How are the results fine-needle aspiration biopsy (FNAB) used in the diagnosis and treatment of thyroid cancer?

Updated: May 14, 2020
  • Author: Pramod K Sharma, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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The 4 results from FNAB are benign disease, malignant disease, indeterminate for diagnosis, and nondiagnostic. In their review of several large series, Gharib and Goellner (1993) found that 69% of FNAB results were benign, 4% were malignant, 10% were indeterminate, and 17% were nondiagnostic. [10] Their false-positive rate was 2.9%, and their false-negative rate was 5.2%. Sensitivity and specificity were 83% and 92%, respectively.

Results of FNAB determine the next step in managing the thyroid nodule. A definitive diagnosis is obtained in as many as 50% of repeated biopsies. Patients whose findings are nondiagnostic despite repeat biopsy can undergo surgery for lobectomy for tissue diagnosis, or they can be monitored clinically. In these circumstances, radioiodine scans can be useful for determining the functional status of the nodule, as most hyperfunctioning nodules are benign.

Indeterminate biopsy findings are labeled suspicious at some institutions. When cellular material is adequate for evaluation but when malignant and benign disease cannot be differentiated, biopsy results can be labeled suspicious. Patients with a suspicious diagnosis should undergo lobectomy for definitive diagnosis.

Malignant diagnoses require surgical intervention. Papillary thyroid carcinoma and MTC are often positively identified on the basis of FNAB results alone. In patients with these carcinomas, definitive surgical planning can be undertaken at the outset. However, it is nearly impossible to distinguish a follicular adenoma from a follicular carcinoma on the basis of FNAB findings. Patients with follicular neoplasm, as determined with FNAB results, should undergo surgery for thyroid lobectomy for tissue diagnosis. These patients require complete thyroidectomy if a malignancy is discovered on review of the pathology. Some controversy exists regarding the extent of thyroidectomy (total thyroidectomy, subtotal thyroidectomy, or lobectomy) for a particular pathologic diagnosis. Each pathologic diagnosis and its corresponding extent of thyroidectomy are discussed below.

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