Thoracic Surgical Problems in Infancy and Childhood

Symposium on Pediatric Surgery, Part II

Thoracic Surgical Problems in Infancy and Childhood Frederick C. RyckrtULn, M.D.,* and]ens G. Rosenkrantz, M.D. t

CONGENITAL ABNORMALITIES

The primitive bronchial tube begins as an outpouching of the endoderm 3 weeks after conception, and septation between the esophagus and trachea is complete by 4 weeks, establishing a defined trachea and esophagus. The primary lung buds begin to form by 5 weeks, and lobar septation is established by 6 weeks of life. Bronchial subdivision continues until the seventh month of development when the distal terminal bronchioles expand into alveoli. Approximately 17 orders of bronchi are ultimately established. The initial vascular supply of the primitive bronchial buds is through the splanchnic plexus, which originates from the dorsal aorta and drains into the cardinal venous plexus. Gradual interconnection with the sixth aortic arch establishes the pulmonary vascular system, leaving only the bronchial vessels as remnants of the original systemic arterial system. Abnormal budding of the primitive foregut and bronchus or abnormalities of bronchial development account for the diverse spectrum of pulmonary anomalies. 68 Pulmonary Sequestration

Pulmonary sequestration is an uncommon anomaly in children and is characterized by the presence of lung tissue that lacks bronchial communication with the normal tracheobronchial tree and a blood supply that is derived from a systemic arterial source. Sequestrations are anatomically subdivided into two forms: extralobar, in which the sequestered pulmonary tissue is invested by its own separate visceral pleura, and intralobar, in which the abnormal pulmonary tissue is incorporated within the normal *Assistant Professor of Surgery, Division of Pediatric Surgery, Children's Hospital Medical Center, Cincinnati, Ohio tProfessor of Surgery, Division of Pediatric Surgery, Children's Hospital Medical Center, Cincinnati, Ohio

Surgical Clinics of North America-Vol. 65, No. 6, December 1985

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visceral pleural investment. Pryce described three types of intralobar sequestration based on the arterial anatomy of the aberrant vessel.B3 In type 1, the anomalous artery supplies only normal lung tissue.2s In type 2, the anomalous artery supplies normal lung and the sequestered lobe, and in type 3, the anomalous artery supplies the sequestered lobe only. Pulmonary sequestration can also be associated with diaphragmatic hernia, patent or obliterated connections between the gastrointestinal tract and the ectopic pulmonary tissue, and all possible combinations of systemic and pulmonary arterial and venous supply. Because the clinical presentation of pulmonary sequestration varies, no single theory adequately explains its embryologic development. However, several mechanisms have been proposed. These include (1) abnormal traction by persistent systemic arteries on the lung bud causing separation from the parent tracheobronchial tree, 84 (2) adhesion of the lung bud to caudally migrating coelomic organs, 22 and (3) insufficient pulmonary arterial supply causing persistence of collateral systemic arteries with subsequent cystic degeneration and fibrosis due to the high pressure of the systemic blood supply. 97 Another, more acceptable theory postulates the formation of an abnormal accessory lung bud developing caudal to the normal lung bud within the tracheoesophageal groove. This accessory foregut keeps its normal systemic blood supply derived from the surrounding thoracic mesenchymal tissue. 33, 48 Extralobar sequestrations are recognized most often in infancy as incidental findings on chest roentgenograms. Eighty per cent of affected children are boys, and two thirds are recognized to have sequestrations by their first birthday.28 In 90 per cent, the sequestration resides in the posterior left costophrenic sulcus adjacent to the esophagus.28 Respiratory insufficiency, associated cardiovascular or thoracic anomalies, and feeding problems are the most common symptoms stimulating evaluation. Pulmonary infection is uncommon unless a persistent esophageal communication to the sequestered lobe exists. 80 The systemic arterial supply is most often from the low intrathoracic or infradiaphragmatic aorta. When the blood supply originates within the abdomen, the systemic artery perforates the diaphragm within the confines of the inferior pulmonary ligament. The venous drainage of the sequestration is usually to the azygos or hemiazygos system, although drainage through esophageal or subclavian intercostal veins and infradiaphragmatic connections to the adrenal and portal systems have been described. 28, so These systemic arteriovenous shunts are rarely of hemodynamic significance. Coexisting congenital anomalies are common with extralobar sequestrations.14· 53, 80 Congenital diaphragmatic hernia is the most common such anomaly. The sequestered lung tissue can also present within the diaphragmatic muscle or completely below a normally formed hemidiaphragm. Other thoracic anomalies associated with extralobar sequestration include pectus excavatum, pericardia! defects, pulmonary arteriovenous fistulas, vertebral anomalies, dextrocardia,. and pericardia} cysts. Atrial septal defects and patent ductus arteriosus have also been found. There is also an increased incidence of thoracic or abdominal enteric duplications with this anomaly.29, 38, oo In extralobar sequestration, 15 to 40 per cent of patients have at least one associated congenital anomaly.l4

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Intralobar sequestrations present relatively late compared with their extralobar counterparts. Few are recognized prior to 1 year of age, and many do not present until early adulthood. Persistent or recurrent pneumonia within the same bronchopulmonary segment is the hallmark of intralobar sequestrations (Fig. 1). Pneumonia occurs when the sequestered tissue is infected by bacteria, which enter the sequestration from collateral ventilation through the pores of Kohn. so Poor ventilation and the absence of normal bronchial clearing mechanisms facilitate progression of the infection. Compression of the normal surrounding pulmonary parenchyma by

Figure 1. A 5-year-old child with recurrent respiratory infections. A to D, Chest roentgenograms during treatment with various antibiotics over 3 months show a persistent abnormality of the right lower lobe. Suspicion of pulmonary sequestration led to arteriography. E and F, A large systemic artery arising from the aorta at the diaphragmatic level perfuses the intralobar sequestration. The venous drainage is to the left atrium via the inferior pulmonary vein. Thoracotomy confirmed the angiographic diagnosis.

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the sequestration can also lead to compromised drainage and secondary infection within the anatomically normal surrounding lung. The sequestered lung typically resides within the posterior-basal area of the lower lobe, with 60 per cent found within the left hemithorax. 28 The systemic arterial supply is from the lower thoracic or intra-abdominal aorta, similar to that of extralobar sequestrations. However, intralobar sequestrations most often drain via the pulmonary veins of the involved lobe to the left atrium. In some large intralobar sequestrations, hemodynamically significant arteriovenous fistulas can be formed. These can occasionally be recognized by the presence of a continuous murmur at the perivertebral lung base. 100 Significant hemodynamic symptoms have been ameliorated by lobectomy in these cases.62, 88· 98 The abundant blood supply within the sequestered segment can also lead to recurrent or massive hemoptysis, spontaneous intrapleural hemorrhage, or massive hemothorax following traumatic laceration of a sequestration. 46 • 124, 125 Associated congenital anomalies are uncommonly seen in conjunction with intralobar sequestrations.2 Both forms of sequestration can usually be recognized on roentgenograms of the chest. The abnormal mass is usually triangular in shape, with its long axis pointed medially and posteriorly. Bronchoscopy and bronchograms usually show only compressive changes, although a segmental bronchus may be absent in the intralobar variant. In extralobar sequestration, the tracheobronchial tree is invariably normal.14 An upper gastrointestinal series should be taken of all patients with suspected sequestrations to identify patent gastrointestinal communication. 32, 48 Angiography is diagnostic of pulmonary sequestration by defining the anomalous systemic blood supply to the sequestered segment. The location and number of systemic vessels perfusing the anomaly and the venous drainage pattern can be clearly defined. More important, patients with chronic inflammatory lung disease without sequestration can be identified by the lack of an aberrant arterial inflow vessel and the associated finding of dilated intercostal and bronchial arteries supplying the inflammatory segment. 10· lll Symptomatic pulmonary sequestrations should be resected. In patients with intralobar sequestrations complicated by pneumonia, the infection should be controlled prior to thoracotomy with appropriate antibiotics. The inflammatory process progressively obliterates the normal segmental architectural planes within the lobe, making segmental resection only occasionally possible. O'Mara and associates found that only 20 per cent of the patients they reviewed could successfully undergo safe segmental resection. 80· 118 Lobectomy is the perferred procedure in most patients to resect the sequestered segment. Extralobar sequestrations unconnected to the tracheobronchial tree rarely become infected. When a patent communication with the esophagus results in dysphagia or infection within the sequestered lobe, sequestrectomy is indicated and can be undertaken without difficulty. As extralobar sequestrations are entirely separated from the surrounding normal lung by a pleural margin, no functioning pulmonary tissue is resected. Although surgical resection is indicated when the sequestration is symptomatic or discovered during diaphragmatic hernia repair, in asymptomatic cases the condition is compatible with long life.

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In both intralobar and extralobar forms, a careful search of the thorax must be undertaken prior to resection to identify and control the aberrant systemic artery or arteries. When the vessel arises from an infradiaphragmatic location and is unrecognized, transection can result in retraction of the systemic artery into the abdomen, causing occult massive hemorrhage. This unfortunate consequence has been associated with intraoperative death. IS, 30, 51 This artery can be located by inspection or palpation of the inferior pulmonary ligament prior to its division (Fig. 2). In all resections for sequestrations, the inferior pulmonary ligament should be sutureligated, even when no specific artery is identified within it prior to its division. The aberrant arteries &re elastic in type and frequently have atherosclerotic changes, making them extraordinarily friable.Is The systemic arterial inflow to the pulmonary malformation is multiple in 15 per cent of

Figure 2. A, A large systemic artery penetrating the diaphragm from its intra-abdominal origin supplies an intralobar sequestration of the left lower lobe. B, A resected specimen of the left lower lobe.

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cases. 93 When the systemic artery is less than 3 mm in diameter, multiple vessels are the rule rather than the exception. 14 Bronchogenic Cysts Bronchogenic cysts are congenital cystic lesions most commonly seen in the pulmonary parenchyma or mediastinum, although they can present in ectopic locations as cutaneous or subcutaneous cysts, cervical masses, or masses in the thoracic wall. When present within the thorax, they often precipitate respiratory or infectious complications secondary to partial airway obstruction or esophageal compression. Bronchogenic cysts are derived from abnormal budding of the primitive tracheobronchial tube. 47 This abnormal tracheobronchial budding can occur at any stage of airway development and at any level of the lung. When the abnormal bronchial budding occurs at the level of the carina or first-order bronchi, the cyst assumes a mediastinal or subcarinallocation. When the distal tracheobronchial tree is the origin of the abnormal budding, an intraparenchymal bronchogenic cyst results. If this primitive outpouching loses its embryologic connections to its parent bronchus, the cyst can migrate with local tissue and assume a cervical, pericardia!, paravertebral, subpleural, or even cutaneous location. On pathologic examination, a bronchogenic cyst has a milky graywhite mucoid central core surrounded by a wall containing remnants of bronchial cartilage, smooth muscle, elastic tissue, and mucus glands. The cyst itself is lined with secretory ciliated columnar or cuboidal epithe·lium. 34 Although bronchogenic cysts are almost always benign, there are two case reports describing the presence of a rhabdomyosarcoma arising within a bronchogenic cyst in a 2¥2-year-old girl and in an 18-month-old girl. 65 Among bronchogenic cysts presenting as intrathoracic masses, 70 per cent are pulmonary and 30 per cent are mediastinal. 115 The presence of air within the cyst suggests enteric or tracheobronchial communication, with air-fluid levels characteristic of partial obstruction. Noncommunicating cysts appear as soft-tissue masses on chest roentgenograms. Mediastinal bronchogenic cysts are usually smoothly contoured single masses, which are recognized following the development of partial respiratory tract obstruction or pulmonary infection. They can also be incidental findings on chest roentgenograms. They most commonly occur along the posterior membranous portion of the trachea at the level of the carina, although paratracheal, hilar, and periesophageal locations are also common. In Ramenofsky's review, half of his patients had specific respiratory symptoms, and 70 per cent had developed infectious complications most often due to partial bronchial obstruction.ss Most of these mediastinal cysts were recognizable only after the surrounding inflammatory infiltrate cleared on antibiotic therapy. When chest roentgenograms were not taken after resolution of the pneumonitis, there was an average delay in diagnosis of 21 months. In infants with mediastinal bronchogenic cysts, partial bronchial obstruction with air trapping produces a radiographic picture indistinguish-

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able from that of congenital lobar emphysema. 34 • 56, 115 Only half of infants with bronchogenic cysts who present with emphysema have mediastinal masses visible on their initial chest radiographs. 43 Therefore, the possibility of an unrecognized bronchogenic cyst must be considered whenever an exploratory thoracotomy is undertaken for congenital lobar emphysema. Because these bronchogenic cysts are located deep in the mediastinal pleura, they are not readily visualized until the mediastinal pleural is opened and the pulmonary root is anteriorly retracted. The bronchogenic cyst can be found attached to the membranous tracheobronchial wall from which it can be dissected. Pulmonary resection is not necessary if resection of the mass relieves the obstruction to the airway. 43, 115 In cases in which compression by the bronchogenic cyst has caused an irreversible obstructing deformity of the bronchial cartilage, conservative pulmonary resection is indicated. When a bronchogenic cyst arises from abnormal bronchial budding of the intraparenchymal bronchial tree, an intraparenchymal cyst develops. Such cysts can be single or multiple and frequently show air-fluid levels that are due to a partially obstructed communication with the tracheobronchial tree (Fig. 3). If infection supervenes, these cysts can erode into the surrounding normal pulmonary parenchyma and be initially indistinguishable from cavitating pneumonia or lung abcesses. 86 Persistence of the intraparenchymal cystic abnormality following resolution of the inflammatory process is characteristic. Intraparenchymal bronchogenic cysts should be resected. In cases in which superimposed infection of the surrounding normal lung would complicate resection, antibiotic administration to control the inflammatory process should precede operative intervention. The inflammatory sequelae often preclude safe segmental resection and necessitate lobectomy. Periesophageal bronchogenic cysts arise from outgrowths along the linear septation of the primitive tracheobronchus and foregut. These are usually single and may present as asymptomatic chest masses or cause esophageal compression symptoms and dysphagia. Barium esophagram can demonstrate esophageal deviation around the mass (Fig. 4). Because periesophageal bronchogenic cysts are extrinsic to the esophagus, esophagoscopy shows only esophageal deviation and is not necessary preoperatively. so Periesophageal bronchogenic cysts are adjacent to but can be easily dissected from the muscular esophageal wall without disturbing its continuity. Local resection is adequate therapy. Ectopic cervical bronchogenic cysts frequently maintain persistent communication with the pharynx, esophagus, or trachea. Partial obstruction of the communication predisposes such cysts to infection or progressive enlargement. Rapid enlargement of cervical cysts may cause stridor and tracheal displacement and require emergent resection, 109 Many cervical bronchogenic cysts present simply as superclavicular masses and mimic branchial cleft cysts, thyroglossal cysts, or thyroid abcesses. Like branchial cleft sinuses, these cysts can have cutaneous openings and mucoid drainage. 44 The suprasternal notch is a common location for subcutaneous bron-

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Figure 3. A 4-year-old child with multiple, recurrent respiratory infections. A and B, Chest roentgenograms show an air-fluid level within a cystic cavity of the right upper lobe. Symptoms resolved with antibiotic treatment, but the cavitary mass persisted. C, An intraparenchymal bronchogenic cyst was found at thoractomy. Inflammatory changes in the upper lobe necessitated a right upper lobectomy.

chogenic cysts. 41 Such cysts slowly increase in size as they accumulate mucus, and on occasion they spontaneously rupture and drain. Local resection is indicated for all ectopic bronchogenic cysts at the time of presentation, even if they are asymptomatic. Cystic Adenomatoid Malformations Cystic adenomatoid malformations are uncommon thoracic hamartomas that can present such severe perturbations of fetal growth that they result in stillborn infants with massive fetal anasarca and polyhydramnios. In other individuals, the disease may not be recognized until later in life when pulmonary infection supervenes. Cystic adenomatoid malformations may also cause acute, life-threatening respiratory distress in the newborn infant. 81

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Figure 4. A 9-month-old infant with feeding difficuties, dyspnea, and expiratory stridor. A and B, Anteroposterior and lateral chest roentgenograms disclose a large mass in the left superior mediastinum, interposed between the tracheal and esophageal contours outlined by intraluminal air. C, A contrast esophagogram confirms the extrinsic displacement. A paraesophageal bronchogenic cyst was found at thoracotomy and resected.

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If the bronchial buds and alveolar mesenchyma fail to join at 16 to 20 weeks of gestation, uncontrolled overgrowth of the bronchioles, especially the terminal branches, occurs and is characteristic of cystic adenomatoid malformations. 113 The noncommunicating alveolar ducts and air sacs develop from the surrounding mesenchyma and contribute the alveolar component to this congenital abnormality. Cystic adenomatoid malformations are thus true hamartomas. Because of variation in the amount of the bronchiolar and alveolar components within the mass, the tumors can range from solid masses without cysts to mixed solid and cystic masses within the lung. Cystic adenomatoid malformations can present at birth with a syndrome incompatible with life. These patients are most often premature infants who are stillborn or who succumb immediately to respiratory insufficiency and overwhelming fetal anasarca. This presentation makes up approximately one fourth to one third of all patients with cystic adenomatoid malformations. Fetal anasarca results from mediastinal venous occlusion by the adenomatoid mass and from heart failure. Polyhydramnios is precipitated by esophageal obstruction and decreased fetal swallowing. Excessive secretion or diminished reabsorption of lung fluid by the abnormal hamartomatous lung may also contribute to material hydramnios. Because of the severity of the fetal hydrops and the often extreme prematurity, survival in this group is not expected. 52 The most common presentation of cystic adenomatoid malformation is progressive respiratory distress in a newborn infant that is associated with a complex cystic and solid pulmonary mass on chest radiograph. Such a patient typically shows a partially air-filled mass within the involved hemithorax, producing mediastinal displacement. Patients presenting at birth are often found to have only solid-tissue masses present on their initial neonatal films as a consequence of delayed clearing of the fetal lung fluid from the adenomatoid malformation. Abnormal lymphatic and venous reabsorption within the malformation augments the already diminished rate of fetal fluid clearing due to poor bronchial drainage. 110 Progressive air trapping precipitates a slow but constant enlargement of the cystic bronchiolar and alveolar component of the lesion. Mediastinal shift and contralateral atelectasis intensify the respiratory insufficiency. Radiographically, the abnormality produced can be indistinguishable from a congenital posterolateral diaphragmatic hernia. 73, 79 This difficult differential diagnosis can be resolved rapidly by means of a contrast enema or upper gastrointestinal study to demonstrate the location of the colon or stomach and small intestine in relation to the diaphragm (Fig. 5). Each will define the pathologic diagnosis and allow the appropriate exploratory approach to be selected. However, the risk of aspiration of contrast material following an upper gastrointestinal series in an infant with respiratory distress makes either technique a less acceptable alternative. The third clinical constellation associated with cystic adenomatoid malformations is recurrent infection. This results from poor bronchopulmonary drainage within the abnormal bronchioles of the adenomatoid malformation. The cystic cavities within the infected adenomatoid malformation can masquerade as pneumatocysts and bronchopneumonia. Repeated

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Figure 5. A newborn infant with respiratory distress. A, The multicystic mass in the left lower thorax with contralateral mediastinal shift could represent a congenital diaphragmatic hernia or cystic adenomatoid malformation of the left lower lobe. B, A contrast upper gastrointestinal series confirms the normal intra-abdominal intestinal position in this case. A cystic adenomatoid malformation of the left lower lobe was resected.

radiographs following antibiotic therapy will disclose the true nature of the underlying pathology, which is often not fully appreciated until the associated pneumonia has resolved. Cystic adenomatoid malformations are not predisposed to one sex, and the disease is usually isolated to a single lobar area. The right and left lungs are equally involved. Bilateral cystic adenomatoid malformations are very uncommon. 20 In a patient in whom a large adenomatoid malformation has encroached on the normal ipsilateral lung, associated pulmonary hypoplasia may be present. 79 In these cases, prolonged respiratory support may be necessary following resection of the malformation. Veda and associates have also reported a single case of embryonal rhabdomyosarcoma within an asymptomatic cystic adenomatoid malformation. 112 This entity is related to the occasional skeletal muscle fibers that can be seen within these malformations. Fortunately, it is rare. The treatment of cystic adenomatoid malformations is pulmonary resection. When medical therapy alone was used, 16 of 32 patients ultimately succumbed to infection and respiratory distress. This was in contrast to the mortality of 2 of 16 patients in a concurrent surgically treated group. 72 Although it is tempting to undertake segmental excision in these patients, the complications arising following segmental resections exceed those of lobectomy. Patients with segmental excisions have a higher incidence of air leak and intrathoracic infection and occasionally require reoperation. Concurrently treated patients undergoing primary lobectomy required no further therapy, and the operative procedure is usually well tolerated. For this reason, primary lobectomy is recommended in all

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patients with this abnormality. 79 At the time of lobectomy, the intrathoracic anatomy in most cases is normal. However, an abnormal systemic arterial supply frorp. an infradiaphragmatic aortic branch to the cystic adenomatoid malforrp.ation has been described. 49• 57 This vascular supply, simil~ to that of an intralobar sequestration, should be searched for even if unexpected. Congenital Lobar Emphysema Infantile congenital lobar emphysema is an uncommon but progressive variety of obstructive emphysema leading to uniform massive distention of the involved lobe. The clinical course can be insidious or rapidly progressive, requiring urgent thoracotomy and lobectomy. Congenital lobar emphysema was rarely reported prior to 1949 but is now well recognized. It is characterized by uniform emphysematous enlargement of the entire involved lobe, affecting most often the left upper lobe or right middle lobe. Approximately two thirds of reported patients are males, and almost all patients are white infants. 11 The syndrome is uncommon in black and premature infants. 54• 58• 60• 70• 108• 123 Symptoms of respiratory distress, such as dyspnea, wheezing, cough, tachypnea, and later cyanosis, are characteristic of the disease. More than half of infants with congenital lobar ,emphysema develop symptoms within the first few days following birth, and 12 per cent are in critical condition prior to treatment. 77 The symptoms can progress rapidly with crying and agitation as air trapping increases, and a vicious circle ensues. Improvement is rarely seen with oxygen inhalation, airway humidification, suctioning, or antibiotic administration. With progressive emphysema and mediastinal shift, increasing compression of the normal ipsilateral and contralateral pulmonary lobes occurs. In this regard, congenital lobar emphysema may mimic tension pneumothorax. Once symptoms appear during infancy, the course of this disease is almost invariably progressive, and surgical therapy is required. Occasional asymptomatic or stable cases of lobar emphysema have been reported but characteristically in patients who were not symptomatic until they were older than 6 months. 61, 67, 77, 78 The pulmonary emphysema is caused by partial airway obstruction due to abnormal cartilaginous support within the bronchial wall. This cartilaginous abnormality is seen in its fullest expression in the involved lobe. However, similar abnormalities can be recognized in the cartilaginous structure of the entire tracheobronchial tree. Under careful pathologic examination, the bronchial cartilages may be shown to be absent, hypoplastic, spidery, or flaccid in more than two thirds of operative specimens with congenital lobar emphysema. 77 On biochemical analysis, a deficiency in hyaluronic acid and chrondroitin sulfuric acid can be recognized. 8 Some individuals have postulated that abnormal collagen deposition and deficient elastic tissue within the alveolar wall are primary factors in the pathophysiology of the disease. However, others have looked for and failed to find such abnormalities. 77 Congenital lobar emphysema should be suspected in infants with progressive respiratory distress and the characteristic radiographic signs of lobar hyperinflation, mediastinal shift, which is fixed at fluoroscopy, and

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contralateral atelectasis.77 Retained fetal lung fluid can often be seen within the involved lobe before the onset of emphysema, if early neonatal roentgenograms are available (Fig. 6). In more than one half of cases, the left upper lobe is involved, and the right middle lobe is the second most commonly involved pulmonary division.1oo Lower lobe involvement is very uncommon. Bronchoscopy will verifY the bronchial collapse and is necessary only to exclude intrinsic obstructive lesions. The differential diagnosis of congenital lobar emphysema includes the following. Intrinsic bronchial obstruction due to mucus plugging can produce surprising degrees of lobar emphysema. Regional obstructive emphysema of infancy is a syndrome of progressive emphysema secondary to partial airway obstruction by viscid secretions. Although its appearance on the initial chest roentgenogram is similar to that of congenital lobar emphysema, this syndrome is associated with primary pulmonary infection. 16 Vigorous chest physiotherapy, suctioning, and aerosolized bronchodilators will facilitate removal of these intrinsic mucus plugs, resolving the air trapping. Lobar atelectasis from complete bronchial obstruction with compensatory emphysema must also be excluded.54 A radiographic picture similar to that of congenital lobar emphysema is also seen with the unilateral hyperlucent lung syndrome (Swyer-James syndrome) and congenital absence of the main pulmonary artery. 24 • 106 Lobar emphysema can arise from extrinsic

Figure 6. Chest roentgenograms in a newborn infant with respiratory distress. A, Retained fetal lung fluid is seen in the right middle lobe. B and C, Progressive clearing is visible at 1 and 4 days following birth. D, At 6 days, right middle lobar emphysema with mediastinal shift and progressive dyspnea necessitated a right middle lobectomy.

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obstruction of a bronchus by an anomalous pulmonary artery, a perihilar bronchogenic cyst, an aneurysmal ductus arteriosus, or enlarged mediastinal nodes.17, 74, 101· 106 These causes of airway obstruction should be excluded by careful mediastinal exploration prior to lobectomy in any patient explored for lobar emphysema. A tension pneumothorax causes physiologic changes similar to those with congenital lobar emphysema. However, the involved lung collapses into the hilum, whereas lobar hyperinflation causes collapse of the uninvolved ipsilateral atelectatic lobe toward the base of the chest when the upper lobe is involved. Polyalveolar lobe can be recognized only on pathologic examination.1o1 The treatment of congenital lobar emphysema is lobar resection. When treated by medical therapy alone, 50 per cent of patients died from progressive respiratory distress, and 75 per cent of the survivors had persistent emphysema. Although the primary defect in congenital lobar emphysema is abnormal bronchial cartilagenous support, poor results following bronchoplasty make this procedure inadvisable. 77 At the time of anesthetic induction, positive pressure ventilation may precipitate severe air trapping and cardiorespiratory collapse. This makes thoracotomy under local anesthesia advisable in severely symptomatic infants to allow delivery of the involved lobe prior to establishment of positive pressure ventilation. 54 Lobectomy is well tolerated in these patients. The generalized abnormality of tracheobronchial support is emphasized by the occasional occurrence of emphysematous changes in other lobes following pulmonary resection. 94 Bilateral simultaneous involvement was seen in 3 of 166 patients reported by Murray and required staged lobar resections. 37, 67. 71, 77 ACQUIRED PARENCHYMAL ABNORMALITIES

Acquired Emphysema Acquired forms of lobar emphysema may be seen with bronchopulmonary dysplasia. This acquired form of segmental emphysema is thought to be due to the cumulative injury of elevated inspiratory oxygen tension, ventilatory pressure, and chronic infection leading to increased mucus production, decreased mucus clearance, and bronchial wall injury. Local injury from endotracheal suctioning is postulated as the reason for the predominant involvement of the lower lobes in these cases. The right lower lobe is involved in 80 per cent of these infants. 23 Most such emphysematous changes are not progressive, and the natural course is one of slow resolution. About 20 per cent of affiicted patients require more than 8 weeks and some require more than 6 months before their chest roentgenograms appear normal. 75 In patients whose emphysema progresses on medical therapy, lobectomy may be indicated. Cooney and associates have used Jl31 lung perfusion imaging to evaluate the perfusion of the involved lobe. In all patients who required surgical intervention, markedly diminished or absent perfusion to the involved area was demonstrated. All patients with normal perfusion scans had resolution of their emphysematous changes. 23 Cooney and associates concluded that the reliability of

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nuclear perfusion imaging in predicting the need for pulmonary resection remained uncertain, but lobectomy should be advised when the emphysema persists or progresses and hypoperfusion is demonstrated. Prior to lobectomy, bronchoscopic examination of the airway is mandatory. Mucus plugging or granulation tissue from local injury can cause partial bronchial obstruction and can be endoscopically corrected without lobectomy. Temporary ventilation of one lung may also be helpful when unilateral disease is present.23 Operative intervention in this group should be undertaken only when the clinical course deteriorates despite medical treatment. Pulmonary Abscess Pulmonary abscesses in childhood are uncommon and must be distinguished from the more common pneumatocysts following staphylococcal infection or secondarily infected parenchymal bronchogenic cysts. However, when abscesses are present, appropriate therapy must be rapidly instituted. Pulmonary abscesses represent a destructive suppurative infection of the lung parenchyma caused by tissue invasion by pyogenic organisms. The infection is usually polymicrobial and often contains anaerobic elements.l 17 Pulmonary abscess is characterized by fever, cough, weight loss, leukocytosis, and anemia. Although the early symptoms cannot be distinguished from those of other pulmonary infections, as confluent infarction proceeds, cavitation and bronchial erosion are heralded by the onset of cough, sputum production, and often defervescence. Chest radiographs show an air-fluid level within a thick-walled cavity. Intraparenchymal pulmonary abscesses are often seen in patients who are prone to aspiration or who have a suppressed cough reflex secondary to anesthesia, head injury, or cough suppressant medications. Aspirated foreign bodies can also lead to pulmonary abscess, as can esophageal functional disorders because of their higher incidence of recurrent aspiration. The site of abscess is determined by the position of the patient at the time of aspiration. The basilar segments are most often involved when the patient is upright, superior segments when the patient is supine, and anterior segments when the patient is prone at the time of the aspiration episode. The most common infecting organisms are oral flora, and polymicrobial infections are the rule. Klebsiella pneumoniae can also form a severe type of intralobar necrosis, which frequently requires lobar resection for therapy. Other uncommon etiologies include actinomyces, amoeba, Salmonella, Yersinia, and Echinococcus.m All must be recognized by appropriately collected bronchoscopic cultures. Multiple interpulmonary abscesses have also been seen with IgE agammaglobulinemia, cystic fibrosis, and Hamman-Rich syndrome. The medical therapy of intrapulmonary abscess requires aggressive antibiotic administration directed against the organism cultured in the individual patient. Cultures are best collected by bronchoscopy. When antibiotic therapy is appropriately selected, 95 per cent of patients with parenchymal lung abscess should resolve. Antibiotics should be continued for at least 1 week following the return of a normal chest roentgenogram. Weiss and Flippin found that only 44 per cent of their patients with pul-

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monary abscess had resolution following 4 weeks of antibiotic therapy, and 70 per cent required 3 months of antibiotics for complete resolution. 116 In patients who fail to achieve adequate spontaneous interbronchial drainage, bronchoscopy with catheter-directed endoscopic drainage of the abscess cavity may speed the resolution of the cavity. If the abscess is not resolved after 3 months of therapy, squamous metaplasia of the abscess wall can occur and complete obliteration may no longer be possible. Operative resection is then necessary. Other indications for operation include massive or continued hemoptysis, bronchial stenosis proximal to the abscess, bronchiectasis, recurrent abscess following medical therapy, and pulmonary abscess in an immunosuppressed patient. Operative resection requires appropriate lobectomy in almost all cases, because inflammatory destruction of the segmental planes within the involved lung makes segmental resection hazardous and prone to complication. Gaining early control of the draining bronchus is essential to minimize endobronchial contamination, and the abscess cavity should be removed without opening it to minimize intrapleural infectious complications. Bronchiectasis Bronchiectasis includes bronchial dilatation associated with acute or chronic infection. Although bronchiectasis can be seen transiently following acute respiratory infections, its presence usually implies permanent changes in the airway. Two potential mechanisms can lead to the common pathologic changes of epithelial squamous metaplasia: loss of ciliated epithelial cells and damage to the muscular and cartilaginous supporting structure. of the bronchioles. The initial insult may be partial obstruction of the airway predisposing to parenchymal infection through diminished bronchial clearance of pathogens. Primary pulmonary infection can also damage the bronchial supporting tissues and mucosa. In either case, persistent infection leads to progressive and permanent damage of the bronchial wall and mucosa. Loss of the normal ciliary transport mechanism further decreases bronchial clearing and perpetuates the infectious process. Bronchiectasis can occur as the result of infection in an otherwise normal individual, or it can represent a complication of various inherited abnormalities. Two thirds of all cases arise following acute pulmonary infections in childhood. 69 Measles and adenovirus are the most common pathogens. Tuberculosis and pertussis are also important causes in selected susceptible populations. Aspiration of foreign bodies with its associated airway inflammation and obstruction is also a well-recognized cause of bronchiectasis.3I Endobronchial tumors can cause similar obstructive changes (Fig. 7). Several genetic abnormalities are associated with recurrent pulmonary infections and bronchiectasis: cystic fibrosis, immotile cilia syndrome, and certain immunodeficiencies.26 Congenital deficiencies of the pulmonary supporting tissues such as bronchomalacia, Williams-Campbell syndrome, and Kartagener' s syndrome are uncommon associated causes of bronchiectasis.ll9, 120 Bronchiectasis is classified according to its gross appearance. The saccular form characteristically shows damage to muscle, cartilage, and elastic tissue, producing bulbous blind-ending bronchiolar sacs with poor com-

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Figure 7. A 9-year-old boy with recurrent right middle lobe pneumonia with cystic changes. Bronchoscopy and bronchogram confirmed right middle-lobe bronchial obstruction and bronchiectasis. A mucoepidermoid carcinoma of the bronchial margin was the cause of the obstruction.

munication with the surrounding parenchyma. Cylindrical bronchiectasis has tubular dilatation of the bronchioles communicating with distal patent airways (Fig. 8). Damage to muscular and elastic tissue predominates with relative sparing of the cartilage in this form. Pseudobronchiectasis mimics cylindrical bronchiectasis but is seen in patients immediately following acute upper respiratory tract infections and resolves if chronic infection or obstruction does not supervene. The symptoms of bronchiectasis are a persistent, productive cough in more than 80 per cent of patients and purulent sputum production in 58 per cent.21 The sputum is often swallowed by small children, and its large volume is not recognized. Forty-three per cent of patients are below the tenth percentile for height and weight. Hemoptysis is rare, being seen in only 5 to 7 per cent of patients.l9, 33 Physical examination may show localized bronchovesicular breath sounds with inspiratory crackles or signs of acute pulmonary infection. Bronchiectatic changes are most commonly seen in the left lower lobe, lingula, or right lower lobe, although combined

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Figure 8. A, Cyclindrical bronchiectasis of the left lower lobe. B, Saccular bronchiectasis of the left lower lobe.

disease within the left lower lobe and lingula is not uncommon. 69 Plain chest radiographs may suggest the diagnosis, with signs of atelectasis and dilated bronchi associated with compensatory hyperinflation in the normal surrounding lung. However, only bronchograms are diagnostic. Medical therapy consists of antibiotic treatment when acute pulmonary exacerbations occur and vigorous pulmonary physiotherapy to facilitate bronchial drainage. Bronchoscopy is occasionally needed to assist in clearance of secretions and acquisition of adequate cultures. Long-term suppressive antibiotics do not favorably affect the clinical progression and are not indicated. Under this management, progression of disease has been slow. Two thirds of patients with bronchiectasis, confirmed by bronchogram remain stable, and approximately one fourth slowly worsen during follow-up. In a survey of 195 children followed over an average period of 9.4 years, only 2 per cent of patients developed new bronchiectatic changes in areas that were normal on the initial bronchogram. However, 26 per cent with ill-defined bronchial lesions on initial bronchograms showed definite progression to bronchiectasis during the study period.I21 Careful observation during the course of medical therapy is thus warranted until the full extent of disease is clearly defined prior to operative intervention. Major indications for surgery are as follows: localized disease producing severe symptoms and interfering with a normal life pattern or causing failure to thrive, localized hemorrhage, and resectable disease in a demonstrated site with recurrent, acute lower respiratory infections. Weaker indications include unstable disease associated with progression, bronchiectasis not easily or totally resectable but associated with failure to thrive, bronchiectasis not totally resectable but associated with life-threatening or disabling symptoms, and localized disease with moderate symptoms. 121 Following surgical resection for localized bronchiectasis, 75 per cent of patients are asymptomatic or greatly improved, and almost all patients

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are improved from their preoperative state.36, 42, 121 Deterioration of pulmonary function following operative intervention is very uncommon. When diffuse disease is present prior to resection, surgical improvement is less striking, with 35 per cent of patients being symptom-free and 50 per cent showing postoperative improvement. The long-term prognosis is, however, more guarded in individuals with diffuse disease. Wilson and Decker have noted that when partially diseased segments are retained following segmental excision, there is a tendency for even slightly altered bronchi to deteriorate.121 Because of this observation, when resection is undertaken, all involved tissue should be included.

PLEURAL ABNORMALITIES Neonatal Chylothorax

Noninflammatory pleural effusions in neonates are uncommon; however, when they are present, their most common etiology is chylothorax. Chylothorax is classified as secondary when it occurs following trauma, thoracic surgery, Intrathoracic neoplasms, or great vessel thrombosis. All other cases are designated as congenital or primary in origin. Although the possibility of in utero trauma has been considered an etiology in primary chylothorax, this concept has never been clearly established. Primary neonatal chylothorax presents with a history of progressive respiratory compromise highlighted by tachypnea, dyspnea, and progressive hypoxia. Fully one half of involved infants are symptomatic within the first 24 hours after bir~h, and more than 75 per cent are symptomatic within the first week. 122 Boys predominate by a 2:1 ratio, and right-sided involvement exceeds left-sided involvement by a 3:2 ratio. Bilateral involvement is uncommon. 5, 12. 40, 45, 102 The diagnosis of chylothorax is initially established by thoracentesis and analysis of the pleural fluid. The pleural effusion is clear in unfed infants; however, it may become slightly yellow from colostrum lactochromes when breast-feeding has just begun. Babies on complex fat-containing formulas or breast milk have opalescent fluid. The protein concentration in the chylous fluid is approximately one half of the plasma protein concentration, and the cholesterol and triglyceride concentrations exceed the plasma concentrations. Cytologic studies reveal 42 to 100 per cent lymphocytes and no red blood cells. 5 The electrolyte concentrations are similar to those in the plasma. In infants who have been recently fed complex fat-containing formulas, microscopic examination of the pleural fluid using lipid stains will disclose fat droplets. 5 Congenital chylothorax is believed to be caused by failure or fusion of peripheral and central lymphatic channels or by rupture of the existing channels at birth. The lymphatic system develops as outgrowths of six primary lymphatic sacs: two paired jugular and sciatic sacs and single retroperitoneal and upper abdominothoracic sacs. The thoracic duct is formed by descending outgrowths of the bilateral jugular sacs and an ascending outgrowth of the abdominothoracic sac, both of which join with many small

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lymphatics alongside the azygos venous system. Failure of fusion of this complex network into a single ductal structure explains the presence of multiple thoracic duct cysts along the path of the thoracic duct within the mediastinum in occasional patients. Rupture of the cysts or duct because of increased central venous or lymphatic pressure has been postulated as the cause of the isolated identifiable lymphatic leak recognized at operation in some patients with chylothorax. The management of chylothorax focuses on relief of respiratory compromise, nutritional support, and closure of the chylous leak. The initial management at the time of diagnostic thoracentesis should include complete evacuation of chyle from the involved hemithorax. Further therapy then depends on the rate of fluid reaccumulation. If more than two aspirations are required to keep the pleural space empty in the first several days of therapy, a thoracostomy tube with continuous drainage of the chyle is preferred to repeated thoracentesis. Decompression of the thoracostomy tube facilitates reliable, complete chylous evacuation and pleural apposition, both of which are necessary for nonoperative closure of the chylous leak. Suction applied to the tube has been associated with increased fluid output from the fistula; therefore, passive drainage is indicated.87 Most cases so treated respond within 3 weeks, showing everdiminishing fluid output. The thoracostomy tube can then be removed and the patient observed by repeated chest radiography for evidence of reaccumulating chyle. The nutritional consequences of persistent chylous leak in newborns are significant. Because of the high protein concentration in the chylous fluid, protein calorie support is essential to replenish ongoing losses. As the thoracic duct is the main route of transport of complex fats from the intestinal tract, elimination of all oral intake will diminish the rate of lymphatic flow and thoracic lymphatic accumulation. Reinfusion of the chylous fluid for nutritional support was first reported in 1908; however, anaphylactic-like reactions discouraged most individuals from pursuing this course. 4, 87 Central intravenous hyperalimentation now serves this role. All infants should be supported with intravenous hyperalimentation and receive nothing by mouth during their initial treatment phase. After the chylous leak has stopped and no reaccumulation has occurred over 1 week, refeeding with a medium-chain triglyceride-based formula should be instituted and maintained for 3 months. Medium-chain triglycerides are absorbed directly into the portal blood and serve as a good lipid and calorie source, without increasing lymphatic flow. 64 Failure of chylous fluid to reaccumulate during this interval is indicative of successful therapy, and further dietary restrictions are unnecessary. Surgical therapy is indicated when conservative therapy fails to bring about resolution after 3 weeks of treatment. Ligation of the thoracic duct is then indicated. The thoracotomy should be performed on the side of the pleural effusion at a level that allows complete visualization of the involved thoracic duct. In right-sided effusions, thoracotomy through the fifth or sixth interspace allows visualization of the thoracic duct from the aortic hiatus to its crossing at the fifth vertebral body. Ligation should be accom-

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plished at the aortic hiatus with silk or monofiliment nylon suture. With a lett-sided chylothorax, an approach through the fourth or fifth interspace is preferred in order to visualize the thoracic duct located posterior and lateral to the descending aorta and aortic arch. Ligation is accomplished at the point where the duct enters the left thorax. Regardless of the side of involvement, when multiple sites of chylous leak can be seen, each individual site requires oversewing. The mediastinum can also be diffusely edematous with many lymphatic leaks. In these cases, the main thoracic duct should be ligated at the aortic hiatus, and the mediastinum should be widely opened to facilitate exposure of all draining sites. Mter these have been individually oversewn, the chest should be thoroughly evacuated by thoracostomy tube drainage to assure pleural apposition to the denuded mediastinum. Visualization of the thoracic duct at the time of operation can be aided by the use of fat-soluble dyes. Some authors advocate the injection of 0.5 mg per kg of a 1 per cent suspension of Evans blue into the thigh at the onset of anesthesia or ingestion of a butter patty with Sudan black dye 2 hours prior to surgery to define the thoracic duct and its site of transgression. 87 Intraoperative fat infusion through a nasogastric tube can also help visualize the draining sites. Although these are all appealing concepts, their clinical usefulness has been limited in our experience. Alternative indirect operative methods to control the chylous effusion have been suggested. Kirkland has described placement of a pleural-toright atrial shunt, and Rodgers and associates have described a pleuralperitoneal shunt for refractory cases of chylothorax. 3• 63 These approaches should be instituted only when a direct surgical attack on the chylous leak has been unsuccessful. Because the thoracic duct returns the bulk of lymphocytes to the central venous circulation, a persistent loss of chylous fluid into the thorax has caused lymphopenia in infants with ongoing high-volume lymphatic fistulas. In 1975 Berberich and colleagues noted a measured decrease in humoral and cell-mediated immunity during prolonged chyle loss. 7 In spite of this, only one case of empyema associated with chylothorax has been reported. 5 This has been attributed to the "bacteriostatic properties of chyle" described by Lampson, who noted an inability of Staphylococcus and E. coli to grow in chylous fluid cultures under laboratory conditions. 66 The immunologic deficits are rapidly reversible when the chylous leak is controlled. Staphylococcal Empyema The treatment of empyema in children has changed with the introduction and improvement of antibiotic therapy. Prior to effective antibiotic therapy, empyema was a common accompaniment of bacterial pneumonia in children most often due to pneumococcus or H. Influenzae. 89 As these microorganisms have become better controlled with antibiotics, staphylococcal empyema has assumed ever-increasing importance and presently constitutes well over 75 per cent of all empyemas in the pediatric age range. 89 The treatment of staphylococcal empyema has also changed with

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the advent of better antibiotic therapy. Open drainage procedures, once recommended, are now rarely required. Antibiotic therapy is the primary mode of treatment, with surgical drainage used in selected cases. Empyema can result from hematogenous sepsis, trauma, or invasive procedures or most often from direct extension or lymphatic spread from suppurative pulmonary disease. Staphylococcal empyema may occur at any age; however, children in the first year are affected in 25 to 75 per cent of cases, and most are affiicted by 3 months.l 9, 55, 91 • 103 Staphylococcal pneumonia has a rapid onset and progression. Within hours, severe tachypnea, fever, dyspnea, and cyanosis can appear. At the time of onset, blood cultures and nasopharyngeal cultures will frequently grow the infecting organism. The clinical forms of staphylococcal pneumonia can be divided into two subgroups. In the pneumonic form, the infection is initially restricted to the lung, leading to lobar pneumonic consolidation. In the empyemataus form, the underlying pneumonic consolidation is accompanied early by empyema, often of extensive dimensions. The pleural fluid is initially poorly loculated, and shifting fluid levels can be demonstrated by chest radiographs or ultrasonography. Infants with the empyematous form have a more severe infection than those with the pneumonic form and frequently have more complicated courses. In both forms, the staphylococcal pulmonary parenchymal infection is characterized by an intense necrosis of the lung with abscess formation within the pulmonary alveoli and along the bronchial walls. This bronchial injury precipitates air trapping and formation of pneumatocysts at the sites of bronchiolar rupture. Persistent air trapping can lead to rapid expansion of the pneumatocysts. Rupture of a subpleural abscess or pneumatocyst into the pleural space establishes a pyopneumothorax. The onset of pyopneumothorax may be insidious or catastrophic according to the size of the air leak. Severe respiratory distress can also be precipitated by the rapid accumulation of fluid within the thoracic cavity (Fig. 9). The principles of surgical intervention are accurate identification of the infecting organism, documentation of appropriate antibiotic sensitivities in order to direct drug therapy, and establishment of adequate drainage of the pleural space. Any approach that follows these principles is associated with success in the treatment of staphylococcal empyema. Identification of the Organism. All patients with staphylococcal pneumonia and associated pleural effusion should have needle thoracentesis for diagnosis and initial thoracic drainage. Whenever possible, all pleural fluid should be removed. Aerobic and anaerobic cultures should be started, and antibiotic sensitivities should be determined. When the pleural fluid is not infected, thoracentesis with complete evacuation of the hemithorax and appropriate antibiotic administration is sufficient therapy. Establishment of Adequate Antibiotic Therapy. Antibiotic therapy for staphylococcal empyema should be directed by the particular sensitivities of the organism cultured at the time of initial thoracentesis. However, until sensitivities are available, methicillin remains the mainstay of therapy. In cases where methicillin-resistant Staphylococci are encountered, alternative antimicrobial agents such as vancomycin may be necessary.

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Figure 9. A 4-year-old boy undergoing antibiotic treatment for staphylococcal pneumonia with widespread pneumatocele developed suddenly increasing dyspnea. The supine anteroposterior radiographic (A) suggests an anterior pneumothorax, which is confirmed by a cross-table lateral film (B). The pyopneumothorax was treated by closed thoracostomy tube drainage.

When staphylococcal pneumonia is associated with cystic fibrosis, nephritis, agammaglobulinemia, or biliary atresia, the possibility of multiple organisms or antibiotic-resistant cocci dictate the need for multiple drug therapy. 89 In these instances, we prefer methicillin or vancomycin and an aminoglycoside until cultures are available. Establishment of Adequate Pleural Drainage. The method by which adequate drainage is established depends on the nature of fluid present within the pleural space. With serous fluid, antibiotic administration and complete evacuation of the hemithorax by needle aspiration on one or several occasions are adequate therapy. Purulent fluid is rarely adequately evacuated by needle aspiration alone. Furthermore, loculation or pulmonary injury can occur when thoracentesis is undertaken on a regular basis for removal of purulent fluid. Thoracostomy is indicated under these circumstances. A thoracostomy tube is placed under fluoroscopic guidance to give adequate dependent drainage of the pleural space. This requires the largest tube that can be accommodated within the costal interspace but does not deform it. Early thoracostomy allows adequate drainage of the pleural space and obviates the need for rib resection and open drainage procedures. In the uncommon patient who presents with a chronic empyema following inadequate primary therapy, further surgical intervention may be required. Raffensperger and associates have advocated "mini-thoracotomy" with digital disruption of loculated cavities to establish complete pleural drainage. 85 Ultrasonography has been helpful in identifying these loculated pleural collections and directing local drainage procedures. 104 Rib resec-

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tion, open drainage, and decortication are rarely required. Following pleural drainage, a thickened pleural margin can be easily recognized on chest radiographs as the pleural inflammation resolves on antibiotics. This should not be interpreted as fibrotic peel, and this finding is not an indication for undertaking decortication. Following appropriate antibiotic therapy, these pleural changes will diminish and eventually resolve over the course of 2 to 3 months. 55 Long-term follow-up has confirmed the return of a normal pleural margin and adequate growth of the hemithorax, without the complications of fibrothorax or scoliosis. 95 Few cases in pediatrics require the constant follow-up necessary as do infants with rapidly enlarging pneumatocysts. When these rapidly enlarge, they may require urgent tube cystostomy to drain the cyst and to allow the expansion of the surrounding parenchyma. This procedure should be undertaken only in cases in which rapid expansion of a pneumatocyst precipitates pulmonary insufficiency. The presence of a pneumatocyst alone is not an indication for intervention. Pneumatocysts are seen in the course of staphylococcal pneumonia in 85 per cent of cases. One quarter of these will rupture and precipitate pyopneumothorax, which can be adequately treated by tube thoracostomy and thoracic drainage. 91 The pulmonary air leak will close with resolution of the inflammatory process. Pneumococcal Empyema The need for treatment of pneumococcal empyema has dramatically decreased with the institution of early appropriate antibiotic therapy. Pneumococcal empyema is more frequently seen in an older age range than is staphylococcal empyema, with the average pediatric patient being 7.3 years old. 76 Infants are uncommonly involved. The clinical presentation is acute pneumonia with respiratory symptoms and systemic toxicity. At the time of presentation, pleural fluid can be minimal or extensive and pneumatocysts may be seen. The clinical picture may mimic staphylococcal empyema, and early bacteriologic diagnosis is important in planning therapy. Early establishment of appropriate antibiotic therapy allows resolution of toxic symptoms following 24 to 48 hours of treatment. Thoracentesis should be undertaken when significant pleural collections exist, to establish the bacteriologic diagnosis and to drain the hemithorax. In cases where extensive pleural fluid has accumulated, clearing the hemithorax of the empyematous accumulation often dramatically improves the patient's respiratory status. The indications for thoracostomy tube drainage are similar to those for staphylococcal disease. The clinical course of pneumococcal empyema is frequently complicated by persistent fever over an average of 7 days, despite adequate antibiotic therapy and thoracic drainage. However, with clinical improvement, no change in antibiotic therapy is indicated. 76 As in staphylococcal disease, the chest radiograph may show thickened pleural margins for many weeks following antibiotic therapy. Decisions regarding surgical intervention should not be hastened by these chest radiograph abnormalities.s2 More extensive drainage procedures are almost never required for pneumococcal empyema.

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MEDIASTINAL MASSES The mediastinum has classically been divided into four anatomic subdivisions. This division is arbitrary but helpful in recognizing mediastinal masses where there is a correlation between the type of mass and its location within the medastinum (Table 1). Anterior and Superior Mediastinum The thymus occupies the anterior and superior mediastinum and becomes of surgical interest most often with myasthenia gravis or when thymic enlargement due to cysts or tumor is present. Surgical interest in myesthenia gravis was first stimulated by Blalock and associates in 1939 when they reported resolution of symptoms in a patient whose thymoma was resected. 9 Further experience has shown that approximately 25 per cent of patients with myasthenia gravis are completely relieved of their symptoms and another 50 per cent have their symptoms more easily controlled following surgical resection of the thymus, even when no thymoma is present. 90• 114 These successful results have stimulated interest in early thymectomy when myasthenia gravis presents in childhood. Although thymectomy for myasthenia gravis has been undertaken in a 2-year-old child, most patients are teenagers at the time of clinical presentation.39, IOS Myasthenia gravis has three presentations in childhood. Transient neonatal myasthenia gravis is seen in infants of myasthenic mothers. It may cause life-threatening symptoms due to respiratory insufficiency within hours to days following birth but resolves completely within 2 to 4 weeks on medical therapy. Persistent neonatal myasthenia is indistinguishable from the transient form except that it persists throughout life. Juvenile myasthenia gravis most often has its onset after age 10 years and has characteristics indistinguishable from those of the adult form of myasthenia gravis. The clinical response to thymectomy in pediatric patients who have significant presistent symptoms on medical therapy is encouraging. In Fonkalsrud and associates' review of 14 patients under 20 years of age, significant improvement was seen in all but one patient. In seven patients, thymic hyperplasia was seen on pathologic examination-two patients had Table 1.

Mediastinal Masses in Children

ANTERIOR

SUPERIOR

MIDDLE

Thymoma Thymic cyst Teratoma Teratodermoid Lymphangioma hemangioma Connective tissue tumors Lipoma Fibroma

Thymoma Thymic cyst Lymphoma Thyrid masses Parathyroid masses

Pericardia cyst Bronchogenic cyst Lymphoma Granulomas

POSTERIOR

Neurogenic tumors Foregut duplications and cysts

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thymomas and five had a histologically normal thymus. However, the clinical response following thymectomy did not correlate with normal or abnormal histology in these patients. 39 Complete removal of the thymus is necessary, and median sternotomy is the best approach to afford adequate visualization of the entire thymus from its cervical origin to its inferior extension about the pericardium.59 When meticulous attention is paid to respiratory support and postoperative care, the procedure is associated with a low mortality rate of approximately 4 per cent. 39 The initial concerns of immunologic and infectious sequelae of thymectomy in children seem unwarranted. Thymectomy performed in infants with congenital heart disease concurrent with cardiac correction does not seem to have an increased risk of infection. Similarly, patients with myasthenia gravis do not appear to be predisposed to infection following thymectomy when followed for prolonged periods. 39 Thymomas are rare in childhood with less than 20 cases reported. 13 They are often locally invasive and have associated symptoms from tracheobronchial, esophageal, or vascular compression. Pleural and percardial effusions may be seen. Complete surgical removal is the treatment of choice with radiation therapy indicated when complete extirpation is not possible. Chemotherapy is indicated in cases with progressive disease in spite of surgery and radiation therapy. Cis-platinum appears to be the most effective agent.l3 Thymic cysts can present as masses in the anterior triangle of the neck and the anterior superior mediastinum or as retropharyngeal cysts. They are lined by ciliated epithelium with lymphatic and normal thymic tissue present within the walls. Occasionally, rapid enlargement secondary to hemorrhage obstructs the airway and requires urgent surgical removal. Cardiac compression by an enlarging thymic cyst has also been reported. 1 However, most thymic cysts are asymptomatic. Total excision is the treatment of choice. Teratomas and teratodermoid tumors are rarely recognized prior to adulthood. They present as smooth anterior mediastinal masses and may have the typical findings of dermoid teratomas on pathologic examination. 92 They are almost always benign, although they may have both endocrine or exocrine function. 99 Lymphangiomas of childhood can involve the anterior and superior mediastinum most often from extension of a cervical primary site. Complete extirpation is often difficult but should be undertaken when the cervical mass is removed. Lymphoma involving the mediastinum can be primary or metastatic from extrathoracic sources. Hodgkin's disease makes up' the majority of these cases, and surgical therapy is indicated only to establish the diagnosis when extrathoracic sources of tissues are not available. The prognosis of mediastinal Hodgkin's disease is related to the stage of the disease rather than the extent of thoracic involvement. Lymphosarcoma is also seen in the anterior mediastinum; occasionally it is primary but more often is in association with lymphosarcoma in other locations. Thyroid adenomas extending into the mediastinum, hemangiomas,

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lipomas, and parathyroid adenomas make up the remainder of rare anterior superior mediastinal masses. Middle Mediastinum

Middle mediastinal lesions include lymphomas and bronchogenic cysts previously discussed and pericardia} cysts. Pericardia! cysts arise from persistence of the ventral parietal recesses of the pericardium, which usually completely obliterate. When the distal portion of the recess persists, a cyst remains. They present as smooth soft-tissue masses most frequently at the right pericardiophrenic junction. Although they may be isolated from the main pericardia! sac, most are freely communicating. Even when they are asymptomatic, they often require thoracotomy for diagnosis, and local resection is then indicated. Posterior Mediastinum

Enteric cysts and neurogenic tumors make up the majority of posterior mediastinal masses. Enteric cysts arise from abnormal caudal outpouching from the primitive dorsal foregut and form tubular or cylindrical muscular-walled masses. Lined by secretory intestinal or gastric epithelium, enteric cysts enlarge progressively, unless connected to the normal gastrointestinal tract. Acid peptic secretion causing ulceration, bleeding, or perforation has also been reported. 90 Erosion and hemorrhage into the tracheobronchial tree can also cause massive hemoptysis.oo Enterogenous cysts are frequently adjacent to or imbedded within the wall of the esophagus and can cause symptoms of compression of the esophagus in young infants. However, some reach substantial size while remaining asymptomatic. Thoracic or cervical vertebral body abnormalities, hemivertebrae, and communication with the meninges and neurocanal are occasionally seen through a tube composed of neural elements, forming "neurenteric canal cysts. "s, 35 Communication to the esophagus is rare. However, communication with the stomach, duodenum, or jejunum by way of a dumbell-like extension through the diaphragm is well recognized. When gastrointestinal communication is present, air-fluid levels are frequently seen within the hemithorax and contrast studies may outline the abnormality. Enterogenous cysts are twice as common on the right as on the left side and are often recognized early in life because of their associated symptoms. Unlike intraabdominal gastrointestinal duplications, they can usually be carefully dissected from the adjacent gastrointestinal tract. Neurogenic tumors make up the remainder of posterior mediastinal masses and form the majority of mediastinal neoplasms in most series. These tumors are classified as neuroblastoma, g:mglioneuroma, neurofibroma, pheochromocytoma, neurilemoma, neurosarcoma, sympathicoblastoma, and paraganglioma, although only the first two are common. Intrathoracic neurogenic tumors arise within the posterior paravertebral gutter from an intercostal nerve or the sympathetic chain. Because of the location of these tumors, back pain, Horner's syndrome, and hoarseness are important findings directing investigation toward the mediastinum.

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Neuroblastomas and ganglioneuromas frequently have associated rib erosion and, if there is intraspinal extension, may produce symptoms of spinal cord compression. They can be huge and lead to tracheobronchial compression, although this presentation is unusual. Their management is further discussed in the article dealing with pediatric tumors. Neurofibromas arise from the nerve sheaths or nerve fibers and are associated with von Recklinghausen's disease. They may present at any time in the course of the disease, be multiple, or recur. Pheochromocytoma can occur as a primary lesion or can be associated with von Recklinghausen's disease. This diagnosis can be made by measurement of elevated catecholamines in the blood. The diagnosis and management of mediastinal masses depend on their location and presentation. Most can be diagnosed from their location and appearance after review of the chest radiograph. Fluoroscopy, barium swallow, and angiography can further refine the diagnosis. Ultrasonography allows an accurate differentiation of cystic and solid masses. Computed tomography of the mediastinum allows axial and sagittal reconstruction of the mass and is the diagnostic procedure of choice in most cases. With use of these radiographic modalities, accurate preoperative diagnosis is now possible in most instances. However, excision is indicated for all mediastinal masses, except generalized lymphomas, to confirm the diagnosis and alleviate symptoms.

REFERENCES 1. Alee, G., Logue, B., Mansour, K.: Thymic cyst simulating multiple cardiovascular abnormalities and presenting with pericarditis and pericardia! tamponade. Am. J. Cardiol., 31:377, 1973. 2. Arcomano, J. P., Azzoni, A. A.: Intralobar pulmonary sequestration and intralobar enteric sequestration associated with vertebral anomalies. J. Thorac. Cardiovasc. Surg., 53:470-476, 1967. 3. Azizkhan, R. G., Canfield, J., Alford, B. A., et al.: Pleuroperitonea! shunts in the management of neonatal chylothorax. J. Pediatr. Surg., 18:842-850, 1983. 4. Baldridge, R. R., and Lewis, R. V.: Traumatic chylothorax. Ann. Surg., 128:1056, 1948. 5. Bensoussan, A. L., Braun, P., and Guttman, F. M:.: Bilateral spontaneous chylothorax of the newborn. Arch. Surg., 110:1243-1245, 1975. 6. Bentley, J. F. R., and Smith, J. R.: Development posterior enteric remnants and spinal malformations: The split notochord syndrome. Arch. Dis. Child., 35:76, 1960. 7. Berberich, F. R., Bernstein, I. D., Ochs, H. D., et al.: Lymphangiomatosis with chylothorax. J. Pediatr., 87:941, 1975. ~ 8. Binet, J. P., Nezelolf, C. H., and Fredet, J.: Five cases of lobar tension emphysema. Dis. Chest, 41:126, 1962. 9. Blalock, A., Mason, M. F., Morgan, H. J., et al.: Myasthenia gravis and tumors of the thymic region. Ann. Surg., 110:544, 1939. 10. Boijsen, E., and Kozuka, T.: Angiographic demonstration of systemic arterial supply in abnormal pulmonary circulation. Am. J. Roentgenol. Radium Ther. Nucl. Med., 106:70-80, 1969. 11. Bolande, R. B., Schneider, A. F., and Boggs, J. D.: Infantile lobar emphysema; etiological concept. Arch. Pathol., 61 :289, 1956. 12. Bornhurst, R. A., and Carsky, E. W.: Fetal hydrothorax. Radiology, 83:476-479, 1964. 13. Bowie, P. R., and Carpenter, B.: Malignant thymoma in a nine-year-old boy presenting with pleuropericardial effusion. J. Thorac. Cardiovasc. Surg., 77:777-781, 1979.

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