Fine needle aspiration (FNA) is a relatively quick procedure to learn and perform, yet it takes a very long time to master this procedure. In the majority of cases, the needles that are used for the spine or rib biopsy procedure range in length from 10 to 20 cm (Fig. 3.2). The objective of this procedure is to make short to-and-fro excursions with a lengthy but small-bore cutting needle, in the range of 25–18 gauge, while applying continuous suction, with a small Luer-Lok syringe attached to the hub of the needle (Fig. 3.3). The suction is stopped immediately prior to removal of the needle tip from the lesion so as not to aspirate cells from normal tissue and to avoid aspiration of hemorrhagic fluid. The latter phenomena, unfortunately, is not an uncommon occurrence that confounds if not prevents a cytologic diagnosis. Lesions which may be amenable to FNA include soft tissue masses that are solid or composed of variable matrix, such as mixed solid cystic lesions (Table 3.1). FNA may be attempted on purely cystic masses in order to sample the cyst wall. When there is either a breach in the osseous cortex or a bone needle has penetrated into the marrow space of the vertebra or rib, it may be possible to perform FNA using a coaxial approach.

The key to performing a successful FNA procedure is preparation. After lesion analysis, for both matrix and measurement, the operator decides upon an approach that will safely access the lesion and provide the best opportunity for specimen yield. Factors that impact on maximizing specimen yield for sampling potentially neoplastic lesions include choosing a solid, non-necrotic portion of the lesion. This may consist of an area that shows contrast enhancement or avid FDG uptake on a pre-procedure examination. Choose a trajectory that maximizes the possibility of passes and the excursion distance of the biopsy needle inside of the lesion. Literally, try to get into the “meat” of the lesion with your biopsy passes and avoid the ill-defined areas where there may be necrosis, cyst fluid, or a possibility of sampling normal tissue. For infection, however, do sample the fluid-containing areas as these might be abscess collections. Given the increased viscosity of the purulent abscess material, large gauge needles, such as 18 gauge or larger, should be considered for use when aspirating a suspected abscess collection.

When sampling a soft tissue mass with an FNA procedure, the objective is to separate a small cell cluster from the mass by using the cutting properties of the needle and then aspirate this cell cluster into the needle bore (Gupta et al. 2002). The to-and-fro or back-and-forth excursions of the FNA needle within the lesion should be short, quick, and choppy. Slight rotations of the needle within the lesion matrix help to exploit the cutting properties of the needle. Also, mild angulations of the needle as it is moved forward help to separate and break up the tissue planes along the needle trajectory. Consistent aspiration with the syringe, by pulling back on the plunger, is applied when the needle tip is within the lesion matrix. Small syringes, 5–10 mL, can be used with smaller gauge needles, such as 25 and 22 gauge needles. A 20 gauge syringe can be used with larger gauge needles, such as an 18 gauge needle, especially when attempting to aspirate an abscess collection. Some commercially available syringes and FNA systems have a locking mechanism that is activated by twisting the retracted plunger in order to provide continuous suction during the aspiration phase of the biopsy. The main property of the syringe is that it should have a Luer-Lok technology that allows for a good twist-on connection to the needle hub. This will prevent an air leak, which would otherwise foil the aspiration. After the operator completes the aspiration, the syringe plunger can be released in order to cease the aspiration. With a basic syringe and fine needle, this can occur with the needle tip still located within the lesion. The FNA needle is then withdrawn, and the sample is expressed either onto a slide or into a cytologic alcohol medium for subsequent microscopic analysis. In other FNA biopsy systems, the syringe plunger remains withdrawn until the operator is ready to deposit the sample, as pushing the plunger ejects the specimen (Fenton and Czervionke 2003). The presence of a cytotechnologist or pathologist greatly enhances the efficiency of the FNA process as these individuals can confirm whether or not the operator has obtained adequate specimens.

The FNA procedure becomes even safer and more efficient with the use of coaxial technique and CT guidance (Table 3.2). With the use of coaxial technique, a guide needle is advanced to the margin of the lesion. This avoids reentry injury to the skin and subcutaneous tissues and enhances patient comfort during the procedure. Coaxial technique provides a safe conduit to the lesion, subjecting adjacent critical structures to fewer chances of needle injury that might otherwise result from multiple needle passes. Once the guide needle is positioned, a CT image is obtained to confirm the position of the guide needle. The guide needle stylet is removed, and multiple sequential FNA passes can be made through the guide needle. The length of the FNA or insert needle should be greater than the length of the guide needle so as to allow for the appropriate movement or excursion of the insert needle within the lesion. The FNA needle is advanced into the margin of the lesion using CT guidance. The FNA needle stylet is removed, and a syringe is connected to the FNA needle hub. By analyzing the CT image, the operator will know how long to make the needle excursions and in which directions. An aspiration is performed, and the needle is removed and replaced by another needle in order to repeat the process. With each needle exchange, a CT image is studied in order to assess the position of the guide needle and the FNA needle relative to the lesion and the adjacent critical structures. By moving and angling the guide cannula hub slightly, the operator is able to redirect the FNA needle in a slightly different trajectory within the lesion. At least three FNA passes should be performed or more if necessary and possible. If specimen is obtained upon the initial passes and the cytopathologist is confident about the diagnosis, then the procedure can be stopped at the discretion of the operator and the pathologist.

A soft tissue core biopsy can be performed after the FNA passes. These soft tissue cores provide additional specimen that might be helpful in the event that special stains are required for further analysis of the tissue in question. The FNA procedure should be performed first because soft tissue core biopsy tends to cause intralesional hemorrhage, and this blood contaminates the cytologic specimen and compromises the cytologic diagnosis.

Soft tissue core biopsy is very helpful in the evaluation of soft tissue masses (Ray-Coquard et al. 2003). This procedure is frequently performed for the evaluation of spine and rib lesions. Initially, this statement appears to be counterintuitive. Many operators assume that this procedure will have no utility in the sampling of osseous structures but, with experience, realize that there are a plethora of destructive lesions that breach the osseous margins of the spine or rib and, therefore, are amenable to soft tissue sampling techniques (Fig. 3.1). A few different types of core biopsy needles are available for soft tissue biopsy. The majority of these, as evidenced by their bulky design, have been developed for use elsewhere in the body. Nevertheless, there are a few of these core biopsy systems that can be used for spine or rib biopsy (Figs. 3.4 and 3.5). The critical aspect of core soft tissue biopsy is a combination of the furthest distance which the needle tip travels within the lesion and the length of the coring chamber that can be deployed within the lesion matrix. In some needle systems, the needle is placed at the proximal margin of the lesion, and the cutting mechanism is activated such that the needle travels a preset distance within the lesion in order to obtain a sample (Fig. 3.6). In other systems the needle tip is advanced deep enough into the lesion in order to subsequently expose the biopsy chamber within the matrix of the lesion so as to then obtain a soft tissue core sample (Fig. 3.4). Yet in another system, the needle is advanced into the lesion, and the biopsy chamber is temporarily exposed within the lesion and then retracted when the biopsy device is fully loaded; when the device is activated or fired, it sends the core needle back into its original position within the lesion with immediate, near simultaneous deployment of the cutting cannula (Fig. 3.7). The practical aspect of soft tissue core biopsy is to be aware of when these needles can be used during the biopsy process. Key factors that influence this decision are the presence of a large soft tissue mass and absence of osseous matrix along the needle trajectory. These are soft tissue cutting needles, not bone cutting needles, and their use for osseous lesions or in the setting of osseous material requires careful and thoughtful preparation. The use of a soft tissue cutting needle within the bone may result in bending or breakage of the needle tip; the needle may get stuck within the lesion which then will require a very extensive conversation with the patient and may require a surgical procedure to remove the device (Fig. 3.8). Only when there is a breach in the osseous margin of a lesion, or a coaxial channel has been made with a larger gauge bone needle, should the operator consider the possibility of approaching a lytic lesion or a marrow space lesion with a soft tissue core biopsy needle.

Soft tissue core needle biopsy is best performed using coaxial technique with a guide needle and CT guidance (Table 3.3). This will facilitate multiple safe biopsy needle passes and maximize the harvest of biopsy specimen. The use of large diameter biopsy needles (e.g., 14 gauge) is desirable, but this is determined by the lesion size and location relative to critical structures and balanced against the risk of hemorrhage. The larger diameter needles are able to obtain larger soft tissue cores, and this in turn improves the likelihood of obtaining a pathologic diagnosis. The guide needle and the soft tissue cutting needle are usually packaged in the same kit; the working diameter of these needles is therefore preset to facilitate coaxial technique. The guide needle is advanced to the margin of the lesion under CT guidance; the stylet of the guide needle is removed prior to insertion of the biopsy needle. Measurements are then made along the trajectory from the guide needle to the opposite margin of the lesion. This enables the operator to determine the optimal length of the biopsy “throw,” or core length, within the lesion matrix. Most soft tissue core biopsy needles have preset “throw” lengths (penetration or depth settings) that can be selected; the length of the “throw” should be less than the diameter of the lesion along the needle trajectory. Once the biopsy needle sample length is selected and set, then the biopsy needle is “loaded” or armed. The biopsy needle can now be deployed at the operator’s discretion in order to obtain a soft tissue core. Some biopsy needles can be loaded prior to coaxial insertion into the guide cannula, and some may require arming after coaxial insertion. CT guidance is required to monitor coaxial needle insertion. A specific semiautomated biopsy system with a lightweight handle allows the core chamber to be exposed within the substance of the lesion prior to firing or activating the cutting mechanism of the needle. This can be imaged with CT in order to show the exposed core chamber within the lesion and confirm the accuracy and safety of the biopsy needle location. The position and the throw length of other soft tissue core needle biopsy systems should always be confirmed using CT guidance. By activating the firing mechanism of the biopsy needle, a core sample is promptly obtained. The firing mechanism is activated by either pressing or sliding a button on the top or side of the needle handle or pressing on the plunger of the needle handle. The cutting needle is removed from the biopsy needle, and the stylet is placed within the guide needle to secure it and minimize back-bleeding. The soft tissue core is then removed from the core biopsy needle and placed in the appropriate transport medium for subsequent pathologic analysis. This often requires some form of manipulation of the soft tissue core with a small needle or a scalpel in order to dislodge the sample from the biopsy chamber. The biopsy needle can be reused if sterile technique has been maintained, or perhaps a different biopsy needle can be used, with a different diameter depending on the lesion in question. An attempt should be made to obtain four soft tissue cores, if possible, in order to optimize the diagnostic yield (Wu et al. 2008).