Radiographic Studies

The chest x-ray (CXR), generally including both posteroanterior and lateral views, is often the first diagnostic study in pts presenting with respiratory symptoms. With some exceptions (e.g., pneumothorax), the CXR pattern is usually not sufficiently specific to establish a diagnosis; instead, the CXR serves to detect disease, assess magnitude, and guide further diagnostic investigation. With diffuse lung disease, CXR can detect an alveolar, interstitial, or nodular pattern. CXR can also detect pleural effusion and pneumothorax, as well as abnormalities in the hila and mediastinum. Lateral decubitus views can be used to estimate the size of freely flowing pleural effusions.

Chest computed tomography (CT), typically performed with helical scanning and multiple detectors, is widely used to clarify radiographic abnormalities detected by CXR. Advantages of chest CT compared with CXR include (1) ability to distinguish superimposed structures due to cross-sectional imaging; (2) superior assessment of tissue density, permitting accurate assessment of the size and density of pulmonary nodules and improved identification of abnormalities adjacent to the chest wall, such as pleural disease; (3) with the use of IV contrast, ability to distinguish vascular from nonvascular structures, which is especially useful in assessing hilar and mediastinal abnormalities (including staging of lung cancer); (4) with CT angiography, ability to detect pulmonary emboli; and (5) due to superior visible detail, improved recognition of parenchymal and airway diseases, including emphysema, bronchiectasis, lymphangitic carcinoma, and interstitial lung disease. In the appropriate clinical context, idiopathic pulmonary fibrosis can be reliably diagnosed based on chest CT. Low dose chest CT is recommended for lung cancer screening among pts aged 55-80 with at least a 30 pack-year smoking history, who have smoked in the past 15 years. With appropriate data reanalysis, chest CT scans can provide a three-dimensional reconstruction of the airways down to at least the sixth generation, providing a virtual bronchoscopy. Virtual bronchoscopies may be helpful in assessing stenotic airways and in planning therapeutic bronchoscopy procedures.

Ultrasound (US)

Diagnostic US is not useful for assessing the pulmonary parenchyma, but it can detect and localize pleural abnormalities and guide thoracentesis of a pleural effusion. As a nonionizing imaging approach, it is safe to perform on pregnant women and children. Real-time US imaging can assess diaphragmatic mobility. Portable US is useful to monitor resolution of pneumothorax and pleural effusion.

Nuclear Medicine Imaging

Ventilation-perfusion lung scans can be used to assess for pulmonary thromboembolism but have largely been replaced by CT angiography. Positron emission tomographic (PET) scanning assesses the uptake and metabolism of a radiolabeled glucose analogue. Because malignant lesions usually have increased metabolic activity, PET scanning, especially when combined with CT images in PET/CT, is useful to assess pulmonary nodules for potential malignancy and to stage lung cancer. PET studies are limited in assessing lesions <1 cm in diameter; false-negative screening for malignancy can result from lesions with low metabolic activity, such as carcinoid tumors or bronchioloalveolar cell carcinoma. False-positive PET signals can be observed in inflammatory conditions such as pneumonia.

Other Imaging Techniques

A variety of other imaging techniques are used less commonly to assess respiratory disease. Magnetic resonance imaging (MRI) is generally less useful than CT for evaluation of the respiratory system but can be helpful to assist in the evaluation of intrathoracic cardiovascular pathology without radiation exposure and to distinguish vascular and nonvascular structures without IV contrast. MRI can also distinguish tumor from post-stenotic atelectasis and assess tumor infiltration of the chest wall or mediastinum. However, the presence of metallic foreign bodies, pacemakers, and intracranial aneurysm clips preclude the use of MRI. Pulmonary angiography can assess the pulmonary arterial system for venous thromboembolism but has largely been replaced by CT angiography.

Blood Samples

Blood samples are useful for testing biomarkers of systemic illnesses, such as autoantibodies. Alpha-1 antitrypsin deficiency, which is a genetic syndrome associated with COPD and liver disease, can be detected through protein levels, protein phenotype, and genotype assessed in blood samples. Blood sources of DNA can also be used for other types of genetic testing.

Sputum Examination

Sputum can be obtained by spontaneous expectoration or induced by inhalation of an irritating aerosol-like hypertonic saline. Sputum is distinguished from saliva by the presence of alveolar macrophages and other inflammatory cells as opposed to squamous epithelial cells. Sputum examination should include gross inspection for blood and color, as well as Gram's stain and routine bacterial culture. Bacterial culture of expectorated sputum may be misleading due to contamination with oropharyngeal flora. Sputum samples can also be assessed for a variety of other pathogens, including mycobacteria, fungi, and viruses. Sputum samples induced by hypertonic saline can be stained for the presence of Pneumocystis jirovecii. Cytologic examination of sputum samples can be used as an initial screen for malignancy.

Bronchoscopy

Bronchoscopy is a procedure that provides direct visualization of the tracheobronchial tree, typically to the subsegmental level. The fiberoptic bronchoscope is used in most cases, but rigid bronchoscopy is valuable in specific circumstances, including massive hemorrhage and foreign body removal. Flexible fiberoptic bronchoscopy allows visualization of the airways; identification of endobronchial abnormalities, including tumors and sites of bleeding; and collection of diagnostic specimens by washing, brushing, biopsy, or lavage. Washing involves instilling sterile saline through the bronchoscope channel onto the surface of a lesion; part of the saline is suctioned back through the bronchoscope and processed for cytology and microorganisms. Bronchial brushings can be obtained from the surface of an endobronchial lesion or from a more distal mass or infiltrate (potentially with fluoroscopic guidance) for cytologic and microbiologic studies. Biopsy forceps can be used to obtain biopsies of endobronchial lesions or passed into peribronchial alveolar tissue (often with fluoroscopic guidance) to obtain transbronchial biopsies of more distal lung tissue. Transbronchial biopsy is particularly useful in diagnosing diffuse infectious processes, lymphangitic spread of cancer, and granulomatous diseases. Complications of transbronchial biopsy include hemorrhage and pneumothorax.

Bronchoalveolar lavage (BAL) is an adjunct to fiberoptic bronchoscopy, permitting collection of cells and fluid from distal air spaces. After wedging the bronchoscope in a subsegmental airway, saline is instilled and then suctioned back through the bronchoscope for analyses, which can include cytology, microbiology, and cell counts. BAL is especially useful in the diagnosis of P. jirovecii pneumonia and some other infections. Immunofluorescent staining with antibodies of nucleic acid analysis with PCR can facilitate rapid diagnosis of some infections.

Additional bronchoscopic approaches to obtain tissue samples from locations adjacent to the trachea or large bronchi for cytologic assessment of malignancy include transbronchial needle aspiration (TBNA). TBNA can be supplemented with endobronchial US (EBUS), which can allow guided aspiration of hilar and mediastinal lymph nodes based on real-time US images. Radial probe EBUS has improved the bronchoscopic diagnostic yield for peripheral pulmonary nodules.

Percutaneous Needle Aspiration of the Lung

A needle can be inserted through the chest wall and into a pulmonary lesion to aspirate material for cytologic and microbiologic studies. Percutaneous needle aspiration is usually performed under CT or US guidance. Owing to the small size of the sample obtained, sampling error is a limitation of the procedure.

Thoracentesis

Thoracentesis should be performed as an early step in the evaluation of a pleural effusion of uncertain etiology. Analysis of pleural fluid can determine the etiology of the effusion (Chap. 137 Diseases of the Pleura). Large-volume thoracentesis can be therapeutic by palliating dyspnea.

Mediastinoscopy

Tissue biopsy of mediastinal masses or lymph nodes is often required for cancer diagnosis and staging. Mediastinoscopy is performed from a suprasternal approach, and a rigid mediastinoscope is inserted-from which biopsies can be obtained. Lymph nodes in the aortopulmonary location typically require a parasternal mediastinotomy to provide access for biopsy.

Medical Thoracoscopy

Medical thoracoscopy, also known as pleuroscopy, focuses on pleural-based diseases. Medical thoracoscopy is commonly used to evaluate pleural effusions or to obtain biopsies from the parietal pleura. General anesthesia is typically not required.

Video-Assisted Thoracic Surgery (Vats)

VATS, also known as thoracoscopy, is widely used for the diagnosis of pleural lesions as well as pesripheral parenchymal infiltrates and nodules. VATS, which requires that the pt tolerate single-lung ventilation during the procedure, involves passing a rigid scope with a camera through a trocar and into the pleural space; instruments can be inserted and manipulated through separate intercostal incisions. VATS has largely replaced “open biopsy,” which requires a thoracotomy.