Pulmonary sequestration

　　First, Etiology

　　During the period of embryonic development, the underdevelopment of the pulmonary artery causes the blood supply of some lung tissue to be impaired, and the branch of the aorta replaces the pulmonary artery to supply the lung tissue in this area. Since the oxygen content of the blood from the aorta is completely different from that from the pulmonary artery, the pulmonary function of this segment of lung tissue cannot be performed, resulting in underdevelopment and the absence of lung function.

　　Second, Pathogenesis

　　The pathogenesis of pulmonary sequestration is unclear, and common theories include the accessory pulmonary bud theory, Prvce's traction theory, and Smith's theory of vascular underdevelopment. Prvce's traction theory is widely recognized, which holds that in the early embryonic stage, there are many visceral capillaries connected to the dorsal aorta around the primitive gut and lung buds. When the lung tissue detaches, these connected vessels gradually regress and absorb. Due to some reason, when vascular remnants occur, they become abnormal branches of the aorta, pulling a part of the embryonic lung tissue to form pulmonary sequestration. This part of lung tissue is isolated from the normal bronchus and pulmonary artery and is supplied with blood by the abnormal artery. When the lung tissue detaches from the primitive gut in the early embryonic stage and is pulled, if the accessory pulmonary bud is located within the pleura, it forms intralobar type pulmonary sequestration. If the abnormal lung bud that appears after the pleura has formed is pulled, it becomes extralobar type pulmonary sequestration. However, the traction theory cannot explain all cases of pulmonary sequestration; there are a few cases without abnormal arteries, or with abnormal arteries but without isolated lung. Regardless of extralobar or intralobar types, the main arteries of pulmonary sequestration mainly originate from branches of the systemic circulation, mainly the descending aorta, but can also originate from the upper part of the abdominal aorta, celiac artery and its branches, ascending aorta or aortic arch, brachiocephalic artery, subclavian artery, internal mammary artery, intercostal artery, diaphragmatic artery, or renal artery, etc. Most enter the isolated lung through the lower pulmonary ligament, usually as one branch, but there are also cases with two or more branches, which are less common. The arteries vary in thickness, with some reaching about 1 cm in diameter. These abnormal arteries have a similar structure to the aorta, containing more elastic fiber tissue, with higher pressure and prone to atherosclerosis. How the systemic circulation vessels develop into the isolated lung is not clear. Normally, the pulmonary artery originates from the 6th embryonic arch and extends its branches to the lung primordium, with the branches of the visceral vascular plexus that originally supplied the lung bud gradually degenerating, leaving only the bronchial artery. According to the widely accepted theory, there are abundant collateral communications between the dorsal aorta and the visceral capillaries around the lung buds, and some of these collateral vessels absorb and regress incompletely, forming abnormal systemic circulation arteries that supply the isolated lung tissue. At the same time, due to the embryonic tissue of pulmonary sequestration being in an abnormal location, it prevents the development of pulmonary circulation vessels. The venous return of pulmonary sequestration is not uniform: the blood of intralobar type pulmonary sequestration returns to the lower pulmonary vein, causing left-to-left shunting, and occasionally it returns to the systemic circulation veins. The blood of extralobar type pulmonary sequestration returns to the hemiazygos vein, azygos vein, inferior vena cava, brachiocephalic vein, intercostal veins, etc., at this time, there is no shunting problem.

　　Complications caused by pulmonary cysts include the following situations:

　　1. Pulmonary cysts themselves have no gas exchange function. Large cysts can compress lung tissue, causing obstruction of pulmonary gas exchange. In severe cases, it can even lead to increased pulmonary artery pressure,加重心脏负担.

　　2. Long-term recurrent infections can easily lead to adhesions in surrounding tissues, affecting lung function, increasing the difficulty of surgery, and affecting postoperative recovery.

　　3. Bleeding and perforation caused by the destruction of the cyst wall of pulmonary cysts can lead to pneumothorax and hemothorax.

　　4. There are reports in the literature that pulmonary cysts may undergo malignant transformation.

　　Pulmonary sequestration is more common in adolescents and young adults, aged between 10 to 40 years, with more males than females, and intralobar type being more common than extralobar type. Due to the different classifications of pulmonary sequestration, the clinical manifestations vary. Common clinical manifestations of pulmonary sequestration include:

　　First, extralobar sequestrated lung:The extralobar sequestrated lung is less common than the intralobar type, with a male-to-female ratio of about 4:1 and a left-to-right ratio of about 2:1. It is mostly located between the lower lobe of the chest and the diaphragm, adjacent to normal lung tissue, or below the diaphragm, within the diaphragm, or in the mediastinum. It often occurs with other congenital malformations, with congenital diaphragmatic hernia being the most common, accounting for about 30%, followed by congenital bronchial cysts, congenital esophageal bronchial fistula, pulmonary hypoplasia, congenital heart disease, ectopic pancreas, pericardium, and other organ malformations. However, the extralobar sequestrated lung, due to its complete pleura, resembles a separate lobe of the lung and can be considered a supernumerary lung lobe. Because it does not communicate with the bronchus, it is soft and flexible, containing multiple cysts of unequal size. Pathology: The extralobar type is completely covered by the pleura, with a spongy black-brown tissue, accompanied by irregularly arranged vessels, more prominent at one end of the specimen. Microscopically, it shows an irregular arrangement of normal lung tissue, with very few tracheal structures, and the solid tissue is often underdeveloped. Because it has its own pleura and does not communicate with the bronchus, unless it communicates with the gastrointestinal tract, the chance of infection is rare. Therefore, if there are no other obvious malformations, the extralobar type is just a soft tissue mass that can survive asymptomatic into adulthood.

　　Common in newborns, generally asymptomatic, often discovered during routine X-ray examination. A small number of extralobar sequestrated lung may be discovered in neonates due to associated malformations, such as recurrent respiratory tract infections, fatigue, dyspnea, and even congestive heart failure in late stages. 60% are associated with ipsilateral diaphragmatic elevation, 30% with left diaphragmatic hernia, 50% are incidentally found during autopsy, physical examination, or examination of other diseases, 90% are located in the left lung.

　　Second, intralobar sequestrated lung:The incidence is low, but it is more common than the extralobar type, with 2/3 located in the posterior basal segment of the left lower lobe or right lower lobe, within the paravertebral groove. It differs from the extralobar type as follows: The incidence is similar in males and females, with a ratio of 1.5:1 to 2:1 between left and right sides, mostly located in the posterior basal segment of the lower lobe, rarely associated with other congenital malformations, most commonly associated with esophageal diverticula, diaphragmatic hernia, and other skeletal, cardiac malformations. The abnormal tissue does not have its own pleura and is isolated from normal lung tissue, so there is no clear boundary between the abnormal and normal lung tissue, coexisting in the same lobe with one or more cystic cavities, more solid tissue, and the cysts are filled with mucus. The intralobar sequestrated lung, especially those communicating with the bronchus, almost all cases develop secondary infection after a certain period of time, most of which appear before the age of 10 with recurrent symptoms of pulmonary infection, such as fever, cough, chest pain, expectoration of sputum, even purulent sputum or blood-streaked sputum. Severe cases may also present with systemic toxic symptoms similar to those of lung abscess. During infection, the cystic cavity is filled with pus, often communicating with the bronchus or the trachea of adjacent lung tissue. Physical examination may show dullness on percussion, reduced respiratory sounds, and sometimes wet rales. Some patients may have clubbing of the fingers, and the abnormal artery is usually from the lower part of the thoracic aorta or the upper part of the abdominal aorta, relatively large, with a diameter of 0.5 to 2 cm. The abnormal artery usually passes through the lower pulmonary ligament to reach the lesion site, and all return through the pulmonary veins. Microscopically, it shows a similar dilated bronchus, occasionally with cartilage plates within the wall, respiratory epithelium, and the abnormal lung tissue is accompanied by inflammation, fibrosis, or abscess.

　　The left lung is more common, 60% in the posterior basal segment of the lower lobe, and the one located in the upper lobe is rare, 15% are asymptomatic, and most appear the following symptoms in young and middle-aged adults: cough, expectoration, hemoptysis, recurrent pulmonary infections, palpitations, shortness of breath, etc. The symptoms are often caused by the communication between the lesion and the bronchus. After anti-infection treatment, the symptoms can be temporarily relieved, but the course of the disease can also last for several months or even years. Cysts can be solitary or multiple, of different sizes, and the surrounding lung tissue often has pneumonia. At this time, it is necessary to wait for the inflammation to subside before confirming the cystic characteristics of the shadow. The size of the lesion can change greatly over time, mainly depending on the internal gas and liquid volume. If the isolated lung is infected, the shape of the shadow can change greatly in a short time, and in the exhalation phase, gas retention can be seen in the isolated lung.

　　Three, Congenital bronchopulmonary foregut anomalies:This term is often used to represent a malformation combined with some bronchopulmonary lesions, but here it refers to pulmonary sequestration communicating with the gastrointestinal tract, the most common being the communication between the cystic cavity of the pulmonary sequestration and the lower segment of the esophagus or the fundus of the stomach. The pathological characteristics are consistent with intralobar or extralobar pulmonary sequestration. Gede first used this term in 1968 to describe it. Before this term was adopted, such pulmonary sequestration was classified as extralobar. The abnormal pulmonary segment is most common in the esophagus (often in the lower segment), and it can also be the stomach, with the right side being more common, accounting for 70% to 80%. The incidence rate is equal between males and females. Although it can occur in adults, it is usually diagnosed before the age of 1. The manifestations are: chronic cough, recurrent pneumonia or respiratory distress, common with other malformations such as extralobar pulmonary sequestration and diaphragmatic hernia.

　　Four, Short scimitar syndrome:Chassinant first described this syndrome in 1836, and the disease containing the following three malformations is called the short scimitar syndrome:

　　1. Underdeveloped right lung.

　　2. Abnormal return of the right pulmonary vein, pulmonary veins merge into the right atrium and/or inferior vena cava.

　　3. Thoracic artery blood supply, named after the curved knife-like abnormal venous shadow adjacent to the right heart margin on the chest film, has a significant familial tendency. Pathological thoracic artery blood supply: The most common manifestation is that the upper and middle lobes of the right lung are supplied by the pulmonary artery, while the lower lobe has one or more thoracic artery vessels supplying blood, which may originate from the lower segment of the thoracic aorta, enter the lung substance through the lower pulmonary ligament, or originate from the abdominal aorta, pass through the diaphragm into the lower pulmonary ligament. The lung tissue supplied by the thoracic artery can be normally ventilated or like a cystic hygroma without ventilation, and shows pulmonary hypertension.

　　Vena cava reflux abnormality:There is only one right pulmonary vein in most cases, but it can also be two, draining the blood of the entire lung or only the middle and lower lobes back to the inferior vena cava. Therefore, this syndrome forms a left-to-right shunt, causing an overload of the right heart, and the right lung also does not have normal physiological function. The confluence point of the abnormal pulmonary veins and the inferior vena cava can be above or below the diaphragm, with a similar incidence rate. Abnormalities of the right lung: Commonly seen are underdeveloped or maldeveloped right lung, which may be accompanied by bronchial anomalies. Other abnormalities: Other anomalies that may be associated with this syndrome include pulmonary artery agenesis or hypoplasia, dextrocardia, atrial septal defect, horseshoe lung, etc. In combination with clinical manifestations and X-ray chest film characteristics, B-ultrasound examination is first used, followed by further CT, MRI, or angiography according to the situation.

　　Congenital pulmonary cysts are a congenital pulmonary developmental anomaly, and the preventive methods are the same as those for other congenital diseases. After clear diagnosis, attention should be paid to preventing infection and actively treating it.

　　1. Avoid fever and colds in the early stages of pregnancy:Women who had a high fever in the early stages of pregnancy may experience adverse effects on brain tissue development even if no obvious external malformations appear in the child, such as intellectual disability, poor learning and response ability. This intellectual disability is irreversible. Of course, fetal malformation caused by high fever is also related to the sensitivity of pregnant women to high fever and other factors.

　　2. Avoid close contact with cats and dogs:Few people know that cats carrying bacteria are also a major source of infectious diseases that can cause fetal malformation, and cat feces are the main route of transmission for this malignant infectious disease.

　　3. Avoid women who wear heavy makeup every day:Surveys show that the incidence of fetal malformation among women who wear heavy makeup every day is 1.25 times higher than that of women who do not. The main adverse effects on the malformation of fetal development are toxic substances such as arsenic, lead, and mercury contained in cosmetics, which affect the normal development of the fetus. The second is that some components in cosmetics can produce aromatic amines with teratogenic effects after being irradiated by ultraviolet light from the sun.

　　4. Avoid emotional tension during pregnancy:Human emotions are controlled by the central nervous system and the endocrine system, and one of the endocrine hormones, adrenal cortical hormone, is closely related to human emotional changes. When pregnant women are emotionally tense, adrenal cortical hormones may hinder the integration of certain fetal tissues, and if this occurs during the first three months of pregnancy, it may cause fetal cleft lip or palate and other malformations.

　　5. Avoid drinking alcohol:Pregnant women who drink alcohol have the risk that alcohol can pass through the placenta to enter the developing embryo and cause severe harm to the fetus. This may result in a small head, extremely small ears and nose, and a thick upper lip.

　　6. Avoid eating mycotoxin-contaminated food:Experts point out that if pregnant women consume food contaminated with mycotoxins (moldy food), mycotoxins can pass through the placenta to harm the fetus, causing chromosomal breakage in fetal cells.

　　1. Chest X-ray:The chest X-ray of extralobar pulmonary sequestration often shows a uniform, triangular shadow with the tip pointing towards the hilum of the lung, which is difficult to diagnose preoperatively and is often diagnosed as an unknown intrathoracic mass and requires thoracotomy for exploration. Intralobar pulmonary sequestration is seen on the chest X-ray with a dense, uniform shadow in the lower lobe and posterior basal segment, closely adhering to the diaphragm surface, most of which are round or oval, a few can be triangular or polygonal, with generally clear boundaries, the long axis pointing posteriorly, indicating a connection with the descending aorta. If it is complicated with infection and communicates with the bronchus, it may appear as a single or multiple circular shadows with liquid levels, similar to the image of lung cysts, with varying wall thickness, surrounding inflammatory changes, and the size of the shadow can change with the evolution of the disease, increasing during infection and decreasing after inflammation absorption, but it will never completely disappear.

　　2. Tomography:The posterior segment of the lower lobe lesions sometimes overlaps with the shadow of the spine or heart on the chest radiograph, and tomography can clearly show the morphology, contour, and internal structure of the lesion. The lesion is usually round, elliptical, or triangular, with clear boundaries, and can present as cystic changes of different sizes. Sometimes, an abnormal blood vessel image connected to the aortic shadow can be seen on the tomography, presenting as comma-shaped or strand-like shadows. The tail of the comma represents the direction of the abnormal artery and has diagnostic significance. However, it is not easy to find abnormal blood vessels with a diameter less than 0.5 cm.

　　3. Bronchography:In most cases, the bronchi within the lesion do not show up, only larger bronchi can be visualized. Moreover, after the angiography, it may cause infection, making bronchoscopy and bronchography usually meaningless.

　　4. Angiography:When there is a high clinical suspicion of pulmonary sequestration and the X-ray chest film and tomography cannot determine it, aortography or selective arteriography can observe the abnormal systemic artery branches supplying the lung tissue of the lesion and can make an accurate diagnosis. By puncturing the femoral artery and inserting a catheter, contrast medium is injected into the beginning of the descending aorta to show the abnormal blood vessels. The abnormal blood vessels generally come from the descending aorta segment above and below the diaphragm, with a diameter of 0.5 to 1 cm, and venous return into the pulmonary veins or the azygos vein, and the inferior vena cava. However, due to the relatively thin abnormal blood vessels, less contrast medium is required, and most cases cannot show venous return. Selective angiography techniques require a higher level of skill, involving puncturing the femoral artery to send a catheter with a special angle, such as a C-shaped or right-angled catheter, to find the abnormal blood vessels above and below the diaphragm in the descending aorta. When the tip of the catheter is inserted into the blood vessel orifice, contrast medium is injected, and the blood vessel diameter and course can be observed. Continuous injection of contrast medium can also observe the venous return. However, this examination is a traumatic examination with certain risks and requires certain conditions and equipment.

　　5. CT examination:It can more clearly show the morphology of the lesion and can also confirm the existence of abnormal arteries. The typical manifestation is that the normal lung bronchial artery and venous bundle are away from or around the periphery of the isolated lung lobe, occasionally calcified. If it communicates with the bronchial tree and causes infection, it presents as a gas-filled cyst, with or without a liquid level, and surrounding inflammatory infiltration can also appear as a cystic appearance, with or without a liquid-gas level, but the positive diagnosis rate is not high.

　　6. Magnetic Resonance Imaging (MRI):It can detect clear mass boundaries within the chest and their internal structures, especially on cross-sections, where they can be clearly displayed. The lobular type feature is the connection between the abnormal mass (black shadow on MRI) within the lung and the abnormal blood vessels, while the extralobular type is the shadow of the abnormally whitened mass outside the lung, also connected with abnormal blood vessels. Magnetic resonance imaging can show the abnormal lung tissue and its relationship with surrounding organs, displaying the origin, course, and venous return of abnormal arteries. The results of the examination are similar to those of angiography, and it is a non-invasive examination method that can replace angiography, but it is more expensive in terms of examination costs.

　　7. B-ultrasound:B-ultrasound can detect clear boundaries, regular circular or elliptical lung masses internally, with different sizes of cystic areas. If there is infection, scattered light points can be seen. There are 1 to 2 blood vessels entering the mass around the mass, which are not the same as the imaging features of other lung lesions. B-ultrasound is a non-invasive examination method with simple operation, high accuracy, and can be observed dynamically repeatedly. However, B-ultrasound cannot distinguish between intralobar or extrapulmonary pulmonary sequestration, nor can it detect pulmonary venous return.

　　What foods are good for people with pulmonary sequestration?

　　1. Fluids, especially fruit juice.

　　2. Fresh fruits and vegetables.

　　3. Foods rich in vitamin A, such as fatty fish, eggs, and other foods rich in vitamin A.

　　(The above information is for reference only, please consult a doctor for details)

　　Treatment

　　1. Intralobar pulmonary sequestration:It can repeatedly develop secondary infections, so it should be treated surgically, usually with pulmonary lobectomy. The surgery should be performed after the infection is controlled, and antibiotics should be used routinely. Due to the frequent occurrence of severe infections, the affected lung often adheres to the chest wall, and attention must be paid to the abnormal artery when separating these adhesions. Abnormal arteries are often found in the pulmonary ligaments, and occasionally, there are abnormal arteries from the abdominal aorta. Improper management can cause massive bleeding during and after surgery.

　　2. Extrapulmonary pulmonary sequestration:If there is no communication with the gastrointestinal tract and no symptoms, treatment may not be necessary, but surgery is often performed due to unclear diagnosis. Extrapulmonary pulmonary sequestration can be treated by resecting the isolated lung, usually with pulmonary lobectomy. Special attention must be paid to the search and treatment of abnormal blood vessels during surgery, especially when dealing with the lower pulmonary ligament. If the abnormal blood vessels are damaged and retract back into the abdominal cavity or mediastinum, it can cause massive bleeding, which is also difficult to manage.