Chapter 506. Tools for Diagnosis and Management of Respiratory Disease

Viewing the pediatric chest and lungs, whether by radiographic or bronchoscopic means, is often central in the evaluation of these patients. Although the chest x-ray has a venerable place in history, radiologic technologies now available include computerized tomography (CT), chest ultrasound, magnetic resonance imaging (MRI), and nuclear medicine. These novel methods allow better evaluation of the respiratory tract both anatomically and physiologically. The rigid bronchoscope has been available since the early part of the twentieth century, but advances in fiberoptics now allow for safer bronchoscopic studies in pediatric patients. These newer technologies improve the evaluation of the infant or child with pulmonary complaints. This section will deal with the various radiographic and nuclear medicine imaging techniques as well as with rigid and flexible bronchoscopic evaluation of the airways. Other diagnostic techniques such as pulmonary function testing are described in Chapter 503.

Imaging has long been important in the evaluation, diagnosis, management and follow-up of pediatric chest diseases; and it contributes greatly to our understanding of the pathophysiology of many entities. The chest is no exception to the increased sophistication and complexity of imaging techniques, with a myriad of available options involving a bewildering array of modalities and choices. This section will provide an overview of these options and their advantages, disadvantages, and most appropriate use in the pediatric population.

Children are often unwilling or unable to cooperate with the maneuvers required to produce high quality imaging. Optimal studies are most often the product of experienced personnel who work with children in friendly surroundings with appropriate distraction, immobilization, analgesic, and sedation techniques.

Although plain film radiography remains the mainstay for chest imaging, cross-sectional techniques provide remarkably detailed images with versatile multiplanar and 3D reconstruction capabilities, sophisticated angiographic and Doppler techniques, and functional imaging even at the molecular level. It has become increasingly important to tailor the imaging studies to the specific clinical questions and concerns or limitations of individual patients. Imaging is no longer “one size fits all” and close collaboration between radiology and clinical colleagues is not just desirable but essential in making the most appropriate choices and providing the best patient care.1-12

Chest Radiographs and Chest Fluoroscopy

Plain radiographs of frontal and lateral views of the chest remain the mainstay of screening imaging of a child with a suspected chest abnormality. Digital imaging systems are now widely available. These radiographs usually include portions of the upper airway, larynx, trachea, and central bronchi as well as the mediastinal structures, heart, lungs, and bony and soft tissue chest wall. Evaluation of a chest radiograph should include an overview of the following:

1. 1. Patient history and specific reason for the current radiograph

   2. Quality of the study: patient positioning, inspiratory effort, motion, or presence of artifacts (eg, jewelry)

   3. Overall pulmonary aeration and symmetry, position, and patency of the airway

   4. Presence and location of any tubes, lines, catheters, foreign bodies

   5. Mediastinum: contour and position; location of the aortic arch; presence of any mass, displacement, or compression of the mediastinum and/or airways

   6. Heart size and configuration

   7. Central and peripheral pulmonary vessels and symmetry

   8. Lung parenchyma: symmetry, vascularity, lucency, density, mass, volume loss, or air trapping

   9. Pleura, diaphragm, and bony and soft tissues of the chest wall

   10. Comparison with prior related imaging studies

Whenever possible, two views of the chest increase diagnostic confidence, determining the location of a lesion more precisely and assessing its impact on adjacent structures such as the diaphragm or airway. Some lesions may look quite different on the frontal and lateral views and others may only be appreciated on one view or the other. It is important to be aware that the normal thymus is much larger in infancy (eFig. 506.1).

Radiographs of the neck, with both frontal and lateral projections, are often helpful in evaluating the upper airway for an intrinsic or extrinsic mass, foreign body, or inflammation such as croup or epiglottitis. High kilovoltage magnified filtered radiographs may be used to obtain a more detailed view of the airway and its relationship to other structures such as abnormal vessels or masses.

Inspiratory and expiratory radiographs may be useful when evaluating for air trapping, as is seen with an aspirated foreign body (see eFig. 506.2A), or pneumothorax (see eFig. 506.3A); these are limited to children who are able to breath-hold. Decubitus views of the chest do not require cooperation for inspiratory and expiratory breath-holding and are more useful for infants and young children. In this circumstance, the dependent lung normally deflates while the opposite lung inflates; the expected deflation of the dependent lung is not seen when a foreign body is present. Decubitus views are also useful for evaluating suspected nonloculated pleural effusion, which layers dependently, or pneumothorax, which rises superiorly. However, decubitus views are of no value in assessing for pleural effusion if the lung in question is completely opacified, as any fluid present cannot be distinguished from the adjacent, completely opacified hemithorax.

Fluoroscopy of the chest and airways is useful, because the dynamic evaluation airway caliber and can demonstrate expiratory airway collapse in tracheo- or bronchomalacia. Fluoroscopy is also helpful in evaluating for the presence of an airway foreign body when plain films are not definitive and for assessing motion of the diaphragm.

A fluoroscopic contrast esophagram still has significant value, including evaluating swallowing function, aspiration of liquids or solid materials, the presence of a tracheoesophageal fistula, esophageal foreign body and other masses, as well as esophageal stricture or dysfunction (see eFig. 506.2A). An esophagram/upper gastrointestinal study has only an adjunctive role in evaluating gastroesophageal reflux, and it is not the preferred test to establish this diagnosis. With regard to extrinsic masses, especially vascular lesions, the esophagram has a limited role.

When a vascular ring is suspected as the cause for clinical symptoms, the best approach is usually to first obtain frontal and lateral chest radiographs. The presence of a right sided aortic arch along with anterior bowing of the trachea on the lateral view is highly suggestive of the presence of a vascular ring. Computerized tomography (CT) or magnetic resonance imaging (MRI) provides exquisite detail of the precise anatomy of these lesions. Although an esophagram may confirm the likelihood of a vascular ring, it usually does not sufficiently define the exact anatomy and is probably an unnecessary additional study.

Ultrasound

Ultrasound is especially useful to image the pleural space and thoracic wall, as the air-filled lungs reflect and distort the ultrasound beam (see eFig. 506.3C). Sonography can evaluate diaphragmatic motion, especially in children who cannot easily be transported. It is also useful in evaluating the amount and nature of pleural fluid collections. The septations and loculations of exudative effusions are usually better appreciated on ultrasound than other cross sectional imaging modalities such as computerized tomography (CT). Ultrasound can also be used to guide percutaneous drainage of pleural fluid.

Ultrasound imaging is of some use in evaluating chest masses, particularly lesions that abut the mediastinum or diaphragm. Ultrasound is particularly useful in differentiating normal thymus from a mediastinal mass or fluid collection and has the advantage of ready availability, lack of ionizing radiation or need for sedation. Although the nature and anatomic extent of a mass may be better defined on CT or magnetic resonance imaging (MRI), ultrasound (US) and Doppler screening will often be helpful in determining whether a lesion is cystic, solid or vascular, and direct further appropriate imaging. Pericardial effusion and complex cardiovascular anatomy and function are regularly imaged and thoroughly evaluated by ultrasound. Depending on local preference, US, CT, and/or MRI are utilized for image guidance of interventional procedures such as pericardial drainage and biopsies.

Computed Tomographic Imaging

Computed tomography (CT) of the chest provides far more anatomic detail than plain radiographs. The use of chest CT has expanded to include the evaluation of trauma, unusual air collections or densities, nodules, masses and metastases, suspected pulmonary emboli, vascular and airway abnormalities, congenital lung anomalies, complicated or unusual infection, and suspected interstitial lung disease or bronchiectasis (see eFig. 506.3B). The image acquisition algorithm may vary depending on the clinical question, however the images are usually reconstructed so that they can be optimally viewed for soft tissue (high contrast resolution algorithm), lung parenchyma, or bone (higher spatial resolution algorithms).

Modern scanners and computer software now permit image reconstructions in planes other than the axial plane to which early scanners were limited. Coronal reconstructions are particularly helpful for lesions especially in the paramediastinal and paradiaphragmatic regions. Curved planar reconstructions, maximum and minimum intensity projections, three-dimensional (3D) volume and surface reconstructions, and “virtual bronchoscopy” programs are available to display complex anatomy. These reconstruction options require thin section contiguous slices and are usually performed on an independent workstation. Subcentimeter volumetric imaging of the entire chest provides exquisite anatomic detail.

Modern multidetector CT scanners image the entire chest in just a few seconds with much less need for patient sedation or anesthesia than previously. However, breath-hold imaging may be critical and can only be obtained in a cooperative patient or in an infant who is sedated or anesthetized. Newer techniques such as controlled ventilation or spirometry-controlled CT imaging provide excellent motion-free images of the chest. A controlled ventilation study relies on imaging during the brief period of apnea that can be induced in infants following a period of hyperventilation.

With the many options available for CT imaging, it is increasingly critical that there is clear communication between clinical and radiologic colleagues to provide an optimal study. Options include contiguous thicker slices (typically 3–5 mm, depending on patient size) or very thin or overlapping volumetric slices (as small as 0.6 mm with a 50% overlap) when detailed 2D or 3D anatomic reconstructions are needed. High-resolution chest computed tomography (HRCT) usually results in thin (1 mm) slices with gap intervals (5–10 mm) and might include both inspiratory and expiratory imaging to evaluate for lung parenchymal or interstitial disease, bronchiectasis and expiratory air trapping.

Depending on the clinical situation, when contiguous images are desired, thinner slices can often be reconstructed from thicker cuts, with some loss of spatial resolution detail (eFig. 506.4). The limits of reconstruction depend on the original detector array used (eg, on the Siemens 64 MDCT scanner, when the 1.2-mm detector array is utilized, slices acquired at 3–5-mm collimation can be retrospectively reconstructed to 1.2 mm or as thin as 0.6 mm when the 0.6-mm detector array is used).

Intravenous dynamic contrast enhancement is often necessary in children, particularly when evaluation of mediastinal or paramediastinal structures is required. Contrast enhancement is usually needed when evaluating vascular lesions, mediastinal masses, adenopathy, and infectious and neoplastic lesions that involve the chest. HRCT, however, is usually obtained without IV contrast. Computed tomographic angiography (CTA) is an emerging technology for improved visualization of vascular structures. By “gating” CTA to the cardiac cycle, small vascular structures that move with the heart (eg, coronary arteries) can be evaluated.

The contrast used for most studies is a low osmolar nonionic agent with an iodine concentration of 300 mg/ml, administered as a dynamic volume bolus of 2 cc/kg. For vascular studies, the concentration can be increased to 350 mg/ml, and if needed in infants the bolus can be increased to 3 to 4 cc/kg and/or diluted with saline to provide a longer bolus profile. Children receiving iodinated contrast intravenously should be well hydrated before and after the study to protect their renal function. Special techniques and drug pretreatment may be needed in the face of decreased renal function and contrast allergy, the details of these are beyond the scope of this overview.

Computed tomographic (CT) angiography consists of contiguous thin cuts (0.6–1 mm) obtained during administration of a large rapid bolus of contrast (2–5 cc/sec), optimally administered via a large bore peripheral IV (18–22 g) using a mechanical injector. One can however produce high quality CTA studies in tiny newborn infants using IV contrast administered by hand bolus technique (1 cc/sec). Whatever the administration technique, specific timing or real time monitoring of the contrast bolus and triggering of the CT scan is often utilized for optimal visualization of the desired vascular structures. Central lines are usually difficult to inject with a rapid bolus and are mostly not compatible with the use of an injector and are therefore not useful for CTA and suboptimal as well for most other chest applications where vascular opacification is desirable. The technique used for CTA generally does not provide good quality parenchymal lung imaging and is not useful as a substitute for thin section high-resolution chest computed tomography (HRCT) imaging.

Electrocardiogram (EKG) gated CT angiography is available to assess very small vascular structures that move with the heart, such as the coronary arteries, and to evaluate cardiac function in patients who are not able to undergo MR imaging, for example, in the presence of a pacemaker. The gating technique increases the radiation dose approximately fourfold over that used for nongated CTA.

Ionizing radiation dose is a major consideration in utilizing chest CT imaging in children. As techniques become more sophisticated and slices ever thinner, radiation doses have tended to significantly increase. Computed tomography (CT) is responsible for the largest percentage of medical radiation dose to the general population. Children are particularly vulnerable; not only are their tissues intrinsically more sensitive to radiation, especially certain organs such as the thyroid gland and breast, but they also have less surrounding soft tissue to attenuate the radiation so that their organ dose is higher than a similar study in an adult. Also, they have a longer time to manifest the possible cancer induction effect of ionizing radiation. The risk of cancer from a single CT examination is controversial but quite small (estimated at about 1 in 1000) relative to the overall lifetime risk of cancer (1 in 5). However, the risk appears to be dependent on dose and is cumulative with multiple studies. It is imperative, therefore, that prospective CT imaging be carefully assessed for risk versus benefit. When appropriate, other modalities such as ultrasound (US) or MRI could be substituted. The as low as reasonably achievable (ALARA) principle should be followed in regard to decreasing radiation dose in children. Imaging sites must have specific pediatric protocols that adjust imaging parameters such as kVp, mAs, slice collimation, gantry rotation, and pitch based on the size and weight of the child and the requirements of the study. For example, on follow-up imaging lower dose technique and limited anatomic coverage may be appropriate. Wherever possible, CT imaging should be limited to a single series; it is usually unnecessary to obtain both noncontrast and contrasted images. Although it has been standard to image at 120 kVp for CT in the past, 80 kVp or 100 kVp are suitable for most pediatric uses and produce significantly decreased radiation dose. Appropriate shielding of radiation sensitive organs such as orbits, thyroid, breasts, and gonads should always be provided.

Magnetic Resonance Imaging

Although magnetic resonance (MR) imaging avoids ionizing radiation, image acquisition is much slower than computed tomography (CT) scanning. Because of this, MR often requires sedation or anesthesia in young children. Magnetic resonance (MR) is inferior to CT in evaluating the lung parenchyma, and its spatial resolution is also less than CT spatial resolution. However, tissue differentiation such as fluid and fat is often clearly depicted by MR, and as a result it is most useful in evaluating mediastinal and spinal or paraspinal lesions, vascular lesions of the chest, and lesions involving the chest wall. MR is also well established in evaluating cardiac anatomy and function. In the heart, MR is used to demonstrate anatomy, as well as cardiac function and vascular flow using EKG-gated techniques. Contrast MR is also possible using gadolinium as the contrast agent. The physics of the multiple imaging modes in MR are beyond the scope of this discussion.

The major contraindication to the use of MR is the presence of a pacemaker and intracranial aneurysm clips. In general other metallic items such as sutures, clips, staples, and coils are not a definite contraindication to MR. Often MR can be successfully performed in such cases although metallic artifact can sometimes be quite marked and obscure anatomy.

Nuclear Medicine Imaging

Nuclear medicine scanning still has considerable value, although many of it’s prior common uses have been supplanted by other technologies. For example, computed tomography (CT) angiography to evaluate pulmonary embolism is faster and more sensitive than nuclear medicine ventilation/perfusion (V/Q) scanning. Ventilation/perfusion scanning, however, is still used to evaluate a wide variety of pulmonary and vascular abnormalities, particularly when differentiating vascular from airway abnormalities. Perfusion scanning and evaluating differential flow to the lungs is still most often obtained by nuclear medicine although phase contrast MR imaging can also provide similar information. Scintigraphic imaging of bone lesions, occult infections, and cardiac function are also possible, although such studies are not performed frequently in children.

Positron emission tomography (PET) and PET/CT scanning are used less in children than in adults. The most common use for PET and/or PET/CT is in evaluating and following select pediatric tumors, lymphoma in particular. In the future, combined PET/MR imaging will also become available.

Contrast Angiography

The development of sophisticated, less invasive computed tomography (CT) and magnetic resonance (MR) angiographic techniques including gated coronary angiography has replaced conventional catheter angiography in many instances. There are, however, limitations to CT and MR, mainly in the lack of detailed visualization of more distal smaller vascular branches that can be seen with conventional angiography. Also, additional data such as vascular dynamics, vascular pressure, and blood gas measurements are more easily done with conventional catheter angiography. Catheterization angiography is most often obtained in cases of complex congenital heart disease, vascular malformations, and for catheter-based interventions. In addition to the invasive nature of the catheterization procedure and frequent need for sedation or anesthesia, ionizing radiation dose and intravenous contrast load are additional concerns.

The airway begins in the nose and mouth and ends in the alveoli. It is often necessary to visualize portions of the airway in order to document anatomic abnormalities, to obtain tissue for pathologic and microbiologic study, and to sample cellular, microbiological, and molecular constituents of the airway lining fluid. Equipment to allow many of these procedures in adults has been available for approximately a century, and newer technologies allow for safer visualization and sampling of the airways of infants and children. The current tools permit the visual inspection of the pediatric airway from the nares to bronchi distal to the lobar orifices. Sampling of the airways surface liquid and its constituents down to the alveoli is also possible, as is the sampling of tissue from the mucosa of proximal airways to the periphery of the lung parenchyma.

Indications and Contraindications

The major indications for nasopharyngoscopy and laryngoscopy as well as bronchoscopy are included in Tables 506-1 and 506-2. Often, several of the indications are present in any particular patient. One can also consider the clinical indication for bronchoscopy as the need to ascertain information or to obtain material from the lower respiratory tract in a situation where bronchoscopy is the most accurate and safest way to obtain it. The decision as to whether rigid or flexible bronchoscopy is the procedure of choice depends on several factors including the availability of equipment and staff with suitable expertise in bronchoscopy, the clinical question being raised, the clinical status, and patient stability. eTable 506.1 outlines the relative advantages and disadvantage of each procedure and instrument, and it should be apparent that they are complementary and that the availability of both types of bronchoscopy is necessary for the care of pediatric patients.

Contraindications to bronchoscopy depend chiefly on the type of procedure planned. Major contraindications include patient instability or cardiac arrhythmias, although in some circumstances, the underlying cause of these contraindications may in fact be the indication for bronchoscopy (eg, massive atelectasis and hypoxemia). Thrombocytopenia is a relative contraindication to bronchoalveolar lavage and transbronchial biopsy, but replacement of clotting factors and platelets usually can permit these procedures. Even very small patients receiving extracorporeal membrane oxygenation (ECMO) have had safe bronchoscopy, usually with the flexible instrument; in these cases, the nasal approach is not advised because of the risk of nasal bleeding in the heparinized patient and instead the patient is “intubated” orally with the flexible fiber-optic bronchoscope (FFB).

Instruments

There are two types of instruments for airway visualization: rigid and flexible. Each has distinct advantages and disadvantages (see eTable 506.1). Rigid and flexible nasopharyngoscopes allow for the evaluation of the upper airway to the glottic opening. They are useful in determining anatomic causes of upper airway obstruction, stridor, or to identify sites of bleeding, but there are several other important indications for the procedure (see Table 506-1). When possible, the flexible instrument should be used first with the patient breathing spontaneously in order to assess airway dynamics and vocal cord movement. If further study or invasive instrumentation is required, the rigid instrument can be used with the patient anesthetized.

The open tube rigid bronchoscope (OTRB) has for years been one of the most important tools in the diagnosis of lung disease. The Storz-Hopkins glass rod telescope can be passed through the OTRB or, in some circumstances, used alone to provide an unparalled magnified view of the airway and was a major advance in rigid endoscopy. The OTRB allows the passage of a variety of instruments, in addition to the telescope. This permits the safe removal of foreign bodies from the airway, the biopsy of airway lesions, and the passage of laser fibers for ablation of lesions or tumors. Further, the ability to ventilate the patient, coupled with the large bore of the rigid bronchoscope, allows for safer suctioning of brisk bleeding in the distal respiratory tract.

There are certain disadvantages of the rigid bronchoscope (see eTable 506.1). It is passed through the mouth of the patient, and therefore the patient, especially the pediatric patient, must be anesthetized. If there are orthodontic or jaw abnormalities that do not permit adequate jaw expansion, it is difficult to pass the OTRB. Patients already intubated and supported by mechanical ventilation must first be extubated before the OTRB can be passed. Those with existing tracheostomy tubes must have the tube removed and the stoma covered while undergoing rigid bronchoscopy. The OTRB may distort the architecture and dynamic properties of the airway wall, making it difficult to appreciate dynamic changes in airway caliber as may be seen with tracheo- or bronchomalacia. Finally, the relative size and inherent rigidity of the OTRB, which is an advantage in some ways, prevents the instrument from reaching more distal airways or those that are at an acute angle to the direction of the instrument, such as the airways to the apices of the lung.

The flexible fiber-optic bronchoscope (FFB) and nasopharyngoscope rely on one fiberoptic bundle to transmit light to their distal tip and a second bundle to serve as a lens; most, but not all, have an internal channel, through which liquids can be instilled, materials in the airway suctioned, and small instruments such as brushes or forceps passed.

Flexible instruments have certain advantages compared with rigid instruments (see eTable 506.1). Because they are flexible, they can be passed transnasally, allowing inspection of the upper and lower respiratory tract with a single procedure. Because they can fit within an endotracheal tube, they can be used as an aid to intubation, particularly in patients with orthodontic abnormalities or limited jaw opening. They can be passed through an endotracheal tube without discontinuing mechanical ventilation when used with a swivel connector. They are smaller and this, combined with their flexibility, allows them to reach more distal sites in the lung as well as areas requiring angulation such as the apices of the lungs. Because of its small size, the flexible fiber-optic bronchoscope (FFB) can be “wedged” or seated in a distal bronchus, where multiple aliquots of fluid (usually sterile, nonbacteriostatic saline) can be instilled through the channel and sequentially aspirated into sterile containers. This technique samples the conducting airways as well as the alveoli subtending the “wedged” bronchus; the aspirated fluid, containing lining fluid, cells, and pathogens from the washed area, is called a bronchoalveolar lavage (BAL). The use of BAL to detect infectious pathogens and to evaluate cytopathologic changes in the returned cells is one of the most important clinical and research uses of the FFB.

For many pediatric patients, flexible bronchoscopy can be accomplished with light sedation, but this will depend upon the age and medical condition of the patient, the planned procedure, and the bronchoscopist. It is not uncommon to perform flexible bronchoscopy in the operating room with deep sedation provided by an anesthesiologist. The transnasal approach or the use of a laryngeal mask will still allow for spontaneous respiration by the patient.

Instrumentation through the FFB is relatively limited. Brushes for obtaining mucosal cells or airway secretions may be useful for pathologic study. Protected brushes, in which the brush is contained within a catheter, which is in turn within a larger catheter, can sample distal airway secretions without risk of contamination while passing through the suction channel. The available protected brush, however, requires a 2-mm suction channel for passage through a bronchoscope and the standard pediatric bronchoscope channel is only 1.2 mm in diameter. Small biopsy forceps can be used to obtain mucosal and/or transbronchial biopsy samples; the latter are central to the evaluation of recipients of lung- or heart-lung transplants and for some selected patients with interstitial lung disease. Bronchial biopsies to study chronic inflammation in poorly controlled asthmatics are increasingly being used at research centers. Laser fibers can also be passed through the suction channel, permitting laser ablation of endobronchial lesions, although at most centers, laser procedures are preferably done through the open tube rigid bronchoscope (OTRB).

There are several disadvantages of the FFB when compared with the OTRB. Ventilation cannot be done through the FFB, and the patient must breathe around it. Although the image is fairly good with a fiber-optic instrument and improved with the newer “videochip” camera systems, the image quality remains below that achievable with the Storz-Hopkins rod telescope used with the OTRB. The suction channel of the FFB will accommodate brushes, biopsy forceps, and laser fibers, but larger instruments, including those designed for foreign body removal, are more applicable to the OTRB.