Imaging Techniques

Several factors are considered in selecting the most appropriate imaging modality to guide percutaneous tissue sampling. These include the site, size, and depth of the lesion; its proximity to the pleura and neurovascular structures; and performance status of the patient.

Integrated Positron Emission Tomography–Computed Tomography

Positron emission tomography (PET) has an established role in the detection and staging of neoplastic diseases. In lung cancer it provides information on the primary lesion, early nodal involvement, and distant metastases. The positron-emitting agent most frequently used is ¹⁸F-fluorodeoxyglucose (FDG). This tracer accumulates at sites of increased glycolysis (e.g., tumor cells), and this activity is then detected by the PET camera. The intensity of activity is displayed on a color scale, and a quantitative assessment is made by measuring the standardized uptake value (SUV).

CT combined with PET allows accurate anatomic localization of FDG-avid foci. This technique is particularly useful in isolating active foci surrounded by benign changes, such as within thickened pleura, or in separating tumor from collapse, allowing greater precision in positioning the biopsy needle (Figure 13-3).

Figure 13-3 Differentiating central tumor from distal lung collapse. A, The computed tomography (CT) scan shows central low-density tumor in the left lower lobe (star) with distal collapse (arrowheads), but differentiation is subtle. A small pleural effusion (arrow) is evident. B, CT–positron emission tomography (PET) study demarcates the FDG-avid tumor from the area of distal collapse. Note normal physiologic left ventricular avidity. FDG, ¹⁸F-2-fluorodeoxyglucose.

The sensitivity of PET is limited by the size of the lesion. Small lesions (usually less than 1 cm) may not accumulate sufficient FDG to be detected on PET imaging, leading to false-negative results. The latter can also occur in tumors with relatively low metabolic activity such as carcinoids and alveolar cell cancers.

Inflammatory conditions such as bacterial pneumonias, abscesses, tuberculosis, and active sarcoidosis are associated with increased granulocytic activity. Such activity promotes increased uptake of FDG, potentially giving rise to false-positive results.

Needles

The two main modes of sampling are fine needle aspiration (FNA) for cytologic study and core biopsy for histopathologic examination. Both methods retrieve samples that are suitable for culture. Although the sensitivity of FNA is improved by having a cytologist present to ensure that an adequate sample is obtained, the diagnostic yield in benign disease remains low (20% to 50%) compared with that for core biopsy (70%) (Greif et al., 1999). In malignant disease, the techniques are analogous, with a sensitivity of 90% to 95% (Klein et al., 1996). The clinical requirement for cores of tissue for immunohistochemical analysis has led to a reduction in the use of FNA, and when feasible, cores are always obtained.

FNA involves inserting a fine needle into a lesion and carefully moving the tip to and fro within the tissue, to obtain an aspirate. Gentle suction can be applied by attaching a 5-mL syringe to the needle hub. A variety of fine needles are available, including the Westcott, Chiba, Franseen, and Rotex needles, which range in size from 20 to 23 gauge. Larger-gauge needles are smaller in caliber and less rigid in design, which can limit their use. The Westcott needle has the advantage of having a trough close to the needle tip, which captures small cores of tissue in approximately 50% of cases. The main use of FNA is to obtain nodal aspirates.

Core biopsy specimens are obtained using cutting needles, which are larger in diameter (14 to 18 gauge) and are available in different lengths (6-, 9-, and 15-cm lengths are commonly used). These needles are more sturdy, allowing greater control in placement. Cutting needles are typically mounted on a spring-loaded mechanism. Older designs such as the Bard Biopty biopsy system, when triggered, simultaneously fire an inner notched stylet and an outer cutting cannula. The handle of the Bard system is bulky but reusable (Figure 13-4). Newer, lighter designs include the Cook Quickcore and Bauer Temno devices, which allow the inner notched stylet to be advanced and secured within the lesion before the cutting cannula is activated. The throw can be increased from 1 to 2 cm to obtain better core samples (Figure 13-5). The Cook device seems to have a slightly sharper needle tip, which in practice can be advanced through tougher tissues.

Figure 13-4 The Bard Biopty biopsy system. The needle is introduced at a point on the thorax so that the tip reaches the area in which biopsy will be performed.

Figure 13-5 The Bauer Temno biopsy instrument. The cutting needle is positioned within the lesion to be biopsied by pushing the plunger. The advantages include that the instrument is lightweight and requires use of only one hand, and that it is easy to use under computed tomography or ultrasound guidance.

Historically, it was believed that use of larger cutting needles carried higher complication rates than those associated with fine needles. A 2002 study of practice based in the United Kingdom analyzed data from 5444 lung biopsy and FNA procedures and found no difference between the two methods, a conclusion supported by other studies (Richardson et al., 2002).

With transpulmonary biopsy, the risk of pneumothorax is more closely related to the number of pleural passes. The introduction of a coaxial system has transformed lung biopsies. A single pleural pass is made with a thin-walled introducer needle (usually 16 gauge). A smaller cutting needle (usually 18 gauge with a 1- or 2-cm throw) is inserted through the introducer and multiple cores are taken without repuncturing the pleura. The process is quicker, simpler, and safer than attempting multiple pleural passes, leading to a reduction in the complication rate with an improved diagnostic yield (Figure 13-6).

Figure 13-6 The Cook coaxial system. A 16-gauge introducer needle, together with its stylet and 18-gauge inner cutting needle, is shown.

Indications

The role of percutaneous lung biopsy in diagnosing malignant disease is well established, with a sensitivity of 90% to 95%. Its main application is in patients with inoperable lung cancer, when sputum cytology and bronchoscopy are nondiagnostic, to provide a means of establishing cell type before chemotherapy and radiotherapy. In the past, both FNA and core biopsy have been comparable in diagnosing and distinguishing small cell lung cancer (SCLC) from non-SCLC (NSCLC), providing oncologists with sufficient information to make choices regarding appropriate chemotherapy regimens. New targeted chemotherapy and biologic agents (e.g., the epidermal growth factor receptor [EGFR] inhibitor drugs) have proven prognostic benefit with particular histologic subtypes. This has meant that core sampling is essential to allow routine performance of detailed tissue analysis. FNA can be adequate to differentiate between subtypes of NCSLC, but it remains less accurate overall than core biopsy. The latter allows sufficient material to be obtained for both accurate histologic subtyping and molecular testing (e.g., to determine EGFR mutation status) (Barnes et al., 2010).

Biopsy also is widely used to exclude lung metastases in patients with potentially operable lung tumors, and in those with extrathoracic malignancies (Figure 13-7).

Figure 13-7 Computed tomography (CT)-guided biopsy of a pulmonary nodule using a coaxial system. The patient is in the prone position. Multiple cystic and solid pulmonary nodules in a patient with a history of lymphoma. The diagnosis was Langerhans cell histiocytosis.

With solitary pulmonary lesions, core biopsy remains the prudent approach for confirming benign disease. The combined use of CT guidance and the coaxial biopsy system, which allows multiple cores to be taken safely, has improved the diagnostic accuracy of this technique in both benign and malignant disease. If malignancy is strongly suspected, it may be best to avoid biopsy and proceed straight to surgery.

Transthoracic biopsy and FNA also have a role in the diagnosis of non-neoplastic disease. Both techniques are increasingly being used to obtain samples for identification of microorganisms, particularly in immunocompromised patients with consolidation and masses. All samples are routinely sent to both histology (or cytology) and microbiology. Communication with the referring clinician is essential. In cases in which infection is suspected, the first sample should be sent to microbiology should the procedure need to be unexpectedly abandoned. The converse is true in suspected cases of malignancy where the first sample is sent to histology. The working diagnosis may also influence the choice of needle size.

Contraindications

The contraindications to percutaneous lung biopsy are largely relative and are summarized in Table 13-1. In general, patients need to be able to cooperate, including lying still in the desired position, resisting excessive coughing, and controlling breathing. In patients with very poor lung function, biopsy of a lesion is still possible, provided that the lesion is peripheral and a carefully considered route is identified (usually with CT) that does not traverse lung parenchyma. In performing the biopsy, care is taken to avoid creating a pneumothorax, which could be life-threatening. Before the procedure, a coagulation screen is performed according to local protocol, and bleeding diatheses are corrected, when appropriate, to keep within safe guidelines. Biopsy of parenchymal hydatid lesions has been documented, but an increased and probably unacceptable risk of anaphylactic reaction has been documented in patients with such lesions.

Table 13-1 Contraindications to Needle Biopsy

FEV₁, forced expiratory volume in 1 second.

Method

Pulmonary lesions are usually sampled under CT guidance using cutting needles rather than fine needles. The coaxial technique is preferred because it allows multiple consecutive cores to be obtained without delay, helping to improve diagnostic accuracy while minimizing risk. The number of biopsy specimens varies, but in practice, two to five samples are required (fewer if the patient is at high risk of complications). The aim is to obtain a diagnosis without compromising patient safety.

Peripheral lesions located away from fissures and large vessels are ideally targeted, to minimize complications of pneumothorax and hemorrhage. When possible, the approach should cover the shortest distance from the skin surface to the lesion, using a route that allows the patient to be positioned comfortably for a period of at least 30 minutes. The latter consideration is important, because patients are often elderly or frail and breathless at rest.

In lesions obscured by atelectasis, intravenous contrast can be administered to localize abnormal tissue from collapsed lung. PET-CT is useful in identifying avid foci in these cases. If the lesion is cavitating or exhibits central necrosis, the biopsy must be taken from the periphery of the lesion.

Procedure