Fine-needle aspiration cytology (FNAC) is the next step in diagnosing thyroid cancer. It’s an outpatient procedure, which means you won’t have to spend the night in hospital.

A small needle is inserted into the lump in your neck to allow a tiny sample of cells to be removed. The sample is then studied under a microscope.

This test can usually reveal whether cancerous cells are present in your thyroid gland and, if they are, what type of thyroid cancer you have.

The FNAC is reported according to the Bethesda system of reporting for Thyroid Cytopathology which has grades 1 to 6.

I. Nondiagnostic or Unsatisfactory
Cyst fluid only
Virtually acellular specimen
Other (obscuring blood, clotting artifact, etc.)

II. Benign
Benign follicular nodule (includes adenomatoid nodule, colloid nodule, etc.)
Consistent with lymphocytic (Hashimoto) thyroiditis in the proper clinical context

III. Atypia of Undetermined Significance or Follicular Lesion of Undetermined Significance

IV. Follicular Neoplasm or Suspicious for a Follicular Neoplasm or Hurthle cell Neoplasm

V. Suspicious for Malignancy (Cancer)
Suspicious for papillary carcinoma, medullary carcinoma

VI. Malignant (Cancer)
Papillary thyroid carcinoma, Poorly differentiated carcinoma, Medullary thyroid carcinoma, Undifferentiated (anaplastic) carcinoma

However, FNAC report is not always correct and in 20-30 percent of patients, it can be incorrect. Many times, FNAC report had been non cancer, but it turns out to be cancer after operation in final reports. Hence, interpretation of FNAC must be done by Thyroid experts only after correlating with symptoms, features in patient, USG/ CT scan/ Nuclear scan reports and any other relevant tests.