Fine-Needle Aspiration Biopsy of the Thyroid Gland

Abstract

Thyroid nodules are common and usually benign, the risk of malignancy varying from 5 to 10%. Steps to diagnose malignancy should include a careful clinical evaluation, laboratory tests, a thyroid US exam and a fine-needle aspiration (FNA) biopsy. Thyroid FNA biopsy is the most accurate test for determining malignancy, and is an integral part of current thyroid nodule evaluation. Results are superior when FNA is performed with ultrasound-guidance (USFNA). We describe herein techniques for palpation-directed FNA as well as US-directed FNA.FNA 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. Benign cytology (60-70%) is negative for malignancy, and includes cysts, colloid nodule, or Hashimoto thyroiditis. Malignant cytology (5%) is almost always positive for malignancy, and includes primary thyroid tumors or nonthyroid metastatic cancers. Papillary thyroid carcinoma (PTC) is the most common malignancy, characterized by increased cellularity, sheets of cells, and typical nuclear abnormalities.Indeterminate or suspicious specimens (10-20%) include atypical changes, Hurthle cells or follicular neoplasms, typically with absent or scanty colloid, hypercellularity sometimes with microfollicular arrangement. The new Bethesda Cytologic Classification has a 6-category classification, subdividing indeterminate further by risk factors. Overall, the indeterminate category has anywhere from 15% to 60% risk of malignancy, depending on the specifics of the report. Recent development of molecular markers are hoped to help further separate benign from malignant nodules with an indeterminate cytology. These tests are new and evolving, and no definite recommendations for use can be offered currently.This chapter also includes recommendations to minimize false-negative FNA results; indications for rebiopsy; use of TSH, TPOAb, & calcitonin; and the application of radioiodine in diagnosis and treatment of goiters.