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2. Fig. 18. Sonographic air bronchograms. Transverse • sonogram shows pleural effusion and lower lobe • consolidation with internal branching bright echogenicities • representing air bronchograms. These may • move with patient respiratory effort

3. first described in pediatric patients. Entrapped fluid or mucoid material within bronchi in necrotizing or postobstructive pneumonias produces hypoechoic branching structures, the sonographic fluid bronchogram. • Pulmonary vascular flow is preserved in simple pneumonic consolidation and is readily demonstrated with color Doppler. • \ With atelectasis, air bronchograms are also present, and blood vessels become crowded together and have a more parallel orientation • . Their orderly linear and branching structure is preserved, however, allowing distinction from the more irregular vasculature found in neoplasms.

4. Distinguishing pneumonic consolidation from simple atelectasis can be difficult radiographically. It has been suggested thatUS can be more specificin this situation • . If there is movement of the air within bronchi, this usually indicates pneumonia, whereas the air bronchograms in atelectasis are most often static. • In a recent study, this dynamic air bronchogram had a sensitivity of 61% and a positive predictive value of 97% in distinguishing pneumonia from atelectasis.

5. Additionally, in adults atelectasis has been reported to transmit cardiac pulsation more readily than pneumonic consolidation, producing the so-called lung pulse sign. • I have not found this sign useful in m personal experience, perhaps because of the smaller thoraces of children and closer proximity of the heart producing pulmonary motion regardless of the cause of the underlying lung disease.

6. As lung infections progress, areas of parenchymal • necrosis may develop. Small areas of • lung necrosis appear as areas of decreased echogenicity • (Fig. 19

8. Fig. 19. Necrotizing pneumonia. Longitudinal sonogram • shows consolidation of the left lower lobe • with air bronchograms (arrowhead). There are several • areas of decreased echogenicity within the lung • (arrows) that showed no flow with color Doppler indicating • foci of necrosis.

9. that lacks color Doppler flow within a region of pulmonary consolidation. • If the area of necrosis progresses and enlarges faster than can be cleared by the body, a lung abscess develops. • Larger abscesses may develop a thick wall, and air fluid levels may be seen if there is cavitation or if the abscess communicates with the bronchial tree (Fig. 20).

11. Fig. 20. Lung abscess. (A) Chest radiograph in a 4-month-old child with a history of bronchopulmonary dysplasia • shows a thick walled cystic mass in the right chest (arrowheads) with internal air (arrow). (B) Transverse sonogram • shows the thick-walled abscess (arrowheads) with internal air (arrow). Percutaneous drainage and antibiotic • treatment lead to a complete resolution.

12. Causative organisms are not always cultured from sputum or peripheral blood. • If abutting the pleura, lung abscess are sonographically visible, and Usguided aspiration and drainage can play an important role in diagnosis and treatment.

13. Masses • Primary lung neoplasms are fortunately rare in children. Pulmonary blastoma is the most common and usually starts as a peripheral lesion, often attaining large size before becoming clinically • apparent. • Other less common tumors include mucoepidermoid carcinoma, rhabdomyosarcoma, and bronchogenic tumors • . Although US can confirm the presence of a mass, like other imaging modalities US cannot be histologically specific and differentiate among tumor types. As with pleural lesions, if a lung mass is sufficiently peripheral and abuts the lung surface, percutaneous US-guided biopsy is a safe and effective method for obtaining a tissue diagnosis.

14. Congenital parenchymal masses include congenital pulmonary airway malformation (CPAM) and sequestration. Although often regarded as separate entities, these malformations are part of a spectrum of congenital pulmonary airway malformations and may have overlapping imaging and histologicfeatures.These masses may be detected prenatally by US or MR imaging, appearing as variably solid or cystic structures.

15. Postnatally, plain radiographs usually show the lesion, often as incidental findings or on images taken for respiratory symptoms. • CPAMs have traditionally classified according to their cystic component, although the usefulness of this is • Questionable • . The US appearance follows this histologic typing, demonstrating cysts of varying size amidst echogenic parenchyma (Fig. 21).

17. Fig. 21. Congenital pulmonary airway malformation. (A) Longitudinal sonogram of the right chest in a newborn • with prenatal diagnosis of a lung mass shows a complex mass with a large central cystic component corresponding • to a type I CPAM. No normal lung was visualized. (B) Longitudinal midline sonogram in another newborn • shows a large echogenic mass (M) representing a type III CPAM. This mass displaces the heart (H) anteriorly • and to the left, and is inverting the diaphragm (arrow) and displacing the liver (L) inferiorly.

18. Although spontaneous regression of CPAMs has been reported, and there is controversy as to whether surgery is indicated, most of these lesions are currently surgically resected in the United States. • Superimposed infection can pose difficulties and complications for surgery. • Like lung abscesses, US-guided percutaneous drainage can allow successful treatment of infected CPAMs and allow a safer delayed surgical resection.

19. Intralobar sequestrations are most often found in the lower lobes, presenting with recurrent infections or persistent radiographic opacities. • These are typically sonographically solid masses, although there may be cystic components. • The key diagnostic feature of sequestration is demonstrating systemic arterial supply, usually from the descending aorta (Fig. 22).

21. Fig. 22. Congenital pulmonary sequestration with • cystic adenomatoid malformation. Coronal sonogram • of the inferior left chest shows an echogenic mass (M) • representing an intralobar sequestration with a large • feeding artery (arrow) arising from the thoracic aorta • (A). Note the cystic components (arrowheads), which • were shown histologically to be elements of cystic adenomatoid • malformation within the sequestration.

22. Color Doppler sonography is diagnostically reliable in this condition in the neonate, infant, and young child, although contrast-enhanced CT and MR imaging are often required in older patients with limited acoustic windows. • Extralobar sequestrations have a separate pleural investment and are usually found in the inferior left chest but may even be nlocated below the diaphragm where they may be confused with adrenal pathology. • Patients present symptomatically at a younger age than those with • intralobar malformation, with cyanosis and dyspnea more common. • US features are similar in both conditions, although associated anomalies are more commonly associated with extralobar sequestrations.

23. MEDIASTINUM • The thymus is the dominant noncardiac mediastinal structure within the pediatric chest. Its appearance on chest radiography is usually clear, although variations in size and position can occasionally be confusing and prompt further imaging for clarification. The characteristic US appearance allows confident diagnosis and obviates the need for further imaging tests (Fig. 23).

25. Fig. 23. Prominent thymus. (A) Chest radiograph of an infant with respiratory symptoms shows an enlarged cardiomediastinal • contour. (B) Transverse sonogram of the superior chest shows a normal thymus (arrowheads) to be • the source of the radiographic findings. The thymus conforms to the contours of the anterior chest wall and • drapes around the aorta (A) and pulmonary artery (PA). Note the hypoechoicsternal cartilage with a small ossification • center (S).

26. Diminished thymic size is seen in infants and children subject to physiologic stress. • DiGeorge syndrome is a cellular immunodeficiency disorder related to hypoplasia or aplasia of the thymus. • Although the associated anomalies are usually sufficient for diagnosis, failure to visualize the infant thymus by US is strongly confirmatory.

27. Primary thymic tumors in children are rare. Thymomas usually occur in older children and adolescents, who often present with paraneoplastic syndromes. • They can present as aggressive tumors particularly in cases of invasive thymomas. • In this age group, mediastinal acoustic windows are more limiting. Therefore, MR imaging and CT are often better imaging choices.

28. Thymomas can be heterogeneous tumors with areas of necrosis and calcification,91,92 whereas thymolipomas are more homogeneously echogenic due to their fatty content. Secondary neoplastic thymic infiltration is more common, and occurs withleukemia, lymphoma, and Langerhans cell histiocytosis.

29. In these cases, the normal sonographic thymic pattern is replaced with variably echogenic and heterogeneous soft tissue and associated abnormal lobulation of the thymic capsule. • Small calcifications have been described with histiocytic infiltration. • An infiltrated thymus loses its normal compliance and may be seen to displace and distort adjacent structures instead of conforming to their shape.

30. The most common benign thymic masses are lymphatic malformations and thymic cysts. • Lymphatic malformations are usually comprised of multiple loculated cysts with thin bands of intervening soft tissue. Normally hypovascular, • lymphatic malformations may contain hemangiomatous components that demonstrates flow with color Doppler. • Cysts contents are usually anechoic, but superimposed hemorrhage or infection produces cyst contents of variable echogenicity or even fluid debris levels.

31. Thymic cysts arise from remnants of the thymopharyngeal ducts,80 thymic tumors, and cystic degeneration of the thymus itself associated with mediastinal trauma or surgery. • Most congenital cases of thymic cysts are diagnosed in childhood, presenting as slowly enlarging masses that may extend into the neck.

32. Thymic cysts typically are unilocular with imperceptible walls and anechoic contents, and sonographic demonstration of their continuity with the thymus allows their diagnosis. • Thymic cysts associated with HIV infection are more commonly multiseptated and may cause more diffuse thymic enlargement.

33. The anterior mediastinum is a common site for other neoplasms, in particular lymphoma. The majority of children with lymphoma have anterior mediastinal involvement, more frequent withHodgkin lymphoma than with non-Hodgkin lymphoma. • Patients may present with constitutional symptoms (fever and weight loss), respiratory complaints (cough and dyspnea), and occasionally masses are discovered incidentally.

34. Sonographically, lymphomas may appear as discrete masses, nodal enlargement, or with diffuse thymic infiltration. They tend to be hypoechoic and hypovascular compared with inflammatory processes and other neoplasms (Fig. 24).

36. Fig. 24. Lymphoma. (A) Contrast-enhanced chest CT of a 14-year-old girl with fatigue shows an anterior mediastinal • mass (M). (B) Longitudinal sonogram just before percutaneous biopsy shows a predominantly hypoechoic • mass (M) anterior to the mediastinal vessels (V). Core biopsies showed nodular sclerosing Hodgkin disease.

37. Teratomas and other germ cell tumors may also arise in the anterior mediastinum. • The US appearance of germ cell tumors is variable, ranging from purely soft tissue masses to heterogeneous masses containing fat, bone, and cystic elements (Fig. 25).

39. Fig. 25. Anterior mediastinal teratoma. Transverse • sonogram of the chest in a newborn shows a complex • solid and cystic mass (M) displacing the heart (H). • (Adapted from Coley BD. Pediatric chest ultrasound. • Radiol Clin NorthAm2005;43:405–18; with permission.)

40. A tissue diagnosis is required before chemotherapy, but airway compromise often associated with large masses located within the anterior mediastinum may make surgical biopsy undesirable. • US-guided percutaneous biopsy is an excellent alternative in these patients and can be don comfortably and safely, even in critically ill patients.

41. Middle mediastinal lesions include cystic (bronchogenic, gastrointestinal, pericardial, and lymphatic) and solid (lymphadenopathy) masses. Visualization of these masses with US may become more difficult with increasing age of patients, but the optimal use of acoustic windows can still make US a valuable diagnostic modality.

42. Lymphadenopathy can arise from underlying neoplasia or infection, appearing abnormally enlarged and hypoechoic, often with color Doppler hyperemia.100 Bronchogenic cysts are usually thin walled, whereas esophageal duplication cysts may have a hypoechoic muscular rim typical of gastrointestinal duplications elsewhere in the body; this differentiation may, however, be difficult. • Pericardial cysts have a typical appearanc on plain radiographs, but US can confirm their cystic nature. Lymphatic malformations in the mediastinum appear similar to those elsewhere in the body, as discussed previously (Fig. 26).

44. Fig. 26. Middle mediastinallymphangioma. (A) Transverse sonogram using the heart as an acoustic window in • a child with abnormal paraspinal widening on chest radiography shows a septated cystic mass (arrows) posterior • to the heart (H) and anterior to the spine (S), surrounding the aorta (A) and esophagus (E). (B) Transverse T2- • weighted MR imaging at a similar level with the same findings. (Adapted from Coley BD. Pediatric chest ultrasound. • RadiolClin North Am 2005;43:405–18; with permission.)

45. Posterior mediastinal cystic masses include lymphatic malformations and neurenteric cysts, the latter often associated with vertebral bodyanomalies. • Most pediatric posterior mediastinal masses, however, are solid and arise from neural crest cells within the sympathetic ganglion. • In order of decreasing malignancy, these include neuroblastoma, ganglioneuroblastoma, and ganglioneuroma.

46. Posterior mediastinal masses can often be best visualized via a posterior thoracic or paraspinal approach. Although sometimes containing calcifications, the sonographic • appearanceof these tumors isnonspecific. • Thoracic neuroblastomas commonly extend through neural foramina, causing extradural compression of the spinal cord that may be symptomatic, and may be demonstrable sonographically. • UScan also demonstrate neoplastic invasion of the chest wall and bon involvement, although CT andMRimagingaremore commonly used and more sensitive than US.

47. DIAPHRAGM • US is a valuable tool in assessing the diaphragm, allowing delineation of juxtadiaphragmatic masses, contour abnormalities and hernias, • and evaluation of diaphragmatic motion. • Congenital diaphragmatic hernias are typically located on the left and usually pose little diagnostic confusion on plain radiographs. When radiographic findings are less clear, especially with right-sided hernias, US becomes a useful modality for confirmation and furthe characterization. • Sagittal and coronal scanning allows depiction of the diaphragm and assessment its integrity. • Discontinuity of the diaphragm is readily seen, and the herniated viscera can be evaluated • (Fig. 27).

49. Fig. 27. Right-sided congenital diaphragmatic hernia. • Sagittal sonogram through the inferior right chest of • an infant with radiographic opacity of unclear • etiology shows a defect (arrow) in the hypoechoic • muscular right hemidiaphragm (arrowheads) with • herniation of liver (L) into the chest.

50. Eventration of the diaphragm results from a congenital weakness or thinness of the central tendon or muscle • Patients may present with respiratory difficulties, but the radiographic findings are often incidental. Although further imaging may not be required, US can confirm the diagnosis by demonstrating an intact hemidiaphragm, thus helping to exclude contained hernias or masses (Fig. 28).