Introduction:
Pulmonary sequestration is a congenital or acquired condition. It is an accessory lung tissue that does not contribute to respiratory function. It is usually diagnosed in children and infants, but it is also seen in adults. It is diagnosed in prenatal scans. Failure of earlier diagnosis increases the risk of complications and morbidity.
What Is Pulmonary Sequestration?
Pulmonary sequestration is an abnormal mass of tissue that develops in the lung. It is supplied by an artery from the systemic circulation and does not receive blood supply from the pulmonary artery. It is not connected to the bronchial airway. It has no function and does not contribute to respiration.
How Does Pulmonary Sequestration Form?
Intralobar pulmonary sequestration develop due to recurrent lung infections in young adults. The extra lobar pulmonary sequestration is formed due to prenatal pulmonary malformation. The accessory lung tissue develops from the ventral aspect of the primitive foregut. It migrates down with the developing lung and the esophagus. If the sequestration forms before the development of pleura and if it is present within the pleural covering, it is called intrapulmonary sequestration. If it develops after the formation of pleura, it is called extrapulmonary sequestration, and it communicates with the gastrointestinal tract. Both of them receive blood supply from the thoracic or abdominal aorta. The intrapulmonary sequestration is located in the posterior basal segment of the lungs. The extrapulmonary sequestration is located above, below, or within the diaphragm.
What Are the Types of Pulmonary Sequestration?
Pulmonary sequestration is classified into intralobar sequestration and extra lobar sequestration.
1. Intralobar Sequestration - It is the common type of sequestration that is seen in seventy-five percent of cases.
- It occurs in adolescents or young adults due to recurrent infections.
- The abnormal tissue is enclosed within the visceral pleura.
- It occurs in males and females.
- The accessory tissue receives blood supply from the lower thoracic or upper abdominal aorta.
- Pulmonary veins carry the venous drainage to the left atrium of the heart.
- Abnormal connections to the vena cava, azygous vein, or right atrium may be present.
- Sometimes, the sequestration is located in the paravertebral gutter in the posterior segment of the left lower lobe.
- This type of sequestration is not associated with developmental abnormalities.
- Signs and symptoms of pulmonary infections of the lower lobe are present. The sequestration becomes infected if it is incomplete.
2. Extra Lobar Sequestration - It occurs in 25 % of patients.
- It occurs in infants.
- It forms an accessory lung tissue within the pleural membrane.
- It is highly prevalent in males.
- It is usually situated in the left hemidiaphragm.
- It may present as a subdiaphragmatic or retroperitoneal mass.
- It receives blood supply from the thoracic aorta.
- Venous drainage is via the systemic venous system to the right atrium, vena cava, or azygous systems.
- Congenital abnormalities like congenital cystic adenomatoid malformation, vertebral anomalies, pulmonary hypoplasia, and colonic duplication are commonly present in patients with extra lobar sequestration.
- The sequestration is closely associated with the esophagus, and abnormal communication may develop.
What Are the Complications?
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Recurrent infection.
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High cardiac output failure.
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Shunting of blood from the gastrointestinal tract results in malabsorption.
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Coughing up blood in adult patients due to high pressure in blood vessels.
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Pleural effusions with bleeding are common in fibrinoid necrosis of the sequestration.
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Malignant transformation in intralobular sequestration.
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Congenital bronchopulmonary foregut malformation (communication of extra lobar sequestration with the gastrointestinal tract).
How Is Pulmonary Sequestration Diagnosed?
Various imaging strategies are used to diagnose pulmonary sequestration. An arteriogram is used to identify the blood supply.
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Chest X-Ray - A sequestration appears as a uniform, dense mass within the thoracic cavity or pulmonary parenchyma. Areas of the cystic lesion can be observed. Air-fluid levels can be seen.
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Ultrasound - It shows a well-defined or irregular echogenic homogenous mass with or without the appearance of cysts. Doppler studies are useful in identifying arterial supply and venous drainage.
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Computed Tomography (CT) Scan - CT scans are ninety percent accurate in diagnosing pulmonary sequestration. The sequestration appears as a solid homogenous or heterogenous mass with or without cystic changes. It may show the presence of a large lesion with an air-fluid level, a collection of many cysts containing air or fluid, or a well-defined cystic lesion. In addition, the CT scan shows emphysematous changes at the margin of the lesion, which are not visible on the chest X-ray. CT with an intravenous contrast dye and multiplanar and 3D (three-dimensional) reconstructions are useful in diagnosing pulmonary sequestration.
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Magnetic Resonance Imaging (MRI) Scan - Conventional and contrast-enhanced MRI scans help diagnose pulmonary sequestration. It also helps in identifying the blood supply and venous drainage. But, CT is more useful in determining the emphysematous changes and shows sharper images of the thin-walled cysts.
How Is Pulmonary Sequestration Managed?
Pulmonary sequestration is surgically removed after birth. It is a safe and effective procedure that does not disrupt lung function. In some cases, complications like fluid collection occur in the chest cavity of the fetus. In such cases, a Harrison catheter shunt is used to drain this fluid into the amniotic fluid. A fetus with a large lesion develops breathing difficulties during birth.
EXIT (ex utero intrapartum treatment procedure - a specialized delivery procedure) procedures or fetal laser ablation procedures are specialized procedures performed during delivery to manage airway compression. It is a minimally invasive interventional procedure done for the fetus. This uses a small needle inserted into the sequestration, and the laser is targeted at the blood vessel supplying the sequestration. This disrupts the blood supply and prevents the growth of sequestration. The heart and the lungs of the fetus grow normally, resulting in shrinkage of the sequestration and the pleural fluid. This is removed through wedge resection, segmentectomy, or lobectomy via video-assisted thoracoscopic surgery (VATS) or thoracotomy.
Conclusion:
An extra lobar and intralobar pulmonary sequestration occur rarely. Early diagnosis in infancy is helpful in the management of lung malformation. It requires the efforts of pulmonologists, radiologists, and thoracic surgeons in treating pulmonary sequestration. Early diagnosis and treatment of this rare lung disorder reduce the risk of morbidity and mortality.
