COLLECTIVE REVIEW. Pulmonary Sequestration. Richard Carter, M.D.

Transcription

1 COLLECTIVE REVIEW Pulmonary Sequestration Richard Carter, M.D. P ulmonary sequestration occurs when a disturbance in embryonic development produces a cystic mass of nonfunctioning lung tissue. Most often the mass is supplied by an anomalous systemic artery and has its own bronchial system, which usually does not communicate with the normal bronchial tree. The term sequestration, derived from the Latin verb sequestrare, to separate, was coined by Pryce in Generally regarded as the result of disturbed embryogenesis, pulmonary sequestration is being recognized more often and consequently has been reported with increasing frequency in the literature. The presenting complaint in the majority of patients harboring sequestered lung tissue is either repeated localized pulmonary infection or an intrathoracic mass. The x-ray abnormalities are strikingly similar in these patients, and the malformation can be diagnosed in most cases by routine radiological studies, without recourse to angiography. Furthermore, recognition is important because the anomaly is amenable to surgical correction. It is the purpose of this study to describe the salient clinical features of pulmonary sequestration, based on a review of 228 of the most instructive reported cases and personal experience in treating 5 additional cases. DESCRIPTION Two types of pulmonary sequestration occur: intralobar and extralobar. Although many authors include both types in the general term pulmonary sequestration, others use this term synonymously with the more common intralobar variety. Many other terms have been employed to describe this type (Table 1) as well as the extralobar variety (Table 2). From the Department of Surgery, University of California, Irvine, Calif THE ANNALS OF THORACIC SURGERY

2 COLLECTIVE REVIEW: Pulmonary Sequestration TABLE 1. SYNONYMS FOR INTRALOBAR SEQUESTRATION Date Author Synonym 1946 Pryce Intralobar sequestration 1910 Bert and Fischer 1952 Petfikova, Polak, and Stolz D ysembryopathy 1957 Breton and Dubois 1950 Hiissli 1957 Roemer and Mollowitz Foregut cyst 1952 Kergin Congenital lung cyst 1952 Wyman and Eyler Intrapulmonary 1958 Eaker, Hannon, and French Congenital bronchopulmonary cyst 1958 Warner, Britt, and Riley Bronchopulmonary sequestration 1958 Zadek and Riegel 1909 Mohr Fiimmerepithelial cyst TABLE 2. SYNONYMS FOR EXTRALOBAR SEQUESTRATION Date Author Synonym Baar and d'abreu Lindskog, Liebow, and Glenn De Bakey, Arey, and Brunazzi Gans and Potts Bruwer Boyden Bergman and Flance St. Raymond, Hardy, and Robbins Borrie, Lichter, and Rodda Howard 1 Tracheal accessory lobe Lower accessory lung or lobe Pulmonary aberration Inferior accessory lung Rokitansky's lobe Supernumerary lung Accessory lobe Accessory lung INTRALOBAR SEQUESTRATION In intralobar sequestration, the abnormal tissue is partly surrounded by normal lung. As described by Talalak [122] in 1960, the lesion is a nonfunctioning, dissociated intrapulmonary mass contained within the visceral pleura of the lower lobes. The mass is supplied by an anomalous systemic artery or arteries originating from the aorta, and the venous drainage is into the pulmonary veins. The bronchial system in the intralobar mass may, and often does, communicate with the tracheobronchial tree. With such intercommunication, repeated infection in the involved area is invariable. EXTRALOBAR SEQUESTRATION In extralobar sequestration, the accessory lung tissue has a distinct pleural investment, which maintains complete anatomical and physiological separation between the cyst and the adjacent normal lung. VOL. 7, NO. 1, JAN.,

3 ~ CARTER TABLE 3. COMPARATIVE FEATURES OF INTRALOBAR AND EXTRALOBAR PULMONARY SEQUESTRATION Feature Intralobar Sequestration Extralobar Sequestration Bronchopulmonary tissue La terali ty Arterial supply Venous drainage Foregut connection Associated anomalies Incidence in neonates aproposed by Smith t1181. Localized to posterior basilar segments; no separate pleural investment 60% on the left From aorta; often large, above or below diaphragm Pulmonary veins Very rare Rare Never Found above or below diaphragm; has separate pleural investment 90% on the left From a systemic or pulmonary artery; usually small and variable Azygos, hemiazygos, or portal venous system More common Frequent and serious Frequent Again, the mass is supplied by an anomalous systemic artery, but the venous drainage is into the azygos or hemiazygos system. In the extralobar as in the intralobar type, the left lower lobe is the site most often involved. Arising from a more complex embryonic defect than does the intralobar type, the extralobar variety may be attached to the diaphragm, gastrointestinal tract, or thoracic wall rather than to the lung itself. The lung mass has even been found below the diaphragm. However, congenital anomalies, particularly diaphragmatic hernia, may be associated with the extralobar type. Bronchial intercommunications are very rare in this form. In the past, intralobar and extralobar pulmonary sequestrations usually have been regarded as distinct entities (Table 3). Recently, Gerle and associates [6 11 have presented evidence that all sequestrations should be regarded as the same congenital anomaly, with a common embryogenesis. They present a classification based on gastrointestinal tract connections and propose bronchopulmonary-foregut malformation as a more inclusive and accurate term for this condition. HISTORY The first description of an aberrant systemic artery supplying the lung was that of Huber [71] in The anomalous artery he observed arising from the thoracic aorta supplied the right lower lobe of the normal lung. In 1861, two reports of pulmonary sequestration appeared, one by Rokitansky [111] and one by Rektorzik [108]. Each reviewed the 12 cases scattered in the literature and added a case of his own. Thus, independently, they defined the condition of extralobar 70 THE ANNALS OF THORACIC SURGERY

4 COLLECTIVE REVIEW: Pulmonary Sequestration sequestration. Both authors believed the anomaly to be an accessory pulmonary lobe, and today Rokitansky s lobe is synonymous with extralobar sequestration. Great interest in pulmonary sequestration was stirred by McCotter s report [94] of 4 cases in The clear description of intralobar sequestration by Pryce [ 1041 in 1946 established pulmonary sequestration as a distinct clinical entity. Six years previously, Harris and Lewis [67] had reported a death from exsanguination during a lung resection due to transection of an anomalous systemic artery. Their significant paper dramatizes the danger at operation if the thoracic surgeon is unaware of this lesion. PA THOGENESIS The most likely explanation for pulmonary sequestration is a disturbance in normal embryonic development, but authorities disagree about the precise nature of the interference. Whatever the cause, the result is known: During lung development, embryonic pulmonary tissue separates from the tracheobronchial tree and degenerates into a cystic accessory to the normally developing lung. The trachea and bronchi are derivatives from the foregut, while connective tissue and vessels are of mesodermal origin. In the earliest stages of fetal development, the primitive foregut is covered by a vast complex of vessels called the splanchnic plexus, which has numerous connections to the primitive dorsal and ventral aortas. The embryonic lung bud grows into the splanchnic capillary plexus, and at the 3- or 4-mm. stage, the pulmonary anlage buds from the primitive foregut by evagination and progresses anteriorly. During this process, a portion of the splanchnic plexus, called by Huntington [72] the postbrunchiul pulmonary plexus, is carried with the developing pulmonary system. The pulmonary artery, originating from the sixth primitive aortic arch, ramifies into this plexus to establish the pulmonary arterial network. The anastomosis between the aorta and the pulmonary vascular plexus normally degenerates or atrophies during the 8-mm. stage. Simultaneously, the primitive lung buds undergo an infolding process, or arborization, to form the lobes and bronchopulmonary segments. If for Some reason connections persist between the aorta and the postbranchial plexus, anomalous arterial anastomoses from the aorta to the future lung will result. In most cases, these abnormal arterial connections to the lung occur in the lower lobe, and most often they are found in the pulmonary ligament. Furthermore, if normal bronchial arborization fails to take place, a functionless pulmonary sequestrum or cyst will develop. Although the term sequestration is firmly entrenched in the litera-

5 CARTER ture, an understanding of the embryonic development of the lung makes the following terms logical: foregut cyst, proposed by Hossli [69] and Roemer and Mollowitz [1101; dysembryopathy, suggested by Bert and Fischer [9], PetFikova and associates [loo], and Breton and Dubois [ZO]; or Gerle s congenital bronchopulmonary-foregut malformation [6 11. Since pulmonary sequestration is a congenital defect arising at the site of differentiation of the gastrointestinal and respiratory tracts from the foregut, it is not surprising to find abnormalities in associated structures in the lower thoracic region. Sites particularly likely to be involved are lower lobe arteries [37, 53, 561, mediastinum [92], pericardium [84, 113, 1281, and diaphragm [35, Current theories of the origin of sequestered cysts have been adequately summarized by Boyd [141, Smith [118], Boyden [16], Claman and Ehrenhaft [33], and Spencer [121]. The major theories are compared in Table 4. Probably the most widely accepted hypothesis of origin is Pryce s vascular traction theory [104]. He held that the fundamental disorder is the traction exerted by aberrant arteries on the developing bronchial buds, leading to their sequestration from the growing tracheobronchial tree. Boyden et al. [17], however, take sharp issue with Pryce s explanation of the capture of bronchial buds by anchored arteries and advance the theory of coincidental occurrence of lung cysts and anomalous systemic pulmonary arteries. Agenesis of the lung and associated anomalies of the aortic arches can be produced experimentally in fetal rats by feeding the mother a diet deficient in vitamin A [131]. Thus, Boyden concludes that chance simultaneous occurrence of cystic degeneration of the lung and an aberrant systemic pulmonary artery is the only hypothesis warranted by presently known facts. Recent investigations have shown that Pryce s vascular traction hypothesis is inconsistent with the known facts of human and other mammalian developmental processes [17]. In addition, Smith [ contends that the differences between intralobar and extralobar sequestration cannot be explained by any mechanism which involves traction by the systemic aberrant artery. Furthermore, it is recognized that systemic arteries may supply normal lungs. On the other hand, in 1904 Hammar [66] described 2 cases of accessory lungs supplied by normal pulmonary arteries. Smith [118] has advanced the attractive theory that after birth the portion of the lung that is subjected to high pressure from the systemic circulation may undergo fibrocystic degeneration. His theory is that vascular insu@ciency, or failure of the pulmonary artery to supply a portion of the lung, results in a persistence of the primitive vascular connection. 72 THE ANNALS OF THORACIC SURGERY

6 Vogel Lemmon, Kirklin, and Docketry Gruenfeld and Gray Cole, Alley, and Jones Pryce TABLE 4. MAJOR THEORIES OF ORIGIN OF BRONCHOPULMONARY SEQUESTRATION Date Name Theory Pathogenesis Smith Boyden Gebauer and Mason Others' Mechanical Vascular traction Vascular insufficiency Coincidental occurrence Acquired Idiopathic Lung impinged on by developing embryological structure (aortic arch, other great vessels, bronchi, etc.) or deepening of fissures. Most often associated with extralobar sequestration and analogous to azygos lobe. Traction exerted by aberrant arteries on developing bronchial buds leads to their sequestration from growing tracheobronchial tree. Cystic degeneration due to lung damage during detachment. Failure of pulmonary artery to supply portion of lung results in persistence of primitive systemic vascular connection. Systemic blood pressure produces cystic and fibrous degeneration. Chance simultaneous presence of cystic lung degeneration, aberrant systemic artery, and, occasionally, defects of the diaphragm. Certain types due to diverticular outgrowth of lower esophagus. Pulmonary lesion acquired by primary pathological process in the lung with coexisting hypertrophy and bronchial and mediastinal arteries. Persistent anomalous vessel or branch between dorsal or ventral aorta to splanchnic plexus. amany authors subsaibe to this theory.

7 CARTER A number of other explanations have been advanced. Eppinger and Schauenstein [51] felt that the cause is related to persistence of abnormal vascular branches from the lung buds, which become dissociated from the normal bronchial tree. According to Breckler [ 181, the abnormality may be explained by imperfect coalescence between the entodermal bronchial segment and the mesodermal alveolar segment. The primary fault, LeRoux [89] postulated, is probably a failure of the pulmonary artery to supply the more distal parts of the lung. CLINICAL ASPECTS INCIDENCE Although exact figures are difficult to obtain, pulmonary sequestration can be called an uncommon but by no means rare disorder. Sequestration cysts have been found in l.1 to l.8% of all pulmonary resections. Intralobar sequestration appears to be more prevalent than the extralobar type, perhaps because the latter is often asymptomatic and consequently unrecognized. In this review 233 cases of pulmonary sequestration 198 were intralobar, 30 extralobar, and 4 were coexisting intralobar and extralobar sequestrations. Five cases from my personal experience, all intralobar, are included in this survey. SEX The incidence of pulmonary sequestration is usually reported as equal in men and women. Two papers, Kilman et al. [79] and Borrie et al. [13], mention a preponderance of men in their series, and this review confirms a slightly more frequent occurrence in men. The malefemale ratio for intralobar sequestration in the literature is 1.5: 1, and for extralobar sequestration, 3: 1. AGE Pulmonary sequestration usually manifests itself clinically in young adults, although the lesion has been reported in patients of all ages. Most of the problems occur during the first two decades of life, as is clear from a tabulation of those reported cases in which the age is known (Table 5). The age listed is based on the time of operation or treatment for complications. The onset of symptoms was usually many years before the time of operation in the older age group. Turk and Lindskog [124] found that more than 50% of their patients with pulmonary sequestration were seen before they were 20 years of age. This condition is rare in patients more than 40 years of age, although isolated cases have been reported in people in their sixth or seventh decades. Extralobar sequestration is most often diagnosed during the first decade of life, usually within the first 7 years. Occasionally, it is an 74 THE ANNALS OF THORACIC SURGERY

8 COLLECTIVE REVIEW: Pulmonary Sequestration TABLE 5. AGE INCIDENCE OF PULMONARY SEQUESTRATION IN 228 RECORDED CASES" Age Extralobar Intralobar (yr.) Sequestration Sequestration 'Based on time of operation or treatment of complications. incidental finding at necropsy in the adult, having gone unrecognized because of a lack of symptoms. ARTERIAL SUPPLY Additional evidence that pulmonary sequestration is a developmental disturbance is the fact that the blood supply of the mass is derived from the aorta rather than from the pulmonary arteries. As mentioned previously, retention of an embryological systemic arterial supply to the involved lung increases the risk of massive or even fatal hemorrhage at operation. Isolated bronchogenic cysts or accessory lungs of the mediastinum also usually possess a systemic arterial supply and venous drainage and thus impose the same surgical risk at resection. Excellent descriptions of anomalous pulmonary arteries have been published by Douglass [45], Findlay and Maier [53], and Mannix and Haight [93]. McCotter [94] was the first to collect a series of patients with abnormal arteries arising from the thoracic aorta to supply the lung. Such arteries may be single or multiple. Anomalous arteries usually enter the cyst at the posterior-inferior and medial corner, ascending in the pulmonary ligament from below the diaphragm. Vascular anomalies such as upper lobe arteries supplying lower lobe segments are not infrequent. In this present review of nearly 200 cases of sequestration, the most common site of origin of the aberrant artery was the thoracic aorta. The reported incidence of supradiaphragmatic origin of the anomalous artery ranges from 66 to 85%; in this review, 90% of intralobar and 8.5% of extralobar cysts received their arterial supply from branches above the diaphragm. The arterial connections in the extralobar variety tend to be small and inconstant. Most of these vessels are at least 5 mm. in diameter and some may be as large as 2 cm. If the artery is 3 mm. or less in diameter, it is likely to be one of several. More than one artery was present in 20% of reported extralobar cases I VOL. 7, NO. 1, JAN.,

9 CARTER The anomalous artery has been described by Pryce [lo41 as combined bronchial-pulmonary or systemic-pulmonary, and by Bergman and Flance [7] as systemic-elastic or hybrid. Because the anomalous artery has elastic rather than muscular walls, it resembles a fragile vessel such as the pulmonary artery, rather than a muscular systemic artery [SO, Microscopic examination showed that the anomalous vessel had the histological characteristics of an elastic artery in 47 of the 62 (77%) reported cases that could be analyzed in this study. In some cases, as Turk and Lindskog emphasize [124], the artery is predominantly muscular near its origin but becomes elastic peripherally. Atherosclerosis was found in 28 of 37 cases (76%) examined for atheromatous change. Some degree of endarteritis obliterans is almost always present in the smaller arterioles near a chronically inflamed lung cyst. VENOUS DRAINAGE It has been accepted that venous drainage enters the pulmonary veins from an intralobar cyst, but enters the azygos, hemiazygos, or portal system from the extralobar type [118]. A search of the literature shows this concept to be erroneous. Of 11 reported cases involving the azygos-hemiazygos system, 8 were associated with intralobar and 3 with extralobar sequestration. Gerle et al. [6 11 also noted this inconsistency. Although systemic venous branches to the right heart via the azygos and hemiazygos systems have been described in a few instances of intralobar sequestration, the venous drainage is almost always into the pulmonary veins, producing a systemic arterial-left atrial shunt. Phlebosclerosis, found in intralobar sequestration by Bergman and Flance [7], has not been mentioned in the extralobar type. Lemmon and associates [88] believed that phlebosclerosis was caused by a communication between an aberrant systemic artery and a pulmonary vein. If this explanation is true, phlebosclerosis should also occur in extralobar sequestration. L ATERALITY The majority of all sequestration cysts are left-sided in location. Parke [99] believed that this constancy of location was due to dependency of the mass on an access to the aortic blood supply. In his opinion, the posterior basal segment, which can be supplied by systemic arteries through the pulmonary ligament, is virtually the only area of lung that could survive without a pulmonary arterial blood supply. In this study, about two-thirds of both intralobar and extralobar pulmonary sequestration cysts have been located on the left side. Turk and Lindskog [124] also found the left lower lobe to be the site of sequestration in about two-thirds of their cases. Smith [118], analyzing 72 cases of intralobar sequestrations, found that 60% were situated on 76 THE ANNALS OF THORACIC SURGERY

10 CoLLEcrivE REVIEW: Pulmonary Sequestration the left side. Valle and White [125] found that 33 of 37 collected cases (90%) were also left-sided in location. Intralobar sequestrations are almost always localized in the posterior basal segment of the left lower lobe, although in some series as many as 14% were localized in the upper lobes [93, This left-sided predominance of pulmonary sequestration is believed by Bolck [ 121 to be related to the greater likelihood of survival of accessory lung roots that are in close proximity to the developing lung. He postulates that since the left leaf of the diaphragm closes later than the right, the chance of survival is greater in the region of the left diaphragm and greatest if the diaphragm is deficient, permitting the separated mass additional room for development. Bolck thus offers an explanation for the laterality of lower accessory lung (extralobar sequestration) and its association with congenital diaphragmatic hernia. CONNECTION WITH THE FOREGUT Gerle and associates [61], in a significant paper, report 3 cases of pulmonary sequestration that had a patent bronchus-like connection with the gastrointestinal tract and review 10 others recorded in the literature. An extralobar malformation communicating with the gastrointestinal tract was first described by Klebs [82] in Although early investigators believed that only the extralobar type could have a gastrointestinal tract communication-and that rarely-it is now recognized that the intralobar type can share this anomaly. Respiratory distress resulting from the communication between the gastroesophageal segment and the accessory lung often results in death from fulminant pulmonary disease. Thus, early recognition is important because surgical treatment is curative and may be lifesaving. ASSOCIATED CONGENITAL ABNORMALITIES Complex, multisystem congenital anomalies may be associated with sequestration cysts of the lung, although rarely with the intralobar type. However, the reported incidence of such anomalies coexisting with extralobar cysts ranges from 15 to 40%. Smith [119] emphasized that the rarity of defects associated with intralobar sequestration is a striking feature of this condition. Anomalous venous return from the involved lung segment to the hemiazygos system or right atrium and other variations have been reported [93, Other congenital aberrations include pulmonary agenesis [85]; eventration or diaphragmatic hernia [33, 34, 37, 1041; ectopic pancreatic tissue [5, lo]; and foregut duplication or diverticulum [39, 611. In patients with extralobar sequestration, a diaphragmatic hernia or eventration or paralysis of the diaphragm may coexist [8, 30, VOL. 7, NO. 1, JAN.,

11 CARTER These defects occur much more frequently in the extralobar than in the intralobar type. Valle and White [125] found congenital diaphragmatic hernias on the left side in 30% of cases of extralobar sequestration; in other studies the incidence ranges from 15 to 30%. Interference with normal closure of the pleuroperitoneal canal by the anomalous mass is a plausible explanation for the association of extralobar sequestration with diaphragmatic herniation [6 l]. Other anomalies associated with extralobar sequestration are congenital absence of pericardium and arteriovenous fistulas [129, Das and associates [39] collected 4 cases of foregut duplication occurring with intralobar sequestration. The associated congenital abnormalities included pulmonary agenesis, diaphragmatic hernia, ectopic pancreatic tissue, and a foregut diverticulum. In the 30 patients with extralobar sequestration reviewed in this study, 50% had one or more associated anomalies. Most frequent was diaphragmatic hernia, present in 7 cases; eventration of the diaphragm and esophageal diverticula were each found in 3 patients. Also reported were single instances of bronchial cleft cyst, absence of mediastinal pleura, absence of pericardium, basilar artery aneurysm, horseshoe kidney, hydroureter, ectopic pancreatic tissue, congenital megacolon, and esophagobronchial fistula. BRONCHIAL COMMUNICATION Classically, the bronchial system in pulmonary sequestration does not communicate with the normal bronchial tree. This system performs no respiratory function and is usually pale in color, lacking carbon pigmentation. As a result of infection and erosion, an intralobar sequestrated area may retain or reestablish a communication with the normal bronchus. Even when a connection to the parent bronchial tree is suspected, it is frequently not bronchographically demonstrable. Secondary infection in an air-containing cyst is an almost constant feature. Once pulmonary infection has developed in the cyst, complete resolution of the process is difficult to achieve because of inadequate drainage from the isolated lung tissue. The incidence of bronchial patency in intralobar sequestration found in this study was 17%. Bronchial communication in extralobar sequestration, although reported, is apparently a rarity. Absence of infection and the extrapleural location of the sequestration are probable reasons for its lack of communication with the main airway system. SYMPTOMS Recurring localized infection in a fluid-filled cyst is the most frequent clinical manifestation of pulmonary sequestration. In the newborn, the lesion may be discovered at the time of surgery for a 78 THE ANNALS OF THORACIC SURGERY

12 COLLECTIVE REVIEW: Pulmonary Sequestration TABLE 6. SYMPTOMS OF PULMONARY SEQUESTRATION Symptom Cough Recurrent pneumonia Purulent sputum Fever Hemop tysis Asymptomatica Chest pain Respiratory difficulty Weakness *Detected on roentgenological examination. No. of Patients symptomatic congenital diaphragmatic hernia. Although both types of cyst may remain asymptomatic and unsuspected for an indeterminate period, intralobar sequestrations are diagnosed more frequently because of the greater incidence of lung infection with the open bronchial connection. Acute suppuration in an extralobar cyst is rare in the absence of a gastrointestinal communication. Many cysts of this type are detected on routine x-ray examination [47, On the film, the mass appears as a homogenous triangular lower lobe tumor. Most patients have no diagnostic physical signs, although the minority demonstrate localized dullness and rales. Table 6 lists the symptoms most commonly encountered in an analysis of 228 cases of sequestration cyst reported in the literature. ROENTGENOLOGICAL FEATURES The most useful aid in diagnosing pulmonary sequestration is a simple x-ray film of the chest, carefully read. Often the film shows evidence of pneumonitis in a lower lobe mass, or frequently just a large simple cyst with an air-fluid level (Fig. 1). Wyman and Eyler [133] point out that the long axis of the lesion may point medially and posteriorly, implying a connection with the aorta. Other suggestive findings on the chest x-ray film include a posteromedial lower lobe density, perhaps with a long, branching vertical disc directed toward a diaphragm that lacks the usual sharp, symmetrical contour. Laminagraphy may be helpful in demonstrating whether bronchi or an abnormal blood vessel enters the sequestration. A bronchogram in a patient with sequestration will show a normal complement of bronchi with displacement of terminal branches by a space-occupying lesion (Fig. 2). Almost invariably the contrast media fails to enter the sequestered pulmonary tissue, even when an air-fluid VOL. 7, NO. 1, JAN.,

13 CARTER level is present [22, 54, If the cyst is acutely infected, bronchoscopy ilsually reveals evidence of pus coming from the adjacent involved bronchus, which is almost always in a lower lobe. Although these roentgenographical findings are not diagnostic, they are suggestive: Evidence of a lesion in the characteristic location A FIG. 1. (A, B) Radiolucency in right lower lobe demonstrates distinctive appearance of intralobar sequestration on chest x-ray film. Right-sided medial location in this patient is atypical, since majority of such cysts occur in posterior basal segment of left lobe. B FIG. 2. Bronchogram of patient with intralobar sequestration demonstrates lack of filling in accessory tissue in right lower lobe. Sli increase of density near spine delineates air-fluid level commonly found in 80 THE ANNALS OF THORACIC SURGERY

14 COLLECTIVE REVIEW: Pulmonary Sequestration in the posteromedial portion of a lower lobe, particularly when found in a young person with recurrent pulmonary infections, makes sequestration cyst a likely diagnosis. Demonstration by intrathoracic aortography of a systemic arterial supply to the involved segment, or by angiography of the absence of pulmonary arteries, is the most direct means of establishing the diagnosis [60, 77, 106, 109, Although LeRoux [89] believes that these additional studies are unnecessary and not without risk to the patient, Turk and Lindskog [ 1241 emphasized the importance of adequate demonstration of the abnormal blood preoperatively to prevent inadvertent transection and hemorrhage during surgery. In addition, angiography is helpful in differentiating pulmonary sequestration from an arteriovenous fistula [loll. DIFFERENTIAL DIAGNOSIS Pulmonary sequestration is often mistaken for pneumonia, empyema, bronchiectasis, or lung abscess. This is understandable for a condition that presents chiefly in the form of recurrent pulmonary infection with cough, purulent sputum, chest pain, fever, and occasionally hemoptysis. In instances of intercommunication with the bronchial tree, air-fluid levels may exist and the course may be indistinguishable from pyogenic lung abscess. A sequestration appearing as a mass lesion or oval density on an adult chest x-ray film may be confused with a bronchogenic or enterogenous cyst, Bochdalek hernia, mediastinal or pulmonary neoplasm, or a rare condition such as an intrathoracic kidney. The diagnosis of pulmonary sequestration may be suspected with a history of recurrent, localized pulmonary infection, especially when occurring in children or young adults. A mass lesion or cavitation with air-fluid levels located in the posterobasal segment of the left lower lobe seen in the chest x-ray film or evidence of a space-occupying tumor on bronchography are important roentgenographic signs. Although definitive preoperative diagnosis of pulmonary sequestration can be made only by angiography, recognition of the condition should not be difficult if these salient symptoms and roentgenographical features are kept in mind. TREATMENT Because reinfection in a dissociated, poorly drained segment of lung is almost invariable, pulmonary resection in a quiescent phase is the only rational treatment of pulmonary sequestration. The ideal method of treatment would be removal of the sequestration itself by segmentectomy, and this method has been advocated by some authors [70, $91. This procedure is rarely feasible or even advisable, however, VOL. 7, NO. 1, JAN.,

15 CARTER because of the presence of chronic intralobar infection. For this reason, lobectomy is the operation of choice. Extralobar sequestration can usually be managed by total excision of the mass. The chief technical hazard at operation is inadvertent transection of the anomalous systemic artery. Once severed, the artery may retract into the mediastinum or below the diaphragm. Several courageous authors have reported lethal hemorrhage from this complication [28, 45, 671. Because of this danger, it is advisable to look for an anomalous vessel when performing a lower lobe resection in a child or young adult. The aberrant systemic artery is most commonly found in the pulmonary ligament. In fact, since anomalous vessels frequently arise in this structure even in the absence of sequestration [53], the ligament should always be palpated carefully before resection. Aberrant vessels may also enter the lung from the diaphragmatic, mediastinal, or lower posterior surfaces of the lower lobes. The anomaly may be a single small artery, multiple arteries, or a single large vessel the size of the femoral artery. Turk and Lindskog [124] and others have stressed the desirability of demonstrating these arteries preoperatively by aortography to minimize the risk of hemorrhage during operation. SUMMARY Pulmonary sequestration is not the rarity it was once believed to be. The more than 200 cases recorded in the literature establish it as a distinct clinical entity and emphasize the importance of diagnosis, since it may be the unrecognized cause of recurrent localized pulmonary infection. Although surgically correctable, the condition presents considerable operative hazard if the surgeon is unaware of the aberrant blood supply that usually accompanies this lesion. The sequestration arises when an embryonic disturbance causes lung tissue to become dissociated from the normal bronchial tree, forming a nonfunctioning cystic mass supplied with blood by an anomalous systemic artery usually arising from the aorta. The mass has a nonfunctional bronchial system, which may communicate with the normal bronchial tree. The anomaly may remain asymptomatic; symptoms, when they occur, are usually manifested in the first or second decade of life. The incidence is slightly greater in men than in women. Accessory lung tissue that has a separate pleural investment is called extralobar sequestration, and if the accessory lung is within normal pulmonary parenchyma, it is termed intralo bar sequestration. Intralobar sequestration is almost always located in the posterior basal segment of the left lower lobe and may have a connection with the normal bronchi, which results in chronic infection. For this reason, an early diagnosis and definitive surgical correction by lobectomy are al- 82 THE ANNALS OF THORACIC SURGERY

16 COLLECTIVE REVIEW: Pulmonary Sequestration ways indicated. At operation, hemorrhage from an aberrant systemic artery is the chief technical hazard. Extralobar sequestration may present as an indeterminate pulmonary mass. Rarely, a patent bronchus-like communication may connect a sequestration cyst with the gastrointestinal tract. In such cases, fulminant respiratory distress is an ever-present danger, and if it occurs, early resection is mandatory for patient survival. ACKNOWLEDGMENTS My thanks go to Dr. M. Hayashi who, as a senior medical student, helped in obtaining the bibliographic material. REFERENCES 1. Abul-wafa, M. Congenital bronchopulmonary cyst associated with anomalous artery. Thorax 9:167, Anderson, A. E., Jr., Brown, J. B., and Roesch, C. B. Aberrant pulmonary artery with intralobar sequestration. Ann. Intern. Med. 46: 1092, Arce, J. Accessory pulmonary artery problem arising from the abdominal aorta. J. Thorac. Surg , Asp, K., Pasila, M., and Sulamaa, M. Diagnosis and treatment of pulmonary sequestration. Acta Chir. Scand. 127:303, Baar, H. S., and d'abreu, A. L. Duplications of the foregut. Brit. J. Surg. 37:220, Batts, M. A pulmonary artery arising from the abdominal aorta. J. Thorac. Surg , Bergman, M., and Flance, I. J. Vascular changes in bronchopulmonary sequestration. J. Thorac. Surg. 31 : 199, Berman, E. J. Extralobar (diaphragmatic) sequestration of lung. A.M.A. Arch. Surg. 76:724, Bert, P., and Fischer, B. Uber Nebenlungen und Versprengte Lungen Keime. Frankfurt. 2. Path. 6:27, Beskin, C. A. Intralobar enteric sequestration of the lung containing aberrant pancreas. J. Thorac. Cardiovasc. Swg. 41:314, Blair, L. G., Pryce, D. M., and Sellors, T. H. Intralobar sequestration of the lung associated with an abnormal pulmonary artery. Brit. J. Surg. 38:18, Bolck, F. Sur Frage der Entslehung von Nebenlungen. Arch. Path. Anat. 319:20, Borrie, J., Lichter, I., and Rodda, R. A. Intrapulmonary pulmonary sequestration. Brit. J. Surg. 50:224, Boyd, G. Intralobar pulmonary sequestration. Dis. Chest 24: 162, Boyden, E. A. Developmental anomalies of the lungs. Amer. J. Surg. 89:79, Boyden, E. A. Bronchogenic cyst and theory of intralobar sequestration. J. Thorac. Surg. 35:605, Boyden, E. A., Bill, A. H., and Creighton, S. A. Presumptive origin of left lower accessory lung from esophageal diverticulum. Surgery 52: 323, , Breckler, F. A. Congenital segmental emphysema of lung. J. Thorac. Surg. 34: 177, Bressler, S., and Weiner, D. Bronchogenic cyst associated with an anomalous pulmonary artery arising from the thoracic aorta. Surgery 35:815, VOL. 7, NO. 1, JAN.,

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