A rare congenital (present at birth) condition known as pulmonary sequestration involves aberrant lung tissue that is not connected to the normal pulmonary arterial blood supply or bronchial airway system. In both structure and function, this portion of lung tissue is essentially “sequestered” or separated from the rest of the lungs.
Unlike normal lung tissue, this sequestered segment receives its blood supply from systemic circulation rather than from the pulmonary artery. In this article, we’ll explore Pulmonary sequestration, its types, symptoms, causes, and available treatments.
Types of Pulmonary Sequestration
The location and type of lung tissue involved determine the two main types of pulmonary sequestration:
Intralobar Sequestration (ILS)
- Intralobar sequestration is more common and accounts for about 75% of all cases of pulmonary sequestration.
- This type is defined by the sequestered tissue being located within the same lobar compartment of the lung as the surrounding normal lung tissue.
- ILS usually lacks its pleural covering, meaning it shares the pleural membrane with the surrounding lung tissue.
- Most cases of intralobular sequestration are diagnosed later in life, typically during adolescence or adulthood, often after repeated lung infections.
Extralobar Sequestration (ELS)
- The remaining 25% of cases involve extralobar sequestration, which is typically located outside normal lung tissue.
- This type has its pleural covering, separating it from the adjacent normal lung.
- Extralobar sequestration often presents earlier in life, even in newborns or infants, as it is sometimes associated with other inherited abnormalities, such as diaphragmatic hernias.
- Unlike ILS, ELS does not share its blood supply with the normal lung and often has a more complex anatomical connection with other organs.
Causes
The exact cause of pulmonary sequestration is not entirely understood. However, it is generally believed to be a result of developmental abnormalities during the embryonic stage, where the lung tissue fails to connect to the developing bronchial system.
Some theories suggest that aberrant lung tissue may develop due to a disruption in the budding process of the lungs or the developing vascular system. Factors contributing to these disruptions may include genetic anomalies or, in utero, environmental factors, although no definitive genetic markers have been associated with pulmonary sequestration.
Symptoms
The symptoms of pulmonary sequestration vary depending on the type, location, and size of the sequestered tissue. Some people might not have any symptoms at all and only learn about the condition by chance when they are doing imaging tests for other problems. When there are symptoms, they may include:
Recurrent Lung Infections
Many patients with pulmonary sequestration experience repeated episodes of pneumonia or other respiratory infections. It happens because the tissue that is sequestered and not connected to regular drainage channels may retain bacteria and mucus, which can lead to an infection’s breeding ground. If untreated, these recurring infections can eventually cause lung damage.
Chronic Cough
Some patients develop a persistent cough due to irritation in the lungs. This cough may be a protective response of the body attempting to clear the sequestered tissue, which often fails to drain properly. The chronic cough can be exhausting, impacting daily activities and quality of life.
Shortness of Breath
It may occur due to the space occupied by the sequestered tissue or as a result of chronic infection. The abnormal tissue can compress surrounding lung areas, reducing functional lung capacity and making it harder to breathe, especially during physical exertion.
Chest Pain or Discomfort
As the condition progresses, some patients may feel discomfort in the affected area of the chest. This can be due to inflammation, recurrent infections, or pressure exerted by the sequestered mass on neighbouring structures, which may become more pronounced over time.
Hemoptysis (Coughing up Blood)
Blood may occasionally appear in the sputum due to bleeding caused by an aberrant blood supply to the sequestered tissue, though this is uncommon. Hemoptysis can be alarming and may indicate complications, such as increased pressure in the abnormal vessels or infection-induced tissue damage.
Complications Associated with Pulmonary Sequestration
Even though some pulmonary sequestration patients have no symptoms, there are some possible side effects that could occur, especially if treatment is not received:
Recurrent Infections
One of the most common complications is recurrent pneumonia due to the inability of the sequestered lung tissue to drain mucus effectively. It can lead to repeated courses of antibiotics, and in severe cases, the infections may spread to nearby lung tissue, exacerbating respiratory issues.
Lung Abscess Formation
Chronic infection within the sequestered tissue can lead to abscess formation. An abscess (a pus-filled cavity) can cause significant pain and fever and, when left untreated, can lead to more severe infections or rupture into surrounding areas.
Haemorrhage
Abnormal blood vessels supplying the sequestered tissue may rupture, leading to bleeding within the lung. It can cause coughing up of blood (hemoptysis) and, in severe cases, may lead to dangerous blood loss, requiring immediate medical intervention.
Cardiac Issues
Large sequestrations may place additional strain on the heart, leading to cardiopulmonary complications. The increased workload on the heart, especially with systemic blood supply involvement, can contribute to conditions like pulmonary hypertension or right-sided heart strain.
Treatment Options
The treatment of pulmonary sequestration depends on the symptoms and risks associated with the condition:
Surgical Resection
Surgical removal, or resection, of the sequestered tissue, is the most common and effective treatment for symptomatic patients. This approach can prevent recurrent infections and alleviate associated symptoms.
In cases of intralobular sequestration, a segmentectomy or lobectomy may be performed, which involves removing part or all of the affected lobe.
Extralobar sequestration can be removed without affecting the surrounding lung tissue since it has its pleural covering.
Endovascular Embolisation
Endovascular embolisation can be used in place of surgery in certain situations. In order to effectively cut off the sequestered tissue’s blood flow and lower the risk of infection or other complications, a catheter is inserted during this minimally invasive procedure.
Embolisation may be preferred for patients who cannot undergo surgery due to age or underlying health conditions.
Observation
Careful monitoring without immediate treatment may be an option in asymptomatic cases, particularly in older children or adults. It is often recommended for individuals who do not experience infections or other symptoms and for whom the risk of surgery outweighs the benefits.
Conclusion
In conclusion, pulmonary sequestration is a rare congenital lung anomaly where non-functional lung tissue is separated from normal lung anatomy, receiving its blood supply from systemic circulation. The condition can cause respiratory issues and recurrent infections despite the fact that it is frequently asymptomatic. Most patients now have a good prognosis due to improvements in imaging and surgical methods that make it easier to identify and treat pulmonary sequestration.
