eMedicine Specialties > Radiology > Pediatrics

Pulmonary Sequestration

Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia
Coauthor(s): Margaret Aird, MBChB, FRCR, Consulting Staff, Department of Radiology, Wythenshawe Hospital; Apam Chiphang, MBBS, Staff Physician, Department of Radiology, North Manchester General Hospital; Lalam Radhesh Krishna, MBBS, MRCS, Specialist Registrar, Department of Radiology, North Manchester General Hospital; Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute; Tufail Ahmed Patankar, MBBS, FRCR, PhD, DMRD, DMRE, DNBE, Consulting Neuroradiologist and Interventional Neuroradiologist, Department of Neuroradiology, Royal Preston Hospital, Lancashire Teaching Hospitals NHS Foundation Trust; Nigel Thomas, MBBS, Vice-Chair, Manchester (North) Research Ethics Committee; Honorary Lecturer, Visiting Professor, University of Salford, UK
Contributor Information and Disclosures

Updated: May 26, 2008

Introduction

Background

Many patients with ELS present in infancy with respiratory distress and chronic cough; some lesions are diagnosed coincidentally. Intrapulmonary sequestration is usually diagnosed later in childhood or adulthood when the patient presents with an infection.⁵

For excellent patient education resources, visit eMedicine's Breathing Difficulties Center, Lung and Airway Center, and Pneumonia Center. Also, see eMedicine's patient education articles Coughs and Acute Respiratory Distress Syndrome.

Related eMedicine topics:

• Acute Respiratory Distress Syndrome
• Bronchogenic Cyst

Pathophysiology

Bronchopulmonary sequestrations are classified as either extralobar or intralobar.

ELSs are masses composed of nonfunctioning primitive pulmonary parenchymal tissue that have no connection to the tracheobronchial tree. They consist of uniformly dilated bronchioles, alveolar ducts, and alveoli, which form the bulk of the lesion, although bronchial structures may be absent. The interstitium is composed of delicate connective tissue, which varies in thickness according to the patient's age. This sequestration is called extralobar because the mass lies outside of the normal investment of visceral pleura; it may also lie outside of the thorax in a subdiaphragmatic position in as many as 10% of patients.

The ELS arterial supply is predominantly via systemic arteries (95%) rather than pulmonary arteries (5%); the systemic arteries are commonly branches of the thoracic aorta or the abdominal aorta (80%). In rare cases, the supply may be from anomalous vessels arising from the splenic, gastric, subclavian, and intercostal vessels. Venous drainage also occurs most commonly via the systemic veins (75%), such as the inferior vena cava [IVC] or azygos or portal veins, rather than the pulmonary veins (25%).

ELS is widely accepted to be congenital in origin. In normal embryologic development of the lung, the primitive bronchial tree develops as a ventral diverticulum of the foregut at 3 weeks' gestation; the bud then elongates and bifurcates into right and left lung buds at 26 days and then into lobes at 5-8 weeks' gestation.

The accepted theory concerning how an ELS arises is that an accessory lung bud develops from the ventral aspect of the primitive foregut.⁶ The accessory lung bud migrates caudally with the foregut and receives its blood supply from the splanchnic plexus, as does the foregut. If the bud arises after the pleurae have developed, it is not incorporated within the lung visceral pleura, and an ELS is formed. Caudal movement explains the lower lobe predomination and the presence of subdiaphragmatic ELS.

The theory that ELS is congenital is supported by the early age of presentation in infants and the association with other congenital abnormalities in as many as 65% of patients. The most common association is with diaphragmatic hernias (20%); others include congenital cystic adenomatoid malformation (CCAM), bronchogenic cysts, and foregut malformations.^2,7,8,9 In addition to a foregut communication, associated anomalies are common and include diaphragmatic hernias, cardiovascular malformations, bronchogenic cysts, pectus excavatum, and other lung anomalies.

Similar to ELS, ILS is also a nonfunctioning area of pulmonary parenchyma and is usually not in communication with the tracheobronchial tree; however, ILS may contain air via the pores of Kohn or a connection to normal small bronchi.¹⁰ ILS is incorporated within the normal visceral pleura of the lung, unlike ELS. Also unlike ELS, an ILS, when discovered, usually contains dense fibrous parenchyma, which has replaced the normal pulmonary tissue as the result of chronic inflammation and fibrosis. Multiple cysts are present that contain viscid fluid or gelatinous material; the pleura is thickened by adhesions to mediastinal and diaphragmatic parietal pleura. Remnants of bronchi and bronchioles are replaced by fibrous connective tissue containing inflammatory infiltrates, as are alveolar ducts and alveoli.

The ILS arterial supply is systemic in origin and arrives via the descending thoracic aorta (73%), the abdominal aorta or celiac axis artery (21%), and the intercostal arteries (4%). In 95% of patients, venous drainage occurs via the pulmonary veins; in 5% of patients, venous drainage occurs via the IVC, the superior vena cava (SVC), the azygos systems, or the intercostal veins.

The origin of ILS has been described in the past as congenital and is explained by the accessory lung bud theory. The accessory lung bud was believed to arise before the development of lung visceral pleura, and thus, it was included within the pleura. Unfortunately, the theory explains the systemic arterial supply but not the pulmonary venous drainage.

In contrast to ELS, ILS is not commonly associated with other congenital anomalies. The lack of association with other congenital anomalies, coupled with the difference in patients' ages at presentation and the associated infective and fibrotic changes revealed on histologic analysis, has led to the theory that ILS may primarily be an acquired postinflammatory process.

The current widely held theory is that ILS is acquired after one or more episodes of necrotizing pneumonia, resulting in obliterative bronchitis and obstruction of a lower lobe bronchus. This phase is followed by interruption of the pulmonary arterial supply to the infected lung parenchyma and hypertrophy of the systemic arterial supply from the thoracic aorta within the inferior pulmonary ligaments. The diaphragmatic pleural supply involves the celiac axis aorta and abdominal aorta, and these vessels may also be recruited. Venous drainage remains via the pulmonary veins.

Most ILSs are likely to be acquired; however, some ILSs may still be congenital in origin, because reports of neonatal ILS, bilateral ILS, and coexistent ILS/ELS exist. Other evidence that some ILSs may be congenital in origin is the association with other congenital anomalies in 6-12% of patients.

Several variants to the pulmonary sequestration spectrum are believed to exist, supporting a congenital etiology. These include scimitar syndrome, horseshoe lung, cystic adenomatoid lung, and pulmonary arteriovenous malformations.

Macroscopically, ELSs are usually single lesions sized 0.5-15 cm (most are 3-6 cm), and they are usually pyramidal or ovoid masses that are gray-white to pink and covered by smooth to fine wrinkled pleurae. In ELSs that communicate with the foregut, a thin to thick hollow stalk joins the ELS sequestration to the esophagus or, more rarely, to the stomach. Microscopically, ELSs have uniformly dilated bronchioles, alveolar ducts, and alveoli. A well-formed bronchus can be identified in approximately 50% of specimens.

Macroscopically, ILS lesions typically have thickened pleura covered with adhesions between adjacent structures. The cut surface of an ILS shows fibrous parenchyma or multiple cysts that range from a few millimeters to larger than 5 cm in diameter. The cysts are typically filled with viscid yellow or white fluid. Microscopically, the pulmonary parenchyma is replaced by chronic inflammatory tissue.

Frequency

United States

Bronchopulmonary sequestration accounts for as many as 6.4% of all congenital pulmonary malformations and 1.1-1.8% of all pulmonary resections. ILS accounts for 75-86% of sequestrations, and ELS accounts for 14-25%.

ELS is seen predominantly on the left side (90%), and it has been described in both the thorax and abdomen (as many as 10% of patients). The most common site is between the lower lobe and the diaphragm (63-77%), but lesions have been described in the upper and middle zones of the thorax.

ILS is seen almost exclusively in the lower lobes (98%) and predominantly on the left side (60%); bilateral involvement is rare.

International

The international frequency of pulmonary sequestration is believed to be the same as that in the United States.

Mortality/Morbidity

• ELS can be complicated by infection if bronchial and gastrointestinal (GI) tract connections are present with associated morbidity. If resection is performed before onset of an infection, mortality and morbidity rates are exceedingly low and the prognosis is good.
• Patients with ILS can present with massive spontaneous hemorrhage, which is potentially fatal but exceedingly rare. Other complications and causes of morbidity include chronic infection and fibrosis. Resection has low mortality and morbidity rates.

Race

No evidence has demonstrated any racial predilection.

Sex

In ELS, males are affected approximately 4 times more often than females. ILS shows no sex predilection.

Age

Most patients with ELS present when they are younger than 1 year old, and 61% present when they are younger than 6 months old. Some pulmonary sequestrations are detected in utero. In 10% of cases, patients are asymptomatic at the time of diagnosis.

ILS appears in older patients, with more than 50% of cases occurring after adolescence. A first presentation is rare in patients older than 50 years. Symptoms in neonates and infants are rare, and 15% of ILSs are asymptomatic at diagnosis.

Anatomy

In ELS, the systemic arterial supply is typically via the thoracic aorta or the abdominal aorta (>80%); however, the arterial supply can be via the pulmonary (5%), subclavian, splenic, gastric, and intercostal (15%) arteries. Venous drainage is usually via the azygos or hemiazygos veins or the IVC (>80%), although the subclavian and portal veins are more rare options. In approximately 25% of patients, venous drainage is at least partially via the pulmonary veins.

In ILS, the systemic arterial supply is via the descending thoracic aorta (72%), abdominal aorta, celiac axis or splenic artery (21%), and intercostal artery (3.7%) and rarely via the subclavian, internal thoracic, and pericardiophrenic arteries. In approximately 16% of patients, more than one systemic artery is present. Most venous drainage (95%) is via the pulmonary veins.

Presentation

ELS

On the first day of life, patients not uncommonly present with dyspnea, cyanosis, and feeding difficulties, although children with ELS can present at any age. In fact, 60% present in the first 6 months of life. Many lesions are diagnosed coincidentally during imaging investigations for surgery or for associated congenital anomalies. Although the lung anomaly is usually not detected antenatally, maternal polyhydramnios, fetal ascites, and hydrothorax may indicate the diagnosis.

Feeding difficulties are usually related to a communication between the ELS and the GI tract. In addition, patients with ELS may present with recurrent chest infections, similar to patients with ILS. Symptoms can occur as a result of other associated anomalies, which are present in 40-60% of patients and range from the relatively innocuous accessory spleen to severe cardiovascular malformations, including truncus arteriosus and total anomalous pulmonary drainage.

In addition, reports describe myocardial ischemia in the left coronary artery caused by vasospastic angina and coronary stealing from the coronary circulation by an anomalous vessel arising from the anterior arterial branch from the left circumflex artery.³ Diaphragmatic hernias with concomitant pulmonary hypoplasia affect approximately 20% of patients. Pulmonary sequestration associated with bronchopleural fistulae, malrotation of the intestines, and a Meckel diverticulum has been reported in the same patient.⁹

ILS

Patients with ILS presented significantly more often (91%) with an infection than patients with ELS (14%). Adult patients had significantly more respiratory infections (67%) than pediatric patients (31%); as a result, greater numbers of lobectomies are performed in adults.¹¹

Symptoms may occur from associated anomalies in approximately 11% of patients with ILS, compared with 60% of patients with ELS, 40% of patients with congenital lobar emphysema, and 25% of patients with CCAM. The most common anomalies associated with ILS are esophagobronchial fistulae and diverticula, implying the presence of a bronchopulmonary foregut malformation.

Anomalies of the chest wall are not uncommon but may be acquired as a result of chronic lung infection. Physical examination may reveal signs of pulmonary consolidation. Rarely, auscultation may identify a bruit or continuous murmur over the sequestered lung segment from a large systemic blood supply. Murmur in the sequestered lung segment may occur in either ILS or ELS.

Preferred Examination

• Chest radiographs can provide a reasonable diagnostic clue to pulmonary sequestration. A mass in the posterobasal segment of the lung in young patients with recurrent localized pulmonary infections is suggestive of ILS. When such a lesion resolves incompletely with appropriate medical treatment, an underlying sequestration should be considered.
• Bronchography (computed tomography [CT] scanning or radiographic studies) may be helpful in excluding other diagnoses.
• CT scans have 90% accuracy in the diagnosis of pulmonary sequestration. The diagnosis of an intralobar pulmonary sequestration can be confirmed by enhanced contrast helical CT scanning with 3-dimensional (3-D) reconstruction, a noninvasive method.^4,12
• Arteriography (conventional or CT angiography [CTA]) is helpful in differentiating the lesion from other abnormalities of the lung, such as pulmonary arteriovenous fistulae, but the CT scans should be correlated with clinical presentation and chest radiographs.^13,14
• Magnetic resonance imaging (MRI) and MR angiography (MRA) can provide information similar to that on CT scans.^{7,12,14,15,16,17}
• Ultrasonography is noninvasive and safe, making its use ideal in prenatal and postnatal settings.^3,8,18,19,20 The diagnosis can be achieved as early as the second trimester.²¹ Color flow and duplex Doppler ultrasound can elegantly depict the ectopic blood supply and drainage.^{22,23,24,25,26}
• Radionuclide angiography is another noninvasive technique that may demonstrate the systemic arterial blood supply to the sequestration, thus establishing the diagnosis.^27,28

Limitations of Techniques

• Use of conventional radiographs must be avoided in women who are pregnant.
• Distinguishing ELS from ILS with the use of plain radiographs is difficult, and differentiation is important in selecting the mode of treatment. Infradiaphragmatic ELS is difficult to detect on plain radiographs.
• Bronchography is invasive, and its findings are nonspecific.
• Diagnosis with arteriography is based on the demonstration of systemic arterial blood supply to the lung sequestration, but arteriography is invasive, and its findings are nonspecific. The same findings have been described in other lung anomalies and in healthy lung segments.
• Use of CT scanning requires a high radiation dose; therefore, performing CT scanning in pregnant women and in infants should be avoided if possible. Infants may require sedation or general anesthesia.
• MRI has limited availability, it is an expensive tool, and it may require the use of heavy sedation or general anesthesia in young patients.
• Ultrasonographic findings are nonspecific in the antenatal and neonatal periods, and the differential diagnosis is wide in these findings. Ultrasonography has limited value in adults with both ILS and ELS.
• The experience with nuclear medicine techniques is limited and mostly anecdotal, and the technique requires the use of ionizing radiation.^27,29

Differential Diagnoses

Other Problems to Be Considered

Scimitar syndrome is a congenital anomaly in which an anomalous pulmonary vein drains into the IVC or its junction at the right atrium. An association exists with hypoplasia of the right lung, hypoplasia of the right pulmonary artery, and an anomalous systemic vascular supply to the lung.

CCAM is a lung parenchymal abnormality resulting from overgrowth of bronchioles. The blood supply to the abnormal lung segment is normal, but rarely, an aberrant systemic blood supply may be present. Clinical and radiologic correlation is important to differentiate between sequestered lobe and CCAM type 2 because they can have similar morphologies, grossly and microscopically.

Horseshoe lung shares some of the characteristics of scimitar syndrome. The abnormality consists of an isthmus of lung tissue that joins the lung bases across the midline behind the pericardium. The blood supply to the horseshoe lung may be anomalous.

Pulmonary arteriovenous fistula/malformation consists of an abnormal pulmonary artery and venous connection but a normal underlying lung parenchyma.

Solid mass in the differential diagnosis for ILS

Bochdalek hernia
Bronchial adenoma
Bronchogenic carcinoma
Empyema
Extramedullary hematopoiesis
Lung abscess
Meningocele
Metastatic lung neoplasms
Neurogenic tumor
Pleural tumor


Cystic mass in the differential diagnosis for ILS

Arteriovenous malformation
Bronchial atresia
Bronchiectasis
Bronchogenic foregut cyst
Cavitating infarct
Cavitating neoplasm
Congenital lobar emphysema
Cystic adenomatoid malformation
Diaphragmatic eventration
Emphysema
Empyema
Fungal pneumonia
Intrapulmonary bronchogenic cyst
Lung abscess
Necrotizing pneumonia
Pericardial cyst
Tuberculous pneumonia


Extralobar sequestration

Adrenal hemorrhage
Foregut duplication
Mesoblastic nephroma
Neuroblastoma
Teratoma

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