Figure 2-3. Fine-needle aspiration biopsy of a papillary thyroid carcinoma showing A, an example of papillary fronds with fibrovas-cular cores as seen on Papanicolaou-stained material (x20 original magnification); B, a nuclear inclusion in the center of the field (arrow) (Papanicolaou stain; x40 original magnification).
Figure 2-5. Photomicrograph showing a section through the capsule of a follicular carcinoma. A tongue of tumor is seen projecting into the capsule as well as into the lumen of a vessel (hematoxylin and eosin stain; x20 original magnification).
are rare. FNAB is less reliable in patients who have been exposed to ionizing radiation or in patients with a family history of thyroid cancer because there is an increased frequency of both benign and malignant thyroid neoplasms in these patients.
Radionuclide thyroid scan may be used to determine the functional status of a nodule that has been interpreted as follicular neoplasm by FNAB, particularly in subjects who are reluctant to undergo surgery. Overall, only about 5% of all thyroid nodules are "hot" by radionuclide scanning; however, the incidence is somewhat higher among patients with follicular neoplasms. As "hot" nodules are rarely malignant, these patients, if euthyroid, can therefore be followed up medically rather than be treated surgically (Figure 2-7).
neoplasm, lobectomy is usually indicated to exclude malignancy, which may be found in 15 to 22% of such nodules. A repeat FNAB is necessary if there is insufficient material for diagnosis, and the use of thyroid ultrasonography may improve the yield in biopsy of deep-seated or mixed cystic nodules.11
When performed by an experienced operator and interpreted by a competent cytopathologist, the sensitivity of thyroid FNAB is 95 to 98% and the specificity is 97 to 99%.9 False-negative results, usually from sampling or interpretive errors, and false-positive results
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