Thyroid gland
General
Cytology / Fine needle aspiration

Author: Shahidul Islam, M.D., Ph.D. (see Authors page)

Revised: 12 January 2017, last major update March 2009

Copyright: (c) 2003-2017, PathologyOutlines.com, Inc.

PubMed Search: fine needle aspiration cytology thyroid

See also cytology section of specific diagnoses

Cite this page: Cytology / Fine needle aspiration. PathologyOutlines.com website. http://pathologyoutlines.com/topic/thyroidcytology.html. Accessed June 27th, 2017.
Definition / general
  • FNA is initial step in management of thyroid nodules, to distinguish benign from neoplastic and to diagnose papillary carcinoma (Cancer 2007;111:306)
  • FNA should be considered a screening test, not a diagnostic test
  • Main contraindication is bleeding diathesis, as formation of large hematoma at biopsy site may compress trachea
  • Sensitivity and specificity of FNA are > 90% if specimen adequate, although high false-negative rate exists for detecting thyroid malignancy in males (Am J Surg 2008;195:396)
  • Scrapes have equal value to frozen sections in intraoperative management
  • Thin Prep may be superior to pap stain for epithelial lesions (Cytojournal 2008;5:3)
  • Ultrafast Pap staining detects Orphan Annie-eyed clear nuclei of papillary thyroid carcinoma
Recommendations
Technique
  • Use 25 gauge needle, approach medial to lateral (see "Technique" in "Diagrams / Tables" section below), make short rapid strokes with only slight changes in direction (CMAJ 2002;167:491)
  • Technique without aspiration may be superior (Cancer 1987;59:1201)
  • Large needle biopsies obtain more tissue and may cause fewer inadequate specimens (Histopathology 2007;51:249)
Terminology
Diagrams / tables

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Technique

Short rapid strokes
with only slight
changes in direction

Limitations
  • Cannot differentiate follicular or Hürthle cell adenomas from carcinoma, which requires surgical excision to detect capsular or vascular invasion
  • Cannot diagnose follicular variant of papillary carcinoma, although cases with features suspicious for papillary carcinoma have higher malignancy rate (72%) than those diagnosed as follicular neoplasm (22%, Cytojournal 2006;3:9)
Adequate specimens
  • 5 groups of 10 cells each of well preserved follicular epithelium on each of 2 slides
Inadequate specimens
False positives
  • 10%
  • Diagnosis of malignancy often based on only 1 or 2 atypical cytologic features
False negatives
  • 25%
  • Marginally adequate specimens; for papillary thyroid carcinoma, may be due to nodule heterogeneity (Cancer 2008;114:27)
Lymph nodes
  • Measurement of thyroglobulin in FNA from lymph nodes in patients with history of papillary thyroid carcinoma is useful in detecting recurrent disease, especially if specimen is or likely will be inadequate for evaluation (Cytojournal 2008;5:1)