Introduction:
Lung agenesis refers to the complete absence of lungs, that is, the absence of bronchial stump or carina, typically found in pulmonary aplasia or hypoplasia. It can be present as unilateral or bilateral lung agenesis. Bilateral lung agenesis refers to an absence of lungs on both sides. It is rare and quite fatal for an infant, as it manifests as severe respiratory distress in the fetus resulting in respiratory failure. Unilateral lung agenesis refers to an absence of lungs only on one side. Among the unilateral type, right lung agenesis has a worse prognosis because of the greater degree of mediastinal shift resulting in compression and distortion of the mediastinal vessels and trachea.
Lung agenesis is an autosomal recessive disorder with an estimated incidence of one in 10,000 to 15,000 births. It is characterized by failure of the development of the primitive lung bud. It is more commonly seen as left-sided agenesis than right-sided agenesis. Left-sided agenesis has greater life expectancy than right-sided agenesis. It may be found as an isolated entity or associated with other congenital anomalies such as a transesophageal fistula, tracheal stenosis, bronchogenic cyst, patent ductus arteriosus (PDA), tetralogy of Fallot, and abnormalities of the great vessels.
Lung development starts at the end of the fourth gestational week or first month of intrauterine life when a ventral bud or respiratory diverticulum arises from the foregut, which elongates and bifurcates to form left and right lung buds. If the primitive bud fails to divide into two, it leads to the formation of only one normal lung and the complete absence of the other lung. It can be either a complete or partial absence of the lungs, depending on the stage of the arrest of lung development.
What Is a Normal and Abnormal Lung?
Normal Structural Development:
1. Embryonic Stage :
The respiratory system starts to form as a diverticulum from the foregut. Lung bud formation occurs, branching into the bronchi and bronchioles. Vascular development begins with the formation of pulmonary arteries and veins.
2. Pseudoglandular Stage :
Continued branching of the bronchial tree occurs, leading to the formation of terminal bronchioles. Development of the lung's conducting airways and the surrounding vascular network progresses.
3. Canalicular Stage:
Terminal bronchioles further divide into respiratory bronchioles. Differentiation of the epithelium and the appearance of primitive alveoli begin. Capillary networks around the terminal airways continue to develop.
4. Saccular Stage:
Alveolar ducts and sacs proliferate. Type I and Type II pneumocytes develop. Type II cells produce surfactant. Capillaries extend around the primitive alveoli to facilitate gas exchange.
5. Alveolar Stage (Begins at Birth and Continues Beyond):
Continued growth and formation of alveoli. Maturation of Type I pneumocytes for gas exchange. Surfactant production increases to reduce surface tension and prevent alveolar collapse.
Abnormal Structural Development:
1. Congenital Anomalies:Congenital cystic adenomatoid malformation (CCAM) is an Abnormal lung tissue development leading to cystic masses. Pulmonary hypoplasia are Incomplete development of lung tissue, often associated with underdevelopment of the thorax or reduced amniotic fluid. Pulmonary sequestration is a Lung tissue that does not communicate with the tracheobronchial tree and receives its blood supply abnormally.
2. Developmental Disorders:
Bronchopulmonary dysplasia (BPD) is an Lung injury in premature infants that disrupts normal lung development, often due to mechanical ventilation and oxygen therapy. Alveolar capillary dysplasia are Abnormal development of alveoli and capillaries, leading to severe respiratory distress in newborns. Pulmonary hypoplasia syndromes are the Conditions like Potter syndrome that can result in pulmonary hypoplasia due to compression of the developing lungs by oligohydramnios (low amniotic fluid).
People Can Live With One Lung?
Living with one lung is possible. The human body can adapt remarkably well to having a single functional lung. After the surgical removal of a lung due to illness or injury, the remaining lung expands to occupy the space within the chest cavity, compensating for the missing lung. While overall lung capacity is reduced, most people with one lung can still breathe adequately and manage day-to-day activities. Some individuals might require medical support like supplemental oxygen or respiratory therapy, especially if they experience difficulties breathing or maintaining proper oxygen levels. Adopting a healthy lifestyle, avoiding smoking, and minimizing exposure to respiratory irritants are crucial for maintaining optimal lung health with one lung.
What Are the Types of Lung Agenesis?
The types of lung agenesis include
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Type 1 or Agenesis: Complete absence of lung, bronchus, and vascular supply on the affected side.
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Type 2 or Aplasia: Complete absence of lungs with a rudimentary bronchus.
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Type 3 or Hypoplasia: Partial existence of lung, bronchial tree, and vascular supply.
What Are the Causes of Lung Agenesis?
Lung agenesis can be because by two causes:
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Primary Cause: It is a congenital abnormality in which the primitive lung bud fails to divide into two, resulting in the development of a single normal lung and the complete absence of the other.
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Secondary Cause: It may be associated with multiple congenital anomalies, including gastrointestinal, cardiovascular, skeletal, upper respiratory tract, and facial, or limbic defects.
What Are the Signs and Symptoms of Lung Agenesis?
The signs and symptoms can vary depending on the individual and the severity of the disease. In a few infants, it can be either asymptomatic or only can be diagnosed later in life as an incidental finding. In some cases, it may present with severe respiratory distress. The survival chances in these cases are questionable.
The signs and symptoms include
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Frequent lung infections.
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Dyspnea or difficulty in breathing.
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Tachycardia or increased heart rate.
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Cyanosis or bluish skin discoloration, especially in the fingernails, tongue, and nose tip.
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Chest asymmetry.
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Decreased or limited exercise tolerance.
What Are the Diagnostic Tests to Be Carried Out?
The diagnostic tests that can be carried out are as follows:
1) Chest X-Ray: A marked homogeneous opacification in the middle and lower zones with a shift of the mediastinum to the ipsilateral side along with scoliosis can be observed. It can also reveal a radio-opaque hemithorax. Further investigations should be carried out for a definitive diagnosis.
2) Contrast Enhanced Computed Tomography (CECT): May reveal features like:
- A marked ipsilateral shift of the mediastinum.
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Herniation of the remaining lung across the midline.
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Small bronchus present in aplasia.
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Complete absence of right pulmonary artery.
3) Angiography: It may show a lack of pulmonary or bronchial arterial circulation.
4) Antenatal Ultrasound: It may reveal the mediastinal shift's presence without a diaphragmatic hernia.
5) Antenatal Echocardiogram: It may reveal a complete absence of pulmonary vessels or the absence of any one of its branches on the affected side.
6) Magnetic Resonance Imaging (MRI): It provides a confirmatory diagnosis for pulmonary agenesis. It can easily evaluate the size of the lung present and the presence of other congenital anomalies.
7) Bronchoscopy: It may confirm the rudimentary bronchus.
After the delivery of the child, the diagnosis can be made with the help of the following factors:
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Diminished breath sounds, particularly at the base and axilla, as this is occupied by the heart and other mediastinal structures.
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Breath sounds may be heard in the upper portions due to the presence of herniated opposite lung in the upper part of the affected hemithorax.
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Displacement of the mediastinum to the ipsilateral side.
What Is the Management of Lung Agenesis?
The management of lung agenesis depends upon the severity of the disorder. If it is asymptomatic, then no treatment is required in such cases. But if there is a presence of recurrent respiratory infections, symptomatic relief can be provided with aggressive antibiotic coverage, bronchodilators, and physiotherapy. If the infection persists even after antibiotic therapy and postural drainage, surgical excision of the hypoplastic bud become the treatment of choice.
The prognosis of the disorder depends upon the following factors:
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The severity of the associated congenital anomalies.
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Involvement of the normal lungs in the disease process.
Conclusion:
Lung agenesis or pulmonary agenesis is a rare congenital anomaly characterized by a complete absence of lungs which can be either unilateral or bilateral. However, bilateral lung agenesis has a poor prognosis and has proven to be fatal. Lung agenesis may be present as a single isolated entity or associated with various other congenital anomalies.
The clinical presentation can be variable depending on individuals and the severity of the disorder. It may be either asymptomatic or present with persistent lung infections and severe respiratory distress.
Asymptomatic cases require no medical intervention, but symptomatic cases with recurrent infections and respiratory distress should be treated aggressively with antibiotics and bronchodilators. Surgical intervention may be needed in case of recurrent infections. Proper diagnosis and early intervention have proven to be beneficial in such cases. Diagnosing a congenital anomaly later in life can be pretty challenging.
