What is Pulmonary Sequestration?
Pulmonary sequestration is a condition where a piece of the lung tissue isn’t normal and has no connection with the overall lung system. It also gets its blood supply differently than the normal lung. This makes it a piece of non-working lung tissue. This condition was first talked about in detail by a person named Pryce in 1946, but similar cases were acknowledged even earlier in 1861 by Rokitansky and Rektorik.
In terms of explaining this condition more, Pryce divided it into two types:
– Intralobar
– Extralobar
He also further divided Intralobar into three subtypes.
In Intralobar sequestration, the abnormal lung is located inside the covering of the working lung. It drains into the pulmonary vein, which is a blood vessel that carries blood away from the lungs to the heart. It is more often found in the left lower part of the lung. In fact, most intralobar sequestrations are found in the back part of the left lower lung. This type is more common and happens in about 75% to 86% of all such cases. One exception is when pulmonary sequestrations are related to “Scimitar syndrome,” where the right-sided locations are more common.
Extralobar sequestration on the other hand, has its own cover and drains into different systemic veins – typically into the lower lobe vein or veins along your spine. There have been cases where it drains into veins in the shoulder or the portal vein (which carries blood from various organs to the liver).
The blood supply to the extralobar type is usually from big blood vessels in the body – most commonly from the descending thoracic aorta (73% of cases). Sometimes, the blood supply might be from other parts like the top part of the abdominal aorta, celiac trunk, or the artery going to the spleen. Other rarer blood supply sources have also been seen, like the pericardiophrenic, right coronary artery, or internal thoracic arteries.
Pulmonary sequestrations are often found between the diaphragm (muscle that helps us breathe) and the lower part of the lungs and, in rare cases, below the diaphragm. Males usually have a higher chance of having pulmonary sequestration. However, the type which is found inside the abdomen is often in women (75% of the time) and it’s typically located at the back of the left side.
What Causes Pulmonary Sequestration?
Pulmonary sequestration refers to a birth defect of the early stages of lung development. The most widely accepted explanation involves the formation of an extra, unnecessary part of the lung that grows beneath the normal lung bud.
This continues migrating with the esophagus in a case called extra-lobar sequestration. Following this, it gets its blood supply from the primitive splanchnic vessels (early vessels supplying organs) that circle the foregut, which is part of the digestive tract. If the lung bud develops before the formation of the pleura (membrane surrounding the lungs), it results in intralobar sequestration, which is a different variation of this defect.
Risk Factors and Frequency for Pulmonary Sequestration
Pulmonary sequestration, a type of lung malformation present at birth, makes up between 0.15% to 6.40% of all such conditions. It’s predominantly diagnosed in people aged 20 or younger, making up 60% of cases. Rarely, it’s found in people over 50. However, this type accounts for most cases in adults. A study from the Mayo Clinic found that the typical age people were diagnosed was 42. It is more prevalent in males, with a male to female ratio of 4:1. Interestingly, 30% of pulmonary sequestrations are discovered accidentally, not because the patient had symptoms.
- Pulmonary sequestration is a type of lung malformation and makes up 0.15% to 6.40% of all congenital lung malformations.
- 60% of these cases are diagnosed in individuals 20 years old or younger.
- It is rarely found in people over 50 years old.
- The condition is more common in adults, with the median diagnosis age being 42.
- There are 4 times as many cases in males as there are in females.
- About 30% of pulmonary sequestrations are found incidentally, without causing symptoms in the patient.
Signs and Symptoms of Pulmonary Sequestration
Intralobar sequestration, a condition where some lung tissue is disconnected from the rest of the lung, often doesn’t cause symptoms and is usually discovered during a chest scan in adulthood. When symptoms do appear, it’s commonly because of repeated lung infections in a certain part of the lung. Other symptoms can include a persistent cough, back pain, or shortness of breath during exercise. Sometimes, this condition can also cause coughing up of blood.
Extralobar sequestration, another variant of the condition, is usually diagnosed early in infancy. Typically, this happens when the sequestration is large and found in a location that leads to symptoms such as breathing difficulties, heart failure or unexpected lung or chest bleeding. Infections are rare with extralobar sequestration as these areas are isolated from the rest of the lungs.
It’s also found that a number of birth defects are often observed with extralobar sequestration. These can include:
- Congenital diaphragmatic hernia (commonest)
- Congenital cystic adenomatoid malformation
- Vertebral defects
- Congenital heart disease
- Tracheoesophageal fistula
- Pulmonary hypoplasia
- Bronchogenic cyst
- Congenital megacolon
Among patients with extralobar sequestration, around 15% to 25% also have a type II cystic adenomatoid malformation of the lung.
Testing for Pulmonary Sequestration
If a medical professional suspects a condition called pulmonary sequestration, it’s usually in the following situations:
– If a pregnant woman’s ultrasound reveals excess amniotic fluid, signs of excessive fluid buildup in the fetus, a build-up of fluid in the chest cavity, or a mass in the lung.
– In infants who have symptoms like difficulty breathing, grunting sounds, and trouble eating.
– In adults and children who experience symptoms like repeated pneumonia, lung abscesses, or coughing up blood.
Pulmonary sequestration can be diagnosed in a fetus using a Doppler ultrasound technique around 18 to 19 weeks into the pregnancy. Interestingly, in some cases, these abnormal tissues in the lung may shrink or even disappear on their own.
The definitive diagnosis of pulmonary sequestration requires identification of a unique blood supply and drainage system in these abnormal lung tissues. Historically, a specific type of imaging, called digital subtraction angiography, was used to identify these lesions and their unusual vascular system.
Now, however, high-resolution CT scans with 3D construction have become preferred methods of diagnosis because they are less invasive. Magnetic resonance angiography (MRI) is also a good alternative tool for diagnosis.
The imaging serves two main purposes:
1. To ensure there are no other diseases present in the chest.
2. To identify an abnormal blood supply.
When a CT scan of the chest is performed with contrast dye, the sequestration can appear to have different patterns. These may include cyst-like structures, a mass, a layered lesion, a lesion surrounded by a capsule with an air-fluid level, collapsed lung tissue, or bronchiectasis, a condition where the walls of the bronchi thicken, causing breathing difficulties. However, over 60% of cases were only correctly diagnosed after surgery, highlighting the substantial issue of misdiagnosis before surgery.
Extra lobar pulmonary sequestration found in the abdominal cavity can be very difficult to differentiate from back abdominal tumors. In patients where this has occurred, the diagnosis has almost always only been made after surgery by examining the removed tissue.
A biopsy of the pulmonary sequestration, a procedure to remove a small bit of tissue for examination, is somewhat controversial due to possible risk of bleeding from the abnormal blood vessels.
As part of the initial investigations, testing the levels of certain hormones and chemicals in your blood and urine could help to identify this condition and differentiate it from other similar tumors.
This condition usually has a mild to moderate effect on lung function, found in about 8.8% of patients. From a lung function perspective, surgical removal of the sequestered tissue is generally well tolerated.
Treatment Options for Pulmonary Sequestration
If a baby, who is yet to be born and is under 30 weeks in development, shows signs of a severe fluid buildup condition known as hydrops, medical professionals may recommend a treatment known as thoracoamniotic shunting.
After the birth, in cases of a large sequestration, which is a health condition where a portion of the lung is not properly connected to the rest of the respiratory system, the baby might need help breathing. This support could come from a ventilator, a high-frequency oscillatory ventilator, or extracorporeal membrane oxygenation (ECMO), which is a treatment that oxygenates the blood outside the body.
In situations of a large buildup of fluid in the chest, an immediate procedure called tube thoracostomy, which involves inserting a tube to drain the fluid, is needed.
For babies showing symptoms, surgery to remove the affected part of the lung is recommended, although this procedure is delayed until the baby’s condition has stabilized, particularly in babies with an underdeveloped lung (pulmonary hypoplasia) and high blood pressure in the lungs (pulmonary hypertension).
Removing a lobe of the lung, called pulmonary lobectomy, is the best treatment for established pulmonary sequestration. This is suggested even for patients without symptoms to avoid lung infection and progressive inflammation. However, for patients without symptoms, it is unclear whether proactive surgery or a more conservative approach is better.
Surgery to remove the affected lung tissue can be performed with an open procedure, or less invasive methods such as video-assisted thoracoscopic procedures (VATS). In VATS, a camera is inserted into the chest through small incisions which allows the surgeon to see and work inside the chest. Recently, a more specific type of VATS called uniportal VATS guided lobectomy has also been successful. Studies have shown no significant differences in surgical length, hospital stay after surgery, or complications when comparing open procedures to VATS.
Surgery is safest after two months of age due to lower anesthesia and surgical risks.
Post-operative complications, which can involve issues like prolonged air leaks from the lung into the chest cavity, abnormal connections between airways and pleural space, coughing up blood, infection within the chest cavity, and arrhythmia, occur in about 25-28% of cases.
In recent years, an alternative treatment option involving endovascular embolization and coiling, which reduce blood flow leading to the affected tissue dying off, have become available. The drawback of this method is a recurrence rate of 25% to 47% due to incomplete closure, displacement of the embolic agent, opening of collateral blood vessels, or formation of shunts.
Some experts are also looking into preoperative embolization of the sequestration to minimize bleeding risks during surgery because the area of sequestration often has abnormally formed, fragile blood vessels, making it prone to bleeding complications during surgery.
What else can Pulmonary Sequestration be?
When doctors diagnose lung-related medical conditions in children, they generally check for certain specific diseases. The most common among these are:
- Cystic adenomatoid malformation (a rare lung condition affecting newborns)
- Bronchogenic cyst (a benign tumor in the chest)
- Focal bronchiectasis (a condition that causes enlargement and damage to parts of the airways)
- Congenital lobar emphysema (a rare lung disorder that usually occurs in infants)
- Retroperitoneal tumors in extra lobar abdominal sequestrations (abnormal tissue growth in inappropriate locations)
What to expect with Pulmonary Sequestration
Some factors can lead to a poorer outlook for treatment, such as the presence of fetal hydrops (a severe condition in which abnormal amounts of fluid build up in two or more body areas of a fetus or newborn) or pulmonary hypoplasia (underdevelopment of the lungs). According to studies, only 22% of babies with a large accumulation of pleural effusion (fluid around the lungs) are able to survive.
On the other hand, babies with an “extra lobar intraabdominal sequestration” (a rare non-functioning mass of normal lung tissue that doesn’t connect to the airway system and gets its blood supply from the systemic circulation) tend to have a better prognosis, improving the chances of survival.
Possible Complications When Diagnosed with Pulmonary Sequestration
Children with early bronchopulmonary sequestration, a lung condition, often have growth abnormalities. These could be due to several reasons including persistent infections, failure of the body to supply enough blood, or blood being diverted from the digestive system which could lead to difficulties in nutrient absorption.
In adults, the main problem associated with this condition is hemoptysis, which is coughing up blood due to high pressure in the blood vessels. They may also have a condition called hemorrhagic pleural effusion, where there is excess fluid in the lungs because of tissue damage.
For those with intralobar sequestration, a type of bronchopulmonary sequestration, recurring infections are common. The most common culprit is the bacterium Pseudomonas aeruginosa, although other organisms such as the tuberculosis bacterium, Nocardia, or a fungus called Aspergillus may also be involved.
Certain rare instances involve cases of extralobar sequestrations, another type of bronchopulmonary sequestration, that are connected to the digestive system. They require tests using a substance called barium for diagnosis and are known as congenital bronchopulmonary foregut malformations (CBPFM).
Lastly, there have been cases where malignant, or cancerous, tumors have developed within intralobar sequestration.
Common Complications:
- Growth abnormalities in children
- Coughing up blood in adults
- Excess fluid in the lungs due to tissue damage
- Recurrent infections particularly by Pseudomonas aeruginosa
- Digestive system abnormalities associated with extralobar sequestrations
- Development of malignant tumors within intralobar sequestration
