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neonatal chest
Anomalies and Malformations Affecting the Fetal/Neonatal Chest Anne M. Hubbard and Timothy M. Crombleholme
ARLY ULTRASOUND detection has provided a better understanding of the natural history and biology of thoracic lesions and their complications. Primary anomalies of lung development, intrathoracic masses, diaphragmatic hernia, and other space-occupying lesions, if large enough, can cause distortion and compress major fetal blood vessels. Obstruction of systemic venous return can lead to nonimmune fetal hydrops which, if untreated, may result in intrauterine fetal demise. In addition, these masses have the potential to cause severe pulmonary hypoplasia resulting in respiratory distress and pulmonary hypertension after birth. In the early 1980s, prenatal magnetic resonance imaging (MRI) was helpful in characterizing uterine and ovarian lesions in the mother; however, it was of little use in evaluating the fetus. The amount of fetal motion that occurred during standard spin-echo sequences which exceeded 2 minutes in acquisition time made fetal MRI impractical. ~ Previously, to suspend motion, diagnostic MRI required either sedation of the mother or an intramuscular or umbilical cord injection of a paralyzing agent into the fetus. With newer ultrafast sequences, such as single shot turbo spin-echo 2 and echo planar imaging? sedation of the mother or baby is unnecessary thus affording MRI great potential in the evaluation of the fetus.
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Between 16 and 24 weeks there is a significant increase in the number of alveolar ducts and blood vessels in the lungs. After 24 weeks there is further flattening of the epithelial cells that line the air spaces, bringing the air spaces and capillaries closer together enabling postnatal gas exchange. The number of alveoli continues to increase until early adolescence and is the principle mechanism of lung growth after birth. 4 Factors that influence normal fetal lung development include adequate size and shape of the thorax, fetal breathing movements, and an adequate amniotic fluid volume. Pulmonary hypoplasia can be the end result when any of these factors are abnormal but is most commonly caused by space-occupying lesions, such as congenital diaphragmatic hernia (CDH), cystic adenomatoid malformation (CAM), bronchopulmonary sequestration (BPS), or fetal hydrothorax. The degree of pulmonary hypoplasia depends on how early the mass develops in gestation as well as how large the lesion is because larger lesions will cause more compression of the developing lungs.
FETAL LUNG DEVELOPMENT
The most important determinant of fetal survival after birth is whether there is adequate development of the lungs. Buds, which are destined to become the epithelial lined tracheobronchial tree, form from the primitive foregut and penetrate into the thoracic mesenchyme, which becomes the pulmonary vascular bed and connective tissues of the lungs. With further division, the bronchi give rise to multiple bronchioles and terminal bronchioles and then give rise to alveolar ducts and alveoli. By 16 to 20 weeks, the development of the major divisions of the tracheobronchial tube is complete. Nevertheless, for adequate gas exchange in the lungs after birth, further development of the alveolar ducts and alveoli is necessary. Seminars in Roentgenology, Vol XXXIII, No 2 (April), 1998: pp 117-125
FETAL LUNG IMAGING
The ultrasound appearance of the normal fetal lung is homogenous and moderately echogenic. The degree of echogenicity relative to the liver increases throughout gestation. The best sonographic predictor of fetal lung maturity in the normal fetus has been measurement of chest circumference relative to the gestational age. For example, in cases of oligohydramnios the chest circumference is decreased indicating pulmonary hypoplasia. Conversely, space-occupying lesions within the chest may cause a larger than normal thoracic cavity spuriously implying advanced lung maturation. 5
From the Departments of Radiology and Surgery, and The Center for Fetal Diagnosis and Treatment, The Children's Hospital of Philadelphia, Philadelphia, PA. Address reprint requests to Anne M. Hubbard, MD, The Children 's Hospital of Philadelphia, Department of Radiology, 34th St & Civic Center Blvd, Philadelphia, PA 19104. Copyright © 1998 by W.B. Saunders Company 003 7-19 8X/98/3 3 02-0005 5 8. 00/0 117
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Echo-planar imaging may prove to be helpful in the evaluation of fetal lung maturity. In a preliminary report, changes in T1 signal were marked between 25 and 30 weeks with longer T1 relaxation times as the lungs became more mature. Significant increases in T2 signal occurred at 30 weeks. Thus, T1 and T2 relaxation times may prove useful in determining lung maturity. 6 Early MRI studies looking at changes in lung volume with increasing gestational age may predict lung maturation more accurately because this technique measures only the lung volume and not the entire thoracic volume. 7
FETAL CHEST LESIONS Accurate prenatal diagnosis of a chest mass is important because the natural history, treatment, and prognosis vary depending on cause. The most commonly identified fetal chest masses are CDH, CAM, BPS, and fetal hydrothorax. Other less common lesions that may effect lung development are duplication cysts of the esophagus, bronchogenic cysts, congenital lobar emphysema, neuroenteric cysts, tracheal atresia, and thoracic neuroblastoma. On prenatal ultrasonography, these lesions may all present as hyperechoic lesions involving part or all of a lung. In one review of fetal lung masses, 64% of affected fetuses survived the prenatal period and of these, 80% ultimately survived after birth. Increasing mediastinal shift was an indicator of a poor outcome: 50% of nonaborted fetuses with severe mediastinal shift died, whereas 90% of fetuses with no mediastinal shift lived. Follow-up scans in utero demonstrated that the size of the mass became smaller in 53% of the fetuses. Polyhydramnios was a bad prognostic indicator, with a survival rate of 50%. Eight percent of these fetuses had associated structural abnormalities or abnormal chromosomes) Another series showed that 9 out of 50 fetal lung masses decreased dramatically in size or disappeared during gestation, demonstrating that the natural history of prenatally diagnosed lung masses is extremely variable. Although a huge mass associated with fetal hydrops had an extremely poor outcome, in the absence of hydrops, the prognosis was not always predictable. 9 Even with high-resolution ultrasonography, differentiation of these lesions may be difficult. Ultrafast MRI can be a useful adjunct in difficult or puzzling cases.
CONGENITAL DIAPHRAGMATIC HERNIA
The muscular diaphragm forms between 6 and 14 weeks' gestation and is usually present by the end of the eighth week. CDH occurs in approximately 1 in 1,000 pregnancies when intrauterine demise, still births, and live births are included. Ninety-two percent are posterior lateral defects, with 97% being unilateral and approximately 80% on the left. Associated malformations including cardiac, neural tube defects, spinal defects, trisomies, and multiple syndromes occur in 20% to 50% of fetuses with CDH. 5 Herniation of viscera in CDH usually occurs during the period of early lung development, thereby reducing the number of bronchial branches and alveoli. Similarly, the vascular bed is abnormal with a reduction of the number of vessels. The ipsilateral lung is most effected, but hypoplastic changes are also seen in the contralateral lung as a result of compression by mediastinal shift. 1° The overall mortality of CDH is very high, that is, greater than 50%, and is even higher among those with other associated anomalies. Over the last 20 years, the survival has not increased dramatically,
Fig 1, Congenital diaphragmatic hernia (MRI). Axial half fourier single-shot turbo spin echo (HASTE) image through the mid-thorax of a fetus of 34 weeks' gestation. Orientation of image: Fetal left to the left, fetal right to the right, spine at the bottom. Note that the stomach (short arrow), which is high in signal intensity, similar to amniotic fluid is in the mid chest anterior and to the left of the spine. Just lateral to the stomach lies small bowel filled with fluid (medium arrow). The liver (long arrow) is low in signal intensity and fills up the anterior half of the left chest. The lungs (curved white arrows) are compressed and displaced into the right chest, The mediastinal structures (large white arrow) are severely displaced into the right chest.
FETAL/NEONATAL CHEST ANOMALIES
even with the advent of high-frequency ventilation, extracorporeal membrane oxygenation (ECMO), and fetal surgery. In a fetus with an echogenic lung, a careful ultrasound examination should be done to exclude the presence of bowel or stomach within the chest. Fluid-filled loops of bowel without peristalsis can easily be confused with cystic adenomatoid malformation. Careful examination of the position of the liver, especially the left lobe, is also important and has implications for survival. 1~ Currently, only fetuses with herniation of the liver are considered suitable candidates for fetal surgery. During ultrasound evaluation of the fetal thorax, the entire diaphragm should be visualized on cross section at the level of the heart as well as on appropriate coronal and sagittal images. Gut or liver should not normally be identified at the same level as the heart. Color Doppler is extremely helpful to evaluate liver position. The umbilical vein, continuing as the
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ductus venosus, should have a straight course within the liver as it goes from the umbilicus to the hepatic vein and heart. When the liver herniates into the chest, color Doppler demonstrates bowing of the umbilical segment of the portal vein to the left of midline and coursing of portal venous branches of the lateral segment of the left hepatic lobe towards or above the diaphragmatic ridge. If the stomach is identified in a posterior or midthoracic position, this also suggests that the liver is herniated into the chest. In our experience, we have found prenatal MRI very helpful in determining fetal liver position in CDH. 12 Using fast scans with T2-weighted halfFourier single-shot turbo spin-echo (HASTE) and more Tl-weighted fast gradient echo sequences, the liver position is easily visualized. On T1weighted sequences, the liver is bright compared with the less intense fluid density thoracic structures (Fig 1A). Hepatic vessels can be identified,
Fig 2. Congenital diaphragmatic hernia (MRI). A coronal Tl-weighted FLASH image through the chest and abdomen of a fetus of 27 weeks' gestation. (A) The liver is high in signal intensity (curved arrows) and the left portal vein (arrow head) can be seen coursing up into the chest. On Tl-weighted images, the high signal intensity meconium filled distal bowel (straight arrows) can be identified from the rectum extending through the diaphragm up to the superior aspect of the left chest. The amniotic filled stomach (open arrow), which is in the chest, is seen as an area of low signal in the mid-thorax. (B) The high signal intense left lobe of the liver (curved arrows) can be seen extending up into the chest, and the high signal bowel (straight arrow) is seen extending well up over the liver and along the left lateral side of the liver.
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which helps confirm the abnormal position of the liver. On Tl-weighted images, meconium-filled bowel is extremely high in signal intensity and differentiates bowel from other cystic lung lesions, which are not high signal intensity with T1 weighting. On T2-weighted HASTE images the amniotic fluid-filled stomach is bright and the lungs, which have intermediate signal intensity, can be distinguished from liver and bowel (Fig 2). In utero treatment of congenital diaphragmatic hernia in highly selected fetuses is technically feasible and currently under investigation. Studies of early in utero complete repair of the diaphragmatic defect showed that those fetuses without herniation of liver into the chest had the same survival as those corrected postnatally. Consequently, in this group of patients, the risk of prenatal repair is not warranted. In those fetuses with liver herniation into the chest that underwent prenatal surgical repair, when the liver was brought down into the abdomen there was frequently kinking of the umbilical vein, associated with hypotension, bradycardia, and death. Consequently, complete prenatal repair of diaphragmatic hernia is not currently recommended. 13 Multiple studies have shown that occlusion of the fetal trachea can prevent pulmonary hypoplasia. In experimental animal models, the entrapment of normal alveolar fluid within the lungs following tracheal occlusion causes accelerated development of the lung, with an increase in the number of alveoli and total lung volume. 14 This procedure is currently under investigation in fetuses with isolated CDH and liver herniation into the chest with the hope that the occlusion of the trachea will promote accelerated lung growth, as well as partially reduce the herniation of the liver and gut. Preliminary results are encouraging. Neonates with CDH are at a high risk for severe pulmonary hypoplasia, which often requires intensive management by pediatric surgeons and neonatologists within a tertiary care setting. Immediate treatment of the newborn usually includes endotracheal tube placement, neuromuscular blockade, high-frequency ventilation, and prompt insertion of a nasogastric tube to decompress the bowel. Surgical repair of the defect is delayed until the pulmonary status is stabilized. 1° The chest radiograph will reveal varying degrees of mediastinal shift away from the side of the diaphragmatic hernia (Fig 3). The course and
HUBBARD AND CROMBLEHOLME
Fig 3. Congenital diaphragmatic hernia. AP chest radiograph of a neonate during the first few hours of life. On the chest radiograph, the heart and mediastinal structures, particularly the trachea (arrow), are displaced towards the right. The lower two thirds of the left chest is opaque, representing the herniated left lobe of the liver as well as non-air-filled loops of bowel. The lungs are partially aerated. Both lungs are small, but note the extremely small size of the hypoplastic left lung.
position of the nasogastric tube may be abnormal because of displacement of the stomach up into the chest. If the patient has been resuscitated without a nasogastric tube, there may be a large amount of air-filled bowel in the chest and paucity of gas in the abdomen. The latter can help differentiate air-filled loops of gut of CDH from a primary cystic lung lesion. Many of these infants require ECMO when the degree of pulmonary hypoplasia and pulmonary hypertension is too severe for adequate oxygenation using positive pressure ventilation. CYSTIC ADENOMATOID MALFORMATION
CAM is a rare lesion characterized by a multicystic mass of pulmonary tissue with proliferation of bronchiolar structures. 15 It represents 25% of all congenital lung lesions. One theory regarding patho-
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Fig 4. Cystic adenomatoid malformation. (A) Sagittal HASTE through the right side of the fetus reveals a large, multicystic mass (straight arrows) in the posterior half of the right chest. Normal lung (large arrow) can be seen anteriorly. There is eversion of the diaphragm (curved arrow) and a large amount of abdominal ascities (black arrow), (B) The orientation is as follows: the fetal right chest is up and the anterior chest is to the left, Transverse ultrasound image through the mid-chest of a 26-week fetus. A large echogenic mass (straight arrows) can be seen filling a large portion of the right hemithorax. The mass contains cysts of various sizes, The heart (short arrow) is displaced into the left, mid-thorax. A small amount of normal right and left lung tissue (large arrows) can be seen.
genesis of CAM is that it represents a failure of normal maturation of bronchiolar structures occurring around the sixth week of gestation. CAM is usually unilobar, although bilateral CAMs have been reported. Most CAMs communicate with the normal tracheobronchial tree and receive their blood supply from a normal pulmonary artery and vein. Anomalous vessels have been reported but are uncommon. The histopathology of CAM has been classified into three types) 5 Type 1 consists of single or multiple large cysts, easily visualized on ultrasound examination. Type 2 consists of more numerous smaller cysts, less than 1 cm in size. On ultrasound examination, it appears as an echogenic mass containing small cysts. This type of CAM is associated with a high incidence of other fetal anomalies. Type 3 is the least common consisting
of a large homogenous microcystic mass, which may appear solid on ultrasound examination. The natural history and prognosis of these lesions are extremely variable. 9The prognosis primarily depends on the size rather than the type of lesion. Large lesions have a higher incidence of mediastinal shift, polyhydramnios, pulmonary hypoplasia, vascular compromise, and hydrops, which may lead to intrauterine fetal demise or neonatal death. However, lesions identified prenatally may involute in utero. Although in utero hydrops may resolve, it is generally considered a sign of impending fetal demise. Careful ultrasound examination is important to rule out associated anomalies, especially renal. Chromosomal abnormalities are rarely associated with CAM. Once the lesion has been identified, careful serial follow-up is necessary to monitor the degree of mediastinal shift and early
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signs of hydrops. Prenatal MRI is helpful in the diagnosis of CAM (Fig 4) distinguishing it from the herniated intestine of CDH, which has a similar sonographic appearance. J2 Fetal surgery is an option for fetuses with life-threatening lesions, usually indicated by the development of hydrops. In cases with an anticipated mortality of 100%, more than 60% can be salvaged by prenatal resection of the CAM. In cases with a large, multicystic lesion, primary resection of the lobe has been performed with subsequent growth of the remaining lung. In fetuses with a single dominant cyst, thoracoamniotic shunts have been placed with partial decompression of the mass. 16 In the newborn, 80% of CAMs present with some degree of respiratory distress secondary to pulmonary hypoplasia. However, they may present later in childhood as an asymptomatic finding on chest radiograph or with infection. During the first hours of neonatal life, the chest radiograph may show shift of the mediastinum by a "soft tissue mass," which represents retained fluid within the CAM. With progressive ventilation and absorption of fluid, an air-filled cystic lesion may become apparent on the chest radiograph (Fig 5). Air
Fig 5. Cystic adenomatoid malformation. AP chest radiograph of a 5-week-old neonate shows marked shift of the heart and mediastinal structures into the left chest. The right lung is extremely hyperinflated and multiple cysts can be seen in the upper portion (arrows).
HUBBARD AND CROMBLEHOLME
trapping within these cystic spaces can cause rapid enlargement of the CAM and subsequent respiratory embarrassment. CAMs identified prenatally which involute during pregnancy may be difficult to detect on the postnatal chest radiograph although the lesion can usually be identified with CT or MRI. In infants who have significant pulmonary compromise, early surgical removal of the mass is advocated as soon as the patient has been stabilized. Although some asymptomatic lesions remain untreated, removal of even asymptomatic masses is recommend because of reports of carcinomas arising in CAM, as well as the risks of secondary infection and hemorrhage.~7
BRONCHOPULMONARY SEQUESTRATION
BPS represents a mass of nonfunctioning lung tissue that does not communicate with the normal bronchial tree and receives its vascular supply from the systemic circulation. Lesions are classified into extralobar (25%) and intralobar (75%) forms. The extralobar form consists of pulmonary tissue that is enveloped in its own pleura, separate from normal lung and is associated with other abnormalities, including foregut anomalies and CDH. Extralobar sequestrations may occur above or below the diaphragm. Although the extralobar form is the one most commonly diagnosed in the prenatal and neonatal periods, the intralobar form is more commonly diagnosed after birth. 5,1° Intralobar sequestration may be associated with scimitar syndrome, that is, hypoplasia of the right lung with anomalous venous drainage of part or the entire lung. It is important to define the venous drainage before surgery to avoid accidental ligation of the pulmonary venous drainage from the normal lung. The in utero ultrasound appearance of BPS is generally a solid, well-defined, highly echogenic mass (Fig 6). Color flow Doppler is useful to detect the feeding systemic artery. It is important to look for systemic vessels, as they will help differentiate BPS from other masses in the lung or CDH. These lesions can also be associated with massive mediasfinal shift, hydrothorax, and fetal hydrops. They frequently involute in utero. 9 Prenatal management of fetal BPS includes
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Fig 6. Bronchopulmonary sequestration. (A) Transverse ultrasound through the chest at the level of a four-chamber view of the heart in a 19-week fetus. A large, homogenous, echogenic mass (large arrow) occupies most of the right thorax. Small portions of the right and left lungs (long-tailed arrows) are noted. The heart (short arrow head) is displaced into the left chest. (B) On an axial T2-weighted HASTE image through the level of the four-chamber view of the heart (short arrow head), the lesion can still be identified in the right lung (short, broad arrow), but is significantly smaller than on the prior ultrasound. The signal intensity of this lesion is significantly brighter than the adjacent right and left lungs (thin arrows). (C) At birth, this child had mild respiratory distress. A CT scan at 2 weeks of life showed a moderate-sized hypodense lesion (arrows) in the right lung. At surgery, this was found to be a bronchopulmonary sequestration with an anomalous feeding vessel.
careful follow-up of the fetus for development of hydrops or polyhydramnios. If the fetus is 32 weeks or older and in difficulty, early delivery may be considered. The hydropic fetus with BPS diagnosed before 32 weeks' gestation may be a candidate for fetal intervention by resection of the chest mass. 1° Thoracoamniotic shunting may be considered to relieve associated hydrothorax. After birth, these lesions most commonly present as recurrent focal infections. They can also present as an asymptomatic pulmonary mass on chest radiograph, and most patients with BPS remain asymptomatic through life. Although prenatally diagnosed sequestrations may not always be visualized on chest radiographs after birth, they can usually be identified on CT or MRI (see Fig 6C).
FETAL HYDROTHORAX
Fetal hydrothorax may be unilateral or bilateral. It may be primary caused by a chylous leak or secondary to generalized fluid retention associated with immune or nonimmune fetal hydrops. Prenatally, it may be difficult to distinguish the cause of fetal hydrothorax, but such effusions are abnormal at any time during gestation. However, a small amount of pericardial fluid is normal. The spectrum of severity of fetal hydrothorax ranges from very small and harmless to severe with mediastinal shift. Overall, mortality is approximately 50%. Polyhydramnios may develop but has not been associated with increased mortality. Hydrops, occurring before 35 weeks and bilateral effusions are associated
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with a worse prognosis. These effusions may increase or decrease in severity during gestation, so close follow-up is important. 18 On ultrasound evaluation, an anechoic collection can be seen peripherally around the compressed lung. There may be marked shift of the mediastinal structures away from the effusion and flattening of the diaphragm. Thorough examination of the chest and abdomen is important to exclude lesions that may be associated with pleural effusions such as CAM, BPS, CDH, cardiac anomalies, Turner's syndrome, Downs' syndrome, and cystic hygroma. These associated anomalies can be seen in up to 40% of cases of hydrothorax diagnosed in the prenatal period.t° Primary hydrothorax may resolve or progress to fetal hydrops. Severe pulmonary hypoplasia caused by large pleural effusions may be incompatible with postnatal survival. Fetal intervention is reserved for hydrothorax occurring before 32 weeks' gestation with marked mass effect. Prenatal thoracentesis has been associated with a good outcome, but some observers have described poor results due to the rapid reaccumulation of fluid. Thoracoamniotic shunting by catheter may allow continuous decompression of the effusion. If instituted early enough, this may allow compensatory growth of the lung and prevent further pulmonary hypoplasia.18 At birth, chest tube drainage is only indicated if the effusion is the cause of respiratory compromise. A thorough review of the chest radiograph should be made to exclude other congenital lesions that may cause pleural effusions. Chylous pleural effusion may increase following feedings with high fat content formula. If the fluid rapidly reaccumulates following thoracentesis, a medium-chain triglyceride-based diet may be effective, otherwise oral feedings may be suspended in favor of parenteral alimentation. Chest tube drainage is reserved for the most severely ill patients because it may result in depletion of lymphocytes and compromise of the immune system. MISCELLANEOUS ANOMALIES
Although laryngotracheal atresia is rare, this diagnosis should be considered whenever bilateral echogenic lung lesions are encountered. Bilateral CAMs are uncommon but can have a similar appearance. When the larynx or trachea becomes completely obstructed, fluids created within the lung become trapped resulting in hyperplasia of
Fig 7. Laryngotracheal obstruction. Transverse echo planar image through the mid-chest of a 24-week fetus with high tracheal occlusion, The heart is small and compressed (open arrow) and is surrounded by pericardial fluid. Both the right and left lungs (long-tailed arrows} are enlarged and high in signal intensity consistent with overdistention of the lungs with alveolar fluid. There is hydrops with marked subcutaneous edema (short arrow heads). Fetal demise occurred shortly after the scan, At autopsy, a small laryngeal cyst was found obstructing the larynx and trachea.
pulmonary alveoli and tracheal dilation. The fetus is at significant risk for developing hydrops due to the marked compression of the cava and obstruction of venous return by the enlarged lungs (Fig 7). Maternal polyhydramnios may occur and there is a high fetal and neonatal mortality.19 Congenital bronchogenic cysts are rarely diagnosed in utero. They are the result of abnormal development of the tracheobronchial tree and lie within the spectrum of foregut abnormalities. They are usually found in the mediastinum near the carina. In those rare cases identified on prenatal ultrasound examination, bronchogenic cysts are usually unilocular or multilocular. The most common finding is a large, unilateral, echogenic lung resulting from obstruction of the adjacent bronchus by the mediastinal cyst. 5,2° SUMMARY
Although significant anomalies of the fetal thorax are uncommon, with improvement in highresolution ultrasonography, more of these lesions are being diagnosed prenatally. Accurate and specific prenatal diagnosis is important because different lesions have different natural histories and prognosis. Prenatal MRI is an increasingly important adjunct for identification and differentiation of these lesions and may help determine in selected cases when and if in utero fetal intervention is indicated. 21
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REFERENCES
1. Weiureb JC, Lowe T, Cohen JM, et at: Human fetal anatomy: MR imaging. Radiology 157:715-720, 1985 2. Levine D, Hatabu H, Gaa J, et al: Fetal anatomy revealed with fast MR sequences. AJR Am J Roentgenol 167:905-908, 1996 3. Mansfield R Stehling MK, Ordidge RJ, et al: Echo planar imaging of the human fetus in utero at 0.5T. Br J Radiol 63:833-841, 1990 4. Hislop AA, Wiglesworth JS, Desai R: Alveolar development in the human fetus and infant. Early Hum Dev 13:1, 1986 5. Goldstein RB: Ultrasound of the fetal thorax, in Callen PW (ed): Ultrasonography in Obstetrics and Gynecology (ed 3). Philadelphia, PA, WB Saunders, 1994, pp 333-346 6. Dowlan BE Moore R, Freeman A, et al: Monitoring fetal lung maturation using echo-planar imaging. Abstract presented at International Society for Magnetic Resonance in Medicine. New York, May, 1996 7. Baker PN, Johnson IR, Gowland PA, et al: Estimation of fetal lung volume using echo-planar magnetic resonance imaging. Obstet Gynecol 83:951-954, 1994 8. Bromley B, Parad R, Estroff JA, et al: Fetal lung masses: Prenatal course and outcome. J Ultrasound Med 14:927-936, 1995 9. MacGillivray PE, Harrison MR, Goldstein RB, et al: Disappearing fetal lung lesions. J Pediatr Surg 28:1321-1325, 1993 10. Morin L, Cromblehome TM, D'Alton ME: Prenatal diagnosis and management of fetal thoracic lesions. Semin Pernatol 18:228-253, 1994 11. MeNus AP, Filly RA, Stringer MD, et al: Sonographic predictors of survival in fetal diaphragmatic hernia. J Pediatr Surg 31:148-152, 1996
12. Hubbard AM, Adzick NS, Crombleholme TM: Value of prenatal MR imaging in preparation for fetal surgery of left congenital diaphragmatic hernia. Radiology 203:636-640, 1997 13. Harrison MR, Adzick NS, Flake AW, et al: Correction of congenital diaphragmatic hernia in utero: VI. Hard learned lessons. J Pediatr Surg 28:1411-1418, 1993 14. Hendrick MH, Estes JM, Sullivan KM, et al: Plug the lung until it grows (PLUG): A new method to treat congenital diaphragmatic hernia in utero. J Pediatr Surg 29:612-617, 1994 15. Stocker JT, Madewell JER, Drake RM: Congenital cystic adenomatoid malformation of the lung: classification and morphologic spectrum. Hum Pathol 8:155-171, 1977 16. Adzick NS, Harrison MR, Flake AW, et al: Congenital cystic adenomatoid malformation of the lung. J Pediatr Surg 28:806-812, 1993 17. Rebet ME, Copin MC, Soots JG, et al: Bronchioalveolar carcinoma and congenital cystic adenomatoid malformation. Ann Thorac Surg 60:1126-1128, 1995 18. Longaker MT, LaBerg JM, Dansereau J, et al: Primary fetal hydrothorax: Natural history and management. J Pediatr Surg 24:573-576, t989 19. Dotkart LA, Reimers FT, Wertheimer IS, et al: Prenatal diagnosis of laryngeal atresia. J Ultrasound Med 11:496-498, 1992 20. Young G, L'Heureux PRL, Krneckeberg ST, et al: Mediastinal bronchogenic cyst: Prenatal sonographic diagnosis. AJRAm J Roentgenol 152:125-127, 1989 21. Crombleholme TM, D'Alton M, Cendron M, et al: Prenatal diagnosis and the pediatric surgeon: The impact of prenatal consultation on perinatal management. J Pediatr Surg 31:156-163, 1996
ARLY ULTRASOUND detection has provided a better understanding of the natural history and biology of thoracic lesions and their complications. Primary anomalies of lung development, intrathoracic masses, diaphragmatic hernia, and other space-occupying lesions, if large enough, can cause distortion and compress major fetal blood vessels. Obstruction of systemic venous return can lead to nonimmune fetal hydrops which, if untreated, may result in intrauterine fetal demise. In addition, these masses have the potential to cause severe pulmonary hypoplasia resulting in respiratory distress and pulmonary hypertension after birth. In the early 1980s, prenatal magnetic resonance imaging (MRI) was helpful in characterizing uterine and ovarian lesions in the mother; however, it was of little use in evaluating the fetus. The amount of fetal motion that occurred during standard spin-echo sequences which exceeded 2 minutes in acquisition time made fetal MRI impractical. ~ Previously, to suspend motion, diagnostic MRI required either sedation of the mother or an intramuscular or umbilical cord injection of a paralyzing agent into the fetus. With newer ultrafast sequences, such as single shot turbo spin-echo 2 and echo planar imaging? sedation of the mother or baby is unnecessary thus affording MRI great potential in the evaluation of the fetus.
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Between 16 and 24 weeks there is a significant increase in the number of alveolar ducts and blood vessels in the lungs. After 24 weeks there is further flattening of the epithelial cells that line the air spaces, bringing the air spaces and capillaries closer together enabling postnatal gas exchange. The number of alveoli continues to increase until early adolescence and is the principle mechanism of lung growth after birth. 4 Factors that influence normal fetal lung development include adequate size and shape of the thorax, fetal breathing movements, and an adequate amniotic fluid volume. Pulmonary hypoplasia can be the end result when any of these factors are abnormal but is most commonly caused by space-occupying lesions, such as congenital diaphragmatic hernia (CDH), cystic adenomatoid malformation (CAM), bronchopulmonary sequestration (BPS), or fetal hydrothorax. The degree of pulmonary hypoplasia depends on how early the mass develops in gestation as well as how large the lesion is because larger lesions will cause more compression of the developing lungs.
FETAL LUNG DEVELOPMENT
The most important determinant of fetal survival after birth is whether there is adequate development of the lungs. Buds, which are destined to become the epithelial lined tracheobronchial tree, form from the primitive foregut and penetrate into the thoracic mesenchyme, which becomes the pulmonary vascular bed and connective tissues of the lungs. With further division, the bronchi give rise to multiple bronchioles and terminal bronchioles and then give rise to alveolar ducts and alveoli. By 16 to 20 weeks, the development of the major divisions of the tracheobronchial tube is complete. Nevertheless, for adequate gas exchange in the lungs after birth, further development of the alveolar ducts and alveoli is necessary. Seminars in Roentgenology, Vol XXXIII, No 2 (April), 1998: pp 117-125
FETAL LUNG IMAGING
The ultrasound appearance of the normal fetal lung is homogenous and moderately echogenic. The degree of echogenicity relative to the liver increases throughout gestation. The best sonographic predictor of fetal lung maturity in the normal fetus has been measurement of chest circumference relative to the gestational age. For example, in cases of oligohydramnios the chest circumference is decreased indicating pulmonary hypoplasia. Conversely, space-occupying lesions within the chest may cause a larger than normal thoracic cavity spuriously implying advanced lung maturation. 5
From the Departments of Radiology and Surgery, and The Center for Fetal Diagnosis and Treatment, The Children's Hospital of Philadelphia, Philadelphia, PA. Address reprint requests to Anne M. Hubbard, MD, The Children 's Hospital of Philadelphia, Department of Radiology, 34th St & Civic Center Blvd, Philadelphia, PA 19104. Copyright © 1998 by W.B. Saunders Company 003 7-19 8X/98/3 3 02-0005 5 8. 00/0 117
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Echo-planar imaging may prove to be helpful in the evaluation of fetal lung maturity. In a preliminary report, changes in T1 signal were marked between 25 and 30 weeks with longer T1 relaxation times as the lungs became more mature. Significant increases in T2 signal occurred at 30 weeks. Thus, T1 and T2 relaxation times may prove useful in determining lung maturity. 6 Early MRI studies looking at changes in lung volume with increasing gestational age may predict lung maturation more accurately because this technique measures only the lung volume and not the entire thoracic volume. 7
FETAL CHEST LESIONS Accurate prenatal diagnosis of a chest mass is important because the natural history, treatment, and prognosis vary depending on cause. The most commonly identified fetal chest masses are CDH, CAM, BPS, and fetal hydrothorax. Other less common lesions that may effect lung development are duplication cysts of the esophagus, bronchogenic cysts, congenital lobar emphysema, neuroenteric cysts, tracheal atresia, and thoracic neuroblastoma. On prenatal ultrasonography, these lesions may all present as hyperechoic lesions involving part or all of a lung. In one review of fetal lung masses, 64% of affected fetuses survived the prenatal period and of these, 80% ultimately survived after birth. Increasing mediastinal shift was an indicator of a poor outcome: 50% of nonaborted fetuses with severe mediastinal shift died, whereas 90% of fetuses with no mediastinal shift lived. Follow-up scans in utero demonstrated that the size of the mass became smaller in 53% of the fetuses. Polyhydramnios was a bad prognostic indicator, with a survival rate of 50%. Eight percent of these fetuses had associated structural abnormalities or abnormal chromosomes) Another series showed that 9 out of 50 fetal lung masses decreased dramatically in size or disappeared during gestation, demonstrating that the natural history of prenatally diagnosed lung masses is extremely variable. Although a huge mass associated with fetal hydrops had an extremely poor outcome, in the absence of hydrops, the prognosis was not always predictable. 9 Even with high-resolution ultrasonography, differentiation of these lesions may be difficult. Ultrafast MRI can be a useful adjunct in difficult or puzzling cases.
CONGENITAL DIAPHRAGMATIC HERNIA
The muscular diaphragm forms between 6 and 14 weeks' gestation and is usually present by the end of the eighth week. CDH occurs in approximately 1 in 1,000 pregnancies when intrauterine demise, still births, and live births are included. Ninety-two percent are posterior lateral defects, with 97% being unilateral and approximately 80% on the left. Associated malformations including cardiac, neural tube defects, spinal defects, trisomies, and multiple syndromes occur in 20% to 50% of fetuses with CDH. 5 Herniation of viscera in CDH usually occurs during the period of early lung development, thereby reducing the number of bronchial branches and alveoli. Similarly, the vascular bed is abnormal with a reduction of the number of vessels. The ipsilateral lung is most effected, but hypoplastic changes are also seen in the contralateral lung as a result of compression by mediastinal shift. 1° The overall mortality of CDH is very high, that is, greater than 50%, and is even higher among those with other associated anomalies. Over the last 20 years, the survival has not increased dramatically,
Fig 1, Congenital diaphragmatic hernia (MRI). Axial half fourier single-shot turbo spin echo (HASTE) image through the mid-thorax of a fetus of 34 weeks' gestation. Orientation of image: Fetal left to the left, fetal right to the right, spine at the bottom. Note that the stomach (short arrow), which is high in signal intensity, similar to amniotic fluid is in the mid chest anterior and to the left of the spine. Just lateral to the stomach lies small bowel filled with fluid (medium arrow). The liver (long arrow) is low in signal intensity and fills up the anterior half of the left chest. The lungs (curved white arrows) are compressed and displaced into the right chest, The mediastinal structures (large white arrow) are severely displaced into the right chest.
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even with the advent of high-frequency ventilation, extracorporeal membrane oxygenation (ECMO), and fetal surgery. In a fetus with an echogenic lung, a careful ultrasound examination should be done to exclude the presence of bowel or stomach within the chest. Fluid-filled loops of bowel without peristalsis can easily be confused with cystic adenomatoid malformation. Careful examination of the position of the liver, especially the left lobe, is also important and has implications for survival. 1~ Currently, only fetuses with herniation of the liver are considered suitable candidates for fetal surgery. During ultrasound evaluation of the fetal thorax, the entire diaphragm should be visualized on cross section at the level of the heart as well as on appropriate coronal and sagittal images. Gut or liver should not normally be identified at the same level as the heart. Color Doppler is extremely helpful to evaluate liver position. The umbilical vein, continuing as the
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ductus venosus, should have a straight course within the liver as it goes from the umbilicus to the hepatic vein and heart. When the liver herniates into the chest, color Doppler demonstrates bowing of the umbilical segment of the portal vein to the left of midline and coursing of portal venous branches of the lateral segment of the left hepatic lobe towards or above the diaphragmatic ridge. If the stomach is identified in a posterior or midthoracic position, this also suggests that the liver is herniated into the chest. In our experience, we have found prenatal MRI very helpful in determining fetal liver position in CDH. 12 Using fast scans with T2-weighted halfFourier single-shot turbo spin-echo (HASTE) and more Tl-weighted fast gradient echo sequences, the liver position is easily visualized. On T1weighted sequences, the liver is bright compared with the less intense fluid density thoracic structures (Fig 1A). Hepatic vessels can be identified,
Fig 2. Congenital diaphragmatic hernia (MRI). A coronal Tl-weighted FLASH image through the chest and abdomen of a fetus of 27 weeks' gestation. (A) The liver is high in signal intensity (curved arrows) and the left portal vein (arrow head) can be seen coursing up into the chest. On Tl-weighted images, the high signal intensity meconium filled distal bowel (straight arrows) can be identified from the rectum extending through the diaphragm up to the superior aspect of the left chest. The amniotic filled stomach (open arrow), which is in the chest, is seen as an area of low signal in the mid-thorax. (B) The high signal intense left lobe of the liver (curved arrows) can be seen extending up into the chest, and the high signal bowel (straight arrow) is seen extending well up over the liver and along the left lateral side of the liver.
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which helps confirm the abnormal position of the liver. On Tl-weighted images, meconium-filled bowel is extremely high in signal intensity and differentiates bowel from other cystic lung lesions, which are not high signal intensity with T1 weighting. On T2-weighted HASTE images the amniotic fluid-filled stomach is bright and the lungs, which have intermediate signal intensity, can be distinguished from liver and bowel (Fig 2). In utero treatment of congenital diaphragmatic hernia in highly selected fetuses is technically feasible and currently under investigation. Studies of early in utero complete repair of the diaphragmatic defect showed that those fetuses without herniation of liver into the chest had the same survival as those corrected postnatally. Consequently, in this group of patients, the risk of prenatal repair is not warranted. In those fetuses with liver herniation into the chest that underwent prenatal surgical repair, when the liver was brought down into the abdomen there was frequently kinking of the umbilical vein, associated with hypotension, bradycardia, and death. Consequently, complete prenatal repair of diaphragmatic hernia is not currently recommended. 13 Multiple studies have shown that occlusion of the fetal trachea can prevent pulmonary hypoplasia. In experimental animal models, the entrapment of normal alveolar fluid within the lungs following tracheal occlusion causes accelerated development of the lung, with an increase in the number of alveoli and total lung volume. 14 This procedure is currently under investigation in fetuses with isolated CDH and liver herniation into the chest with the hope that the occlusion of the trachea will promote accelerated lung growth, as well as partially reduce the herniation of the liver and gut. Preliminary results are encouraging. Neonates with CDH are at a high risk for severe pulmonary hypoplasia, which often requires intensive management by pediatric surgeons and neonatologists within a tertiary care setting. Immediate treatment of the newborn usually includes endotracheal tube placement, neuromuscular blockade, high-frequency ventilation, and prompt insertion of a nasogastric tube to decompress the bowel. Surgical repair of the defect is delayed until the pulmonary status is stabilized. 1° The chest radiograph will reveal varying degrees of mediastinal shift away from the side of the diaphragmatic hernia (Fig 3). The course and
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Fig 3. Congenital diaphragmatic hernia. AP chest radiograph of a neonate during the first few hours of life. On the chest radiograph, the heart and mediastinal structures, particularly the trachea (arrow), are displaced towards the right. The lower two thirds of the left chest is opaque, representing the herniated left lobe of the liver as well as non-air-filled loops of bowel. The lungs are partially aerated. Both lungs are small, but note the extremely small size of the hypoplastic left lung.
position of the nasogastric tube may be abnormal because of displacement of the stomach up into the chest. If the patient has been resuscitated without a nasogastric tube, there may be a large amount of air-filled bowel in the chest and paucity of gas in the abdomen. The latter can help differentiate air-filled loops of gut of CDH from a primary cystic lung lesion. Many of these infants require ECMO when the degree of pulmonary hypoplasia and pulmonary hypertension is too severe for adequate oxygenation using positive pressure ventilation. CYSTIC ADENOMATOID MALFORMATION
CAM is a rare lesion characterized by a multicystic mass of pulmonary tissue with proliferation of bronchiolar structures. 15 It represents 25% of all congenital lung lesions. One theory regarding patho-
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Fig 4. Cystic adenomatoid malformation. (A) Sagittal HASTE through the right side of the fetus reveals a large, multicystic mass (straight arrows) in the posterior half of the right chest. Normal lung (large arrow) can be seen anteriorly. There is eversion of the diaphragm (curved arrow) and a large amount of abdominal ascities (black arrow), (B) The orientation is as follows: the fetal right chest is up and the anterior chest is to the left, Transverse ultrasound image through the mid-chest of a 26-week fetus. A large echogenic mass (straight arrows) can be seen filling a large portion of the right hemithorax. The mass contains cysts of various sizes, The heart (short arrow) is displaced into the left, mid-thorax. A small amount of normal right and left lung tissue (large arrows) can be seen.
genesis of CAM is that it represents a failure of normal maturation of bronchiolar structures occurring around the sixth week of gestation. CAM is usually unilobar, although bilateral CAMs have been reported. Most CAMs communicate with the normal tracheobronchial tree and receive their blood supply from a normal pulmonary artery and vein. Anomalous vessels have been reported but are uncommon. The histopathology of CAM has been classified into three types) 5 Type 1 consists of single or multiple large cysts, easily visualized on ultrasound examination. Type 2 consists of more numerous smaller cysts, less than 1 cm in size. On ultrasound examination, it appears as an echogenic mass containing small cysts. This type of CAM is associated with a high incidence of other fetal anomalies. Type 3 is the least common consisting
of a large homogenous microcystic mass, which may appear solid on ultrasound examination. The natural history and prognosis of these lesions are extremely variable. 9The prognosis primarily depends on the size rather than the type of lesion. Large lesions have a higher incidence of mediastinal shift, polyhydramnios, pulmonary hypoplasia, vascular compromise, and hydrops, which may lead to intrauterine fetal demise or neonatal death. However, lesions identified prenatally may involute in utero. Although in utero hydrops may resolve, it is generally considered a sign of impending fetal demise. Careful ultrasound examination is important to rule out associated anomalies, especially renal. Chromosomal abnormalities are rarely associated with CAM. Once the lesion has been identified, careful serial follow-up is necessary to monitor the degree of mediastinal shift and early
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signs of hydrops. Prenatal MRI is helpful in the diagnosis of CAM (Fig 4) distinguishing it from the herniated intestine of CDH, which has a similar sonographic appearance. J2 Fetal surgery is an option for fetuses with life-threatening lesions, usually indicated by the development of hydrops. In cases with an anticipated mortality of 100%, more than 60% can be salvaged by prenatal resection of the CAM. In cases with a large, multicystic lesion, primary resection of the lobe has been performed with subsequent growth of the remaining lung. In fetuses with a single dominant cyst, thoracoamniotic shunts have been placed with partial decompression of the mass. 16 In the newborn, 80% of CAMs present with some degree of respiratory distress secondary to pulmonary hypoplasia. However, they may present later in childhood as an asymptomatic finding on chest radiograph or with infection. During the first hours of neonatal life, the chest radiograph may show shift of the mediastinum by a "soft tissue mass," which represents retained fluid within the CAM. With progressive ventilation and absorption of fluid, an air-filled cystic lesion may become apparent on the chest radiograph (Fig 5). Air
Fig 5. Cystic adenomatoid malformation. AP chest radiograph of a 5-week-old neonate shows marked shift of the heart and mediastinal structures into the left chest. The right lung is extremely hyperinflated and multiple cysts can be seen in the upper portion (arrows).
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trapping within these cystic spaces can cause rapid enlargement of the CAM and subsequent respiratory embarrassment. CAMs identified prenatally which involute during pregnancy may be difficult to detect on the postnatal chest radiograph although the lesion can usually be identified with CT or MRI. In infants who have significant pulmonary compromise, early surgical removal of the mass is advocated as soon as the patient has been stabilized. Although some asymptomatic lesions remain untreated, removal of even asymptomatic masses is recommend because of reports of carcinomas arising in CAM, as well as the risks of secondary infection and hemorrhage.~7
BRONCHOPULMONARY SEQUESTRATION
BPS represents a mass of nonfunctioning lung tissue that does not communicate with the normal bronchial tree and receives its vascular supply from the systemic circulation. Lesions are classified into extralobar (25%) and intralobar (75%) forms. The extralobar form consists of pulmonary tissue that is enveloped in its own pleura, separate from normal lung and is associated with other abnormalities, including foregut anomalies and CDH. Extralobar sequestrations may occur above or below the diaphragm. Although the extralobar form is the one most commonly diagnosed in the prenatal and neonatal periods, the intralobar form is more commonly diagnosed after birth. 5,1° Intralobar sequestration may be associated with scimitar syndrome, that is, hypoplasia of the right lung with anomalous venous drainage of part or the entire lung. It is important to define the venous drainage before surgery to avoid accidental ligation of the pulmonary venous drainage from the normal lung. The in utero ultrasound appearance of BPS is generally a solid, well-defined, highly echogenic mass (Fig 6). Color flow Doppler is useful to detect the feeding systemic artery. It is important to look for systemic vessels, as they will help differentiate BPS from other masses in the lung or CDH. These lesions can also be associated with massive mediasfinal shift, hydrothorax, and fetal hydrops. They frequently involute in utero. 9 Prenatal management of fetal BPS includes
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Fig 6. Bronchopulmonary sequestration. (A) Transverse ultrasound through the chest at the level of a four-chamber view of the heart in a 19-week fetus. A large, homogenous, echogenic mass (large arrow) occupies most of the right thorax. Small portions of the right and left lungs (long-tailed arrows) are noted. The heart (short arrow head) is displaced into the left chest. (B) On an axial T2-weighted HASTE image through the level of the four-chamber view of the heart (short arrow head), the lesion can still be identified in the right lung (short, broad arrow), but is significantly smaller than on the prior ultrasound. The signal intensity of this lesion is significantly brighter than the adjacent right and left lungs (thin arrows). (C) At birth, this child had mild respiratory distress. A CT scan at 2 weeks of life showed a moderate-sized hypodense lesion (arrows) in the right lung. At surgery, this was found to be a bronchopulmonary sequestration with an anomalous feeding vessel.
careful follow-up of the fetus for development of hydrops or polyhydramnios. If the fetus is 32 weeks or older and in difficulty, early delivery may be considered. The hydropic fetus with BPS diagnosed before 32 weeks' gestation may be a candidate for fetal intervention by resection of the chest mass. 1° Thoracoamniotic shunting may be considered to relieve associated hydrothorax. After birth, these lesions most commonly present as recurrent focal infections. They can also present as an asymptomatic pulmonary mass on chest radiograph, and most patients with BPS remain asymptomatic through life. Although prenatally diagnosed sequestrations may not always be visualized on chest radiographs after birth, they can usually be identified on CT or MRI (see Fig 6C).
FETAL HYDROTHORAX
Fetal hydrothorax may be unilateral or bilateral. It may be primary caused by a chylous leak or secondary to generalized fluid retention associated with immune or nonimmune fetal hydrops. Prenatally, it may be difficult to distinguish the cause of fetal hydrothorax, but such effusions are abnormal at any time during gestation. However, a small amount of pericardial fluid is normal. The spectrum of severity of fetal hydrothorax ranges from very small and harmless to severe with mediastinal shift. Overall, mortality is approximately 50%. Polyhydramnios may develop but has not been associated with increased mortality. Hydrops, occurring before 35 weeks and bilateral effusions are associated
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with a worse prognosis. These effusions may increase or decrease in severity during gestation, so close follow-up is important. 18 On ultrasound evaluation, an anechoic collection can be seen peripherally around the compressed lung. There may be marked shift of the mediastinal structures away from the effusion and flattening of the diaphragm. Thorough examination of the chest and abdomen is important to exclude lesions that may be associated with pleural effusions such as CAM, BPS, CDH, cardiac anomalies, Turner's syndrome, Downs' syndrome, and cystic hygroma. These associated anomalies can be seen in up to 40% of cases of hydrothorax diagnosed in the prenatal period.t° Primary hydrothorax may resolve or progress to fetal hydrops. Severe pulmonary hypoplasia caused by large pleural effusions may be incompatible with postnatal survival. Fetal intervention is reserved for hydrothorax occurring before 32 weeks' gestation with marked mass effect. Prenatal thoracentesis has been associated with a good outcome, but some observers have described poor results due to the rapid reaccumulation of fluid. Thoracoamniotic shunting by catheter may allow continuous decompression of the effusion. If instituted early enough, this may allow compensatory growth of the lung and prevent further pulmonary hypoplasia.18 At birth, chest tube drainage is only indicated if the effusion is the cause of respiratory compromise. A thorough review of the chest radiograph should be made to exclude other congenital lesions that may cause pleural effusions. Chylous pleural effusion may increase following feedings with high fat content formula. If the fluid rapidly reaccumulates following thoracentesis, a medium-chain triglyceride-based diet may be effective, otherwise oral feedings may be suspended in favor of parenteral alimentation. Chest tube drainage is reserved for the most severely ill patients because it may result in depletion of lymphocytes and compromise of the immune system. MISCELLANEOUS ANOMALIES
Although laryngotracheal atresia is rare, this diagnosis should be considered whenever bilateral echogenic lung lesions are encountered. Bilateral CAMs are uncommon but can have a similar appearance. When the larynx or trachea becomes completely obstructed, fluids created within the lung become trapped resulting in hyperplasia of
Fig 7. Laryngotracheal obstruction. Transverse echo planar image through the mid-chest of a 24-week fetus with high tracheal occlusion, The heart is small and compressed (open arrow) and is surrounded by pericardial fluid. Both the right and left lungs (long-tailed arrows} are enlarged and high in signal intensity consistent with overdistention of the lungs with alveolar fluid. There is hydrops with marked subcutaneous edema (short arrow heads). Fetal demise occurred shortly after the scan, At autopsy, a small laryngeal cyst was found obstructing the larynx and trachea.
pulmonary alveoli and tracheal dilation. The fetus is at significant risk for developing hydrops due to the marked compression of the cava and obstruction of venous return by the enlarged lungs (Fig 7). Maternal polyhydramnios may occur and there is a high fetal and neonatal mortality.19 Congenital bronchogenic cysts are rarely diagnosed in utero. They are the result of abnormal development of the tracheobronchial tree and lie within the spectrum of foregut abnormalities. They are usually found in the mediastinum near the carina. In those rare cases identified on prenatal ultrasound examination, bronchogenic cysts are usually unilocular or multilocular. The most common finding is a large, unilateral, echogenic lung resulting from obstruction of the adjacent bronchus by the mediastinal cyst. 5,2° SUMMARY
Although significant anomalies of the fetal thorax are uncommon, with improvement in highresolution ultrasonography, more of these lesions are being diagnosed prenatally. Accurate and specific prenatal diagnosis is important because different lesions have different natural histories and prognosis. Prenatal MRI is an increasingly important adjunct for identification and differentiation of these lesions and may help determine in selected cases when and if in utero fetal intervention is indicated. 21
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12. Hubbard AM, Adzick NS, Crombleholme TM: Value of prenatal MR imaging in preparation for fetal surgery of left congenital diaphragmatic hernia. Radiology 203:636-640, 1997 13. Harrison MR, Adzick NS, Flake AW, et al: Correction of congenital diaphragmatic hernia in utero: VI. Hard learned lessons. J Pediatr Surg 28:1411-1418, 1993 14. Hendrick MH, Estes JM, Sullivan KM, et al: Plug the lung until it grows (PLUG): A new method to treat congenital diaphragmatic hernia in utero. J Pediatr Surg 29:612-617, 1994 15. Stocker JT, Madewell JER, Drake RM: Congenital cystic adenomatoid malformation of the lung: classification and morphologic spectrum. Hum Pathol 8:155-171, 1977 16. Adzick NS, Harrison MR, Flake AW, et al: Congenital cystic adenomatoid malformation of the lung. J Pediatr Surg 28:806-812, 1993 17. Rebet ME, Copin MC, Soots JG, et al: Bronchioalveolar carcinoma and congenital cystic adenomatoid malformation. Ann Thorac Surg 60:1126-1128, 1995 18. Longaker MT, LaBerg JM, Dansereau J, et al: Primary fetal hydrothorax: Natural history and management. J Pediatr Surg 24:573-576, t989 19. Dotkart LA, Reimers FT, Wertheimer IS, et al: Prenatal diagnosis of laryngeal atresia. J Ultrasound Med 11:496-498, 1992 20. Young G, L'Heureux PRL, Krneckeberg ST, et al: Mediastinal bronchogenic cyst: Prenatal sonographic diagnosis. AJRAm J Roentgenol 152:125-127, 1989 21. Crombleholme TM, D'Alton M, Cendron M, et al: Prenatal diagnosis and the pediatric surgeon: The impact of prenatal consultation on perinatal management. J Pediatr Surg 31:156-163, 1996