Fine-Needle Aspiration Biopsy of the Thyroid Gland

Fine-needle aspiration (FNA) biopsy of the thyroid gland is now an established, accurate diagnostic test that is routinely used as the first step in the evaluation of nodular thyroid disease (1-4). Epidemiologic studies suggest that nodular thyroid disease is a common clinical problem, with a prevalence of 4% to 7% in the adult population in North America and an annual incidence of 0.1%, which translates into approximately 300,000 new nodules in the United States (5). A recent survey of clinical members of the American Thyroid Association revealed that most (96%) of them would perform FNA biopsy for diagnosis of thyroid nodules (6). Therefore, we would estimate that somewhere between 250,000 and 300,000 thyroid FNA biopsies will be performed annually in the United States alone. Worldwide, the number of thyroid aspirations would most likely be in the millions. Thus, the importance of FNA biopsy in thyroid practice cannot be overemphasized.

This chapter reviews biopsy techniques, cytologic diagnosis, complications, FNA results, diagnostic pitfalls, and other information that may be useful to clinicians who manage patients with nodular thyroid disease.

In modern times, diagnosis of thyroid nodules by needle biopsy was first described by Martin and Ellis (7) in 1930, who used an 18-gauge needle aspiration technique. Subsequently, cutting needle biopsy using Silverman or Tru-Cut needles were used for tissue examination. None of these techniques gained wide acceptance because of fear of malignant implants in the needle track, false-negative results, and serious complications. However, Scandinavian investigators introduced small‑needle aspiration biopsy of the thyroid in the 1960s; this became well-accepted but came into wide use in North America only in the 1980s (8,9).

For FNA biopsy, most use "fine" or "thin" needles ranging from 22 to 27 gauge (commonly, 25 gauge). As the name indicates, the biopsy technique uses aspiration to obtain cells or fluid from a thyroid mass. In contrast to percutaneous large‑needle biopsy, which obtains tissue specimens and requires histologic fixation, aspiration biopsy offers cytologic examination of the specimen. Another technique, fine‑needle nonaspiration (FNNA) biopsy, avoids aspiration but still permits cytologic review of thyroid masses.

Although the FNA technique appears simple, considerable time and experience are required to acquire and maintain a skillful biopsy technique. Debate continues about who is best qualified to perform FNA biopsy, but it is clear that the best results are obtained if the person performing the biopsy has mastered the technique. In the opinion of the author, endocrinologists are best qualified to perform FNA biopsy because they are most experienced in thyroid palpation, they acquire and maintain expertise in performing biopsies, and they provide definitive and continued care to patients with nodular thyroid disease.

EQUIPMENT

The basic equipment needed to perform FNA biopsy is simple and relatively inexpensive (5,6,8). The following items are essential (Fig. 1):

Figure 1. FNA biopsy equipment is simple and inexpensive. It includes an alcohol wipe, 4 x 4 gauze pads, 10-mL plastic syringes, 25-gauge 1 1/2-inch stiff noncutting, bevel-edged needles, glass slides, alcohol bottles, and a pistol-grip mechanical syringe holder.

THE PATIENT

The thyroid gland should be palpated carefully and the nodule(s) to be biopsied identified. The procedure should be explained carefully to the patient, and all the patient's questions should be answered completely. We inform our patients that local anesthetic is not used, that the biopsy will take several minutes, that 2 to 4 aspirations are made, and that we expect no significant complications, but there will be slight pain with minor hematoma or swelling at the biopsy site(s).

The biopsy can be performed with the patient on a hospital bed or in the office on an examining table. In either place, a nurse or clinical assistant should always be available to assist with the procedure. The patient may be seated or supine; we prefer the supine position. The patient is placed supine with the neck hyperextended to expose the thyroid; for support, a pillow is placed under the shoulders (Fig. 2 A). The patient is asked not to swallow, talk, or move during the procedure. It is best to talk to the patient and keep him/her informed of the progress of the biopsy. After the biopsy has been completed, firm pressure is maintained on the biopsy site(s). The patient is then asked to sit for a few minutes. Occasionally, patients complain of dizziness or pain. It is best to observe patients for a few minutes, and if no problems are noted, they are allowed to leave. We prefer that a nurse or clinical assistant be present for help during the procedure.

Figure 2. A, Position of patient during FNA. Note: supine position and pillow under patient's shoulder to allow hyperextension of the neck and maximal exposure. B, Syringe is placed in syringe-holder. C, Nodule is identified and stabilized with operator's "nonaspirating" hand. The operator stands on the side of the patient opposite to that of the thyroid nodule. Current OSHA regulations require the use of gloves because of concern about blood-borne diseases. D, With a quick motion, the needle passes through the skin and enters the nodule. Immediate mild suction follows. As soon as aspirate appears, suction is released and the needle is withdrawn.

FNA BIOPSY

Numerous reports, reviews, and even textbooks provide detailed descriptions of various FNA biopsy techniques (10-15). Although most reports agree on the principles of the technique, variations have been described to improve results. It is important to position the patient correctly, to identify and locate the mass, to provide adequate light during the biopsy, and to have a clinical assistant available for help. The physician performing the biopsy should be positioned at the patient's side, preferably contralateral to the lesion. The nodule(s) to be aspirated is identified, and the overlying skin is cleansed with alcohol. The use of betadine or sterile technique is not necessary. A 10‑mL plastic syringe is attached to a Cameco syringe holder and held in the right hand by a right‑handed operator (Fig. 2 B). Two fingers of the free (left) hand firmly grasp the nodule while the other hand holds a pistol-grip syringe holder (Fig. 2 C). The needle is then rapidly inserted through the skin and into the nodule. Once the needle tip is in the nodule, gentle suction is applied while the needle is moved back and forth within the nodule vertically (Fig. 2 D). This maneuver allows the dislodging of cellular material and easy suction into the needle. During this period of 5 to 10 seconds, suction is maintained, and as soon as fluid or aspirate appears in the hub of the needle, the suction is released and the needle is withdrawn. The appearance of fluid suggests that the nodule is cystic; suction is maintained and all the fluid aspirated. It is important to release the syringe plunger and remove the vacuum before withdrawing the needle; this allows the aspirate to remain in the syringe and not be sucked into the syringe. Next, the needle is detached from the syringe (Fig. 3 A), and 5 mL of air is drawn into the syringe (Fig. 3 B). The needle is reattached to the syringe, and with the bevel pointing down, 1 drop of aspirated material is forced onto each of several glass slides (Fig. 3 C). It is important that all slides be labeled and placed in order on a nearby table before the aspiration. Smears are prepared by using a second glass slide in a manner similar to that of making blood smears (Fig. 3 D). The slides for wet-fixation should be placed immediately in 95% alcohol for staining with the Papanicolaou stain. For Giemsa staining, air-dried smears are necessary, and prepared slides are left unfixed and transported to the laboratory.

Figure 3. A, The needle is removed quickly from syringe. B, Five milliliters of air is aspirated into the syringe, and the needle placed back on the syringe. C, With needle bevel pointing down, one drop of aspirated material is expelled onto each of several glass slides. Slides are labeled and placed on the table before aspiration, ready for use. D, With a second slide, smears are prepared in a manner similar to that for blood smears. Slides are then immediately wet-fixed by placing them in alcohol bottle.

Usually, 2 to 4 aspirations are made (10,12,13), although some authors suggest at least 6 punctures should be made (16). Frequently, 8 to 10 slides are made for each nodule. Preferably, the aspirates should be obtained from the peripheral areas and different parts of the nodule, in a sequential manner, to ensure representative sampling (10,12). For larger nodules, the deep center of the mass should be avoided because it is more likely to contain degeneration and fluid, decreasing the chance of a diagnostic specimen. For cystic lesions, the fluid should be completely aspirated and FNA attempted on residual tissue. Aspirated fluid should be placed in a plastic cup and saved for cytologic evaluation. We use a new needle and syringe for each biopsy.

FNNA BIOPSY

Fine-needle nonaspiration (FNNA) technique has been described by several authors (1,12,17). This technique is thought to minimize trauma to thyroid tissue and to reduce blood contamination. For this technique, patient preparation is similar to that for FNA. However, no syringe or suction is necessary. The hub of a 25-gauge needle is held in a pencil-grip fashion, and the needle is gently inserted into the nodule and then moved in and out over 5 to 10 seconds (Fig. 4). Aspirate flows into the needle through capillary action, and as soon as aspirate appears in the hub, the needle is withdrawn and attached to the syringe with air inside. Next, the plunger is used to expel the material onto glass slides. The procedure is repeated several times, and the slides are prepared as described above for FNA.

Figure 4. Fine-needle nonaspiration (FNNA) biopsy showing needle, position, and direction for biopsy. After needle is placed into target tissue, it is moved with short back and forth movements until aspirate appears in hub. The needle is then withdrawn.

After the biopsy has been completed, firm pressure is applied to biopsy site(s) with a 4  4 gauze pad. Once bleeding has stopped, an adhesive bandage (Band-Aid) is placed on the puncture site(s) and the patient is observed for a few minutes and, if there are no problems, allowed to leave (Fig. 5).

COMPLICATIONS

Thyroid FNA biopsy is very safe. No serious complications such as tumor seeding, nerve damage, tissue trauma, or vascular injury have been reported (10-14). Needle puncture may cause slight pain and some skin discoloration at the aspiration site(s). However, even a minor hematoma is not common. The use of anticoagulants or salicylates does not preclude FNA biopsy. Needle tract implantation of thyroid carcinoma is extremely rare; it has been poorly documented and is not considered a real problem by most experts (18). Post‑aspiration hemorrhage within a cystic lesion can occur, and the author has seen one patient who, within several hours after FNA biopsy, developed severe pain from bleeding into the nodule that warranted surgical excision. The specimen contained fresh blood consistent with hemorrhage caused by biopsy. However, this is the only example we have had among more than 15,000 biopsies performed at our institution.

CYTOLOGIC DIAGNOSIS

Aspirates from normal glands often have scant thyroid follicular cells and colloid. Wet‑fixed smears are usually prepared with a modified Papanicolaou stain, which shows nuclear detail. Air-dried smears are often prepared with a Romanovsky stain. May‑Grunwald-Giemsa (MGG) is a modified Romanovsky staining procedure that is sometimes used in thyroid cytologic preparations. The cytologic diagnosis includes four categories: benign (negative), suspicious (indeterminate), malignant (positive), or unsatisfactory (nondiagnostic).

Benign Cytology

Aspirates obtained from multinodular goiters, benign microfollicular adenoma, or normal thyroid are referred to as "colloid nodules" and show loosely cohesive sheaths of follicular epithelium, colloid, blood, and rare macrophages. Colloid nodules contain an abundance of colloid with sparse follicular cells. There is considerable variation in the number of cells as well as the type and amount of colloid present (Fig. 6).

Another benign diagnosis is Hashimoto's thyroiditis; it has a fairly characteristic pattern on FNA smears, showing hypercellularity with lymphocytes, H�rthle cells, and minimal or no colloid (Fig. 7).

Figure 7. Hashimoto's thyroiditis. A, Group of H�rthle cells, with large cytoplasm and prominent nuclei, surrounded by a teratogeneous population of lymphocytes. (Papanicolaou; x60.) B, Hypercellular aspirate with lymphocytes and H�rthle cells. (May-Gr�nwald-Giemsa; x250.)

Subacute (granulomatous) thyroiditis is a rare condition with a benign aspirate. Typically, the smear shows multinucleated giant cells, epithelioid histiocytes, and scattered inflammatory cells (Fig. 8).

Malignant Cytology

Papillary carcinoma, the most common thyroid malignancy, is readily diagnosed by FNA. Typically, cytology shows a papillary configuration, large irregular nuclei, and nuclear grooves. Psammoma bodies may or may not be present, but if present, they are highly suggestive of papillary thyroid carcinoma (Fig. 9).

Figure 9. Papillary thyroid carcinoma. A, Follicular cells with large irregular nuclei, nuclear grooving, and pale chromatin. (Papanicolaou; x400.) B, Histologic preparation showing typical papillary configurations. (Hematoxylin-eosin; x50.)

Medullary thyroid carcinoma accounts for 5% to 10% of thyroid cancers and may present as a thyroid nodule or neck mass. Typically, aspirates from a medullary thyroid carcinoma are hypercellular, composed of large poorly cohesive cells, and are predominantly spindle‑shaped. Amyloid is often, but not invariably, present, and there is no colloid (Fig. 10).

Figure 10. Medullary thyroid carcinoma. A, Cellular specimen staining positively for calcitonin with immunoperoxidase. (x100.) B, Loosely cohesive fragments of spindle-shaped cells; amyloid is present as amorphous blue material intimately associated with neoplastic cells. (Papanicolaou; x400.)

High-grade carcinoma can be diagnosed cytologically but distinguishing between primary and metastatic cancer is not easy.

FNA RESULTS

The accumulated experience of the past 2 decades has confirmed the reliability and usefulness of FNA as a diagnostic test (11-14,16,19-24). The role of FNA biopsy in the evaluation of thyroid nodules is now firmly established, and FNA has become the initial test because it is both safe and cost-effective. In most clinics, FNA has become a standard test, performed most often by an endocrinologist.

Diagnostic Cytology

An adequate specimen of good technical quality is considered diagnostic or satisfactory and may be "benign," "suspicious," or "malignant." A benign cytologic diagnosis is reported for 50% to 90% of the specimens (average, 70%) (10,14,22,25,26). From 10% to 30% of FNA cytologic specimens may be suspicious for malignancy or indeterminate (average, 20%) (25,26). A malignant or positive cytologic diagnosis varies from 1% to 10% (average, 5%). For example, Caruso and Mazzaferri (25) reported the following results from 9 series that included more than 9,000 patients: benign, 74%; malignant, 4%; inadequate and suspicious, each 11%. We reviewed more than 18,000 specimens from seven large series and obtained similar cytologic results: benign, 69%; malignant, 4%; suspicious, 10%; and nondiagnostic, 17% (26).

False-Negative Diagnoses

False-negative results mean missed malignancy. False-negative rates generally vary from 1.5% to 11.5% (average, <5%) (16,19,25,26). The false-negative rate is defined as the percentage of patients with "benign" cytology in whom malignant lesions are later confirmed on thyroidectomy. The frequency of false-negative cytologic diagnosis depends on the number of patients who subsequently have surgery and histologic review. In most retrospective series, less than 10% of patients with a benign cytologic diagnosis subsequently have thyroid surgery, suggesting that false-negative rates should be interpreted with some skepticism (25,26). Despite this note of caution, most authorities agree that the true false-negative rate is less than 5% if all patients have thyroid surgery. False-negative rates are lower in centers experienced with the procedure and with cytologic interpretation by expert cytopathologists.

False-Positive Diagnoses

False-positive rates vary from 0 to 8% (average, 3%) (19,25,26). A false‑positive diagnosis indicates that a patient with "malignant" FNA results was found on histologic examination to have benign lesions.

Causes of False Diagnoses

Interpretive or sampling errors account for false diagnoses (12,13,26,27). Hashimoto's thyroiditis probably is the most common cause of false‑positive cytology. Misclassification of follicular and H�rthle cell adenomas as papillary carcinomas accounts for other errors. FNA biopsy of thyroid lymphomas may produce lymphocytes that can be interpreted as Hashimoto's thyroiditis, accounting for a false‑negative diagnosis. Inadequate or improper sampling accounts for some false-negative errors. For example, nodules smaller than 1 cm in size may be too small for accurate needle placement, and nodules larger than 4 cm in diameter are too large to allow proper sampling from all areas, thereby increasing the likelihood of misdiagnosis. Finally, the cytopathologist should establish and observe criteria to exclude a diagnosis of malignancy (5).

The Problem of Cellular Tumors

Hypercellular specimens from follicular or H�rthle cell lesions may have features suggestive of, but not diagnostic for, malignancy (8,10,12,13,28). Thus, the cytopathologist labels these "suspicious for malignancy" because cytologic features neither confirm nor rule out malignancy. Histologic examination is necessary for definitive diagnosis. Hypercellularity may be seen with non‑neoplastic lesions, and H�rthle cell changes may be seen in patients with lymphocytic thyroiditis. The diagnosis of follicular neoplasm is indicative of an underlying malignancy in 14% of cases and H�rthle cell neoplasm in 15% (20,26). Kini (29) believes that follicular adenomas and follicular carcinomas usually can be differentiated on the basis of nuclear size but H�rthle cell lesions are problematic to diagnose cytologically. Other pathologists maintain that benign and malignant follicular/H�rthle cell tumors cannot be distinguished on the basis of aspirated cells only and the lesion must be removed for histopathologic examination (8,12,13,28).

Several authors have discussed the problem of follicular neoplasm. In a study of 149 patients with the cytologic diagnosis of follicular neoplasm, Tuttle et al. (30) reported that risk of malignancy was higher for males, solitary nodules, and nodules larger than 4 cm. In a study of 219 patients with follicular neoplasm, Schlinkert et al. (31) showed that nodules are more likely malignant in younger patients, in males, if the nodule is solitary, and if it is larger than 4 cm. Recently, Baloch et al. (32) studied 184 cases of follicular neoplasm and reported that risk factors for malignancy included male sex, older age (> 40 years), and larger nodules (> 3 cm). Overall, they found that 70% of these lesions are benign.

Recent studies suggest that immunohistochemical and genetic markers may be useful in improving diagnostic accuracy in this group. Two such markers, HBME-1 and galectin‑3, have shown most promise in reliably distinguishing between benign and malignant follicular neoplasms. In one report (33) all papillary (145/145) and follicular (27/27) cancers showed staining not present in normal thyroid tissue. Galectin-3 is also reported as staining positive for papillary/follicular cancers but not for nodular hyperplasia (34). Further studies are needed to validate these results before their routine clinical application is recommended.

Nondiagnostic Cytology

Inadequate specimens are labeled "nondiagnostic" or "unsatisfactory" and account for 2% to 20% of specimens (average, 15%) (19,25,26). Several factors influence nondiagnostic rates for FNA results, including the skill of the operator, vascularity of the nodule, criteria used to judge adequacy of the specimen, and the cystic component of the nodule (35‑37). Overall, a satisfactory smear contains at least six clusters of well‑preserved cells, with each group consisting of at least 10 to 15 cells. Reaspiration yields satisfactory specimens in at least 50% of cases that are considered nondiagnostic on initial FNA (16,28). Although it has been suggested that more aspirations will increase the diagnostic rates, the optimal number of aspirations is a matter of debate. In general, most reports indicate that two to four aspirates per nodule are adequate (12,13,28).

In a recent report, Chow et al. (38) found a 7% malignancy rate in 153 patients with initial nondiagnostic smears. Among 27 patients treated surgically, 37% had cancer. Reaspiration with ultrasonographic (US) guidance was diagnostic in 66% and 56% without US; overall, 62% of reaspirations were diagnostic.

Diagnostic Accuracy

Analysis of the data reveals that the sensitivity of FNA ranges from 65% to 98% (mean, 83%), and specificity ranges from 72% to 100% (mean, 92%) (19,25). The predictive value of a positive or suspicious cytologic result is approximately 50%. The overall accuracy for cytologic diagnosis approaches 95%.

FNA Guidelines

Guidelines have been published to help improve the adequacy and accuracy of cytology specimens (39). FNA biopsy should be performed by individuals who have had training in both thyroid examination and thyroid biopsy. Thyroid FNA in the hands of experienced operators achieves high diagnostic accuracy. Aspirates should be obtained from different portions of the nodule, preferably peripheral areas, in an organized and sequential manner. It is essential to ensure that an adequate number of follicular cells is present. A cytopathologist, preferably one with experience in thyroid cytology, should review and interpret the slides. If reaspiration yields insufficient material, US-guided FNA (US-FNA) biopsy is the next test. In the event that the final result is still insufficient, surgical excision is warranted for most nodules.

Several authors have offered suggestions to minimize false-negative rates (1,3,10,16). In a recent review of thyroid FNA, Belfiore and La Rosa (40) suggested the following steps to reduce false-negative results:

To minimize false‑negative results, we follow the guidelines summarized in Table 1.

Table 1. Steps That Improve Accuracy of Fine-Needle Aspiration (FNA) and Lead to Better Nodule Management*
Step	Explanation
Endocrinologist performs biopsy	Offers better thyroid examination; accumulates experience with FNA
Experienced cytopathologist reviews slides	Improves cytologic interpretation
Careful with small (< 1 cm) or large (> 4 cm) nodules	Increased chance of misdiagnosis; US-FNA improves accuracy
2-4 aspirates from different nodule sites	Improves cytologic sampling
Rebiopsy if cytology is nondiagnostic	One-half will be diagnostic on reaspiration
Nondiagnostic cytology is not negative	5%-10% of nondiagnostic nodules harbor malignancy
Aspirates with no follicular cells are unsatisfactory	These should not be considered "negative for malignancy"
Excise large (> 4 cm) or recurrent cysts	Higher likelihood of malignancy
Excise nodules yielding "suspicious" cytology	10%-30% chance of malignancy
Excise clinically suspicious, cytologically benign nodules	Consider cytology false-negative until proved otherwise

*Modified from Gharib ⁵. By permission of Mayo Foundation for Medical Education and Research.

ULTRASOUND-GUIDED FNA BIOPSY

High-frequency sonography demonstrates the anatomy of the neck and morphology of the thyroid in exquisite detail (1). Current US equipment is sensitive, portable, adaptable to office use, simplified for use by nonradiologists, and less costly than previous machines. As a result, an increasing number of endocrinologists are now using US in the setting of an office practice. Widespread use of US has resulted in the discovery of unsuspected nodules, often smaller than 1 cm, referred to as "thyroid incidentalomas." Endocrinologists are seeing an increase in referrals for incidentally discovered micronodules (41).

Indications for US use are multiple. US can be used to supplement the physical examination when neck palpation is difficult because the neck is short, full, or fat. US examination may not only detect impalpable small (< 1 cm) nodules, it may also show a 2.0- to 3.0-cm nodule that may be impalpable because of its location or because of the anatomy of the neck. US may also be used to evacuate cystic fluid or to reaspirate a nodule found to be nondiagnostic on initial palpation-guided biopsy. Finally, US should be used for alcohol ablation (41,42).

Several studies have suggested that the diagnostic accuracy of US‑FNA is superior to that of palpation-guided FNA (43-46). A satisfactory biopsy rate for US-FNA ranges from 80% to 95%. By means of US guidance, the biopsy site(s) can be precisely selected and the needle correctly positioned, allowing sampling of the cyst wall or solid component and thereby providing enhanced diagnostic accuracy (43-45). Furthermore, US‑FNA permits complete evacuation of cystic material, resulting in near‑collapse of cystic lesions. Some reports have suggested that with the combined use of FNA and US, thyroid cancers are detected more frequently and at earlier stages.

Percutaneous ethanol injection (PEI) during US guidance was first used for recurrent or persistent hyperparathyroidism, especially in surgically high-risk patients. More recently, alcohol therapy has been applied to thyroid nodules (47-51). Lippi and colleagues (49) reported results of a large multicenter Italian study that included 429 patients: 56% had toxic nodules and 44% had hyperfunctioning but nontoxic nodules. Under US guidance, ethanol was injected into the nodules and 12 months after treatment, 74% of the patients were biochemically euthyroid. Papini and coworkers (48) recently reviewed the role of PEI in the treatment of benign thyroid nodules. They found indications for treatment of patients with toxic hot nodules, nontoxic hot nodules, toxic multinodular goiters, and thyroid cysts. In patients with solitary nodules, nodules that had a volume less than 10 mL were more likely to respond to treatment with complete remission than were nodules with a large volume. PEI is performed on outpatients. The procedure is short, never exceeding 10 minutes, and requires no local or general anesthesia. US-guided PEI is safe and effective in centers with experience. Valcavi and Frasoldati (52) used PEI to treat benign thyroid cysts. Complications included transient dysphonia and pain; no permanent injuries were recorded. Two-thirds of the patients required only one injection to reduce nodule size. Of note, there is often an acute, marked increase in the serum level of thyroglobulin but only a slight increase in the serum level of thyroid hormones. There is no evidence that injected ethanol enters the circulation, because serum levels of ethanol do not increase after PEI.

Zingrillo and colleagues (53) treated large (>10 mL) cold benign thyroid nodules in 41 patients with PEI. Follow-up ranged from 12 to 36 months. Symptoms were significantly reduced. The authors concluded that PEI is a safe and effective treatment of symptomatic large cold benign nodules and should be considered an alternative treatment for high-risk surgical patients or when patients refuse surgical treatment.

In a recent prospective randomized trial, Bennedbaek and colleagues (54) compared the effect of a single PEI treatment with suppressive doses of thyroxine (T₄) in euthyroid patients with a single solid colloid thyroid nodule. The thyroid nodules were small (estimated volume, <10 mL). After 12 months, the median nodule reduction in the PEI group was greater than in the T₄ group, indicating that a single PEI treatment is more effective than thyroxine therapy. Clearly, additional studies with longer follow-up are needed.

FNA PITFALLS

The experience as well as the expertise of the cytopathologist is critical in avoiding pitfalls. Determining the adequacy of an aspirate, cellular atypia, application and interpretation of immunostains, and differentiation of lymphocytic thyroiditis from lymphoma are but a few of these problems. Larger nodules are more likely to yield false‑negative results. To improve sampling, aspirates should be obtained from multiple sites of the nodule rather than repeatedly from one spot. The absence of malignant cells in an otherwise acellular specimen does not exclude malignancy. It is good practice to biopsy all accessible nodules in a multinodular gland.

Indications for rebiopsy include an enlarging nodule, recurrent cyst after aspiration, initial nondiagnostic FNA, and persistent nodule after suppressive T₄ therapy. In general, routine rebiopsy of cytologically benign nodules is not suggested. However, for those who begin FNA biopsy in their practice, rebiopsy in 6 to 12 minutes is helpful to provide data on biopsy results, to minimize false-negative rates, and to improve quality of care. In a recent report, Chehade et al. (55) showed that repeated biopsy can decrease the rate of false-negative FNA to < 1.3%. Thus, reaspiration biopsy may be a safeguard against a high rate of missed cancer (false-negative), which is a recognized limitation of FNA.