Diaphragm Eventration

Etiology

Congenital eventrations are caused by abnormal diaphragm muscle development and can occur anteriorly, posterolaterally, and medially. Embryologically, there is a defect in the migration of myoblasts to the septum transversum, causing partial or total replacement of the diaphragm muscle with fibroelastic tissue. This creates a thin and weakened hemidiaphragm, resulting in a cephalic displacement on the affected side. Eventration can also occur in association with other congenital conditions and infections. These conditions include spondylocostal dysostosis, Kabuki syndrome, Beckwith-Wiedemann syndrome, Poland syndrome, chromosomal defects, pulmonary hypoplasia, spinal muscular atrophy, malrotation, and congenital heart disease. Mitochondrial respiratory chain disorder has been linked to diaphragmatic dysfunction in the neonatal period. Infectious associations include fetal rubella and cytomegalovirus infections.[5][6][7]

Acquired cases are more common and are due to etiologies that result in phrenic nerve injury and muscle atrophy. Injury may be due to blunt or penetrating trauma, birth trauma, or thoracic surgery. Phrenic nerve dysfunction or damage may also occur as a complication of other illnesses, including multiple sclerosis, Guillain-Barre syndrome, nerve compression, radiation therapy, and connective tissue diseases. Paralysis or phrenic nerve damage can lead to muscle atrophy and thinning of the diaphragm with cephalic displacement.[2][8] Eventrations, congenital and acquired, of the diaphragm are further divided on an anatomical basis as complete, partial, or bilateral. 

Epidemiology

Due to the rarity of diaphragmatic eventration, there is limited data on the incidence and prevalence of this condition. A limited number of case reports have suggested the incidence is as low as less than 0.05%, with a predominance in men, most commonly affecting the left hemidiaphragm. Others have suggested the incidence to be 1 in 10,000 live births. The incidence is likely higher than reported as most patients are asymptomatic, and many remain undiagnosed.[6][9][10]

Pathophysiology

Diaphragmatic eventration refers to a localized elevation or bulging of 1 side of the diaphragm (hemidiaphragm) without any break in the continuity of the diaphragm. This condition may feature a distinct transition to the elevated area, sometimes resembling a mushroom shape (see Image. Diaphragm Eventration).[1] Neurogenic muscular aplasia of the diaphragm is the term used to describe stretched-out and aponeurotic scattered muscle fibers in a congenital diaphragm eventration. However, these changes are lacking in acquired form.[11]

History and Physical

History

Patients with eventration of the diaphragm have variable presentations. Most patients are asymptomatic, and the condition is discovered incidentally on chest x-rays; however, some may present with significant respiratory distress or gastrointestinal symptoms. Bilateral congenital diaphragmatic eventration in the neonate may present with acute respiratory failure and cyanosis. Respiratory symptoms in adult and pediatric cases may include dyspnea on exertion, orthopnea, tachypnea, and shallow breathing.

In adults, recurrent respiratory infections, lung atelectasis, or chronic productive cough may cause initial presentation. Adults may also complain of chest pain, which may be caused by arrhythmias or palpitations. Gastrointestinal symptoms in the adult population may worsen with increased intraabdominal pressure (eg, exercise, pregnancy, ascites, infection, fluid sequestration) and present with dyspepsia, dysphagia, gastroesophageal reflux, and epigastric pain. 

In infants, respiratory symptoms are largely attributed to shifting the mediastinal structures to the contralateral side. Gastrointestinal involvement is common and may manifest as vomiting, bloating, constipation, poor weight gain, and poor oral intake. In severe cases, gastric volvulus may be present. All patients should be assessed for a history of trauma and other causes of respiratory distress.[2][11]

Physical Examination

The physical examination findings are variable and often nonspecific. Below is a list of physical findings that may be found in adults and pediatrics (shared), acquired (adult) cases, and congenital (pediatric) cases.

• Shared findings in adults and infants
  •  General:
    • Tachypnea
    • Central cyanosis if hypoxia is present (rare in unilateral cases)
  • Lungs/thorax:
    • Accessory muscle use
    • Paradoxical movement of the chest wall during inspiration (on the affected side)
    • Decreased tactile fremitus and dullness to percussion on the affected side
    • Decreased breath sounds (unilateral or bilateral involvement)
  • Gastrointestinal:
    • Abdominal pain with palpation (usually epigastric or periumbilical areas)
    • Bowel sounds within the thoracic cavity
• Congenital (infants)
  • Lungs/thorax:
    • Apparent signs of blunt or penetrating thoracic trauma
  • Gastrointestinal:
    • Scaphoid abdomen
    • Severe epigastric pain related to gastric volvulus
  • Musculoskeletal/neurological:
    • Findings of Erb palsy (C5 and C6 injury) in those with birth trauma
      • Clavicular fracture
      • Arm is adducted and internally rotated
      • Forearm is extended and pronated
• Acquired (adults)
  • Lungs/thorax:
    • Apparent signs of blunt or penetrating thoracic trauma
  • Cardiovascular:
    • Chest wall pain
    • Tachycardia or arrhythmia
  • Gastrointestinal:
    • Abdominal pain due to causes of increased intraabdominal pressure
      • Ascites
      • Infection
      • Fluid sequestration (third-spacing)
      • Pregnancy

Evaluation

Acquired Diaphragm Eventration

Most patients with diaphragmatic eventration are asymptomatic. They are often unaware of their condition, and the diagnosis is typically an incidental finding on chest imaging. After a thorough history and physical examination, patients who are symptomatic should undergo chest imaging; radiographic findings on chest x-rays confirm the diagnosis of diaphragmatic eventration. 

Chest x-ray imaging should include both posterior-anterior and lateral views. X-ray images will show an elevation of the affected portion of the hemidiaphragm and normal cardiomediastinal contours. Chest computed tomography (CT) may be done if the diagnosis is unclear or intrathoracic or intraabdominal abnormalities are suspected. A chest CT will show elevation of the affected portion of the hemidiaphragm and a sharp edge of the eventration. Diaphragmatic eventration can be differentiated from hernia due to the normal attachment sites of the diaphragm.[10][12]

Further evaluation is often reserved for assessing lung volumes and diaphragm function. These tests include pulmonary function testing (PFT), maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), fluoroscopic sniff testing, and ultrasonography. Laboratory testing may be necessary if there is suspicion of associated congenital diseases or infectious etiologies.

PFTs show a restrictive pattern with reduced forced vital capacity and forced expiratory volume in 1 second. This restrictive pattern is more commonly seen when eventration is bilateral. This has improved with diaphragm plication, which is further discussed in the next section.[12] The MIP and MEP measure the pressure generated during maximal inspiratory or expiratory effort and indicate the respiratory muscles' strength. As the diaphragm plays a role in the inspiratory phase, the MIP is reduced in patients with diaphragm eventration; the MEP is generally expected.[13]

Fluoroscopic sniff testing is used to examine diaphragm function under continuous fluoroscopy. The patient is asked to take hard and fast inspirations (sniffs) and assess the direction and motion of each hemidiaphragm. In diaphragm eventration, only a portion of the hemidiaphragm may show abnormal movement. Sniff testing may aid in distinguishing diaphragm paralysis from eventration, as paralysis may have paradoxical motion during sniffing. This is of limited value as diaphragm eventration and paralysis are treated with plication when conservative measures fail. In infants, the sniff test may be difficult to obtain. Ultrasonography of the diaphragm is often used in place of fluoroscopy to evaluate diaphragm function due to its lack of exposure to radiation to patients.[12][14]

Congenital Diaphragm Eventration

Diagnosis can be made prenatally with a high-resolution fetal ultrasound, CT, or magnetic resonance imaging (MRI). Prenatally, diaphragm eventration is challenging to differentiate from congenital diaphragmatic hernia as the lung appears hypoplastic, and the fetal stomach or liver is visualized in the same transverse plane as the heart. Postnatally, eventration is suspected when a portion of the diaphragm is elevated on chest radiography when evaluating for respiratory distress. Confirmatory testing for diaphragm eventration includes fluoroscopy, dynamic MRI, or ultrasound to assess diaphragm function. Further evaluation should be tailored to the patient's clinical history and physical findings to determine the underlying etiology (eg, infections, malignancy, developmental and degenerative diseases).

Treatment / Management

Managing diaphragm eventration mostly depends on the disease’s etiology and severity. In asymptomatic or mild cases, supportive care is recommended. In cases of hypoxemia, oxygen supplementation should be provided to maintain appropriate oxygen saturation. When supplemental oxygen via nasal cannula is inadequate, patients may require nasal continuous positive airway pressure. As infants commonly present with gastrointestinal symptoms and failure to thrive, nutritional support should be optimized. Infants in significant respiratory distress may require gavage feeding or parenteral nutrition to maximize calorie intake, fluid intake, and electrolyte replenishment to meet metabolic demands. Conservative management may also include physical therapy and pulmonary rehabilitation.[10][11]

Surgical plication may be indicated in severe cases requiring mechanical ventilation or when patients fail to respond to medical management. Diaphragmatic plication is a known surgical treatment for eventration. The procedure involves creating pleats with U-stitches in the weakened hemidiaphragm and anchoring down. This results in a flattened and lowered hemidiaphragm, allowing for increased intrathoracic volume and lung expansion. Diaphragm plication can be done via open thoracotomy, video-assisted thoracoscopic surgery, laparoscopic, or robotic-assisted surgery. After the surgery, a thoracostomy tube is placed for pleural drainage until the output is less than 200 mL/day. Notably, surgical plication does not improve the function of the hemidiaphragm.[12][15][16]

The indications for surgical plication are outlined below:

• Respiratory distress unresponsive to conservative treatment
• Dyspnea that is not due to another process (ie, heart failure or primary lung diseases)
• Infants with inadequate nutritional intake or failure to thrive
• Life-threatening or recurrent pneumonia
• Inability to be removed from mechanical ventilation

Patients should be monitored postoperatively, and the frequency of follow-up is variable depending on symptoms or complications. Follow-up tests may include posterior-anterior/lateral chest x-rays and PFTs. The St George Respiratory Questionnaire can monitor a patient’s quality of life, activity level, and psychosocial impact.

Differential Diagnosis

The differential diagnoses to consider in cases of possible diaphragm eventration include:

• Diaphragmatic paralysis
  • Difficult to distinguish from eventration
  • Paralysis will involve the entire hemidiaphragm
  • Eventration may involve a smaller portion or the whole hemidiaphragm
• Phrenic nerve palsy
• Diaphragmatic hernia
• Lung consolidation
• Subpulmonic pleural effusion
• Pleural mass
• Traction injury
• Iatrogenic injury during thoracic surgery
• Ascites
• Hepatic or splenic enlargement

Prognosis

The prognosis is generally good and may depend on the severity and etiology of the event. Most patients are asymptomatic and may not need any intervention. Those with extensive eventration may develop severe respiratory distress requiring mechanical ventilation. Diaphragm plication has significantly improved symptoms and quality of life in patients with extensive eventration. The procedure has also improved the forced expiratory volume in the first second and forced vital capacity by up to 30% on follow-up PFTs.[16][17]

Complications

Complications of diaphragm eventration include:

• Acute or chronic respiratory failure
• Pneumonitis
• Nutritional deficiency
• Failure to thrive
• Cardiac arrhythmias are possible due to acute mediastinal shifts
• Complications of surgical correction
  • Pneumonia
  • Deep venous thrombosis
  • Pleural effusions
  • Cardiac events