Diagnosis of thyroid nodules by needle biopsy was first described by Martin and Ellis in 1930; they used an 18-gauge-needle aspiration technique. Scandinavian investigators introduced “small-needle” aspiration biopsy of the thyroid in the 1960s, and this technique came into widespread use in North America in the 1980s [1, 2].

The diagnostic accuracy of US-guided FNAB (Fig. 24.1) vs. “free-hand” FNAB is 88% resp. 76% [3].

Efficacy of Fine-Needle Aspiration Biopsy (FNAB) and its role in the management of a nodular goiter was clearly established. Accuracy of cytologic diagnosis approached 95%.

FNAB is a reasonable approach for thyroid nodules; its costs have decreased substantially because it facilitates selection of patients needing to undergo surgical excision.

Selecting patients for operation on the basis of results of FNAB has more than doubled the yield of carcinoma.

Limitations of cytologic examination, nondiagnostic results, and cellular follicular neoplasms should be remembered but need not negate continued use of FNAB.

Negative (benign) and positive (malignant) cytologic results are conclusive; careful clinical follow-up of benign nodules and surgical excision of malignant nodules are recommended.

Nondiagnostic results are inconclusive; further evaluation by repeated FNAB, ultrasound-guided biopsy, or radionuclide scanning is necessary.

Suspicious cytologic results are also inconclusive and are associated with a 20% chance of malignant involvement; surgical treatment is necessary for clarification.

FNAB is a safe, inexpensive, minimally invasive, highly accurate, and cost-effective means in the diagnosis of nodular thyroid disease.

The procedure has a central role in the management of thyroid nodules and should be used as the initial diagnostic test.

The introduction of FNAB had a substantial effect on the management of patients with thyroid nodules. The percentage of patients undergoing thyroidectomy decreased by 25%, and the yield of carcinoma in patients who undergo surgery increased from 15% to at least 30%. FNAB decreased the cost of care by 25% [5].

Four cytologic diagnostic categories are used. Prevalence of these categories: benign, 69%; suspicious, 10%; malignant, 4%; and nondiagnostic, 17%.

Analysis of FNAB data suggests false-negative rate of 1–11%, false-positive rate of 1–8%, sensitivity of 65–98%, and specificity of 72–100%.

Limitations of FNAB are related to the skills of the aspirator, the expertise of the cytologist, and the difficulty in distinguishing some benign cellular adenomas from their malignant counterparts.

Thyroid FNAB is the most accurate test to determine malignancy, and is an integral part of current thyroid nodule evaluation. Results are superior when US-guided FNAB is performed.

FNAB results are classified as diagnostic (satisfactory) or nondiagnostic (unsatisfactory). Unsatisfactory smears (5–10%) result from hypocellular specimens usually caused by cystic fluid, bloody smears, or suboptimal preparation.

Diagnostic smears are conventionally subclassified into benign, indeterminate, or malignant categories:

The new Bethesda Cytologic Classification has a six-category classification, further subdividing indeterminate by risk factors. Overall, the indeterminate category has anywhere from 15% up to 60% risk of malignancy.

Recent development of molecular markers should help to further separate benign from malignant nodules with an indeterminate cytology.

Caution! Benign lesions on FNAB have an approximate 3% risk of malignancy, and may be followed with US. Repeating FNAB decreases the risk of a false negative result to 1.3% [7].

Typical malignant nodule: solid (14.3%), hypoechoic (15.2%), with punctuate calcifications (23.3%), solitary (14%).

Prevalence of thyroid cancer was similar between the patients with solitary nodule (14.8%) and the patients with multiple nodules (4.9%).

Solitary nodules represent twice the risk of malignancy when compared to nonsolitary nodules and more than 1.5 times higher in a man than in a woman.

In patients with multiple nodules ≥10 mm, cancer was multifocal in 46%, and 72% of cancers occurred in the largest nodule.

Risk ranges from a 48% likelihood of malignancy in a solitary solid nodule with punctate calcifications in a man to less than 3% in a noncalcified predominantly cystic nodule in a woman.

In patients with one or more thyroid nodules ≥10 mm, likelihood of thyroid cancer per a patient is independent of number of nodules, whereas likelihood per nodule decreases with increasing number of nodules.

In patients with two or more nodules, aspiration of only the largest nodule would have missed almost one-third of the malignancies. For exclusion of cancer in a thyroid with multiple nodules ≥10 mm, up to four nodules should be considered for FNAB. Sonographic characteristics can be used to prioritize nodules for FNAB based on their individual risk of cancer.

Features with the highest specificity (median > 90%) for thyroid cancer are microcalcifications, irregular margins, and taller-than-wide shape.

Diagnostic FNAB of a nodule <10 mm should be performed only in suspicious cases or in patients with personal history of radiation exposure or familial thyroid cancer.

US patterns and FNAB guidance for thyroid nodules: see Table 24.1.