Bethesda Classification of Thyroid Nodule Fine Needle Aspirations
I. Nondiagnostic or Unsatisfactory
In these biopsies not enough thyroid cells were obtained to render a diagnosis. This can happen when a cyst is aspirated or when the specimen is almost entirely composed of blood. This accounts for 10 percent of the biopsies, even in the most experienced hands. Generally a repeat biopsy is needed several weeks after the first one.
In this category, the specimen was adequate and the cytopathologist can definitively call the nodule benign. Diagnoses that fall into this category include benign follicular nodules (includes adenomatoid nodules, and colloid nodules), lymphocytic (Hashimoto) thyroiditis, and granulomatous (subacute) thyroiditis. These diagnoses typically do not require surgical intervention. The risk of cancer in this category is 0 to 3%.
III. Atypia of Undetermined Significance or Follicular Lesion of Undetermined Significance
Biopsies in this category are adequate specimens, but the features seen on cytology are not diagnostic of either a benign process or of a tumor. The general recommendation is to repeat the fine needle aspiration biopsy in 6 weeks. The risk of malignancy in this category is in the range of 5 to 15%.
IV. Follicular Neoplasm or Suspicious for a Follicular Neoplasm
Nodules in this category are tumors. Most of these will turn out to be follicular adenomas which are benign. However, needle biopsy cannot distinguish between benign and malignant follicular tumors. For this reason, nodules in this category typically require surgical removal to make a definitive diagnosis. This usually means that half of the thyroid will be removed. The risk of malignancy is 15 to 30%.
V. Suspicious for Malignancy
Nodules in this category are very suspicious for malignancy, but the cytopathologist does not see all of the required features to make a definitive diagnosis. Because of the high risk of malignancy, the general recommendation is to remove the entire thyroid. The risk of malignancy is 60 to 75%.
In this category, the cytopathologist sees all of the features necessary to make the diagnosis of malignancy. Patient with nodules in this category should undergo removal of the entire thyroid. The risk of malignancy is 97 to 99%.