Diagnostic Ultrasound for Chest Diseases in Children

Diagnostic ultrasound has not had widespread use heretofore in assessing or diagnosing pediatrie respiratory problems. This has been primarily because of the physical limitations imposed by the aerated lung and the surrounding bony thorax, since both air and bone transmit the ultrasound beam poorly.

Figure 1. Transducer positions for imaging intrathoracic structures in infants and children. (This and subsequent figures in this article are reproduced with permission from the author's Pediatrie Ultrasound* and "Sonographic evaluation of the chest in infants and children."* A: suprasternal position; B: transosseous; C: intercostal; D: subxyphotd; E: subcostal.)

Despite these problems, sonography can provide valuable information when examinations are tailored to specific problems. This article will discuss how ultrasound can be used to characterize and localize disease processes that either partly or completely opacify the hemithoracic, paracardiac, or juxtadiaphragmatic region.

TECHNIQUE

Children usually need no preparation for sonography, and sedation is rarely required. The transducer is placed in specific locations along the chest wall, as indicated in Figure 1. The goal is to avoid the bony ribs and take full advantage of contiguous soft tissues that act as sonic windows.* This positioning makes it possible for the sonic beam to image the disease process, avoiding the aerated lung. The right juxtadiaphragmatic region, for example, is imaged by placing the transducer over the liver. The transducer is placed over the heart to scan juxtacardiac masses. In each case, the heart and liver act as sonic windows. Figure 1).

Children are usually scanned in the supine position unless the disease process abuts the posterior chest wall; when this is the case, the prone position is used. When it is necessary to study fluid collections, patients may be scanned in the sitting or the decubitus position.

ILLUSTRATIVE EXAMPLES

The five following case histories (previously reported1,2} may help to show how chest sonography is sometimes helpful in resolving diagnostic problems.

Figure 2. At left, x-ray posteroanterior view of the chest shows opacification in the left hemithorax and a mediastinal shift to the right. Arrow indicates level of transverse scan. Right: Sonograph. A supine transverse scan shows a homogeneous moderately echogenic mass (M) that occupies the left hemithorax at this level. The heart (H) can be recognized by the sawtooth appearance of the valves. Reverberation echoes (r) from the normal aerated lung can be seen adjacent to the heart border. (Transverse scans are viewed with the patient's right side [R] on the viewer's left.)

Case No. 1: No fluid following thoracocentesis. A child was found to have stage IV Wiíms' tumor at the age of three. The tumor was resected from her left lung, and chemotherapy was administered, causing the nodular lung metastases to disappear. A year later she was hospitalized again, with marked tachypnea and respiratory distress. An x-ray frontal view of the chest showed complete opacification m the left hemithorax (Figure 2, left).

Repeated attempts at thoracocentesis failed to yield any fluid. An ultrasound examination of the chest was performed (Figure 2, right), showing that the entire left hemithorax was occupied by a solid echogenic mass (i.e., a mass that caused sonic echoes to be reflected, indicating that it was a solid rather than a fluid-filled mass). The child died shortly thereafter. Autopsy revealed metastatic Wilms' tumor completely occupying the left hemithorax, with no evidence of pleural effusion.

Comment. Ultrasound can be very helpful in assessing the cause of chest opacities in the x-ray. We have examined a number of children with massive primary and secondary neoplastic disease of the lung and, by means of the sonograph, were able to demonstrate the absence of pleural fluid - thus preventing futile attempts at thoracentesis that otherwise would have been made. Sonography has been quite successful in distinguishing consolidation (due to either mass or infiltrate) from pleuralfluid collections.3 Also, we have been able to accurately localize small loculated fluid collections associated with massive cardiomegaly. This has allowed the clinician to avoid the myocardium during thoracentesis, a procedure that is quite difficult by radiographie guidance alone.

Case No. 2: Localizing small fluid collections. A 16-month-old developed a rapidly progressive respiratory distress. Radiographs taken over the course of a week demonstrated a density in the right chest, which enlarged rapidly as the week progressed (Figure 3). Thoracocentesis was performed and yielded serosanguineous fluid. Further attempts, however, failed to elicit any fluid.

Sonographs were then taken and indicated that the right chest was primarily occupied by solid material representing either consolidated lung or a mass, although there was a small amount of pleural fluid (Figure 4.) At thoracotomy, a malignant schwannoma was found involving the right hemithorax and mediastinum. Sixty cubic centimeters of serosanguinous fluid was also found in the right costo vertebral gutter.

Figure 3. X-ray anteroposterior view of the chest of a 16-monthold boy, showing almost complete opacification in the right hemithorax. The displacement of the nasogastric tube far to the left indicates the marked mediastinal shift that has taken place. Arrow indicates level of longitudinal scan.

Comment. While sonography cannot distinguish between various kinds of consolidation - for example, between that caused by pneumonia and that caused by a neoplasm - it can help localize small fluid collections. And, by defining the hemidiaphragm, it can ascertain that a process is purely supradiaphragmatic in origin, as in this case.4

Case No. 3: Needle guidance for thoracocentesis. A four-year-old girl had low-grade fever of unknown origin. An x-ray frontal view of the chest showed extensive consolidation in the right hemithorax, with a slight shift of the mediastinum to the left (Figure 5). Several attempts at thoracentesis were made, all unsuccessful. Sonographic examination (Figure 6) revealed an echo-free area in the chest, consistent with fluid that was predominantly posterior in location. Under sonographic guidance, fluid was aspirated from the posterior chest, resulting in a final diagnosis of tuberculous effusion.

Figure 4. Supine longitudinal scan of the chest of the boy whose x-ray was shown in Figure 3 shows a highly echogenic structure (M) surrounded by echo-free regions that correspond to the pleural space (p), indicating the pleural cavity is probably filled with fluid. L: liver. Longitudinal scans are viewed as if the patient were lying with his head (H) to the viewer's left and his feet to the viewer's right.

Figure 5. X-ray anteroposterior view of the chest of a four-yearold girl, taken In the supine position. The mediastinum is minimally displaced to the left. Arrow marks level of longitudinal scan.

Comment. This is a case in which several unsuccessful aspiration attempts led to the erroneous assumption that the radiographie opacity in the x-ray was due primarily to thickened pleura. The child and her parents were understandably distressed that the repeated painful thoracocenteses had not resolved the condition. We have found that sonography gives fast and, for the most part, successful results when used to guide the needle in this uncomfortable procedure.

Figure 6. Sonogram of girl shown in Figure 5. Prone longitudinal scan indicates an echo-free region (E) occupying the entire right hemithorax at this level. The posterior chest wall (p), the diaphragm (arrows), and kidney (k) are also visualized, (ic: iliac crest level.)

Case No. 4; Delineating a mass for radiotherapy. An eight-year-old boy was admitted to the tumor clinic for follow-up of stage IV pelvic rhabdomyosarcoma. He had initially received radiation and chemotherapy after surgical removal of his tumor but complained of exertional dyspnea for several months following the surgery. Chest radiographs revealed a right paracardiac mass with widening of the superior mediastinum (Figure 7). Sonographic examination confirmed that the mass was solid, and it outlined the dimensions of the mass so that radiotherapy could be administered to the right paracardiac and superior mediastinal region (Figure 8). The mediastinum and right paracardiac region returned to normal following additional chemotherapy and radiotherapy. The child subsequently died from progression of the initial disease.

Comment. In this case the sonogram made it possible to delineate the mass in relation to the heart, so that radiotherapy portals could be applied. s Because the mass abutted the heart (a softtissue, fluid-filled organ adjacent to the chest wall), the sound beam could reach the mass without having to traverse aerated lung. While aerated lung does not transmit the sound beam, it creates distinct artifacts known as reverberations (Figure 2, right; Figure 8), making it possible for the sonographer to distinguish the margins of aerated lung from the disease process.

Flgure 7. Open arrows point to right paracardiac mass in this x-ray posteroanterior view of the chest of an eight-year-old boy. Note widening of the superior mediastinum and irregularity of both hemidiaphragms. Black arrows mark level of the transverse scan.

Figure 8. Sonograph of the chest of boy shown in Figure 7. Supine transverse scan shows a well-defined, moderately echogenic mass (M) adjacent to the heart (H). Strong reverberation artifacts (r) are present at the interface between the mass and the lungs; similar artifacts can be seen posterior to the heart.

Case 5: Delineating epidiaphragmatic fluid collections. An eight-year-old boy underwent a thoracotomy for removal of a fragment of a plastic toy that had penetrated the esophagus. The child developed a spiking fever postoperatively, and chest radiographs revealed an opacification in the right lower zone, with foci of segmental atelectasis (Figure 9). Sonographic examination of the area delineated an epidiaphragmatic fluid collection, which was percutaneously drained under Sonographic guidance (Figure 10). Eleven cubic centimeters of purulent fluid was obtained, and Hemophilus influenzae was cultured.

Figure 9. X-ray posteroanterior view of the chest of an eightyear-old boy who had swallowed a plastic toy that had penetrated the esophagus. Note opacification of the right lower zone and foci of segmentai atetectasis. Arrow marks level of transverse scan.

Figure 10. Sonograph indicates that an abscess is probably the cause of the opacification shown in Figure 9. This prone transverse scan shows a well-defined, predominantly echo-free epiphrenic mass (arrowheads) with few central echoes. These findings are consistent with an abscess. (P: posterior chest wall.)

Comment. We have seen a number of cases in which precise sonography led to successful percutaneous aspiration and drainage of various types of localized fluid collections (empyema, abscess, loculated effusion, infected hematoma).6 Sonography is also useful in determining the diaphragmatic position vis-à-vis these fluid collections - i.e., it can be helpful in distinguishing a subphrenic abscess from a supradiaphragmatic process both may look the same on a radiograph).7

CONCLUSION

Sonography can be helpful in assessing diseases of the chest in children. It can distinguish solid from liquid opacities and differentiate infra- from supradiaphragmatic processes. It can successfully delineate fluid collections for both diagnostic and therapeutic purposes.

In infants and children, sonography generally complements radiographie and radionuclide examinations of the chest. While sonography has a number of inherent limitations, it often provides necessary information that can be obtained at a lower cost than other imaging procedures and without exposing the child to additional ionizing radiation.

Sonography should be the initial study of choice for the localizing and characterizing of fluid collections (particularly if percutaneous aspiration or drainage is contemplated), for assessing an opaque hemithorax before thoracocentesis (particularly in patients with metastasis), and for determining the extent of extradiaphragmatic disorders .