You are in: eMedicine Specialties > Radiology > PEDIATRICS Pulmonary SequestrationArticle Last Updated: May 26, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 13
  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 Ali Nawaz Khan is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the United States, Royal College of Radiologists, and Royal College of Surgeons of England 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 Editors: S Bruce Greenberg, MD, Professor of Radiology, University of Arkansas for Medical Sciences; Consulting Staff, Department of Radiology, Arkansas Children's Hospital; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Clinical Assistant Professor of Radiology, University of Washington Medical School Author and Editor Disclosure Synonyms and related keywords: lung sequestration, bronchopulmonary sequestration, extrapulmonary sequestration, intrapulmonary sequestration, lung bud, lung sequestrum, bronchopulmonary-foregut malformation, scimitar syndrome, horseshoe lung, cystic arteriovenous fistula, cystic arteriovenous malformation, extralobar sequestration, ELS, intralobar sequestration, ILS, acute respiratory distress syndrome, ARDS INTRODUCTIONSection 2 of 13
  BackgroundPulmonary sequestration is an embryonic mass of lung tissue that has no identifiable bronchial communication and that receives its blood supply from one or more anomalous systemic arteries.1, 2, 3, 4 Multiple feeding vessels may be present. This congenital anomaly can be classified as extralobar sequestration (ELS) or intralobar sequestration (ILS). 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 PathophysiologyBronchopulmonary 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. 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. FrequencyUnited StatesBronchopulmonary 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. InternationalThe international frequency of pulmonary sequestration is believed to be the same as that in the United States. Mortality/Morbidity
Related Medscape topics: RaceNo evidence has demonstrated any racial predilection. SexIn ELS, males are affected approximately 4 times more often than females. ILS shows no sex predilection. AgeMost 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. AnatomyIn 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. Clinical DetailsELS 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 Preferred Examination
Limitations of Techniques
DIFFERENTIALSSection 3 of 13
Bronchiectasis Bronchogenic Cyst Emphysema Empyema Lung, Arteriovenous Malformation Lung, Carcinoid Lung, Metastases Neuroblastoma Pneumonia, Atypical Bacterial Pneumonia, Neonatal Pneumonia, Typical Bacterial Solitary Pulmonary Nodule Other Problems to Be ConsideredScimitar 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 RADIOGRAPHSection 4 of 13
Findings
Degree of ConfidenceChest radiographic findings are usually distinctly abnormal in most patients, and these can provide reasonable diagnostic clues of pulmonary sequestration. An indolent process in the posterobasal segment of the lower lobe in a young person with recurrent localized pulmonary infections is suggestive of ILS. Distinguishing ELS from ILS is difficult when using plain radiographic findings. Extralobar lesions are more often solid and are associated with elevation of the ipsilateral diaphragm, whereas intralobar lesions appear more cystlike, and air is present if a pulmonary communication exists. The opacity of the sequestration increases with the presence of an infection. When such a lesion resolves incompletely with appropriate medical treatment, an underlying sequestration should be considered. Lack of filling or lack of demonstration of a communication on bronchography images of the tracheobronchial tree through a normally located bronchus is a characteristic finding that can help to make the diagnosis with reasonable certainty in conjunction with other clinical and radiologic findings. Bronchography or CT scanning may be helpful in excluding other diagnoses (see Differentials and Other Problems to Be Considered). The occasional presence of contrast material in the cystic area during bronchography may suggest the confusing diagnosis of cystic bronchiectasis. False Positives/NegativesPulmonary sequestration in asymptomatic individuals may be confused with a bronchogenic cyst, CCAM, Bochdalek hernia, and mediastinal or pulmonary neoplasm. In symptomatic individuals, the differential diagnosis includes pneumatoceles, pneumonia, bronchiectasis, and lung abscess. Lesions considered in the differential diagnosis for infradiaphragmatic lesions include neuroblastoma, teratoma, adrenal hemorrhage, mesoblastic nephroma, and foregut duplication. The occasional presence of contrast material in the cystic area during bronchography may suggest the confusing diagnosis of cystic bronchiectasis. Bronchographic findings may be misleading because the failure of the contrast agent to enter the bronchus is not pathognomonic of a sequestrated lung segment and may occur as a result of a foreign body, mucous plug, or bronchial atresia. CT SCANSection 5 of 13
FindingsThe role of CT scanning is to define vascular anatomy and to provide supporting evidence that opacities depicted on chest radiographs or antenatal sonograms may be sequestrations. Simple sectional CT scan studies can reveal the anatomic position of an abnormality and may contribute to knowledge of the vascular supply in only two thirds of patients. With the advent of volumetric slip-ring scanning (either spiral or multisection), the vascular supply and venous drainage of both ILS and ELS lesions can be defined with a much higher degree of certainty. Volumetric slip-ring CT scans can provide information regarding the morphologic structure and attenuation values of any focus. Powerful computing with 3-D reconstruction provides excellent spatial resolution and definition of the spatial relationships of structures, which can obviate invasive angiographic procedures. Sequestration may be either ILS (75%) or ELS (25%).10
The position of the lesion and its persistence in a relatively young individual raises the index of suspicion that the underlying pathology may be the result of a sequestered segment. Demonstration of a dominant feeding vessel, usually from the aorta or its major vessels, and venous drainage to the pulmonary veins suggests the diagnosis. Alternative venous drainage patterns in ILS include a route directly into the left atrium via the azygos or hemiazygos systems, into intercostals veins, or into the IVC or SVC. The finding of alternative venous drainage patterns separates pulmonary sequestration from other diagnoses, such as infection and tumor, round atelectasis, Bochdalek hernia, and pulmonary infarction. Enlargement of the associated abnormal feeding vessels is a constant feature, and the azygos vein is also frequently enlarged. Multiple supply arteries are found in 15% of sequestrations; 73% of sequestrations develop blood vessels leading off the abdominal aorta, and 18% develop blood vessels leading off the thoracic aorta. Rare documented origins include the ascending aorta and the arch, subclavian, innominate, celiac, right coronary, and circumflex arteries. Eighty percent of ELS lesions occur in males, and they may occur above or below the diaphragm, sometimes in the retroperitoneum. Eight percent of the lesions are subdiaphragmatic and can mimic masses arising in various organs, such as the adrenal gland. In addition, ELS frequently is associated with other congenital extrapulmonary anomalies. Venous drainage occurs via the systemic circulation. Degree of ConfidenceMultidetector CTA not only allows simultaneous imaging of the aberrant artery and venous drainage but also has the potential to become the first-line examination in the preoperative assessment of pulmonary sequestration. Accuracy of diagnosis of a pulmonary sequestration is approximately 90% if a lesion is depicted in a typical site, if it has solid and cystic components, and if it is associated with emphysema and an abnormal blood supply and venous drainage into either the pulmonary veins or the systemic veins. False Positives/NegativesLung abscess, congenital adenomatoid cystic malformation, lung tumor, round atelectasis, Bochdalek hernia, and pulmonary infarction may mimic pulmonary sequestration. If an aberrant blood supply and drainage cannot be demonstrated, a false-negative examination may occur. MRISection 6 of 13
FindingsContrast-enhanced MRA or even conventional T1-weighted spin-echo (SE) images may help in the diagnosis of pulmonary sequestration by demonstrating a systemic blood supply, particularly from the aorta, to a basal lung mass. In addition, MRA may demonstrate venous drainage of the mass and may obviate more invasive investigations. Degree of ConfidenceMRI and MRA can provide information similar to that of CT scans without the need for ionizing radiation; however, MRI is less accessible, takes longer to perform, is subject to motion artifacts, and requires sedation in infants and small children. False Positives/NegativesSufficient experience has not been accumulated in the use of MRI in the diagnosis of pulmonary sequestration. Demonstration of aberrant blood supply to the sequestrated segment is pivotal to the diagnosis; therefore, meticulous technique is necessary because respiratory and cardiac motion may theoretically degrade the images. Moreover, a systemic artery supplying lung tissue is not pathognomonic of sequestration, because anomalous systemic arterial supply to normal segments of the lung is a rare but well-recognized congenital anomaly. As in any imaging technique, MRI findings must be interpreted in the light of the clinical presentation and the ultrasonographic and chest radiographic findings. ULTRASOUNDSection 7 of 13
FindingsILS lesions appear as solid intrathoracic masses that may contain small cystic areas secondary to multiple fluid-filled bronchi. The left lower lobe is the most common site. The appearances are nonspecific and can be complex solid homogeneous or inhomogeneous lesions and echogenic or cystic, depending on the histologic components in the lesion. These findings are suggestive of a number of possibilities in the pulmonary sequestration spectrum. Demonstration of a systemic arterial supply and left atrial venous drainage by color-flow and duplex ultrasonography establishes the diagnosis. Ultrasonographic demonstration of a vascular supply may be difficult, and the failure to depict the supply does not exclude the diagnosis. The arterial supply is most commonly derived from the descending aorta, but it can arise, in descending order of frequency, from the celiac, splenic, intercostal, subclavian, internal thoracic, or pericardiophrenic arteries. In ILS, 16% of lesions can have multiple blood supplies. Prenatal diagnosis of retroperitoneal ELS is not rare, accounting for 2-5% of all lung sequestrations. Analysis of ultrasound-guided fine-needle biopsy specimens of respiratory epithelium confirms the diagnosis of extrapulmonary ELS, but most of the time, surgical resection follows imaging evaluation. Ultrasonography is useful in the prenatal diagnosis of pulmonary sequestration and its complications, in assessing progression, and in forming a prognosis, which, in turn, is important for appropriate parental counseling and fetal therapy.30, 31, 32 Serial prenatal sonograms are necessary in patients in whom pulmonary sequestration is suspected to search for poor prognostic factors such as increasing mediastinal shift and increasing size of the sequestration. In fetuses with chest masses, 8% have additional structural abnormalities and an abnormal karyotype. In ELS, 65% of patients have associated anomalies, such as an accessory spleen, congenital heart disease, or a diaphragmatic hernia. In patients with ELS, complications can include tension hydrothorax, polyhydramnios, and hydrops fetalis.23, 33 Ultrasonography can demonstrate absent or reversed diastolic flow in a torsed vascular pedicle, which is believed to cause complications in patients with ELS. In patients with ILS, prenatal complications are unlikely because the sequestrated segment is well anchored in the thorax and is unable to undergo torsion. Degree of ConfidenceUltrasonography is important in the diagnosis of pulmonary sequestration. This imaging modality is noninvasive and safe, which make its use ideal in the prenatal and postnatal periods. The basal location of most of the lesions provides an excellent acoustic window for ultrasonography. The diagnosis can be made as soon as the early second trimester. Demonstration of a systemic arterial supply and pulmonary venous drainage by using color-flow and duplex ultrasonography establishes the diagnosis. False Positives/NegativesMimics of ILS include congenital diaphragmatic hernia, CCAM, tracheobronchial atresia, cystic mediastinal teratoma, and bronchogenic and enteric cysts. Absence of peristalsis and presence of an intact diaphragm excludes a diagnosis of diaphragmatic hernia. If the CCAM is microcytic type 3, it can be ultrasonographically indistinguishable from pulmonary sequestration. If bronchial communication occurs after infection in patients with ILS, highly echogenic reverberation artifacts caused by air may be seen. In the retroperitoneal location, mimics of ELS include neuroblastoma, adrenal hemorrhage, teratoma, and lymphangioma.34, 35 One ELS is diagnosed for every 2.5 neuroblastomas. A neuroblastoma is characterized by poorly defined margins and low or mixed echogenicity with foci of calcification. A neuroblastoma is more often cystic, right sided, and seen in the third trimester; ELS is more often echogenic, left sided, and possibly seen as early as the second trimester. Adrenal hemorrhage typically has cystic components and involves the adrenal gland, either wholly or in part. Differentiating adrenal hemorrhage from pulmonary sequestration may be a function of time rather than initial appearances. Teratomas and lymphangiomas occur considerably less frequently. On antenatal and neonatal sonograms, an extralobar pulmonary sequestration may mimic a neuroblastoma.36 The differential diagnosis of an infradiaphragmatic extralobar sequestration includes neuroblastoma, teratoma, adrenal hemorrhage, and mesoblastic nephroma and foregut duplication cysts. NUCLEAR MEDICINESection 8 of 13
FindingsA single case of ILS has been described in which xenon-133 (133Xe) was used to further the diagnosis.24 In a 29-year-old male patient, dynamic single-photon emission computed CT (SPECT) scanning with 133Xe gas showed the retention of the radionuclide within a hyperlucent lung mass that was demonstrated on CT scans. A left lower lobectomy was subsequently performed and showed no fistulous communication between an anomalous and the normal bronchial trees, but noncontiguous, incompletely developed visceral pleura was demonstrated between the sequestered segment and the adjacent normally ventilated lung.24 Thus, retention of the radionuclide supports the role of intralobar collateral air drift and air trapping in producing secondary changes of a focal hyperlucent lung area within the lung segment in ILS. Radionuclide angiography has been used to delineate the systemic blood supply to a sequestered lung segment. In a series of 5 patients, radionuclide angiograms obtained with technetium-99m (99mTc) macroaggregated albumin and 99mTc pertechnetate were obtained.27 Perfusion lung scans showed segmental perfusion defects in the lower lobes at the site of the sequestered lung segments. Radionuclide angiography revealed abnormal systemic blood flow through the descending aorta to the left lower lobe. Subtraction scans were obtained from the 2 images in different phases in the aortic phase on the radionuclide angiograms; these images revealed abnormal systemic blood flow through the descending aorta more clearly than images from conventional radionuclide angiography.27 Degree of ConfidenceVentilatory abnormalities in ILS and the adjacent lung have been suggested by the results of CT attenuation analysis with ultrafast electron-beam CT scanning in a patient with pathologically proven emphysematous changes. However, it has also been shown that regional lung attenuation analysis, as assessed using CT scans, reflects not only aeration but also coincidental hemodynamic change. Dynamic 133Xe SPECT scanning is more accurate and sensitive for detection of regional ventilatory abnormalities associated with air trapping and for estimation of regional 133Xe clearance.24 Radionuclide angiography is noninvasive and can reveal a systemic arterial system, rather than pulmonary circulation, as the source of supply to the lung sequestration. Fourier-phase analysis of first-pass data also allows noninvasive detection of pulmonary sequestration, although experience with this is limited.37 False Positives/NegativesScimitar syndrome may be indistinguishable from pulmonary sequestration on radionuclide angiography. ANGIOGRAPHYSection 9 of 13
FindingsThe blood supply of 75% of pulmonary sequestrations is derived from the thoracic or abdominal aorta. The remaining 25% of sequestrations receive their blood flow from the subclavian, intercostal, pulmonary, pericardiophrenic, innominate, internal mammary, celiac, splenic, or renal arteries. The arterial supply typically enters the lung via the pulmonary ligament if the artery originates above the diaphragm. Arteries originating below the diaphragm reach the sequestration by piercing the diaphragm or via the aortic or esophageal hiatus. In the rare instance of sequestration in an upper lobe, arterial supply from the internal thoracic artery has been reported. If aortography is unrevealing, a coronary source should be included in the preoperative search. The arterial supply is usually composed of a single vessel that is disproportionately large. This vessel is typically 0.5-2.0 cm in diameter, and multiple arteries are present in 15-20% of cases in which the arteries are 3 mm or smaller in diameter. Venous drainage occurs most often via the pulmonary vein in ILS, establishing a left-to-right shunt; in ELS, the drainage occurs via bronchial or other systemic veins. Occasionally, drainage is solely to the azygos or hemiazygos system. In rare cases, drainage is to the intercostal, innominate, or portal veins. Dual venous drainage to both pulmonary and systemic veins is the most uncommon situation. Degree of ConfidenceThe definitive diagnosis is made by using angiography (conventional, CTA or MRA), which delineates the feeding vessel to the sequestration along with its venous system. Aortograms and pulmonary angiograms may be needed in some patients in whom pulmonary sequestration is suspected. False Positives/NegativesArteriography is helpful in differentiating pulmonary sequestration from other abnormalities of the lung, such as pulmonary arteriovenous fistulae. However, demonstration of a systemic artery supplying lung tissue is not pathognomonic of sequestration because a congenital anomalous systemic arterial supply to normal segments of the lung is rare but well known. Arteriography must be interpreted along with clinical and chest radiographic findings. INTERVENTIONSection 10 of 13
Transarterial embolization of the aberrant arterial supply to an ILS may be used as a definitive procedure or as a preoperative procedure to minimize the risk of vascular complications during resection.28, 38, 39 In a series of 16 children with pulmonary sequestrations treated with endovascular embolization of the feeding systemic artery, embolization alone cured the sequestration in 10 children. Some patients may have significant arteriovenous shunting through the lesion, which can benefit from a transarterial coil-spring or particulate embolization. Laparoscopic approaches have been used in the resection of an abdominal ELS.6 Advances in imaging have made the distinction of sequestrations from other suprarenal masses, including neuroblastomas, possible in most cases. However, resection provides absolute tissue diagnosis and remains the treatment of choice.1, 7 Laparoscopic resection offers the benefit of minimally invasive therapy in addition to providing tissue for confirmation. If resection is performed before the onset of infection, the mortality and morbidity rates are exceedingly low, and the prognosis is good. Fetal hydrops is a common complication in patients with ELS and is associated with a high perinatal mortality rate and severe respiratory problems at birth.23, 33 In a 27-week-old fetus with this condition, an injection of 1 mL of pure alcohol and pleuroamniotic shunting achieved resolution of the hydrops.23 The pregnancy reached maturation, and a full-term healthy neonate was delivered who did not require postnatal intervention. Medical/Legal Pitfalls
Related Medscape topic: ACKNOWLEDGMENTSSection 11 of 13
The authors and editors of eMedicine gratefully acknowledge the contributions of previous coauthor Dr. David Iain Hodgson in development and writing of this article. MULTIMEDIASection 12 of 13
REFERENCESSection 13 of 13
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