Introduction
Pulmonary agenesis is a rare congenital disorder. It is diagnosed during childhood. It is the complete absence of one or both lungs. It is a fatal condition that may present with cardiovascular, gastrointestinal, musculoskeletal, and urogenital comorbidities. But, individuals without any comorbidities or those with mild disorders reach adulthood.
What Is Pulmonary Agenesis?
Agenesis means the complete absence of the organ. It is due to the failure to develop an organ during embryonic growth. Pulmonary agenesis is the complete absence of lungs, bronchi, bronchioles, blood vessels, and respiratory parenchyma. It is due to the complete developmental arrest of the primitive lung in the embryonic stage. It may be unilateral or bilateral.
What Are the Types of Pulmonary Agenesis?
Pulmonary agenesis can be unilateral or bilateral depending on one or both the lungs affected. It is classified into:
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Type 1 Pulmonary Agenesis - Complete absence of one or both the lungs, bronchus, blood vessels, and pulmonary parenchyma.
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Type 2 Pulmonary Aplasia - Immature bronchus with complete absence of pulmonary parenchyma.
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Type 3 Pulmonary Hypoplasia - Incomplete development of the bronchial tree, pulmonary parenchyma, and blood vessels.
What Are the Causes of Pulmonary Agenesis?
The exact cause is not known. It is due to the developmental arrest of the primitive lung during the embryonic stage. Pulmonary agenesis is unilateral or bilateral, depending on the stage in which the developmental arrest occurs. The agenesis is usually bilateral if the developmental arrest occurs early in embryonic life. It is a rare condition with complete failure in developing the primordial respiratory structure that gives rise to the respiratory tract. Thus, both lungs are absent. It is a highly fatal condition.
Unilateral agenesis occurs when the developmental arrest occurs at the end of the fourth week of gestation when the respiratory primordium divides into right and left primitive lung buds. This fails to develop one of the lungs. The exact cause of agenesis is unknown, but scientists suggested various theories to explain the cause of pulmonary agenesis. The theories are vitamin A deficiency during pregnancy causes pulmonary agenesis, iatrogenic and viral factors are the cause, and genetic factors are responsible for agenesis.
What Are the Signs and Symptoms of Pulmonary Agenesis?
The lungs, parenchyma, blood vessels, and supporting structures are completely absent, and only the primitive bronchus is present. Hence, the exchange of gasses does not take place. In bilateral pulmonary agenesis, both the lungs are absent, and the fetus loses the ability to survive. In unilateral pulmonary agenesis, the severity depends on the area of tissue affected. Symptoms can be seen in infancy, childhood, teenage, or adulthood.
The symptoms include:
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Recurrent pulmonary infections due to retention of bronchial secretions.
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Limited tolerance to exercise due to reduction in forced expiratory volume and forced vital capacity.
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Increased heartbeat.
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Cyanosis (bluish discoloration of the skin).
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Chest asymmetry.
What Are the Associated Conditions?
Pulmonary agenesis is sometimes associated with gastrointestinal, genitourinary, and ocular abnormalities. The congenital abnormalities associated with pulmonary agenesis include tracheal stenosis, esophageal atresia, bronchogenic cysts, tracheoesophageal fistula, patent ductus arteriosus, Fallot’s tetralogy, and anomalies of the blood vessels.
How Is Pulmonary Agenesis Diagnosed?
It is possible to diagnose pulmonary agenesis before birth.
Prenatal Diagnosis:
The prenatal diagnosis includes:
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Prenatal Sonographic Evaluation - It is also called a biophysical profile. A high frequency of associated abnormalities can be detected.
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2-Dimensional Color Doppler Imaging - It is used to determine the presence of pulmonary blood vessels since they are absent in pulmonary agenesis. It visually captures the blood flow.
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Congenital Diaphragmatic Hernia - It is a possible reason for pulmonary agenesis. A diaphragmatic hernia is the upward displacement of the diaphragm and the abdominal organs.This is due to space in the chest wall created by the absence of lung tissue.
Diagnosis After Birth:
Various techniques are available to diagnose pulmonary agenesis. This includes:
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Chest X-Ray - It is used to detect the presence of lung herniation. The unaffected portion of the lung becomes hypertrophied and moves into the space on the opposite side of the chest wall. The herniation progresses with age and can be easily detected in adults. Fluoroscopy is used to detect herniation.
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Pulmonary Angiography - It detects the presence of pulmonary artery branches. This differentiates pulmonary agenesis, hypoplasia, and aplasia.
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Electrocardiogram - It is used to detect dextrocardia. If the right lung is absent, the heart rotates in the empty space in a clockwise direction, shifting its location for apex beat occurrence. If the left lung is absent, heart sounds are louder than normal.
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Chest Asymmetry - It is more obvious in males. In females, the breasts are conical in shape and highly placed on the affected side.
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Other Imaging Studies: CT (Computed Tomography) Scan, MRI (Magnetic Resonance Imaging) Scan, Bronchoscopy, and Bronchography are also used to observe lung anatomy.
How Is Pulmonary Agenesis Treated?
The treatment for pulmonary agenesis depends on the severity of the disorder. The nonfunctioning lobe or the defective lung is surgically removed to reduce symptoms and infections. A surgical procedure called pulmonary plombage was done in the past to shift the mediastinum to its anatomical position. It is also called extraperiosteal or extrapleural pneumolysis. A cavity is created by the intrathoracic placement of inert materials like acrylic balls, ping pong balls, oil, rubber sheets, paraffin wax, and gauze to shift the mediastinum to the anatomical position.
A recent technique involves the implantation of a tissue expander via thoracotomy. This preserves the remaining functional tissue and prevents musculoskeletal disfigurement. A special procedure called ex-utero intrapartum treatment (EXIT) is performed during the delivery of the fetus. This is done for babies with extensive lung defects which require airway support. The baby is partially delivered through an incision in the uterus. The baby remains attached to the mother’s placenta. Lung resection is performed to provide a functioning airway while the baby still receives support from the placenta. Once the airway is established, the baby is fully delivered.
Conclusion
Pulmonary agenesis is a rare congenital disorder. It can be diagnosed before birth or during childhood. Individuals with unilateral pulmonary agenesis have a higher survival rate than bilateral pulmonary agenesis. Early diagnosis and treatment can help in preventing life-threatening complications.
