic nerve related to neuromuscular disease or trauma including operative trauma. Most commonly diagnosed in pediatric patients, the incidence in adulthood is low, estimated to be between 1 in 10,000 and 1 in 13,000. It is more common in males and affects the left hemidiaphragm more frequently.
AnatomyCongenital DE is an abnormal elevation of the diaphragm resulting from failure of muscle fibers to develop within the pleuroperitoneal membrane during the 8th to 10th week of gestation. Etiologic factors such as failure of migration of myoblasts along normal phrenic nerve branches or from the peripheral chest wall, failure of normal innervation of the primordial diaphragm, congenital infection with Toxoplasma or Cytomegalovirus, and premature return of the midgut to the peritoneal cavity during development have been postulated as causes of congenital DE. The sparsely distributed muscle fibers are mechanically nonfunctional, resulting in a lax, thin, elongated membrane characterized microscopically by few muscle fibers and diffuse fibroelastic changes. With diaphragmatic paralysis, the muscle fibers are present but become atrophic with time.
Normally the diaphragm projects from the 10th rib posteriorly to the dome at the level of the 5th or 6th rib anteriorly. In the majority of patients the dome of the left hemidiaphragm is one interspace lower than the right. Elevation of the diaphragm in cases of eventration results from arching of the diaphragm as a result of the relatively higher intra-abdominal pressures.
Eventrations are frequently unilateral; however, a few cases of bilateral eventration have been reported in the literature. Although a complete eventration of the hemidiaphragm is more common in males, and on the left side, partial eventration is more common on the right side and is of equal sex distribution. The most common site of partial eventration is the anteromedial aspect of the right hemidiaphragm, which can occur commonly in patients over 60 years of age, and is of no clinical significance.
Disorders that may accompany congenital DE are the same as those that may accompany congenital diaphragmatic hernia (CDH). These include facial (cleft lip and palate), cardiovascular (patent ductus arteriosus, aortic stenosis, ventricular septal defect, and coarctation of the aorta), gastrointestinal (GI) (malrotation, gastric volvulus, megacolon), situs inversus, tracheomalacia, genitourinary (horseshoe kidney), musculoskeletal (hemivertebrae, arthrogryposis, and Werdnig–Hoffmann disease, Ehlers–Danlos syndrome), and chromosomal (trisomy 18) abnormalities. Therefore, when congenital disorders of the diaphragm are suspected, it is essential to be aware of the possible coexistence of other anomalies.
Acquired or secondary DE is often due to pathologic or iatrogenic insult to the phrenic
nerve resulting in paralysis of the diaphragm and DE. External trauma, inflammation (pleural, mediastinal, or pulmonary source), or neoplastic invasion of the nerve usually results in complete DE. Birth trauma is by far the most common cause of acquired DE and is usually related to breech presentation or shoulder dystocia resulting in a stretch injury to the C3 to C5 nerve roots—those that give rise to the phrenic nerve and brachial plexus. Fractures of the clavicle or humerus are often seen in association. If nerve roots are avulsed, no improvement in the DE is predicted, whereas lesser degrees of injury may potentially recover with time. Acquired DE is also seen after open cardiac procedures, due to surgical dissection, electrocautery, or ice placement. Again, recovery depends on the nature and completeness of the nerve lesion.
nerve resulting in paralysis of the diaphragm and DE. External trauma, inflammation (pleural, mediastinal, or pulmonary source), or neoplastic invasion of the nerve usually results in complete DE. Birth trauma is by far the most common cause of acquired DE and is usually related to breech presentation or shoulder dystocia resulting in a stretch injury to the C3 to C5 nerve roots—those that give rise to the phrenic nerve and brachial plexus. Fractures of the clavicle or humerus are often seen in association. If nerve roots are avulsed, no improvement in the DE is predicted, whereas lesser degrees of injury may potentially recover with time. Acquired DE is also seen after open cardiac procedures, due to surgical dissection, electrocautery, or ice placement. Again, recovery depends on the nature and completeness of the nerve lesion.
Clinical PresentationThe anatomic diagnosis of DE is largely based on imaging studies but the clinical presentation is critical to the management algorithm and varies slightly based on the age of the patient. Dyspnea is the primary presenting symptom and the degree to which it is clinically significant determines the need for surgical intervention.
Adults
Most adults with congenital DE are asymptomatic and do not require surgical treatment. DE acquired during adulthood as a result of phrenic insult represents the atrophy and progressive laxity of the diaphragmatic muscle. These patients are likely to present with incidental findings on a chest radiograph obtained for unrelated reasons. When the patient is symptomatic, they typically present with signs and symptoms related to inadequate ventilation (e.g., dyspnea on exertion or with recumbency). In an adult with a previously asymptomatic DE, conditions that cause atelectasis or mild respiratory infection may result in respiratory distress, tachypnea, tachycardia, and even cyanosis. Chest pain (either spontaneous or provoked by flexion) or palpitations caused by cardiac arrhythmias can also be seen. Alternatively, abdominal symptoms including epigastric pain, dysphagia, dyspepsia, belching, and gastroesophageal reflux may be associated with displacement of viscera into a large DE.
Infants and Children
DE commonly results in respiratory symptoms in infants and children similar in nature to a flail chest. This is due to a more mobile pediatric mediastinum, shifting to the contralateral side and thus resulting in compression of contents of both hemithoraces, significantly compromising overall cardiopulmonary function. In addition, infants rely much more on diaphragmatic excursions than accessory muscles for respiration, resulting in a greater susceptibility to symptomatic DE. Less commonly, infants and children with DE may present with abdominal symptoms, the most catastrophic of which is acute gastric volvulus, requiring urgent operative intervention.
DiagnosisThe diagnosis of DE is based on a combination of clinical and radiographic characteristics that are necessary to differentiate it from an underlying primary pathologic condition involving the lungs or chest wall or diaphragmatic hernia. A thorough history is important to provide clues to the presence of other pathology as well as to document the degree of respiratory symptoms, which are the basis for any surgical intervention. The findings from a physical examination are nonspecific but include dullness to percussion, decreased breath sounds on the affected side, and paradoxic movement of the chest wall with inspiration.
Prenatal diagnosis of congenital DE is possible, with high-resolution maternal sonography, computed tomography (CT), or magnetic resonance imaging (MRI). DE and CDH may appear similar during fetal imaging, with a hypoplastic ipsilateral lung, and fetal stomach or liver seen in the same transverse sonogram as the heart. With DE, polyhydramnios is relatively infrequent and abdominal circumference is normal or slightly smaller than gestational dates would indicate. Occasionally, a hypoechoic, thin diaphragmatic membrane can also be seen in cases of DE.
Postnatally, dullness of the involved hemithorax, with poor diaphragmatic excursion, may be found on physical examination but the diagnosis is often first suspected based on marked elevation of the hemidiaphragm on a chest radiograph obtained to investigate respiratory distress. The subsequent workup is based on the clinical context. In the absence of a history suggesting the cause of adult DE (e.g., prior thoracic surgical procedure), investigations to elucidate the reason for DE should be conducted. In particular, occult neoplastic, infectious, and degenerative diseases of the cervical or mediastinal regions should be considered. Most can be excluded with cervicothoracic CT scan. Upper-abdominal CT is useful for excluding subphrenic abnormalities such as abscess or Chilaiditi syndrome, which may be associated with diaphragmatic paralysis. Treatment would then focus on the underlying cause rather than the anatomic abnormality of the diaphragm itself.
In order to confirm the diagnosis of DE, some form of dynamic imaging must be done to assess the function of the diaphragm. Fluoroscopy, ultrasound, or dynamic MRI can be used to determine whether absent, decreased, or the classic “paradoxical” movement of the diaphragm is present during spontaneous ventilation. Paradoxical motion is observed when paralysis or further elevation of the involved hemidiaphragm is seen during inspiration, whereas depression of the contralateral (normal) hemidiaphragm occurs. This finding can be accentuated during fluoroscopic examination using the “sniff” maneuver in older patients. Ventilation–perfusion scanning is less commonly used to demonstrate DE, but can show loss of ventilation on the involved side. Upper-GI contrast study has also been described as a useful diagnostic modality to assess GI symptoms.
It is important to realize that characteristic physical examination and radiologic findings will not be evident in patients who are undergoing mechanical ventilation. Positive-pressure ventilation eliminates the diaphragmatic asymmetry that is used to secure the diagnosis in spontaneously breathing patients. For patients with a good history for DE who cannot be extubated, fluoroscopy during brief discontinuation of mechanical ventilation may provide radiologic information to exclude or support the diagnosis of DE. In addition, DE must be considered in infants who have unexplained respiratory distress and require urgent intubation before baseline chest radiography can be obtained.
TreatmentThe goals of surgical therapy should be (a) to restore the diaphragm to a normal location within the involved hemithorax, (b) to restore normal capacity to the hemithorax to allow lung growth in infants and children, (c) to restore normal visceral location in the abdomen, and (d) to stabilize the mediastinum by eliminating paradoxical motion of the diaphragm. These goals have classically been achieved surgically via open thoracotomy first described in 1923 by Morrison. Evolution of the open technique has involved with either plication of the redundant diaphragm or resection of excess tissue with primary closure of the resulting diaphragmatic defect. More recently, minimally invasive approaches have been described using thoracoscopic or laparoscopic approaches. The obvious advantage of these techniques is to reduce the operative morbidity of a large open thoracotomy, which may in turn reduce the threshold for pursuing an operative repair.
IndicationsIndications for operative correction of either congenital DE or DE acquired after severe birth or surgical injury in infants include (a) progressive respiratory distress with atelectasis or pneumonia or (b) failure to wean from mechanical ventilation. In either of these settings, early operative correction (at the time of diagnosis) is warranted, because of the limited morbidity of the operative correction, and the often dramatic improvement with fixation. For patients in whom respiratory symptoms are less severe and the etiology is thought to be phrenic nerve injury, and the potential for recovery exists, a delay of several weeks to months to allow for improvement is justified. Lack of improvement or deterioration in respiratory function during observation is an indication for immediate operative repair.
A relative indication for operation in an infant who has congenital DE is the presence of significant elevation of the hemidiaphragm. Occupation of greater than or equal to half of the volume of the hemithorax with displaced abdominal viscera would constitute significant elevation of the hemidiaphragm. With that degree of diaphragmatic elevation, compromise of growth of the ipsilateral lung, similar to that seen in CDH, results. Normal lung growth is permitted after surgical repair of DE, thus suggesting that early operation in this setting is clinically justified.
Surgical correction of DE in an older child or adult is less common than in infants, because an older patient can compensate to a greater degree than an infant with the more compliant chest and mediastinum. In the older child and adult, phrenic nerve injury caused by cardiac or aortic surgery rarely results in sufficient respiratory insufficiency to require operative correction of DE. A more compelling indication for correction of acquired DE in older patients is development of abdominal pain due to displacement of abdominal structures into the chest or cardiac arrhythmias related to compression. In addition, gastric volvulus or significant gastroesophageal reflux associated with DE should be seen as indications for surgical fixation. Conversely, for asymptomatic DE, surgical correction is generally not indicated. Treatment of DE caused by aggressive malignancy or other underlying pathology should be directed at the underlying cause.
Surgical TechniqueOpen Operative Repair
The traditional operative approach uses a posterolateral thoracotomy in most cases. Right-sided DE is best approached through the chest. Left-sided DE can be approached via thoracotomy or laparotomy. Thoracotomy offers better anatomic exposure of phrenic nerve branches. Bilateral eventrations, although rare, are best approached through the abdomen. Patients who present with gastric volvulus and eventration should undergo laparotomy for gastric fixation and diaphragmatic plication.
We prefer diaphragmatic plication to resection for both open and minimally invasive approaches. The open procedure can be performed through a standard posterolateral thoracotomy incision, using the seventh to eighth intercostal space (ICS). The initial examination of the diaphragmatic tissue should concentrate on the identification of the phrenic nerve branches (Fig. 1). Their preservation should be planned even though their potential for recovery is often limited.
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