Chapter 19 Interventional Techniques
Several interventional techniques are performed in thoracic radiology. The most important is percutaneous transthoracic needle biopsy (TNB) of lung and mediastinal lesions. Other interventional procedures that are mostly related to the pleura include drainage of fluid collections, catheter drainage of pneumothoraces, and sclerotherapy.
TRANSTHORACIC NEEDLE BIOPSY
Transthoracic needle biopsies (Box 19-1) are performed most commonly for the diagnosis of an indeterminate solitary pulmonary nodule. Not all solitary pulmonary nodules that are suspect for bronchogenic carcinoma require biopsy. If the pretest probability is very high for lung cancer or a biopsy is unlikely to have any impact on management, TNB should not be performed. For example, if a patient presents with a long history of smoking and a new, irregular, spiculated nodule in the lung, the likelihood is extremely high that this represents a lung cancer, and it is reasonable to proceed directly to staging and resection. Other indications for TNB include undiagnosed mediastinal masses, a hilar mass when the bronchoscopy result is negative, single or multiple pulmonary nodules in a patient with a known extrathoracic malignancy or a suspicion of metastatic disease, and suspected infectious lesions manifesting as solitary nodules, masses, or very focal areas of consolidation, particularly in the immunocompromised host.
Box 19-1 Indications for Transthoracic Needle Biopsy
Indeterminate solitary pulmonary nodule
Hilar mass when bronchoscopy is negative
Single or multiple nodules when metastases are suspect
There are several diagnostic alternatives to TNB. The most important is bronchoscopy. However, bronchoscopy is preferred for central lesions, particularly if a prebronchoscopy CT scan shows evidence of endobronchial involvement. Transthoracic biopsy may be used to diagnose hilar masses when the result of bronchoscopy is negative and extraluminal compression of the airway is identified. Transbronchial needle aspiration (i.e., Wang needle) is primarily used to establish metastatic malignancy in mediastinal nodes for the purposes of staging lung cancer. A needle is inserted using the bronchoscope through the tracheal wall or carina to facilitate the biopsy of the nodes. In the absence of a visible endobronchial lesion, the diagnostic yield for bronchoscopy in peripheral nodules is low (in the range of 58% to 80%) and is lowest for nodules less than 2 cm in diameter. Video-assisted thoracoscopy enables the diagnosis of peripheral subpleural pulmonary lesions. However, this is an operative procedure that requires an inpatient stay and general anesthesia, and it is more expensive than bronchoscopy or transthoracic needle aspiration biopsy.
Most contraindications to TNB are relative rather than absolute (Box 19-2). The most important are bleeding diatheses. A prebiopsy prothrombin time (PT), partial thromboplastin time (PTT), and platelet count are recommended. A careful history of coagulation abnormalities or the ingestion of drugs such as aspirin, which may lead to abnormal platelet function, should be obtained. Patients with low platelet counts who require an emergent biopsy, such as an immunocompromised patient with pulmonary infection, can receive platelet transfusions. Biopsy of lesions that have a marked vascular supply should be avoided.
Box 19-2 Relative Contraindications to Transthoracic Needle Biopsy
COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in 1 second.
Another relative contraindication is pulmonary hypertension. Needle biopsy can be safely attempted in patients with mild pulmonary hypertension if the nodule is peripheral. In the case of deep nodules or hilar masses, it is not recommended. Other relative contraindications include mechanical ventilation, bullae, or severe emphysema in the path of the lesion to be biopsied, severe chronic obstructive pulmonary disease (COPD, defined by a forced expiratory volume in 1 second [FEV1] of less than 1 L), and intractable cough.
Patients should be cooperative and be able to maintain a certain position. Biopsies are performed with patients in the supine or prone position. The decubitus position is less preferable because it is difficult for the patients to maintain the position.
Local Anesthesia and Sedation
Lung biopsies can be performed under local anesthesia and breath-hold technique or under local anesthesia and intravenous conscious sedation with quiet breathing. Uncooperative patients need conscious sedation.
Computed tomography (CT) is highly recommended before TNB. CT is useful in providing a specific benign diagnosis in certain instances, such as a calcified granuloma or hamartoma, and it can provide information concerning the optimal approach to the lesion (Figs. 19-1 and 19.2). Areas of necrosis within large masses can be identified. Such areas should be avoided because they often produce nondiagnostic samples. 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) is also useful for identifying the viable portion of the tumor (Fig 19-3). Vascular lesions such as aneurysms or arterial venous malformations can be easily recognized on contrast-enhanced CT.
Figure 19-1 Anterior approach to a lesion in the left upper lobe. The patient was placed in a slightly oblique position, and an oblique anterior approach was chosen to avoid bullae surrounding the mass.
Figure 19-2 Prone biopsy of a cavitary lesion. A, New left upper lobe cavitary nodule was identified in a patient with treated nodular sclerosing Hodgkin’s lymphoma. B, The biopsy specimen from the wall of the cavity showed coccidioidomycosis.
Fluoroscopy or CT can be used for imaging guidance. Ultrasound is occasionally used for chest wall or peripheral lesions abutting the pleura. Fluoroscopically guided biopsies are usually reserved for large masses (Fig. 19-4). Fluoroscopy allows real-time, moment-to-moment visualization and often enables the biopsy to be performed in less time than that required for a CT-guided biopsy. However, we prefer to use CT for imaging guidance in all transthoracic needle biopsies. It allows a more complex approach, and safe and accurate sampling of hilar or mediastinal masses is possible. CT also provides better visualization of severe emphysematous areas or bullae, which may lie within the path of a needle. Real-time, continuous CT fluoroscopy combines the advantages of standard fluoroscopy with CT guidance.
A variety of needles can be used for TNB. Small-bore, 18- to 22-gauge needles are preferred because larger-bore needles have been associated with high complication rates, particularly bleeding and pneumothorax. Aspirating needles commonly used include Chiba and Greene varieties. These needles provide only cytologic material from aspirates. Automatic biopsy devices that provide small cores of tissue, sometimes referred to as biopsy guns, are available. The length of the needle selected should be greater than the depth of the lesion from the skin and preferably 3 to 5 cm longer. If coaxial technique is used, the inner needle length should be 5 cm longer than the introducer needle.
The high diagnostic accuracy of TNB can be attributed to improved radiologic techniques such as CT guidance and, even more importantly, to advances in cytologic techniques and interpretation. The TNB technique should be a cooperative effort between the cytologist and the radiologist. We prefer to have a cytologic technician available during the biopsy. Quick stains can be performed, and a cytologist can be called to provide a rapid interpretation of the specimen. This allows for repeat biopsy if the specimen is nondiagnostic or inadequate and permits the use of core-needle specimens as a supplement to the aspiration when the diagnosis cannot be obtained from the aspirated sample.
The shortest, most vertical biopsy path should be chosen based on the prebiopsy CT scan (Fig. 19-5). Interlobar fissures, pulmonary vessels, bullae, and areas of severe emphysema should be avoided (see Fig. 19-1). Sometimes, this can be achieved by tilting the CT gantry (Fig. 19-6). Paraspinal and extrapleural saline injection creates safer access to paramediastinal lesions (Fig. 19-7). The patient is placed in a position that provides a safe approach—prone, supine, or occasionally, decubitus—as indicated. After a scanogram is performed, thin-section, 2- to 5-mm CT slices are obtained through the lesion with a localizing grid in place on the skin overlying the lesion. A desired skin puncture site is identified using the grid, and the patient is prepared and draped in a sterile manner. After the injection of local anesthesia, a small puncture is made in the skin and subcutaneous tissues with a scalpel.
Figure 19-5 Biopsy of the left upper lobe nodule. The patient was placed in the supine position, and the most direct vertical path (avoiding the large vessels and bronchi) was used. The histologic diagnosis was metastatic adenocarcinoma from prostate cancer.
Figure 19-6 Biopsy with tilt of the CT gantry. A, CT of the left upper lobe nodule obtained with the patient in a prone position reveals ribs (thick arrow) and a left major fissure (arrows) in the path. B, CT obtained with 20 degrees of tilt of the gantry toward the head reveals a safe approach without intervening ribs or a fissure. The histologic diagnosis was hamartoma.
Figure 19-7 Biopsy after injection of paravertebral saline. A, CT of the left upper lobe with the patient in the prone position reveals a subpleural nodule surrounded by emphysematous bullae (arrows). B, Needle placement through the paravertebral soft tissue was achieved after injecting saline to increase the soft tissue thickness and avoid the bullae. The biopsy specimen was positive for non–small cell lung cancer.
An introducer 19-gauge spinal needle is advanced through the chest wall using intermittent CT scans to verify the position of the needle. When performing TNB, the introducer needle must be perfectly aligned with the lesion before the pleural puncture. It is difficult to reposition or reorient the path of the needle after the lung is entered. Attempting to do so often produces a pleural tear.
Although the biopsy needle may be introduced alone, we prefer a coaxial technique. The 19-gauge introducer spinal needle is placed through the skin and chest wall and through the pleura just adjacent to or into the lesion to be biopsied. A 21- or 22-gauge aspirating needle is then used for the biopsy, and it is placed by way of the introducer needle. Ultrathin, 19-gauge introducer needles can accommodate 20-gauge automatic biopsy devices for core specimens. The coaxial technique allows several specimens to be obtained with only one pleural puncture.
After the introducer needle has been correctly positioned immediately adjacent to or in the lesion, the stylet is removed, and the 21- or 22-gauge aspirating needle is placed through the introducer needle into the lesion. A 10-mL syringe is then attached to the thin needle, and using a series of up and down and rotatory motions, an aspirate is obtained. The specimen should be immediately placed on glass slides and fixed with a number of available quick stains. If a core biopsy is used, the tissue can be rinsed with formalin or saline. A small amount of saline is placed in the introducer needle before withdrawing the stylet to reduce the risk of air embolism and reduce friction between the needles. If the cytologist thinks the original pass with the aspirating needle is nondiagnostic or negative, additional samples may be taken, as well as core samples, using the coaxial technique. If inflammatory changes are present or there is a suspicion of active infection, specimens should be sent to the bacteriology laboratory.