The American Thyroid Association recommends using the Bethesda system for reporting the findings of an FNA biopsy. There are six different categories:
Nondiagnostic: This indicates an insufficient sample from the FNA procedure and repeat FNA is indicated.
Benign nodules: This indicates that the pathologist saw normal thyroid cells and nothing unusual or atypical was seen in the sampling.
Categories 3 and 4
Atypical or suspicious indeterminant: This category means that abnormal cells were seen but the characteristics seen were not distinct enough to determine whether the lesion was benign or cancerous.
Suspicious for cancer: The pathologist saw very unusual cells matching many of the criteria for thyroid cancer but is not saying with 100% certainty that the thyroid has cancer. This category is highly dependent upon the pathologist reading the cytology. Many pathologists will use this category even if they are completely convinced of the presence of thyroid cancer.
Malignant thyroid cancer is present in the cells and the cytology reading is clear that this is the case.