Pediatric Pulmonary Sequestration

Pulmonary sequestration is believed to result from abnormal diverticulation of foregut and aberrant lung buds.[2]

The most frequently supported theory of sequestration formation involves an accessory lung bud that develops from the ventral aspect of the primitive foregut. The pluripotential tissue from this additional lung bud migrates in a caudal direction with the normally developing lung. It receives its blood supply from vessels that connect to the aorta and cover the primitive foregut. These attachments to the aorta remain to form the systemic arterial supply of the sequestration.[3]

Early embryologic development of the accessory lung bud results in formation of the sequestration within normal lung tissue. The sequestration is encased within the same pleural covering. This is the intrapulmonary variant. In contrast, later development of the accessory lung bud results in the extrapulmonary type that may give rise to communication with the GI tract. Both types of sequestration usually have arterial supply from the thoracic or abdominal aorta. Rarely, the celiac axis, internal mammary, subclavian, or renal artery may be involved.[4]

Intrapulmonary sequestration occurs within the visceral pleura of normal lung tissue. Usually, no communication with the tracheobronchial tree occurs. The most common location is in the posterior basal segment, and nearly two thirds of pulmonary sequestrations appear in the left lung. Venous drainage is usually via the pulmonary veins.[5] Foregut communication is very rare, and associated anomalies are uncommon.

Extrapulmonary sequestration is completely enclosed in its own pleural sac. It may occur above, within, or below the diaphragm, and nearly all appear on the left side. No communication with the tracheobronchial tree occurs. Venous drainage is usually via the systemic venous system. Foregut communication and associated anomalies, such as diaphragmatic hernia, are more common.

United States statistics

Pulmonary sequestration represents approximately 6% of all congenital pulmonary malformations.[6] Intrapulmonary sequestrations are the most common form, and 60% of these are found in the posterior basal segment of the left lower lobe. Overall, 98% occur in the lower lobes. Bilateral involvement is uncommon. About 10% of cases may be associated with other congenital anomalies.[7] A case of intrapulmonary sequestration associated with a bronchogenic cyst has been reported.[8]

Extrapulmonary sequestrations occur on the left in 95% of cases. Of these, 75% are found in the costophrenic sulcus on the left side. They may also be found in the mediastinum, pericardium, and within or below the diaphragm. They are associated with other congenital malformations in more than 50% of cases, such as congenital diaphragmatic hernias, congenital pulmonary airway malformation (CPAM) type II (hybrid lesions), and congenital heart disease.[9]

Sex- and age-related demographics

In the extrapulmonary form, males are affected approximately 4 times more often than females. Incidence is equal in males and females in the intrapulmonary type.[10]

More than one half of intrapulmonary sequestrations are diagnosed in later childhood or even in adulthood. Neonates and infants are usually asymptomatic.[11] In contrast, more than one half of extrapulmonary sequestrations are diagnosed in patients younger than 1 year. Often, this is because other congenital anomalies are present, including congenital diaphragmatic hernia, cardiac malformations, and GI malformations.

In the absence of perioperative complications, surgical resection of the abnormal segment is usually curative. Prognosis may also be determined by the presence of any accompanying anomalies.

A study by Trabalza Marinucci et al, which compared the outcomes of pediatric and adult patients who underwent surgical treatment of pulmonary sequestration, found that early surgery during childhood may prevent the development of respiratory symptoms. Patients who received a prenatal diagnosis and underwent surgery after the age of 1 year were more likely to have symptoms than those who were treated before the age of 1 year (57% vs 23%; P = .08).[12]

Morbidity/mortality

The morbidity and mortality rates are exceedingly low if resection of the mass precedes repeated infection. Postoperative results are uniformly good.[13]

Intrapulmonary sequestration

Although an intrapulmonary sequestration is usually diagnosed later in childhood or adolescence, symptoms may begin early in childhood with multiple episodes of pneumonia. A chronic or recurrent cough is common. Intrapulmonary sequestration shares the visceral pleura that covers the adjacent lung tissue and is usually located in the posterobasal segment of the lower lobes. The thoracic or abdominal aorta often provides the arterial blood supply. Venous drainage is commonly provided to the left atrium via the pulmonary veins.

An elemental communication with other bronchi or lung parenchyma may be present, allowing infection to occur. Rarely, an esophageal bronchus may be present. Resolution of infection is usually slow and incomplete because of inadequate bronchial drainage.

Overdistension of the cystic mass with air can result in compression of normal lung tissue with impairment of cardiorespiratory function. Aeration probably occurs through the pores of Kohn.

Other congenital anomalies may appear in 10% of cases.

Extrapulmonary sequestration

Many patients present in infancy with respiratory distress and chronic cough. The American College of Chest Physicians has established guidelines for the evaluation of chronic cough.[14]

Lesions are commonly diagnosed coincidentally during investigation of, or surgery for, an associated congenital anomaly. Therefore, clinical symptoms may be absent or minor.

Extrapulmonary sequestration may manifest as GI symptoms if communication with the GI tract is present. As a result, infants may have feeding difficulties. In addition, extrapulmonary sequestration may manifest as recurrent lung infection, similar to the intrapulmonary form. This type of sequestration does not contain air unless communication with the foregut is present.

The lung examination may reveal signs consistent with consolidation.

Occasionally, patients may have a systolic bruit or continuous murmur over the affected area. This is related to flow through the sequestration from the large systemic arterial supply.

No laboratory studies are needed in pulmonary sequestration.

Chest radiography is indicated.[15]

Chest radiography findings vary depending on the size of the sequestered lung tissue and whether infection is present. If no communication between sequestration and normal lung tissue is present, radiography usually reveals a dense opacity in the posterior basal segment of the lower lobe. A cystic appearance may also be observed.[16]

The multicystic lesion in the left lower lobe seen on the chest radiograph of this patient was causing repeated respiratory infections.

Lesion density often increases with secondary infection and appears as a uniform consolidation. When this area fails to clear after a course of appropriate medical therapy, the presence of a malformation, such as sequestration, should be considered, particularly if the lesion is localized to the posterior basal segment of the left lower lobe.

Distinguishing an intrapulmonary sequestration from extrapulmonary sequestration is difficult using plain radiography.[17]  Intrapulmonary lesions tend to be heterogeneous and are not well defined. Extrapulmonary masses are usually observed as solid, well defined, and retrocardiac.

Bronchography and arteriography are unnecessary because of current noninvasive imaging available.[18]

Presence of systemic arteries revealed by chest imaging is the major diagnostic feature of pulmonary sequestration. CT scanning with contrast[19] or magnetic resonance angiography (MRA) have been very useful.[20] The arterial supply and venous drainage both should be outlined because of the unpredictability of vascular connections. CT angiography is helpful in identifying aberrant systemic arterial supply, and the 3-dimensional rendering of multidetector row CT scanning can reveal venous drainage.[21, 22]

The sequestration (S) is linked by an aberrant vessel (arrows).

Real-time ultrasonography and Doppler imaging are reliable methods of demonstrating systemic origin or blood supply, as well.[23] On prenatal ultrasonography, a sequestration usually appears as well-defined echodense, homogeneous mass. Detection by color flow Doppler of a systemic artery from the aorta to the fetal lung lesion is a pathognomonic feature.

Bronchoscopy

Bronchoscopy is not necessary unless an alternative cause of the radiographic abnormalities, such as an inhaled foreign body, is suspected.

Balloon occlusion

Consider balloon occlusion or embolization of the aberrant systemic arteries at the time of catheterization.

Some patients may have a considerable shunt through this anomalous circuit to the extent that, once the segment has been removed, the improvement in cardiovascular status may be striking.

If surgical resection is necessary, risk of vascular complications is greatly reduced with this procedure.

Upper GI contrast examination

Upper GI contrast examination may be useful if communication with the GI tract is considered.

Because no communication with the bronchial tree occurs, sequestration appears to have loose, spongy tissue with numerous small cystic spaces containing clear, mucoid fluid. Structures that may resemble bronchi are present near the center. Dilated subpleural lymphatics may also be present.[6]

Medical care

No specific medications are useful in pulmonary sequestration. No medical therapy is indicated in the management of pulmonary sequestration, unless an infection requires the use of antibiotics.

Surgical care

Management of an asymptomatic pulmonary sequestration with no connection to the surrounding lung is controversial; however, most references advocate resection of these lesions because of the likelihood of recurrent lung infection, the need for larger resection if the sequestration becomes chronically infected, and the possibility of hemorrhage from arteriovenous anastomoses.[24]

Surgical resection is the treatment of choice for patients who present with infection or symptoms resulting from compression of normal lung tissue.

Extrapulmonary lesions can usually be excised without loss of normal lung tissue.

Intrapulmonary lesions often require lobectomy because the margins of the sequestration may not be clearly defined. Complete thoracoscopic resection of pulmonary lobes in infants and children has been described with low mortality and morbidity.[25]

No special dietary requirements are necessary.

Activity restriction is not necessary.