Standard radiographs of the chest are usually the first-line imaging modality to assess for pleural abnormalities in children, given their wide availability, relative inexpensiveness, and easy acquisition. Typical examination includes anteroposterior (AP) radiograph of the chest in infants and young children or posteroanterior (PA) radiograph of the chest in older children. Radiographs optimally should be obtained with the patient in the standing position, with an appropriate inspiratory effort. However, depending on the age and condition of the patient, radiographs may only be able to be obtained in the supine position. Lateral decubitus radiographs can be added for further characterization of a questionable abnormality seen on an AP or PA radiograph, such as an opacity, which may represent a pleural effusion, or to evaluate for a pneumothorax (Fig. 7.1). Although radiographs are an excellent first-line imaging modality to assess pleural abnormalities, additional imaging studies may be necessary for confirmation and further characterization of radiographic findings.

Ultrasound (US) is a frequently used noninvasive modality for evaluation of the pleura in the pediatric population. It is relatively accessible and easy to perform, with the additional advantage of allowing for real-time imaging. In addition, US can be performed portably, does not require sedation or intravenous access for contrast administration, and is unique in that children are not exposed to the potentially harmful effects of ionizing radiation. However, proper technique is essential for obtaining diagnostic quality US information in the pediatric population.

Three major technical factors that affect the quality of US imaging include proper US transducer selection, appropriate patient positioning, and optimal imaging approach.¹ For optimal evaluation of pleural abnormalities in pediatric patients, curved or linear array transducers (7.5 to 15.0 MHz) should be used. Real-time gray-scale US is the standard imaging used to visualize most pleural abnormalities. However, color Doppler imaging can provide added value, particularly in order to differentiate vascular and nonvascular pleural lesions.

Chest US for evaluation of pleural disorders is usually performed with the patient in the supine position, with imaging typically performed via either frontal or lateral approach. Imaging can also be performed with the patient in upright position via a posterior approach, which permits optimal visualization of the posterior pleural lesions and small layering effusions.

Currently, US is often used in evaluation of pediatric patients with an opaque hemithorax on chest radiograph in order to delineate pleural effusion from underlying parenchymal pathology.² When a pleural effusion is present, it can also aid in estimating the size of a pleural effusion and characterize a pleural effusion as simple or complex (Fig. 7.2).³ Finally, US can aid in therapy by serving as a guidance tool in chest drain insertion or thoracentesis.²

In conjunction with radiographs and US, computed tomography (CT) is an effective imaging modality to help further evaluate abnormal pleural findings, which may be difficult to be characterized on radiographs and US alone. CT is a superior imaging modality to delineate complex anatomy, allowing for evaluation of the pleural space in addition to lung parenchyma, mediastinum, and chest wall. However, CT should be reserved for indeterminate or challenging cases that need additional information for proper pediatric patient management in order to limit exposure of children to ionizing radiation. Another advantage of CT is the ability to use intravenous contrast for characterization of pleural fluid or lesion. For instance, contrast-enhanced CT can show pleural thickening and enhancement, which suggests empyema, and help differentiate a lung abscess (Fig. 7.3). CT can optimally show the presence of a pleural effusion or pneumothorax, especially if small in volume. However, unlike US, CT is not optimal to visualize internal septations and debris within complex pleural effusions. Lastly, CT is the preferred modality for imaging of primary and metastatic pleural neoplasms allowing prompt diagnosis and guidance of treatment (Fig. 7.4). Not only the primary mass can be characterized with CT but also disease extent and additional lesions can be identified.

Magnetic resonance imaging (MRI) is an excellent imaging modality for evaluating pleural abnormalities, particularly in pediatric patients, because of its superior ability to characterize soft tissues without ionizing radiation exposure. However, MRI may not be as widely available as CT, making it more challenging to obtain in all cases. In addition, MRI is a longer examination given the multiple sequences performed; therefore, it may require sedation in the young pediatric population to obtain optimal and diagnostic images. Currently, the role of MRI in the evaluation of pleura is reserved for
problem-solving in specific situations when further characterization of the pleural lesions is necessary after other imaging studies. Various signal characteristics on MRI can help diagnose pleural disease and help differentiate benign from malignant pleural processes. However, histologic evaluation is often ultimately necessary for a definitive diagnosis (Fig. 7.5). MRI examinations for evaluation of the pleura mainly consist of T1- and T2-weighted MR images, as well as postcontrast T1-weighted MR images in axial and coronal planes. MR images in sagittal plane can be useful for assessing pleural abnormalities adjacent to the sternum or spine.

Pneumothorax is defined as air within the potential pleural space. Although there are various underlying etiologies of pneumothorax, they can be broadly categorized into either spontaneous (i.e., primary) or iatrogenic (i.e., secondary) pneumothorax. Spontaneous pneumothorax can occur in a previously healthy child resulting from spontaneous rupture of a preexisting bleb, usually located in the apex of the lung (Fig. 7.8), or may be a consequence of an underlying pulmonary disorder, such as asthma or cystic fibrosis. Secondary or iatrogenic pneumothorax can occur in the setting of a
recent intervention, such as a lung biopsy, thoracentesis, or mechanical ventilation.⁵ Iatrogenic pneumothorax can be also secondary to blunt or penetrating trauma, with or without an associated rib fracture (Fig. 7.9). Air can be introduced into the pleural space not only from an external wound but also secondary to pulmonary, esophageal, or tracheobronchial injuries.

The incidence of spontaneous pneumothorax is ˜1.2 to 6 cases per 100,000 girls and 7.4 to 18 cases per 100,000 boys, with a mean age at presentation being 14 to 15.9 years in the pediatric population.⁵ The common demographic of pediatric patients with a spontaneous primary pneumothorax is tall, thin boys with low body mass index.⁶ Affected pediatric patients typically present with sudden-onset shortness of breath and unilateral chest pain. In the setting of thoracic trauma, one-third of thoracic injuries are associated with pneumothorax. A concerning adverse outcome of a traumatic pneumothorax is a tension pneumothorax, which occurs when the pleural defect acts as a one-way valve, allowing air to flow into the pleural cavity without escape. The increasing volume and accumulation of air in the pleural space cause mass effect on the adjacent structures, resulting in mediastinal shift to the contralateral side and possible vascular compromise of the heart and the great vessels (Fig. 7.10).⁵ Physical examination findings specific to tension pneumothorax include engorged neck veins and deviation of the airway to the contralateral side.

Standing AP or PA radiographs are an initial imaging method for evaluating pediatric patients clinically suspected of having pneumothorax. On frontal chest radiographs, pneumothorax typically presents as lucency and collapsed lung with visible pleural surface (Fig. 7.11). When the pneumothorax is localized in the subpulmonic region, lucency can be localized and projects over the lower lung zone, just above the diaphragm (Fig. 7.12). In the setting of both air and fluid in the pleural space, which is known as hydropneumothorax, the interface between the air and fluid can be seen on an erect radiograph as a horizontal line extending across the entire length of the hemithorax (Fig. 7.13). In critically ill pediatric patients who cannot tolerate standing, chest radiographs can be obtained in the supine position, which unfortunately decreases sensitivity for evaluation of pneumothorax. However, given air rises to the nondependent position, pneumothorax can be seen on a supine radiograph as global lucency in the chest without clear visualization of pleural line, especially in neonates and infants (Fig. 7.14). Lateral radiographs are not necessary as the initial evaluation; however, lateral decubitus radiographs can be useful in challenging cases particularly when the amount of intrathoracic free air is small. In severely ill
patients, a cross-table lateral radiograph or decubitus radiograph can be performed.