Thyroid nodule: Fine needle aspiration biopsy (FNA)
Fine needle aspiration biopsy (FNA)
Figure 3: FNA of thyroid nodule
FNAFNA - fine needle aspiration biopsy biopsy is the most accurate test for evaluating thyroid nodules. The biopsy may be performed under ultrasound guidance. A very thin needle is guided into the thyroid nodule and a small sampling of cells is aspirated or sucked into the needle. These cells are then examined under a microscope by a cytologist. An experienced thyroid cytologist is important to increase the accuracy of diagnosis.
A FNA biopsy may give one of four results:
A non-diagnostic biopsy means that there were not enough cells for the cytopathologist to make a diagnosis. Typically, a repeat biopsy will be necessary. However, in some cases where there is a high suspicion of cancer or if the patient has already had two non-diagnostic FNA biopsies, an operation may be recommended (See Thyroid Surgery).
A benign pathology result means that there is no evidence of cancer. The accuracy of a benign biopsy is usually 95 to 97%.Most patients with a benign result will not need surgery, unless the nodule is large and causing compressive problems in the neck.
A diagnosis of cancer on biopsy is about 95 to 98% accurate. Typically, when the biopsy demonstrates a cancer, it is either a papillary thyroid cancer (most common) or a medullary thyroid cancer. (See Thyroid Cancer) Most thyroid cancers will be treated with a total or near-total thyroidectomy and possible removal of some of the lymph nodes in the neck. The addition of postoperative RAIRAI - radioactive iodine therapy will ultimately depend on the type of cancer, how big the cancer is, and if there is any spread outside the thyroid. Occasionally, the biopsy will be "suspicious for cancer" which means that there is roughly an 80 to 90% chance of cancer.
There are a number of different types of tumors that are considered indeterminate: follicular neoplasmFollicular neoplasm - follicular cell tumor (benign or malignant), Hurthle cell neoplasmHurthle cell neoplasm - variant of follicular neoplasm, and atypical lesion. The word "neoplasmNeoplasm - tumor that can be either benign or malignant" means abnormal growth and it can be either benign or malignant (cancer). An indeterminate lesion means that the cells do not look normal, but that in order to make a diagnosis of cancer the whole nodule has to be examined under the microscope to see if there is invasion or growth outside of the nodule. This can only be done by removing part or all of the thyroid. In general, there is a roughly 20% chance of having a thyroid cancer with indeterminate lesions.