Fine-needle aspiration (FNA) with sonographic guidance is a widely accepted technique for the confirmation of suspected malignant masses and characterization of many benign lesions in various locations. Even with a palpable, discrete lesion, ultrasound allows controlled sampling of different regions within the lesion. For this type of biopsy, a “fine” or “thin” needle, most often 20G to 27G, is utilized and attached to a syringe (Fig. 26-1). These needles allow for multiple passes and are considered low risk because of the needle’s relative thickness. As the name indicates, this technique uses aspiration to sample cells or fluid from a mass and is optimal for lesions lying superficially or at a moderate depth.² Specimens may also be obtained using a capillary action technique involving an up-and-down motion of the needle within the mass. This technique reduces trauma to the cells, which in turn decreases the amount of background blood on cytologic evaluation. FNA is a reliable and safe method of obtaining tissue samples, allowing cellular evaluation for cytologic examination. FNA success is measured in terms of aspirating enough cells and maintaining patient comfort. The overall accuracy increases when a cytopathologist evaluates the specimens during the procedure to determine if additional tissue aspiration is required for diagnosis.⁷ With FNA, the cells are disorganized and no longer maintain the spatial arrangement they originally had in the lesion. In order to preserve the spatial arrangement of the cells, a core biopsy sample must be taken.⁸ FNA is performed predominately on thyroid nodules, parathyroids, and lymph nodes. It is important to make sure that the appropriate transducer is selected. The transducer should offer the highest frequency while maintaining visualization of the area to be sampled.

A core needle biopsy is a procedure that involves removing small samples of tissue using an automated hollow core needle commonly referred to as a “biopsy gun” (Fig. 26-2). The biopsy gun makes a loud noise when activated. It is important to make the patient aware of the noise to minimize patient alarm and patient motion during the procedure. As the name implies, the core biopsy needle facilitates the removal of a core sample of tissue and is a larger gauge than the needle used for FNA. Core biopsy needles are most often 14G to 19G, offer various throw lengths, and have a tissue-cutting tip. The device is cocked and then inserted within the mass. A button is then pushed lunging the needle forward, which takes and stores a sample within a slot on the inner needle. In a core biopsy, the larger needle allows for a “core” tissue sample for analysis. The larger sample can be recut into smaller samples, which can be used for further analysis, offering a more definitive histologic evaluation.⁹ The larger sample can aid in the diagnosis of parenchymal disease, involving the breast, kidney, liver, prostate gland, and transplanted organs.

Each biopsy technique has its advantages and disadvantages, as does each needle type. There are a wide variety of needles commercially available, which vary in gauge, length, and tip configuration. An important consideration when choosing the appropriate needle is the amount of tissue required for accurate pathologic diagnosis.¹⁰ The bore size of the needle is inversely related to its gauge. For example, a 16G needle will offer a larger specimen than a 27G needle. The choice of needle should be made with respect to the area being sampled and the risks that may be increased due to complications associated with larger bore needle.

Although real-time visualization of the needle is one of the greatest strengths of sonography, it is often the most technically challenging. The sonographic appearance of a needle is either a hyperechoic line or dot depending on which imaging plane is used (Figs. 26-2 and 26-3). Larger-caliber needles with a larger reflectivity surface are more readily visualized than the smaller-gauge needles. If the needle is not visualized at first because of misalignment, usually, maneuvering the transducer should allow for visualization. The needle and transducer should be in the same plane to produce the best visualization. The ability to see the needle tip will improve the more perpendicular the needle is to the transducer. Needles that are made specifically for sonography-guided procedures are commercially available and are designed to aid in visualization, although any needle used for biopsy should be able to be visualized sonographically if aligned correctly. Experience results in improving both needle alignment and needle visualization.