Fine needle aspiration biopsy (FNA) is the key step in selecting most patients with thyroid nodules for or against surgery. Accurate acquisition of cytologic samples from suspicious lesions is achieved by adding ultrasound guidance to optimize targeting as well as to enable sampling from nonpalpable lesions. This article discusses the indications, variations, and technical details of ultrasound-guided FNA.
Key points
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Although palpation-guided fine-needle aspiration (FNA) continues to be a successful approach to the evaluation of palpable lesions, ultrasound-guided FNA (USGFNA) enhances precision, documentation, and diagnostic yield in nonpalpable, and even in palpable, masses.
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Both long-axis (parallel) and short-axis (perpendicular) approaches to performing USGFNA should be available, because certain lesions and conditions lend themselves better to one approach than the other.
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A consistent, step-by-step approach to performing USGFNA and collaboration with one’s cytopathology colleagues will lead to the greatest diagnostic success in the management of thyroid pathology.
Introduction
Fine-needle aspiration (FNA) biopsy is an indispensable component of the evaluation and management of thyroid pathology. Since its widespread adoption in the 1980s, it has come to be recognized as the gold standard for evaluation of a thyroid nodule. Traditionally, FNA has been used to obtain cells for cytologic diagnosis, supplemented by immunocytochemistry. More recently, as noted in later articles in this issue, FNA has been used to obtain material for genetic and molecular testing. FNA also is useful for obtaining tissue samples for chemical testing, and the same techniques used for diagnostic FNA can be applied to needle placement for a variety of therapeutic procedures. The application of ultrasound (US) technology to FNA is useful for biopsy of nonpalpable and even palpable nodules, and enhances precision, feedback, and documentation to the FNA and other needle-placement procedures.
Introduction
Fine-needle aspiration (FNA) biopsy is an indispensable component of the evaluation and management of thyroid pathology. Since its widespread adoption in the 1980s, it has come to be recognized as the gold standard for evaluation of a thyroid nodule. Traditionally, FNA has been used to obtain cells for cytologic diagnosis, supplemented by immunocytochemistry. More recently, as noted in later articles in this issue, FNA has been used to obtain material for genetic and molecular testing. FNA also is useful for obtaining tissue samples for chemical testing, and the same techniques used for diagnostic FNA can be applied to needle placement for a variety of therapeutic procedures. The application of ultrasound (US) technology to FNA is useful for biopsy of nonpalpable and even palpable nodules, and enhances precision, feedback, and documentation to the FNA and other needle-placement procedures.
Ultrasound-guided FNA
FNA biopsy is a critical step in the evaluation of thyroid and related neck masses. Although the acronym FNA has persisted and implies a component of aspiration, the procedure is more accurately described as FNB, or fine-needle biopsy, as aspiration is not a requirement. Traditionally, FNA is performed by method of manual palpation. The size threshold for palpating thyroid nodules is 1.5 to 2.0 cm, and up to 30% of FNA biopsies without ultrasound guidance can be nondiagnostic. The introduction of US guidance to thyroid FNA has reduced the number of inadequate samples by half, from 8.7% to 16.0% down to 3.5% to 7.0%. US in conjunction with US-guided FNA (USGFNA) also has been shown to assist in identification of suspicious nodules that should be sampled. Not uncommonly, the most suspicious nodule on US for malignancy is not the largest nodule, and if only dominant (by size) or palpable nodules were aspirated, malignancy could easily be missed. In one series, patients given benign diagnoses based on palpation-guided FNA were reevaluated with USGFNA, resulting in 14% reclassification to diagnoses of malignancies. The accuracy, sensitivity, and specificity of USGFNA, reported at 80%, 83%, and 77%, respectively, is improved compared with palpation-guided FNA.
After FNA is performed, specimens are reviewed by a cytopathologist. On-site evaluation by a team composed of clinical physicians and pathologists has been shown to provide the most accurate results, while at the same time reducing patient discomfort. Reduction of patient discomfort is achieved by leveraging US guidance to limit the number of needle passes required and improve sampling adequacy rate, as well as provide immediate examination of the material obtained so as not to require multiple separate sampling procedures. In this instance, a desktop or portable microscope must be available for slide review ( Fig. 1 ). In part because of these advantages, immediate on-site pathologic evaluation has been strongly advocated by some as the standard of care. However, a study by Bhatki and colleagues demonstrated that on-site cytologic specimen evaluation was not necessary to confirm cytologic adequacy; that a combination of experienced USGFNA and 3 to 4 needle passes produce comparable results while conserving costs and resources. Also, for practical and cost-effective purposes, FNA without US guidance still may be appropriate or preferable for palpable thyroid masses.
Thyroid FNA biopsy
A detailed description of cytologic findings in benign and malignant thyroid disease can be found in an earlier article. However, certain preliminary findings can suggest specimen adequacy as well as a diagnosis. Benign thyroid nodules often yield grossly visible watery or viscous colloid material in addition to microscopic clusters of follicular cells in a monolayer or “honeycombed” pattern, and round to oval nuclei with uniform chromatin and foamy (degenerating) cells. In addition to the cytologic features of subacute thyroiditis (de Quervain thyroiditis) that include scant colloid, giant cells, mixed inflammatory background (depending on early vs late stage), a very painful FNA procedure may be an additional clue to this diagnosis.
Follicular patterned lesions are a cytopathological dilemma, as they cannot distinguish between benign and malignant nonpapillary follicular and Hurthle cell lesions. Surgical excision and histopathological analysis for vascular or capsular invasion have traditionally been necessary in these cases to give a definitive diagnosis. In our experience, FNA of follicular neoplasms tends to be bloodier than FNA of other thyroid lesions.
Technical aspects of USGFNA
FNA techniques vary between individuals and institutions, yet there are several common components that are universal. In this section, we aim to evaluate modifications, including US guidance, that can improve the diagnostic success of FNA. A step-by-step guide is presented in Box 1 . US guidance allows the practitioner to visualize the tip of the needle as it passes through tissue, ensuring that the cells examined are indeed from the intended area. Orienting the bevel of the needle toward the US transducer improves visualization of the needle tip. Even within a target lesion, there are areas that may give a higher diagnostic yield when biopsied, such as the solid component of a mixed solid-cystic nodule. An area of initial hemorrhage from a first pass on USGFNA also can be avoided on subsequent passes.
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Diagnostic ultrasound complete
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Target lesion reconfirmed, may mark needle entry site with surgical marking pen
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Informed consent obtained, perform Time Out.
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Local anesthesia administered
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“Prep and drape”
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Room lighting off (except small backlight)
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USGFNA:
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Transducer in nondominant hand, needle in dominant hand
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Insert needle into lesion under ultrasound visualization
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Traverse diameter of lesion multiple, times until flash in hub of needle
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Withdraw needle and apply direct pressure with gauze (transfer pressure-holding to patient)
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Hit “Freeze” on ultrasound system
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Eject specimen onto slide and smear (or pass to cytopathologist/tech)
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Rinse needle for immunohistochemistry/chemistry/flow cytometry
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Annotate and save video for documentation
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Repeat with new needles as necessary for additional passes
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Apply bandage to skin
Informed consent should be obtained before the procedure. The most significant possible complication is the development of a neck hematoma, but this complication is exceptionally rare. The patient should be questioned for a history of anticoagulant therapy, such as warfarin or aspirin, although it is rarely necessary to discontinue such medication before the biopsy. In general, only if there has been a previous unsuccessful USGFNA while the patient was taking anticoagulation therapy should USGFNA be repeated with an adequate interval of discontinuation of anticoagulation therapy.
When possible, the patient is placed in the supine position with the neck slightly extended. The head can be turned to improve visualization and access to the target lesion. Both patient and operator should be comfortable during the procedure. Depending on the location of the lesion, the operator may stand or sit at the patient’s side or at the head. Although diagnostic US uses conventional transverse and sagittal planes for imaging, once a lesion has been visualized and targeted for FNA, the transducer can be oriented in any position that will better facilitate the procedure. For instance, to approach a lesion in the left lobe of the thyroid, a right-handed operator may prefer to stand at the patient’s head to approach the lesion from the trachea side as opposed to the carotid side, thus performing the procedure “upside-down.” Many US devices have special features to assist practitioners in USGFNA. Some have attachable needle guides, but these tend to be discouraged by experienced clinicians, as they are an added expense and they limit flexibility in biopsy direction.
The issue of sterility during US-guided office-based procedures can be regarded as similar to the sterility recommended for phlebotomy. Preparations range from a simple hand-washing and no transducer cover to an iodine-based skin disinfectant, use of sterile aqueous jelly, and a sterile transducer cover. A reasonable compromise involves the use of an alcohol-based skin disinfectant and nonsterile aqueous gel applied to the footprint of the transducer before and after its coverage with a plastic wrap or disposable glove secured with a rubber band ( Fig. 2 ). These inexpensive techniques have been used extensively by the senior author (LAO) and infectious complications have not been encountered.
