lesions in the lungs.
An additional, specialized technique that has been developed within the past decade is called electromagnetic navigational bronchoscopy (often shortened to navigational bronchoscopy). Using a previously obtained CT scan of the chest, sophisticated software creates a three-dimensional image of the chest and a “map” with directions for guiding a steerable navigation catheter, advanced through a flexible bronchoscope, into a small peripheral nodule. Without this type of guidance, it is very difficult for the bronchoscopist to choose the correct path for steering the bronchoscope and any sampling tools to a peripheral lesion through the progressively branching system of airways. Because of the tiny size of the distal airways, a technique called robotic bronchoscopy has been developed that permits the bronchoscopist to make smaller, more accurate manipulations using a computer-assisted device that holds and directly moves the bronchoscope.
There are many indications for bronchoscopy, usually with a flexible instrument, although the rigid instrument is used under some circumstances. When appropriate, the flexible instrument is preferred because the procedure can be performed using only mild sedation and the patient need not be hospitalized. In contrast, rigid bronchoscopy is performed only under general anesthesia. Some indications for bronchoscopy include (1) evaluation of a suspected endobronchial malignancy, (2) sampling of an area of parenchymal disease by BAL, brushings, or biopsy, (3) evaluation of hemoptysis, and (4) removal of a foreign body (with special instruments that can be passed through the bronchoscope and are capable of retrieving objects). A variety of newer therapeutic modalities are being delivered to the airways via either flexible or rigid bronchoscopic techniques. These modalities include laser techniques for shrinking endobronchial tumors causing airway obstruction; placement of stents to maintain patency of airways having a compromised or obstructed lumen; procedures for dilation of strictures; placement of radioactive seeds directly into malignant airway lesions (brachytherapy); and delivery of electric current (electrocautery), low temperature (cryotherapy), or certain wavelengths of light (photodynamic therapy) to endobronchial masses. Deployment of these novel therapeutic opportunities has spawned a relatively new and rapidly evolving area of subspecialization within pulmonary medicine called interventional pulmonology.
Since the invention of the fiberoptic bronchoscope in 1966, flexible bronchoscopy has become a common and useful technique in evaluating and managing pulmonary disease. Even though the physician who first suggested placing a tube into the larynx and bronchi was censured in 1847 for proposing a technique that is “an anatomical impossibility and an unwarrantable innovation in practical medicine,” bronchoscopy is generally well tolerated, and complications are infrequent.
Evaluation on a microscopic level
Microscopy often provides the definitive diagnosis of pulmonary disease suggested by the history, physical examination, or imaging of the chest. Several types of disorders are particularly amenable to diagnosis by microscopy: lung tumors (by either histology or cytology), pulmonary infection (by microscopic identification of a specific organism), and a variety of miscellaneous pulmonary diseases, particularly those affecting the interstitium of the lung (by histology). Frequently, when a diagnosis is uncertain, the same techniques are used to obtain samples that are processed both for histologic (or cytologic) examination and for identification of microorganisms. This section provides a discussion of how specimens are obtained and then considers how the specimens are processed. The more recent identification and use of tumor markers on lung cancer specimens, which has become important for developing targeted therapeutic plans, will be discussed in Chapters 20 and 21.
Obtaining specimens
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The three main types of specimens the physician uses for microscopic analysis in diagnosing the patient with lung disease are (1) tracheobronchial secretions, (2) tissue from the lung parenchyma, and (3) fluid or tissue from the pleura. A number of methods are available for obtaining each of these types of specimens, and knowledge of the yield and the complications determines the most appropriate method.
The easiest way to obtain a specimen of tracheobronchial secretions is to collect sputum expectorated spontaneously by the patient. The sample can be used for identifying inflammatory or malignant cells and for staining (and culturing) microorganisms. Collecting sputum sounds simple, but it presents several potential problems. First, the patient may not have any spontaneous cough and sputum production. If this is the case, a strong cough that produces sputum can frequently be induced by having the patient inhale an irritating aerosol, such as hypertonic saline (“induced sputum”). Second, what is thought to be sputum originating from the tracheobronchial tree is frequently either nasal secretions or “spit” expectorated from the mouth or the back of the throat. Finally, as a result of passage through the mouth, even a good, deep sputum specimen is contaminated by the multiplicity of microorganisms that reside in the mouth. Because of this contamination, care is required in interpreting the results of sputum culture, particularly with regard to the normal flora of the upper respiratory tract. Despite these limitations, sputum remains a valuable resource when looking for an infectious process such as bacterial pneumonia and tuberculosis. Its role in diagnosing lung cancer is more limited due to its low sensitivity.
Tracheobronchial secretions can also be obtained by two other routes: transtracheal aspiration and bronchoscopy. With transtracheal aspiration, a small plastic catheter is passed inside (or over) a needle inserted through the cricothyroid membrane and into the trachea. The catheter induces coughing, and secretions are collected with or without the additional instillation of saline through the catheter. This technique avoids the problem of contamination by mouth and upper airway flora. It also allows collection of a sample even when the patient has no spontaneous sputum production. However, the technique is not without risk. Bleeding complications and, to a lesser extent, subcutaneous emphysema (air dissecting through tissues in the neck) are potentially serious sequelae. Because of these potential complications, the availability of alternative methods of sampling, and physicians’ inexperience with the procedure, transtracheal aspiration is now rarely performed.
Tracheobronchial secretions are provided by:
1.Expectorated sputum (either spontaneous or induced by hypertonic saline)
2.Transtracheal aspiration (rarely used)
3.Flexible bronchoscopy
Flexible bronchoscopy is a suitable and direct way to obtain secretions from the tracheobronchial tree. It has the additional benefit of allowing visualization of the airways. Bronchoscopy has distinct advantages in collecting material for cytologic analysis because specimens can be collected from a localized area directly visualized with the bronchoscope. However, because the instrument passes through the upper respiratory tract, collection of specimens for culture is subject to contamination by upper airway flora. Specially designed systems with a protected brush can decrease contamination, and quantifying the bacteria recovered can be helpful in distinguishing upper airway contamination from true lower respiratory infection.
BAL has become a widely employed method for obtaining specimens from the lower respiratory tract. The fluid obtained by BAL has been used quite effectively for detecting Pneumocystis jirovecii, particularly in patients with acquired immunodeficiency syndrome (AIDS) or other causes of immunocompromise. In some diffuse parenchymal lung diseases (see Chapters 9 and 11), analysis of the
cellular and biochemical components of BAL may provide information that is useful diagnostically and for research about basic disease mechanisms.
As is true of tracheobronchial secretions, tissue specimens for microscopic examination can be collected in numerous ways. A brush or a biopsy forceps can be passed through a bronchoscope. The brush is often used to scrape cells from the surface of an airway lesion, but it can also be passed more distally into the lung parenchyma to obtain specimens directly from a diseased area. The biopsy forceps is used in a similar fashion to sample tissue from a lesion in the airway (endobronchial biopsy) or from an area of disease in the parenchyma (transbronchial biopsy, so named because the forceps must puncture a small bronchus to sample the parenchyma). In the case of bronchial brushing, the specimen that adheres to the brush is smeared onto a slide for staining and microscopic examination. For both endobronchial and transbronchial biopsies, the tissue obtained can be fixed and sectioned, and slides can be made for subsequent microscopic examination.
A lesion or diseased area in the lung parenchyma can also sometimes be reached with a needle through the chest wall, particularly when the lesion is near the periphery of the lung. This type of biopsy, called a percutaneous needle biopsy, is typically performed using simultaneous CT imaging to ensure placement of the needle in the desired area. Depending on the type of needle used, a small sample may be either aspirated or taken by biopsy. Bleeding and pneumothorax are potential complications, just as they are for a transbronchial biopsy through a bronchoscope.
Lung biopsy specimens can be obtained by:
1.Flexible bronchoscopy
2.Percutaneous needle aspiration or biopsy
3.Video-assisted thoracic surgery
4.Open surgical procedure
Lung tissue is frequently obtained by a surgical procedure involving an approach through the chest wall. Traditionally, a surgeon made an incision in the chest wall, allowing direct visualization of the lung surface and removal of a small piece of lung tissue. This type of open lung biopsy has largely been supplanted by a less invasive procedure called thoracoscopy (video-assisted thoracic surgery or VATS). VATS involves placement of a thoracoscope and biopsy instruments through small incisions in the chest wall; a high-quality image obtained through the thoracoscope can be displayed on a monitor screen. The surgeon uses the video image as a guide for manipulating the instruments to obtain a biopsy sample of peripheral lung tissue or to remove a peripheral lung nodule.
Finally, fluid in the pleural space is frequently sampled in the evaluation of a patient with a pleural effusion. A small needle is inserted through the chest wall and into the pleural space, usually with ultrasound guidance, and fluid is withdrawn. The fluid can be examined for malignant cells and microorganisms. Chemical analysis of the fluid (see Chapter 15) often provides additional useful diagnostic information. A biopsy specimen of the parietal pleural surface (the tissue layer lining the pleural space) may also be obtained blindly, with a special needle passed through the chest wall, or under direct visualization using a thoracoscope. The tissue can be used for microscopic examination and microbiologic studies.
Processing specimens
Once specimens are obtained, the techniques of processing and types of examination performed are
common to those used for many types of tissue and fluid specimens.
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Diagnosis of pulmonary infections depends on smears and cultures of the material obtained, such as sputum, other samples of tracheobronchial secretions, or pleural fluid. The standard Gram stain technique often allows initial identification of microorganisms, and inspection may reveal inflammatory cells (particularly polymorphonuclear leukocytes) and upper airway (squamous epithelial) cells, the latter indicating contamination of sputum by upper airway secretions. Final culture results provide definitive identification of an organism, but the results must always be interpreted with the knowledge that the specimen may be contaminated and that what is grown is not necessarily causally related to the clinical problem.
Specimens can be processed for staining and culture of microorganisms and for cytologic and histopathologic examination.
Identification of mycobacteria, including the causative agent for tuberculosis, traditionally required special staining and culturing techniques. Mycobacteria are stained by agents such as carbolfuchsin or auramine-rhodamine, and the organisms are almost unique in their ability to retain the stain after acid is added. Hence, the expression acid-fast bacilli is used commonly when referring to mycobacteria. Frequently used staining methods are the Ziehl-Neelsen stain or a modification called the Kinyoun stain. A more sensitive and faster way to detect mycobacteria involves use of a fluorescent dye such as auramine-rhodamine. Mycobacteria take up the dye and fluoresce and can be detected relatively easily even when present in small numbers. Because mycobacteria grow slowly, they may require 6 to 8 weeks for growth and identification on culture media. More recently, genetic probes have been employed to identify the presence of specific mycobacterial species with much greater speed and precision (see later). However, culture is generally still performed to confirm the initial genetic test results and to allow drug sensitivity testing.
Organisms other than the common bacterial pathogens and mycobacteria often require other specialized staining and culture techniques. Fungi may be diagnosed by special stains, such as methenamine silver or periodic acid–Schiff stains, applied to tissue specimens. Fungi can also be cultured on special media favorable to their growth. P. jirovecii, a pathogen now classified as a unique category of fungi (see Chapter 26) and most common in patients with impaired defense mechanisms, is stained in tissue and tracheobronchial secretions by methenamine silver, toluidine blue, or Giemsa stain. An immunofluorescent stain using monoclonal antibodies against Pneumocystis is particularly sensitive for detecting the organism in sputum and BAL fluid. The organism identified in 1976 as Legionella pneumophila, the causative agent of Legionnaires disease, can be diagnosed by silver impregnation or immunofluorescence staining. The organism also can be grown (with difficulty) on some special media.
Cytologic examination for malignant cells is available for expectorated sputum, specimens obtained by needle aspiration, bronchial washings or brushings obtained with a bronchoscope, and pleural fluid. A specimen can be smeared directly onto a slide (as with a bronchial brushing), subjected to concentration (bronchial washings, pleural fluid), or digested (sputum) prior to being smeared on the slide. The slide is then stained by the Papanicolaou technique, and the cells are examined for findings suggestive or diagnostic of malignancy.
Pathologic examination of tissue sections obtained by biopsy is most useful for diagnosis of malignancy or infection, as well as for a variety of other processes affecting the lungs and pleura. In many circumstances, examination of tissue obtained by biopsy is the gold standard for diagnosis, although even biopsy results can show false-negative findings or yield misleading information.
Tissue obtained by biopsy is routinely stained with hematoxylin and eosin for histologic examination. A wide assortment of other stains is available that specifically stain collagen, elastin, and a variety of microorganisms. Immunohistochemical stains applied to neoplasms in the lung are useful to identify and