12 The chest
Ultrasound of the pediatric chest is an area often neglected because of the presence of air in the lungs and the difficulty which the bony rib cage poses to access. However, as a result of the smaller footprint and higher resolution of modern equipment, there are a number of chest conditions where ultrasound can be usefully used in children. While CT and MRI are still considered the techniques for evaluating the chest, ultrasound has a definite and useful role in certain circumstances. In particular, ultrasound is most useful in the remote intensive care situation where children are often too ill and unstable to be moved to a scanner.1
TECHNIQUE OF ULTRASOUND EXAMINATION
All patients should be examined in the knowledge of what the chest radiograph shows and the exact clinical question to be answered. Always look at the chest radiograph before starting the ultrasound examination.
Depending on the location of the abnormality, different approaches can be used (Fig. 12.1).
Figure 12.1 Windows of access to the chest and thoracic cavity. The chest can be examined superiorly from the suprasternal notch, the supraclavicular approach (A). It can be examined inferiorly by the subcostal or sub-xiphisternum approach (B). For masses within the thoracic cage it can be examined by an intercostal approach (C). Mediastinal masses can be examined by a sternal or parasternal approach (D).
Patients with superior mediastinal abnormalities can be examined from the supraclavicular or suprasternal notch. This can be achieved by positioning the patient’s shoulders on a pillow to help extend the neck for better access.
For juxtadiaphragmatic lesions the abdominal approach is best, with particular views of the diaphragm using the transdiaphragmatic and sub-xiphisternum views. Use a curvilinear transducer with the liver or spleen as an acoustic window. When examining any juxtadiaphragmatic mass the upper abdomen must be carefully examined as well, in particular the liver, spleen and kidneys in case of herniation. Pathology in the liver parenchyma, such as an abscess, may cause a sympathetic effusion in the chest.
Intrathoracic pathology is best examined using the intercostal and parasternal approaches. The posterior chest must always be examined in suspected pleural effusions, as fluid tends to accumulate posteriorly as the patient lies supine in bed.2
Doppler and color flow imaging must be used in all lesions next to the diaphragm. In particular when assessing for suspected pulmonary sequestration, anomalous feeding vessels may be demonstrated arising from the aorta in the abdomen.
Mass lesions in the chest are usually described according to their location either in the anterior, middle or posterior mediastinum (Fig. 12.2).3 Table 12.1 gives a differential diagnosis of the more common masses seen in children and where they lie in the mediastinum.
Figure 12.2 The anterior, middle and posterior mediastinum. Table 12.1 gives a differential diagnosis of masses in these three regions.
Table 12.1 Causes of mediastinal masses
| Anterior | Middle | Posterior |
|---|---|---|
SVC, superior vena cava.
JUXTADIAPHRAGMATIC LESIONS
Lesions next to the diaphragm, whether they be anterior or posterior, should be scanned with a sub-xiphoid or transdiaphragmatic approach.
Lesions will fall into three broad groups:
Masses arising in the chest
The clue to the potential diagnosis will usually lie on the appearances on the chest radiograph and the clinical presentation. The contour of the mass and whether it is lying anterior or posterior in the chest is important in the differential diagnosis.4
Neurogenic tumors
These arise posteriorly along the sympathetic chain, are often incidental findings and are usually ganglioneuromas. They are usually well defined, clearly posterior and hyperechoic, often containing small granular calcification. There may be associated rib erosions on the chest radiograph. Posterior mediastinal masses are almost always neurogenic in origin, and if the patient is young can be turned prone and a spinal examination undertaken to look for spinal extension. Neuroblastoma is the malignant form of neurogenic tumor, and intraspinal extension must be sought.
Ultrasound is particularly useful to help differentiate lateral intrathoracic meningoceles from solid masses.
Neurenteric cysts
Neurenteric cysts are essentially cysts of bowel that have failed to separate from the neural canal during development. On the chest radiograph there may be a spinal abnormality, and usually this is higher than the lesion (Fig. 12.3). On ultrasound the neurenteric cyst has a well-defined border with a thin wall similar to a duplication cyst of the bowel. It may be completely hypoechoic or, if infection or hemorrhage has occurred, the cyst may contain cellular debris due to blood, mucus or white cells.
Figure 12.3 Neurenteric cyst. Chest radiograph on a child with a mass in the right chest. There is a well-defined oval mass in the right chest with displacement of the heart to the left. There are multiple abnormal ribs and a spinal abnormality higher than the mass. These are the typical appearances of a neurenteric cyst with a spinal deformity higher than the mass (arrow).
Pulmonary sequestration
Also called a bronchopulmonary foregut malformation, pulmonary sequestration refers to a segment of lung which does not function, has an anomalous arterial blood supply from the systemic circulation and has no communication with the tracheobronchial tree. It is due to a developmental abnormality in which there is an accessory tracheobronchial foregut bud.5
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