Chapter2C Lung Pathology: Embryologic Abnormalities Content and Objectives Pulmonary Sequestration 2C-3 Chest X-ray Findings in Arteriovenous Malformation of the Great Vein of Galen 2C-7 Situs Inversus Totalis 2C-10 Congenital Cystic Adenomatoid Malformation of the Lung 2C-14 VATER Association 2C-20 Extralobar Sequestration with Congenital Diaphragmatic Hernia: A Complicated Case Study 2C-24 Congenital Chylothorax: A Case Study 2C-37 Continuing Nursing Education Test CNE-1 Objectives: 1. Explain how the diagnosis of pulmonary sequestration is made. 2. Discuss the types of imaging studies used to diagnose AVM of the great vein of Galen. 3. Describe how imaging studies are used to treat AVM. 4. Explain how situs inversus totalis is diagnosed. 5. Discuss the differential diagnosis of congenital cystic adenomatoid malformation. (continued) Neonatal Radiology Basics Lung Pathology: Embryologic Abnormalities 2C-1 6. Describe the diagnosis work-up for VATER association. 7. Explain the three classifications of pulmonary sequestration. 8. Discuss the diagnostic procedures for congenital chylothorax. 2C-2 Lung Pathology: Embryologic Abnormalities Neonatal Radiology Basics Chapter2C Lung Pathology: Embryologic Abnormalities EDITOR Carol Trotter, PhD, RN, NNP-BC Pulmonary Sequestration pulmonary sequestrations is cited as the 1902 theory of Eppinger and Schauenstein.4 The two postulated an accessory he clinician frequently cares for infants who present foregut tracheobronchia budding distal to the normal buds, Twith respiratory distress and/or abnormal chest x-ray with caudal migration giving rise to the sequestered tissue. The findings of undetermined etiology. One of the essential com- type of sequestration, intralobar or extralobar, would depend ponents in the process of patient evaluation is consideration on the timing of the accessory foregut budding (Figure 2C-1). of differential diagnosis with correlation to radiologic find- Early gestational development of an accessory bud would ings and clinical presentation. Sequestrations are estimated result in development of the anomalous tissue in the intralobar to account for 0.15–1.7 percent of all congenital pulmonary area, with resultant intralobar sequestration. Later embryonic malformations.1 Although rare, often asymptomatic, and fre- development would allow the separation of normal lung tissue quently not presenting in the neonatal period, pulmonary and pleura, resulting in extralobar sequestration.6 sequestrations or bronchovascular foregut malformation Foregut connections are not present in the majority of anomalies (with or without respiratory distress) can result in cases. Because nonpatent stalks and esophageal diverticulae abnormal radiographic findings and should be considered in have been observed between the foregut and the sequestra- the differential diagnosis. tion, the absence of these connections could be postulated to be a result of an involution of the original foregut connection.6 DEFINITION Vascular supply is thought to occur from the persistence of A pulmonary sequestration is a mass of abnormal pulmo- portions of intercommunicating capillary networks that supply nary tissue that does not have normal bronchial communica- the early tracheal bud from the sixth aortic arch (pulmonary tion with the tracheobronchial tree and that receives its blood artery) and the fourth arch (aorta). The anomalous lung tissue supply from anomalous systemic arteries rather than from the and its persistent vessels descend with the celiac axis to supply pulmonary artery. Venous drainage can be into systemic or the lung from the thoracic aorta or from the aorta below the dia- pulmonary veins.2,3 Traditionally, a sequestration that has phragm.6 Pathologically, the sequestered lung tissue is embry- its own separate pleural investment is called extralobar. It is onic and profusely cystic. It contains disorganized, airless alveoli, called intralobar if it is located within the normal lung without bronchi, cartilage, and respiratory epithelium. On x-ray, seques- a separate pleural covering. Because the lesion is so variable trations usually appear as medially located, triangular or oval- and gastroenteric connections may exist, it has been sug- shaped lung masses. The mass may appear cystic and similar to gested that the term bronchovascular foregut malformation be other forms of congenital cystic lung disease, such as congenital used.4,5 However, the intra-extralobar terminology remains in adenomatoid malformation. The diagnosis is confirmed by doc- common use and will be used in this article. umenting the anomalous blood supply through aortography, ultrasonography, or contrast CT scanning. Other radiographic EMBRYOLOGY findings may include pleural effusion, atelectasis of normal lung The theory of embryogenesis that best explains the pul- tissue, or displacement of mediastinal structures due to the mass monary, vascular, and foregut anomalies associated with effect of the sequestration.5 Neonatal Radiology Basics Lung Pathology: Embryologic Abnormalities 2C-3 FIGURE 2C-1 n Drawings illustrating successive stages in the development of the bronchi and lungs. From: Moore KL, and Persaud TVN. 2008. Before We Are Born: Essentials of Embryology and Birth Defects, 8th ed. Philadelphia: Saunders, 203. Reprinted by permission. CLASSIFICATION OF SEQUESTRATIONS anomalies—such as tracheoesophageal fistula, congenital Sequestrations have been classified as intralobar, extralobar heart disease, and diaphragmatic hernia—are more common. (accessory lobe), or Scimitar syndrome. Differentiating char- Communications with the trachea, bronchi, stomach, and acteristics of these three types of sequestrations are presented small bowel have been reported but are rare. Most extralobar in Table 2C-1. sequestrations are diagnosed at an earlier age than are intralo- Intralobar sequestration (Figure 2C-2) is anomalous lung bar sequestrations.8,9 tissue located within normal lung tissue and visceral pleura Scimitar syndrome (Figure 2C-3) is an anomaly of the and is most commonly located in the posterior basal segments entire right lung in which the lung may have only two lobes of the lower lobe, slightly more often on the left.7 Rarely, it and is hypoplastic. The anomalous pulmonary vein drains can be located in upper lobes or bilaterally. It is the most into the inferior vena cava. There may be an associated dex- common type of sequestration occurring 75 percent of the trocardia or congenital cardiac anomalies.8,10 time.7 The clinical presentation may be recurrent pneumonias or other chronic respiratory problems, such as abscesses of the CASE STUDY affected lobe. Therefore, intralobar sequestrations are more A full-term 3.31 kg male was delivered by cesarean section frequently diagnosed after the neonatal period.5 Associated to a 34-year-old gravida 5, para 3, ab 1 mother. The delivery anomalies are less frequent with intralobar than with extralo- was uncomplicated, and the infant received Apgar scores of bar sequestrations.1 8 and 9 at one minute and five minutes. The pregnancy was Extralobar sequestration (see Figure 2C-2) is less common complicated by iron-deficiency anemia, a urinary tract infec- than intralobar, with a male predominance. The sequestration tion during the first trimester, and oligohydramnios during can be located above or below the diaphragm, and, unlike the third trimester. During the pregnancy, an ultrasound of with an intralobar sequestration, the anomalous lung tissue the fetus revealed a possible abdominal mass. Subsequent pre- is outside the visceral pleura and receives its blood supply natal magnetic resonance imaging of the fetus confirmed the from the aorta, usually below the diaphragm. Associated 2C-4 Lung Pathology: Embryologic Abnormalities Neonatal Radiology Basics TABLE 2C-1 n Classification of Pulmonary Sequestrations Extralobar (Accessory Lobe) Intralobar Scimitar Sequestration Sequestration Syndrome Frequency Rare; four times more common in males Six times more common than extralobar; slight male predominance Age at diagnosis Approximately 60% <1 year 50% >20 years Infancy Parenchyma Separated from remainder of lung by Two types: (1) absence of major Hypoplasia of right lung often pleural investment bronchus; (2) bronchial tree and associated with bronchial lung complete; sequestration of anomalies (aplasia, hypoplasia, superfluous portion of lung stenosis) Vascular: Arterial From aorta—usually from below From descending aorta, above or May have hypoplastic right diaphragm below diaphragm, as one or pulmonary artery, anomalous several arteries, occasionally from subdiaphragmatic arterial supply intercostal or innominate artery to right lower lobe Venous Systemic (drainage into hemizygous, Drainage toward pulmonary veins, Anomalous pulmonary venous azygous veins) or portal system rarely into systemic veins drainage of right lung to vena cava (left-toright shunt) causing curved vascular shadow in right lower lung field Location In left costodiaphragmatic sinus or below Two-thirds left; rare bilateral; dorsal Right lung diaphragm segment of lower lobes; rarely upper lobes or lingula Diaphragmatic defect 60% Rare Associated anomalies Frequent, including tracheoesophageal Occasional cystic change or Dextroposition of heart with or and gastric fistulas, tracheal anomalies, sequestered portion of lung; other without congenital cardiac ectopic gut, diaphragmatic hernia and anomalies and malformations anomalies, hemivertebrae other diaphragmatic malformations, similar but much less frequent