Thyroid Cytology

After review of the microscopic slides, thyroid nodules can be classified into one of six different categories according to the Bethesda Classification:

  • A benign (noncancerous) result is found in 60-70% of biopsies.
  • A definite cancer is found in about 5% of biopsies.
  • Ten percent of nodules may be suspicious for cancer. The final risk of cancer in the group is approximately 75%, but 25% of these nodules will prove to be benign. Thyroid removal is necessary to make a definitive diagnosis.
  • About 20% of nodules are classified as suspicious for a follicular neoplasm. These neoplasms can be benign (75%) or they can be malignant in approximately 25% of cases. These nodules may be reevaluated with a second fine-needle aspiration (FNA) biopsy for molecular testing or may need to be removed by surgery to make a definitive diagnosis.
  • Atypical cells of undetermined significance or follicular cells of undetermined significance is the result in 10-15% of cases. This category is associated with a 5-30% risk of cancer. As with follicular neoplasms, these nodules may be reevaluated by molecular testing, repeat FNA biopsy in 3-4 months, or surgical removal for definitive diagnosis.
  • Inadequate biopsies, from which no diagnosis can be made, are rare. These nodules need repeat biopsy.
Microscope slide -- FNA biopsy of a benign thyroid nodule

FNA (fine needle aspiration) biopsy of a benign thyroid nodule. Slide courtesy of Dr. Carrie Marshall, University of Colorado School of Medicine, Dept. of Pathology.

 

Microscope slide -- FNA biopsy showing evidence of papillary thyroid cancer

FNA (fine needle aspiration) biopsy showing cytology consistent with Papillary Thyroid Cancer. Slide courtesy of Dr. Carrie Marshall, University of Colorado School of Medicine, Dept. of Pathology.


This information is provided by the Department of Surgery at the University of Colorado School of Medicine. It is not intended to replace the medical advice of your doctor or healthcare provider. Please consult your healthcare provider for advice about a specific medical condition.